U.S. Environmental Protection Agency

Region III

Chesapeake Bay Program Office

Annapolis, Maryland

1-800-YOUR-BAY
I

n April 2003, the U.S. Environmental Protection Agency (EPA) Region III issued

guidance entitled Ambient Water Quality Criteria for Dissolved Oxygen, Water

Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries

(Regional Criteria Guidance). The development of the Regional Criteria Guidance

was the realization of a key commitment in the Chesapeake 2000 agreement. In that

agreement, the signatories (the states of Pennsylvania, Maryland and Virginia; the

District of Columbia; the Chesapeake Bay commission and the EPA) committed to,

“by 2001, define the water quality conditions necessary to protect aquatic living

resources.” New York Delaware and West Virginia agreed to the same commitment

through a separate six-state memorandum of understanding with the EPA. 

The EPA, in the Regional Criteria Guidance, defined the water quality conditions

called for in the Chesapeake 2000 agreement through the development of Chesapeake Bay-specific water quality criteria for dissolved oxygen, water clarity and

chlorophyll a. The EPA also identified and described five habitats, or designated

uses, that provide the context in which the EPA Region III derived adequately

protective Chesapeake Bay water quality criteria for dissolved oxygen, water clarity

and chlorophyll a. Collectively, the three water quality conditions provide the best

and most direct measures of the effects of too much nutrient and sediment pollution

on the Bay’s aquatic living resources—fish, crabs, oysters, their prey species and

underwater bay grasses. These criteria were developed as part of a larger effort to

restore Chesapeake Bay water quality.

The Technical Support Document for the Identification of Chesapeake Bay Designated Uses and Attainability (Technical Support Document) was developed by the

EPA and its watershed partners to be a companion document to the Regional Criteria

Guidance. Because it describes the development and geographical extent of the

designated uses to which the water quality criteria may apply, the Technical Support

Document serves as a resource to the states to assist them in the development and

adoption of refined water quality standards. Specifically, the EPA developed the

▼vii

Foreword

Foreword
Technical Support Document to help states in conducting use attainability analyses

(UAA) which they may conduct as part of their water quality standards development

and adoption processes. 

The Technical Support Document is not law or regulation; it is guidance that states

in the Chesapeake Bay watershed may consider in the development and adoption of

revised water quality standards. 

REBECCA W. HANMER, Director

Region III Chesapeake Bay Program Office

▼viii

Foreword
I

n May 2003, the U.S. Environmental Protection Agency (EPA) Region III issued

guidance entitled Ambient Water Quality Criteria for Dissolved Oxygen, Water

Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional

Criteria Guidance). The EPA developed this guidance to achieve and maintain the

water quality conditions necessary to protect aquatic living resources of the Chesapeake Bay and its tidal tributaries. The Regional Criteria Guidance is intended to

assist the Chesapeake Bay jurisdictions—Maryland, Virginia, Delaware and the

District of Columbia—in adopting revised water quality standards to address nutrient

and sediment-based pollution in the Chesapeake Bay and its tidal tributaries. Part of

the jurisdictions’ water quality standards development process may be to conduct use

attainability analyses (UAAs). The EPA developed the Technical Support Document

for Identifying Chesapeake Bay Designated Uses and Attainability (Technical

Support Document) to assist states in developing their individual UAAs.

The UAA process is traditionally conducted by individual states. However, the

multi-stakeholder body that guided the development of the water quality criteria for

the Chesapeake Bay, the Water Quality Steering Committee, determined that

providing UAA-related information on a watershed-wide scale would help promote

coordination and consistency across all jurisdictions. To that end, the Technical

Support Document provides a compilation of the basinwide analyses assimilated

collaboratively by the affected jurisdictions. The Technical Support Document is not

a regulation or a mandatory requirement. Rather, the EPA encourages the jurisdictions to use the information in this document and, when appropriate, to perform

additional analyses tailored to each jurisdiction during their respective water quality

standards development processes.

In providing technical background information for the Bay jurisdictions to use in

their own UAAs, the Technical Support Document explains and documents why it

appears that the current designated uses for aquatic life protection cannot be attained

in all parts of the Chesapeake Bay and its tidal tributaries. The Technical Support

Document provides scientific data showing that natural and human-caused

▼ix

Executive Summary

Executive Summary
conditions that cannot be remedied are the basis for the nonattainment and proposes

refined designated uses for the states to consider during their upcoming water quality

standards development and adoption processes. The document also provides scientific data indicating that the refined designated uses are viable in many areas of the

Chesapeake Bay and its tidal tributaries and documents that the refined designated

uses protect existing aquatic life uses. Finally, the document briefly summarizes

economic analyses performed by the Chesapeake Bay Program, including estimates

of the cost of implementing three of the four levels of control scenarios.

REGULATORY BACKGROUND

The Water Quality Standards Regulation (40 CFR 131.3) defines a UAA as “. . . a

structured scientific assessment of the factors affecting the attainment of a use which

may include physical, chemical, biological, and economic factors. . . .” (40 CFR

131.10[g]). The Water Quality Standards Regulation requires a state to conduct a

UAA when it designates uses that do not include those specified in Section 101(1)(2)

of the Federal Water Pollution Control Act .1 A state must also conduct a UAA when

it wishes to remove a specified designated use of the Federal Water Pollution Control

Act or adopt subcategories of those specified uses that require less stringent criteria. 

When conducting a UAA, a state must demonstrate that attaining the designated use

is not feasible due to one or more of six factors specified in Section 131.10(g) of the

Water Quality Standards Regulation. These factors are:

1. Naturally occurring pollutant concentrations prevent the attainment of the use;

2. Natural, ephemeral, intermittent, or low-flow conditions or water levels prevent

the attainment of the use, unless these conditions may be compensated for by

the discharge of a sufficient volume of effluent without violating state water

conservation requirements to enable uses to be met;

3. Human-caused conditions or sources of pollution prevent the attainment of the

use and cannot be remedied or would cause more environmental damage to

correct than to leave in place;

4. Dams, diversions or other types of hydrologic modifications preclude the

attainment of the use, and it is not feasible to restore the water body to its original condition or to operate such modifications in a way that would result in the

attainment of the use;

5. Physical conditions related to the natural features of the water body, such as the

lack of a proper substrate, cover, flow, depth, pools, riffles and the like, unrelated to chemical water quality, preclude attainment of aquatic life protection

uses; and

▼x

Executive Summary

1Section 101(a)(2) of the Federal Water Pollution Control Act states that “...it is the national goal that

wherever attainable, an interim goal of water quality which provides for the protection and 

propagation of fish, shellfish, and wildlife and provides for recreation in and on the water be achieved

by July 1, 1983.”
▼xi

Executive Summary

6. Controls more stringent than those required by sections 301(b)(1)(A) and (B)

and 306 of the Act would result in substantial and widespread economic and

social impacts.

The Water Quality Standards Regulation also specifies that any change in designated

uses must show that the existing uses are still being protected. The EPA’s 1983 Water

Quality Standards Handbook provides two definitions for an existing use. First, an

existing use can be defined as fishing, swimming or other uses that have actually

occurred since November 28, 1975. The second definition of an existing use is that

the water quality of a water body is suitable to allow the use to be attained—unless

there are physical problems, such as substrate or flow, that prevent use attainment.

The Water Quality Standards Regulation, in turn, requires state anti-degradation

policies to protect existing water quality. Therefore, any recommendations regarding

refined designated uses for the Chesapeake Bay and its tidal tributaries must ensure

that existing aquatic life uses continue to be protected. 

DOCUMENTING WHY CURRENT DESIGNATED USES

MAY NOT BE ATTAINABLE

The determination documented in the Technical Support Document that current

designated uses in the Chesapeake Bay and its tidal tributaries may not be attainable

is based on two of the six factors noted above—natural and human-caused conditions that cannot be remedied. Output from model-simulated scenarios as well the

paleoecological record of the Chesapeake Bay ecosystem both provide evidence that

these two conditions prevent attainment of current designated uses. 

To understand the feasibility of attaining current designated uses in the Chesapeake

Bay and its tidal tributaries, the Chesapeake Bay Program developed three watershed

modeling scenarios: ‘all-forest,’ ‘pristine’ and ‘everything, everywhere by everyone,’

or the E3 scenario. The ‘all-forest’ and ‘pristine’ scenarios represent the Chesapeake

Bay Program’s best effort to simulate water quality conditions prior to European

settlement and, in so doing, help characterize existing, naturally occurring pollutant

concentrations that prevent attainment of current designated uses. To represent

human-caused conditions that cannot be remedied and to determine the upper

boundaries of the watershed’s technological capability for reducing nutrient and

sediment pollution, the Chesapeake Bay Program also developed the E3 scenario,

which the watershed partners consider physically implausible.

Figure 1 illustrates the results of these three model scenarios, which show that significant portions of the deep channel and deep waters of the Chesapeake Bay and its

tidal tributaries cannot meet a dissolved oxygen concentration of 5 mg/l. For the

pristine scenario, on a baywide basis for all tidal-water segments that have 

deep-channel and deep-water areas, attainment is not achieved for portions (i.e.,

approximately 3 percent and 1 percent, respectively) of these areas during the

summer months. For the E3 scenario, 59 percent, 23 percent and 2 percent 
▼xii

Executive Summary

non-attainment are exhibited in the deep-channel, deep-water and open-water areas,

respectively, even after implementation of nutrient reduction measures that represent

limits of technology.

In addition to modeled information, the Chesapeake Bay Program has evidence from

the paleoecological record of the Chesapeake Bay ecosystem to support the concept

that natural conditions prevent attainment of current designated uses. An evaluation

of this information suggests that the main channel of the Chesapeake Bay most likely

experienced oxygen depletion before large-scale post-colonial land clearance took

place, due to natural factors such as climate-driven variability in freshwater inflow. 

DEVELOPMENT OF THE REFINED DESIGNATED USES

Current designated uses for the Chesapeake Bay and its tidal tributaries do not fully

reflect natural conditions and are too broad in their definition of use to support the

adoption of more habitat-specific aquatic life water quality criteria. The current uses

also change across jurisdictional borders within the same water body. Therefore, in

0%

10%

20%

30%

40%

50%

60%

70%

Deep-Channel Deep-Water Open-Water Migratory

Refined Tidal-Water Designated Uses

Percent Nonattainment of 5 mg/l Monthly Average

Dissolved Oxygen Concentration Over Time and Volume

Figure 1. Percent nonattainment of a 5 mg/l monthly average dissolved oxygen concentration over

the June through September period for the E3 (physically implausible) ( ), all-forest ( ) and pristine 

( ) model scenarios by the refined tidal-water designated uses.
refining the tidal-water designated uses, the six Bay watershed states and the District

of Columbia considered five principal factors:

• Habitats used in common by sets of species and during particular life stages

should be delineated as separate designated uses;

• Natural variations in water quality should be accounted for by the designated

uses;

• Seasonal uses of different habitats should be factored into the designated uses;

• The Chesapeake Bay criteria for dissolved oxygen, water clarity and chlorophyll a should be tailored to support each designated use; and

• The refined designated uses applied to the Chesapeake Bay and its tidal tributary waters will support the federal Clean Water Act goals and state goals for

uses existing in these waters since 1975.

The five refined designated uses reflect the habitats of an array of recreationally,

commercially and ecologically important species and biological communities. The

vertical and horizontal breadth of the designated use boundaries are based on a

combination of natural factors, historical records, physical features, hydrology,

bathymetry and other scientific considerations (Figure 2). 

The migratory fish spawning and nursery designated use protects migratory and

resident tidal freshwater fish during the late winter to late spring spawning and

nursery season in tidal freshwater to low-salinity habitats. Located primarily in the

upper reaches of many Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay, this use will benefit several species including striped bass, perch, shad,

herring, sturgeon and largemouth bass.

The shallow-water bay grass designated use protects underwater bay grasses and the

many fish and crab species that depend on the vegetated shallow-water habitat

provided by underwater grass beds. 

The open-water fish and shellfish designated use focuses on surface water habitats

in tidal creeks, rivers, embayments and the mainstem Chesapeake Bay and protects

diverse populations of sport fish, including striped bass, bluefish, mackerel and sea

trout, as well as important bait fish such as menhaden and silversides. 

The deep-water seasonal fish and shellfish designated use protects animals inhabiting the deeper transitional water-column and bottom habitats between the

well-mixed surface waters and the very deep channels. This use protects many

bottom-feeding fish, crabs and oysters, and other important species such as the bay

anchovy. 

The deep-channel seasonal refuge designated use protects bottom sedimentdwelling worms and small clams that bottom-feeding fish and crabs consume. Low

to occasional no dissolved oxygen conditions occur in this habitat zone during the

summer. 

▼xiii

Executive Summary
ATTAINABILITY OF REFINED DESIGNATED USES

The Chesapeake Bay Program assessed attainability for the refined designated uses

based on dissolved oxygen for the migratory and spawning, open-water, deep-water

and deep-channel designated uses. Attainability for the shallow-water designated use

was assessed based on historic and recent data on the existence of underwater bay

grass acreage. The Chesapeake Bay Program did not assess attainability for the

chlorophyll a criteria, which applies to the open-water designated use, because this

▼xiv

Executive Summary

Deep-Channel

Seasonal Refuge Use

Deep-Channel

Seasonal Refuge Use

A. Cross-Section of Chesapeake Bay or Tidal Tributary

B. Oblique View of the Chesapeake Bay and its Tidal Tributaries

Shallow-Water

Bay Grass Use Open-Water

Deep-Water Fish and Shellfish Use

Seasonal Fish and

Shellfish Use

Deep-Water

Seasonal Fish and

Shellfish Use

Migratory Fish

Spawning and

Nursery Use

Shallow-Water

Bay Grass Use Open-Water

Fish and Shellfish Use

Figure 2. Conceptual illustration of the five Chesapeake Bay tidal-water designated use zones.
criteria is expressed in narrative terms and does not provide a numeric value around

which to perform attainability analyses. 

For the refined designated uses to which the dissolved oxygen criteria applies, the

Chesapeake Bay Program evaluated attainability by comparing the modeled water

quality response to a series of technology-based nutrient reduction scenarios. This

series of scenarios was developed to represent the watershed’s nutrient and sediment

reduction potential in terms of the types, extent of implementation and performance

of best management practices (BMPs), wastewater treatment technologies and storm

water controls.2 These scenarios range from Tier 1, which represents the current

level of implementation plus regulatory requirements implemented through 2010, to

a theoretical limit-of-technology scenario referred to as the E3 scenario (‘everything,

everywhere by everybody’). Tier 2 and Tier 3 are intermediate scenarios between

Tier 1 and the E3 scenario. It is important to note that these tiers are artificial

constructs of technological levels of effort and do not represent actual programs that

the jurisdictions will eventually implement to meet the water quality standards.

Rather, the Chesapeake Bay Program developed the tiers as an assessment tool to

determine potential load reductions achievable by various levels of technological

effort, and to model water quality responses to controls.

The Chesapeake Bay Program used the Chesapeake Bay Watershed and Water

Quality Models to determine the water quality response to the pollutant reductions in

each scenario (Table 1) and then compared these modeled water quality observations

within the five refined designated uses to determine the spatial and temporal extent of

nonattainment with the respective dissolved oxygen criteria. Specifically, comparison

of model results for dissolved oxygen were made to a monthly average dissolved

oxygen concentration of 6 mg/l for the migratory and spawning use, 5 mg/l for the

open-water use, 3 mg/l for the deep-water use and 1 mg/l for the deep-channel use. 

▼xv

Executive Summary

2Sediment reduction is only reflected in the scenarios as that incidental to nutrient removal.

Table 1. Summary of pollutant loadings that result from applying the load

reductions associated with each scenario across all nutrient and sediment 

sources (except shoreline erosion) in the watershed. 

2000 2010 2010 2010 2010

Pollutant Progress Tier 1 Tier 2 Tier 3 E3 

Nitrogen 284.8 260.9 221.3 180.8 116.4 

Phosphorus 19.12 18.96 16.41 13.38 10.10

Sediment 5.044 4.644 4.144 3.625 2.953 
▼xvi

Executive Summary

MIGRATORY AND SPAWNING DESIGNATED USE

Current monitoring data and Chesapeake Bay Water Quality Model outputs indicate

that the migratory and spawning designated use is essentially being attained in the

Chesapeake Bay and its tidal tributaries for dissolved oxygen. The few segments that

are not fully attaining the dissolved oxygen criterion would fully attain this use in

the Tier 1 scenario (lowest level of control technologies). 

OPEN-WATER, DEEP-WATER AND DEEP-CHANNEL 

DESIGNATED USES

Table 2 provides the results of the attainability analysis for dissolved oxygen for the

open-water (including shallow-water)3, deep-water and deep-channel designated

uses, by Chesapeake Bay Program segment. As Table 2 illustrates, current monitoring data (presented under the ‘observed’ column) indicate that the open-water

designated use is seldom fully attained. However, at Tier 3, attainment for about 60

percent of the segments is achieved for this refined designated use. In most cases

where nonattainment is indicated for open-water at Tier 3, it is less than 2 percent

nonattainment, and often, less than 1 percent. For the deep-water designated use for

dissolved oxygen criteria, almost no attainment is achieved based on current monitoring data and only some degree of attainment is seen at reduction levels equivalent

to Tier 2. At the reduction levels represented by the E3 scenario, attainment is

achieved for all segments of the Chesapeake Bay except for one (middle central

Chesapeake Bay, CB4MH). Table 2 illustrates that, under observed conditions, the

proposed dissolved oxygen criteria are not attained for the deep-channel designated

use. With increasing load reductions, however, 100 percent attainment is achieved at

the E3 scenario, and, at the levels of reduction represented by Tier 3, percent nonattainment is primarily less than 2 percent. 

SHALLOW-WATER BAY GRASS DESIGNATED USE 

Attainability for the shallow-water bay grass designated use is based on historic and

recent data on the distribution of underwater bay grasses. Detailed analyses using

this data—including historical aerial photographs—were undertaken to map the

distribution and depth of historical underwater bay grass beds in the Chesapeake Bay

and its tidal tributaries. These analyses led to the adoption of the single best year

method that considers historical underwater bay grass distributions from the 1930s

through the early 1970s as well as more recent distributions since 1978 to present.

Using this method, the Chesapeake Bay Program and its watershed partners established a baywide underwater bay grass restoration goal of 185,000 acres. Because of

limitations associated with mapping underwater bay grasses using historical photography, the estimate of past underwater bay grass distributions is conservative.

Therefore, the restoration goal is conservative as well and considered attainable. 

3Because the dissolved oxygen criteria is the same for the open-water as for the shallow-water use,

attainability for the shallow-water designated use is presented under the open-water designated use in

Table 2.
▼xvii

Executive Summary

Table 2. Percent nonattainment of monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentrations

applied to open-water, deep-water and deep-channel designated uses, respectively.

Model Scenarios

Chesapeake Bay Program Segment DU Observed Tier 1 Tier 2 Tier 3 E 3 

Northern Chesapeake Bay(CB1TF) OW A A A A A 

Upper Chesapeake Bay (CB2OH) OW 1.92 0.68 0.43 0.17 A 

Upper Central Chesapeake Bay (CB3MH) OW A A A A A

DW 4.18 2.24 1.61 0.73 A 

DC 13.52 7.21 5.03 1.84 A 

Middle Central Chesapeake Bay (CB4MH) OW 0.05 A A A A

DW 19.64 14.28 12.05 8.51 0.69 

DC 45.19 28.94 18.81 3.93 A

Lower Central Chesapeake Bay (CB5MH) OW A A A A A 

DW 6.16 3.75 2.58 1.08 A 

DC 13.79 6.00 2.59 0.15 A 

Western Lower Chesapeake Bay (CB6PH) OW 5.87 3.68 2.71 1.30 0.01 

DW 0.36 A A A A 

Eastern Lower Chesapeake Bay (CB7PH) OW 4.55 2.81 1.82 0.74 A 

DW A A A A A 

Mouth of Chesapeake Bay (CB8PH) OW A A A A A 

Upper Patuxent River (PAXTF) OW A A A A 0.38 

Middle Patuxent River (PAXOH) OW 9.79 1.84 1.62 0.86 A 

Lower Patuxent River (PAXMH) OW 7.40 1.69 1.04 0.01 A 

DW 5.52 0.82 0.50 0.07 A 

Upper Potomac River (POTTF) OW A A A A A 

Middle Potomac (POTOH) OW 2.10 1.08 0.63 0.31 0.01 

Lower Potomac (POTMH) OW 0.78 A A A A 

DW 6.90 4.53 3.11 1.12 A 

DC 18.89 8.64 5.07 0.19 A 

Upper Rappahannock River (RPPTF) OW A A A A A 

Middle Rappahannock River (RPPOH) OW A A A A A 

Lower Rappahannock River (RPPOH) OW 0.44 0.10 A A A 

DW 5.58 1.09 0.01 A A 

DC 6.39 3.38 1.65 A A 

Piankatank River (PIAMH) OW 0.12 A A A A 

Upper Mattaponi River (MPNTF) OW 33.26 25.87 27.23 33.73 52.14 

Lower Mattaponi River (MPNOH) OW 46.88 28.95 31.86 28.99 48.11 

Upper Pamunkey River (PMKTF) OW 62.25 42.07 30.35 32.94 54.50 

continued
CONFIRMATION THAT EXISTING USES ARE MET

In establishing the refined designated uses, the Chesapeake Bay Program took

explicit steps in developing the requirements and boundaries to ensure that existing

aquatic life uses would continue to be protected as the EPA Water Quality Standards

Regulation require. For some refined designated uses—the migratory fish spawning

and nursery, the deep-water and the deep-channel—the application of new dissolved

oxygen criteria will result in improvements to existing water quality conditions. The

refined open-water fish and shellfish designated use dissolved oxygen criteria will

provide an equal level of protection as the current state water quality standards afford

to the same tidal waters. Likewise, the refined shallow-water bay grass designated

use also ensures protection of existing underwater bay grass-related uses because the

single best year method is based on historical (1930s through the early 1970s) and

more recent (1978–present) underwater bay grass distributions. 

▼xviii

Executive Summary

Lower Pamunkey (PMKOH) OW 42.15 12.66 13.86 10.32 11.39 

Middle York River (YRKMH) OW 18.08 3.31 2.32 0.42 A 

Lower York River (YRKPH) OW 1.48 A A A A

DW 0.01 A A A A 

Mobjack Bay (MOBPH) OW 2.30 1.60 1.10 0.34 A 

Upper James River (JMSTF) OW 0.66 A A A A

Middle James River (JMSOH) OW A A A A A 

Lower James River (JMSMH) OW A A A A A 

Mouth of the James River (JMSPH) OW A A A A A 

Eastern Bay (EASMH) OW A A A A A 

DW 3.26 2.00 0.90 0.36 A 

DC 20.23 11.26 6.49 0.67 A 

Middle Choptank River (CHOOH) OW 0.14 A A A A 

Lower Choptank River (CHOMH2) OW 2.27 1.78 1.51 1.08 0.43 

Mouth of the Choptank River (CHOMH1) OW 0.33 A A A A 

Tangier Sound (TANMH) OW 0.15 0.06 0.05 0.36 0.22 

Lower Pocomoke River (POCMH) OW A A A A A 

A = Applicable dissolved oxygen criteria fully attained; analysis based on monthly averaged dissolved oxygen concentrations 5 mg/l, 3 mg/l and

1 mg/l for open-water, deep-water and deep-channel designated uses. 

DU = designated use; OW—open-water; DW—deep-water; DC–deep-channel. 

Table 2. Percent nonattainment of monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentrations

applied to open-water, deep-water and deep-channel designated uses, respectively (cont.).

Model Scenarios

Chesapeake Bay Program Segment DU Observed Tier 1 Tier 2 Tier 3 E 3 
▼xix

Executive Summary

ECONOMIC ANALYSES

The Technical Support Document summarizes three types of economic analyses that

the Chesapeake Bay Program performed in conjunction with developing revised

water quality criteria, designated uses and boundaries for those uses in the Chesapeake Bay and its tidal waters. One analysis was undertaken to estimate the costs of

implementing the hypothetical control scenarios (represented by the Tier 1-3

scenarios). Screening-level analyses are the second type of analysis summarized.

These analyses were conducted to rule out areas that would not experience substantial and widespread economic and social impacts if states implemented controls

more stringent than those required by sections 301 and 306 of the Clean Water Act.

The results of analyses to model regional economic impacts is the third type of

analysis summarized in the Technical Support Document. 

A separate document entitled Economic Analyses and Impacts of Nutrient and

Sediment Reduction Actions in the Chesapeake Bay Watershed (Economic 

Analyses) presents detailed descriptions of these three types of analysis and the

attendant findings. 

Table 3 summarizes the results of the cost analyses described in detail in the

Economic Analyses document. Captured in the table are the total capital and annual

costs (annualized capital plus annual operation and maintenance [O&M] costs) associated with the tier scenarios. The cost analysis and other economic analyses provide

information related to evaluating impacts from the implementation of the nutrient

reduction measures defined in the tier scenarios. However, the Chesapeake Bay

Program did not use these analyses to delineate boundaries for the refined designated

uses. Although this information may be useful to them in developing their own

UAAs, states will need to conduct more rigorous economic analyses than the

analyses performed by the Chesapeake Bay Program. 

Table 3. Estimated cumulative costs and pollutant loading reductions associated

with the Tier 1–3 scenarios and the E3 scenario. 

Total Nitrogen Reduction

from Levels in 2000 Total Capital Costs Total Annual Costs

Tier (millions pounds per year)1 (in millions 2001 dollars)2 (in millions 2001 dollars)2

Tier 1 23.9 $1,391 $196 

Tier 2 63.5 $3,593 $553 

Tier 3 104.0 $7,713 $1,125 

E33 168.4 Not estimated Not estimated 

1. Loadings based on Phase 4.3 of the Chesapeake Bay Program’s Watershed Model.

2. Costs include those paid by private-sector businesses and households in addition to those paid by public entities

that provide cost-share funding for nutrient reduction controls and BMPs.

3. The E3 scenario represents a theoretical limit-of-technology control scenario that provides a maximum loadings

reduction estimate. 
This Technical Support Document for Identifying Chesapeake Bay Designated

Uses and Attainability was developed through the collaborative efforts, collective knowledge and applied expertise of the Chesapeake Bay Program Water Quality

Steering Committee’s Use Attainability Analysis Workgroup; the Chesapeake Bay

Program’s Modeling, and Monitoring and Assessment subcommittees; the Chesapeake Bay Program’s Nutrient Subcommittee workgroups: the Agricultural Nutrient

Reduction Workgroup, the Forestry Workgroup, the Point Source Workgroup, the

Urban Storm Water Workgroup, the Tributary Strategy Workgroup and the Sediment

Workgroup. 

USE ATTAINABILITY ANALYSIS WORKGROUP

Cheryl Atkinson, U.S. EPA Region III; Michael Bowman, Virginia Department of

Conservation and Recreation; Thomas Burke, Maryland Department of Natural

Resources; Eloise Castillo, SAIC; Karen Clark U.S. EPA Office of General Counsel;

Jared Creason, U.S. EPA National Center for Environmental Economics; Elleanore

Daub, Virginia Department of Environmental Quality; Robert Ehrhart, Virginia

Department of Environmental Quality; Richard Eskin, Maryland Department of the

Environment; David Frackelton; William Gerlach, Chesapeake Bay Foundation;

Jean Gregory, Virginia Department of Environmental Quality; Samuel Hamilton,

Virginia Agribusiness Council; Katherine Bunting Howarth, Delaware Department

of Natural Resources and Environmental Control; Lisa Huff, U.S. EPA Office of

Water; Wayne Jackson, U.S. EPA Region II; Jim Keating, U.S. EPA Office of Water;

Robert Krehely, Wyoming Valley Sanitary Authority; Norm LeBlanc, Hampton

Roads Sanitation District; Gary Madson; Chris Miller, U.S. EPA, Garrison Miller, U.

S. EPA Region III; Mark Morris, U.S. EPA Office of Water; Doug Parker, University

of Maryland; George Parsons, University of Delaware; Alan Pollock, Virginia

Department of Environmental Quality; Christopher Pomeroy, AquaLaw; John

Schneider, Delaware Natural Resources and Environmental Conservation; Roy

Seward, Virginia Department of Agriculture and Consumer Services; Carol Ann

▼xxi

Acknowledgments

Acknowledgments
Siciliano; U. S. EPA Office of General Council; Tanya Tomasko Spano, Metropolitan Washington Council of Governments; Allison Wiedeman, U.S. EPA Chesapeake

Bay Program Office; Robert Wieland, Main Street Economics; Clyde Wilber, Greely

and Hanson; and Carol Young, Pennsylvania Department of Environmental Protection.

MODELING SUBCOMMITTEE

Lowell Bahner, National Oceanic and Atmospheric Administration; Mark Bennett,

US Geological Survey; Peter Bergstrom, NOAA Chesapeake Bay Office; Mike

Bowman, VA Department of Conservation and Recreation; Bill Brown, PA Department of Environmental Protection; Arthur Butt, VA Department of Environmental

Quality; James R. Collier, DC Department of Health; Robin Dennis, US Environmental Protection Agency; Lewis Linker, US Environmental Protection Agency;

Charles A Lunsford, VA Department of Conservation and Recreation; Robert

Magnien, MD Department of Natural Resources; Ross Mandel, Interstate Commission on the Potomac River Basin; Timothy J. Murphy, Metropolitan Washington

Council of Governments; Narendra Panday, MD Department of the Environment;

Kenn Pattison, PA Department of Environmental Protection; Jeff Raffensperger, US

Geological Survey; Helen Stewart, MD Department of Natural Resources; Peter

Tango, MD Department of Natural Resources; and Harry Wang, VA Institute of

Marine Science.

MONITORING AND ASSESSMENT SUBCOMMITTEE

Kurt Brandstaetter, Chesapeake Research Consortium; Mike Bowman, VA Department of Conservation and Recreation; Claire Buchanan, Interstate Commission on

the Potomac River Basin; Jerry Griswold, Natural Resources Conservation Service;

Carlton Haywood, Interstate Commission on the Potomac River Basin; Rick

Hoffman, Department of Environmental Quality; Lewis Linker, US Environmental

Protection Agency; Robert Magnien, MD Department of Natural Resources; Paul

Massicot, MD Department of Natural Resources; Beth McGee, US Fish and Wildlife

Service; Hassan Mirsajadi, DE Department of Natural Resources and Environmental

Conservation; Matt Monroe, Department of Agriculture; Derek Orner, National

Oceanic and Atmospheric Administration; Scott Phillips, US Geological Survey;

Steve Preston, US Geological Survey; Richard Shertzer, PA Department of Environmental Protection; and John Sherwell, MD Department of Natural Resources.

NUTRIENT SUBCOMMITTEE

Mike Bowman, VA Department of Conservation and Recreation; Terry Black, PA

Department of Environmental Protection; Michael Brown, DE Department of

Natural Resources and Environmental Control; Katherine Bunting-Howarth, DE

Department of Natural Resources & Environmental Control; Collin Burrell, DC

Department of Health; Sally Claggett, US Forest Service; Kim Collini, Chesapeake

▼xxii

Acknowledgments
Research Consortium; Martha Corrozi, Chesapeake Research Consortium; Scott

Crafton, VA Chesapeake Bay Local Assistance Department; Melanie Davenport,

Chesapeake Bay Commission; Bob Ehrhart, VA Department of Environmental

Quality; J Michael Foreman, VA Department of Forestry; Jeffrey Halka, MD

Geological Survey; Maggie Kerchner, National Oceanic and Atmospheric Administration; Mike Langland, US Geological Survey; Scott Macomber, MD Department

of the Environment; Russell Mader, Natural Resources Conservation Service; Matt

Monroe, WV Department of Agriculture; John Murtha, PA Department of Environmental Protection; Kenn Pattison, PA Department of Environmental Protection; Russ

Perkinson, VA Department of Conservation and Recreation; Steele Phillips, Citizens

Advisory Committee; Royden Powell, MD Department of Agriculture; Kelly Shenk,

US Environmental Protection Agency; John Sherwell, MD Department of Natural

Resources; Thomas W. Simpson, University of Maryland; Randolph Sovic, WV

Department of Environmental Protection; and Mark Waggoner, Natural Resources

Conservation Service.

AGRICULTURAL NUTRIENT REDUCTION WORKGROUP

Martha Corrozi, Chesapeake Research Consortium; John Davis, USDA-NRCS;

Doug Goodlander, PA State Conservation Commission; Jerry Griswold, Natural

Resources Conservation Service; Tom Juengst, PA Department of Environmental

Protection; Maggie Kerchner, National Oceanic and Atmospheric Administration;

Matt Monroe, WV Department of Agriculture; Russ Perkinson, VA Department of

Conservation and Recreation; Herb Reed, University of MD–Cooperative Extension;

Diana Reynolds, MD Department of Natural Resources; William Rohrer, Delaware

Nutrient Management Commission; Fred Samadani, MD Department of Agriculture;

Ron Wood, VA Chesapeake Bay Local Assistance Department.

POINT SOURCE WORKGROUP

Martha Corrozi, Chesapeake Research Consortium; Bob Ehrhart, VA Department of

Environmental Quality; Marya Levelev, MD Department of the Environment;

Russell Mader, Natural Resources Conservation Service; John Murtha, PA Department of Environmental Protection; William Ruby, DC Department of Health;

Randolph Sovic, WV Department of Environmental Protection; Tanya Spano,

Metropolitan Washington Council of Governments; Allison Wiedeman, U.S. EPA

Chesapeake Bay Program Office; and Ning Zhou, VA Tech.

SEDIMENT WORKGROUP

Mike Bowman,VA Department of Conservation and Recreation; Owen Bricker, US

Geological Survey; Grace S. Brush, Johns Hopkins University; Kim Collini, Chesapeake Research Consortium; Thomas M Cronin, US Geological Survey; Lee Currey,

MD Department of the Environment; Robert E Edwards, Susquehanna River Basin

Commission; Jeffrey Halka, MD Geological Survey; Allen Gellis, US Geological

▼xxiii

Acknowledgments
Survey; Normand Goulet, Northern VA Regional Commission; Jerry Griswold,

Natural Resources Conservation Service; Amy Guise, US Army Corps of Engineers;

Julie Herman, VA Institute of Marine Science; Lee Hill, VA Department of Conservation and Recreation; Timothy Karikari, DC Department of Health; Mike Langla,

US Geological Survey; Kenn Pattison, PA Department of Environmental Protection;

Scott Phillips, US Geological Survey; Brian Rustia, Metropolitan Washington

Council of Governments; Larry Sanford, University of MD Center for Environmental Science; Gary Shenk, US Environmental Protection Agency; Sean Smith,

MD Department of Natural Resources; Steve Stewart, Baltimore County Department of Environmental Protection & Resource Management; and Debra Willard, US

Geological Survey.

TRIBUTARY STRATEGY WORKGROUP

Mark Bennett, US Geological Survey; Sheila Besse, DC Department of Health;

Mike Bowman, VA Department of Conservation and Recreation; Katherine BuntingHowarth, DE Department of Natural Resources & Environmental Control; Twila

Carr, WV Department of Environmental Protection; Kim Collini, Chesapeake

Research Consortium; Donald Fiesta, PA Department of Environmental Protection;

Normand Goulet, Northern VA Regional Commission; Jerry Griswold, Natural

Resources Conservation Service; V’lent Lassiter, VA Department Of Conservation &

Recreation; Lewis Linker, US Environmental Protection Agency; Scott Macomber,

MD Department of the Environment; Russell Mader, Natural Resources Conservation Service; Kenn Pattison, PA Department of Environmental Protection; Diana

Reynolds, MD Department of Natural Resources; Brian Rustia, Metropolitan Washington Council of Governments; Gary Shenk, US Environmental Protection Agency;

Thomas W. Simpson, University of Maryland; Helen Stewart, MD Department of

Natural Resources; and Jeffrey Sweeney, University of Maryland.

URBAN STORM WATER WORKGROUP

Meg Andrews, Maryland Dept. of Transportation; Joseph Battiata, VA Department

of Transportation; David Beale, VA Department of Conservation and Recreation;

Ronald Bowen, Anne Arundel County Dept. of Public Works; Ted Brown, Center

for Watershed Protection; Walter Caldwell, DC Department of Health; John Carlock,

Hampton Roads Planning District Committee; R. Scott Christie, PA Department of

Transportation; Kim Coble, Chesapeake Bay Foundation; Larry Coffman, Prince

George’s County; Martha Corrozi, Chesapeake Research Consortium; Scott

Crafton, VA Chesapeake Bay Local Assistance Department; Larry Gavan, VA

Department of Conservation and Recreation; Normand Goulet, Northern VA

Regional Commission; Lisa Grippo, US Navy; Timothy Karikari, DC Department of

Health; Kenneth Murin, PA Department of Environmental Protection; Ratilal B

Patel, PA Department of Environmental Protection; Ken Pensyl, MD Department of

the Environment; Brian Rustia, Metropolitan Washington Council of Governments;

Kelly Shenk, US Environmental Protection Agency; Bill Stack, Baltimore City;

▼xxiv

Acknowledgments
Steve Stewart, Baltimore Co. Dept. of Env. Protection & Resource Management;

Nancy Stoner, Natural Resources Defense Council; Burt Tuxford, VA Department of

Environmental Quality; and Raja Veeramachaneni, Maryland State Highway

Administration.

INDIVIDUALS

Richard Batiuk, U. S. EPA Chesapeake Bay Program; Christopher Day, U.S. EPA

Region III, Dave Jasinski, University of MD; Wendy Jastremski, U.S. EPA Region

III, Bob Koroncai, U.S. EPA Region III; Marcia Olson, Chesapeake Bay Program

NOAA; Nita Sylvester, U.S. EPA Chesapeake Bay Program; and Howard Weinberg,

UMCES.

The technical editing, document preparation and desk-top publication contributions

of Donna An, Robin Bisland, Lois Gartner, Lauren Petruzzi and Susan Vianna are

hereby acknowledged.

▼xxv

Acknowledgments
iii

Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

I. Introduction ..............................................................1

 

 Background ..........................................................1

Technical Support Document ............................................4

Objective .............................................................4

 

 Structure and Content .................................................4

Approach to Refining Tidal-Water Designated Uses .........................6

Determining attainment of current designated uses is not feasible . . . . . . . . . . . 7

Justifying the refined tidal-water designated uses . . . . . . . . . . . . . . . . . . . . . . . . 8

Assessing attainability of the refined tidal-water designated uses ...........9

Consideration of economic and social impacts . . . . . . . . . . . . . . . . . . . . . . . . . 11

Jurisdiction Water Quality Standards and Tributary Development Process . . . . 12

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

II. The Chesapeake Bay and Its Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Chesapeake Bay Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Chesapeake Bay Tidal-Water Quality Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Causes of Chesapeake Bay water quality problems . . . . . . . . . . . . . . . . . . . . 23

 Human population increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 Loss of habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

 Excess nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

 Excess sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

 

 Sources of Nutrient Loads to the Chesapeake Bay Tidal Waters . . . . . . . . . . . . . . 28

 Nonpoint sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

 Point sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
iv

 Atmospheric sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

 Anthropogenic source inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

 

III. Why Attaining the Current Tidal-Water Designated Uses Appears Not 

 to be Feasible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Natural Conditions That May Prevent Attainment of Current Designated Uses . 43

Paleoecological record of natural conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 44

 Water quality conditions under completely forested and pristine 

 watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

 Strengths and limitations of the all-forest and pristine scenarios . . . . . . . . . . . 48

 Model-simulated natural dissolved oxygen conditions . . . . . . . . . . . . . . . . . . 49

 Human-Caused Conditions That Cannot Be Remedied Which Appear to Prevent 

 Attainment of Current Designated Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

 Findings and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

IV. Refined Designated Uses for the Chesapeake Bay and Its Tidal Tributaries

 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Renewed commitment to restore Chesapeake Bay Water quality . . . . . . . . . . . . 63

Current state tidal-water designated uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

 

 Refining Tidal-Water Designated Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Living resource-based refined designated uses and protective criteria . . . . . . . . 72

Chesapeake Bay Tidal-Water Designated Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Migratory fish spawning and nursery designated use . . . . . . . . . . . . . . . . . . . . . 76

Shallow-water bay grass designated use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Open-water fish and shellfish designated use . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Deep-water seasonal fish and shellfish designated use . . . . . . . . . . . . . . . . . . . . 87

Deep-channel seasonal refuge designated use . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Chesapeake Bay Tidal-Water Designated Use Boundaries . . . . . . . . . . . . . . . . . . . . 92

Migratory fish spawning and nursery designated use boundaries . . . . . . . . . . . . 92
v

Open-water, deep-water and deep-channel designated use boundaries . . . . . . . . 96

Flow and circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Vertical density gradients and pycnoclines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Delineating the designated use boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

The boundary delineated process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Shallow-water bay grass designated use boundaries . . . . . . . . . . . . . . . . . . . . . 125

Maximum depth of persistent or abundant plant growth-based boundaries . . . 126

Benefits of deeper underwater bay grass distribution . . . . . . . . . . . . . . . . . . . . 127

Historical underwater bay grass distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Underwater bay grass no-grow zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Determining the maximum depth of persistent/abundant plant growth . . . . . . 132

Underwater bay grass restoration goal-based boundaries . . . . . . . . . . . . . . . . . 139

Shallow-water habitat area to support restoration goal-based boundaries . . . . 144

Confirming That the Refined Designated Uses Meet Existing Uses . . . . . . . . . . . . 152

Migratory spawning and nursery existing use . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Shallow-water existing use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Open-water existing use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Deep-water and deep-channel existing uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

V. Technological Attainability of the Refined Recommended Designated Uses

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Defining and Determining Technological Attainability for Dissolved Oxygen . . 160

Development of level-of-effort scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

 Point sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Onsite treatment systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Nonpoint source agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Nonpoint source urban . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

Nonpoint source forestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

 Atmospheric deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Load reductions by tier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Development of the criteria attainability tables . . . . . . . . . . . . . . . . . . . . . . . 174

Assessing criteria exceedance through the cumulative frequency 

distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

 Applying the Kolmogorov-Smirnov test for criteria attainability using the 

 CFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Use of the ‘10 percent default reference curve’ versus biological reference

curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Consideration of Different Hydrology Periods . . . . . . . . . . . . . . . . . . . . . . . . 179
vi

Technological attainability of the open-water, deep-water and deep-channel

designated uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Migratory fish and spawning and nursery designated use attainability . . . . . 181

Open-water fish and shellfish designated use attainability . . . . . . . . . . . . . . . 181

 Deep-water seasonal fish and shellfish designated use attainability . . . . . . . 184

Deep-channel seasonal refuge designated use attainability . . . . . . . . . . . . . . 184

Sediment Reduction and Its Effect on Water Quality . . . . . . . . . . . . . . . . . . . . . . 185

Attainability of the Shallow-Water Designated Use . . . . . . . . . . . . . . . . . . . . . . . . 185

 Attaining the shallow-water bay grass designated use . . . . . . . . . . . . . . . . . 185

Measures to Attain the Shallow-Water Designated Use . . . . . . . . . . . . . . . . . . . . 187

 Stream/Riverine BMPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

 Shoreline BMPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

In-water BMPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

VI. Summary of Economic Analyses

 Estimated Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

 Screening-Level Impact Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

 Economic Impacts and Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

 

Appendices

A. Development of the Level-Effort Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

 B. Data Supporting Determination of the Shallow-Water Designated Use Depths and 

 Underwater Bay Grasses Restoration Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

C. Underwater Bay Grasses No-Grow Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

D. Vertical Stratification and the Pycnoclines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-1
BACKGROUND

In 1987, the governors of Maryland, Virginia and Pennsylvania; the Mayor of the

District of Columbia, the U.S. Environmental Protection Agency (EPA) administrator and the chair of the Chesapeake Bay Commission signed the Chesapeake Bay

Agreement. This historic agreement stated that a 40 percent reduction in nutrients

entering the Chesapeake Bay would be necessary to restore its health (Chesapeake

Executive Council 1987). The goal targeted a 40 percent reduction of controllable

nutrient loads from point and nonpoint sources from 1985 levels by the year 2000.

The partners to the Chesapeake Bay Agreement committed that once achieved, these

levels of reduced nutrient loads would continue to be maintained into the future.

In spite of the widespread implementation of best management practices (BMPs) and

enhanced treatment technologies across the Chesapeake Bay watershed, nutrient- and

sediment-related water quality problems have persisted. Figure I-1 illustrates the listed

nutrient- and/or sediment-impaired waterbodies in the Chesapeake Bay watershed.

Maryland’s portion of the Chesapeake Bay and its tidal tributaries were listed on its

1996 and 1998 Clean Water Act (CWA) Section 303(d) lists of impaired waters. In

May 1999, EPA Region III included Virginia’s portion of the Chesapeake Bay and

portions of several tidal tributaries on Virginia’s 1998 CWA Section 303(d) list.

Delaware listed its tidally influenced portions of the Chesapeake Bay waters on their

1996 and 1998 lists, and the District of Columbia listed its Chesapeake Bay waters in

1998. Streams and rivers also are listed for nutrient and/or sediment in the nontidal

portions of the Chesapeake Bay watershed in all seven Chesapeake Bay watershed

jurisdictions, including West Virginia, Pennsylvania, and New York.

The new Chesapeake 2000 agreement was developed in response to a comprehensive assessment of the Chesapeake Bay’s restoration needs and delineated an

ambitious list of new restoration commitments (Chesapeake Executive Council

2000). The significant focus on restoration of Chesapeake Bay water quality resulted

from the listing of most of the Chesapeake Bay and its tidal tributaries on the 303(d)

list of impaired waters. Subsequently, the governors of Delaware, New York and

West Virginia signed a Memorandum of Understanding with Maryland, Virginia,

▼1

chapter i • Introduction

chapteri

Introduction
▼2

chapter i • Introduction

Figure I-1. Nutrient, sediment and dissolved oxygen impaired waterbodies in the Chesapeake Bay watershed from the 1998 303(d) list illustrated as points (•), linear (–) or area (solid black) events.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
Pennsylvania, the District of Columbia and the EPA committing to implement the

Water Quality Protection and Restoration section of the agreement (Chesapeake Bay

Watershed Partners 2001).

Chesapeake 2000 specifies a goal to remove the Chesapeake Bay and its tidal tributaries from the list of impaired waterbodies for nutrients and sediments by 2010.

Thus, the development of a total maximum daily load (TMDL) for the entire Chesapeake Bay was delayed until 2011, anticipating that the Chesapeake Bay Program

partners can cooperatively achieve water quality standards by that time, making a

baywide TMDL unnecessary.

Chesapeake 2000 lists the following specific commitments as steps to achieve its

water quality goal of eliminating nutrient- and sediment-related impairments from

tidal waters:

1. By 2001, define water quality conditions (i.e., criteria) necessary to protect

aquatic living resources and then assign load reductions for nitrogen, phosphorus and sediment to each major tributary;

2. By 2002, complete a public process to develop and begin implementing revised

Tributary Strategies to achieve and maintain the assigned loading goals; and

3. By 2003, jurisdictions with tidal waters will use their best efforts to adopt new

or revised water quality standards consistent with the defined water quality

conditions.

Although the above commitments still stand, the schedule has changed. The current

schedule that all seven watershed jurisdictions and the EPA agreed to calls for:

• Final definitions of water quality conditions (i.e., criteria) by April 2003;

• Development of new and revised tributary strategies by April 2004; and

• Adoption of new and revised state water quality standards by 2005.

To implement and coordinate these actions, the Chesapeake Bay Program formed the

Chesapeake Bay Water Quality Steering Committee, composed of senior managers

from the EPA, state environmental quality, natural resource management, and agricultural agencies, the Chesapeake Bay Commission, interstate river basin

commissions, the environmental community and wastewater treatment operators.

Under the Water Quality Steering Committee, a Use Attainability Analysis (UAA)

Workgroup was convened to collaboratively assess the attainability of the refined

designated uses for the Chesapeake Bay and its tidal tributaries.

TECHNICAL SUPPORT DOCUMENT

This document provides the Chesapeake Bay jurisdictions4 with information to assist

them in adopting water quality standards to protect aquatic life in the Chesapeake

▼3

chapter i • Introduction

4The jurisdictions that will develop and adopt revised water quality standards in response to this effort

are those with Chesapeake Bay and tidal tributary waters listed as state waters: Maryland, Virginia,

Delaware and the District of Columbia.
Bay and its tidal tributaries against nutrient and sediment enrichment impairments.

Part of the jurisdictions’ water quality standards development process may be to

conduct use attainability analyses. The Technical Support Document may be used to

assist states in developing their individual UAAs and state-specific documents.

While a UAA is traditionally a process conducted independently by a state, the

multi-stakeholder Water Quality Steering Committee decided to provide information

on a watershed-wide scale to promote coordination and consistency across all

jurisdictions.

OBJECTIVES 

The EPA developed the Technical Support Document to:

• Document why it appears that the current designated uses for protecting

aquatic life cannot be attained in all parts of the Chesapeake Bay and its tidal

tributaries due to irremediable natural and human-caused conditions;

• Document the rationale and scientific basis for the refined designated uses for

the Chesapeake Bay and its tidal tributaries;

• Document that the refined designated uses are potentially attainable; and

• Provide technical background information for the four Chesapeake Bay jurisdictions with tidal waters to use in developing their own jurisdiction-specific UAAs.

STRUCTURE AND CONTENT

Chapter II provides background information regarding Chesapeake Bay tidal-water

quality problems caused by excess nutrients and sediments. Chapter III demonstrates that two factors–natural conditions and irremediable, human-generated

conditions–provide sufficient evidence that the current designated uses cannot be

met in certain portions of the Chesapeake Bay and its tidal tributaries.

Chapter IV provides information that jurisdictions may use in adopting refined tidalwater designated uses based on the habitat quality needs of the plants and animals

that inhabit the different Chesapeake Bay tidal-water habitats and the Bay and its

tidal rivers’ natural physical processes and features. The refined designated uses are

subcategories of current aquatic life protection uses, protected by new Chesapeake

Bay regional criteria for dissolved oxygen and, where appropriate, chlorophyll a and

water clarity (U.S. EPA 2003a). This chapter also presents the scientific basis underlying the geographic and temporal extent (‘boundaries’) of the refined designated

uses and documents that the refined designated uses protect uses existing since

November 1975, as required by the EPA Water Quality Standards regulation.

Assessments of the technological attainability of the refined designated uses—

migratory spawning and nursery habitat, open-water habitat, deep-water habitat and

▼4

chapter i • Introduction
deep-channel habitat—were conducted by comparing model-simulated water quality

responses (measured as dissolved oxygen criteria attainment) of four level-of-effort

scenarios (or tiers) to the nutrient and sediment reductions accomplished at each

level. The water quality responses are summarized in Chapter V in a series of ‘attainability tables,’ that show which Chesapeake Bay tidal waters achieve attainment for

dissolved oxygen for each of the recommended refined designated uses. Attainability

of the shallow-water habitat designated use is assessed by examining the historical

and recent distributions of underwater bay grasses.

Chapter VI provides an overview of the estimated costs for each set of tiered levels

of implementation scenarios. This information is used also to conduct economic

impact analyses, which also are described in Chapter VI. The objective is to provide

the jurisdictions with preliminary estimates of the types of potential impacts that

could occur as a result of implementing the tier scenarios throughout the watershed.

However, it may be necessary for states to perform more comprehensive analyses for

their own state-specific UAAs. At the basinwide level, economic impacts were not

considered in determining the boundaries of designated uses. Rather, it will be up to

the individual jurisdictions conducting their own UAAs to determine where there

may be substantial and widespread social and economic impacts and to adjust their

final use boundary delineations as a result. The present economic information and

methodologies are intended only to assist the states with that decision.

The Technical Support Document is a compilation of basinwide guidance on UAArelated analyses and was assembled collaboratively by the relevant jurisdictions; it

does not represent a regulation or a set of mandatory requirements. The EPA encourages jurisdictions to use the information in this document and, when appropriate, to

perform additional analyses relevant to their respective water quality standards

development process. The general descriptions provided here may not apply to all

circumstances. Interested parties may raise questions and objections about the

substance of the Technical Support Document and its specific applications. The EPA

and other decision-makers retain the discretion to adopt approaches that differ from

those described in this document, where appropriate.

The Technical Support Document does not include a determination as to whether the

refined designated uses are attainable in specific areas; such decisions belong to the

states. Instead it provides information based on scientific data to show that revisions

of the current designated uses may be justified and that the refined designated uses

are viable in many areas of the Chesapeake Bay and its tidal tributaries. 

It should be noted that the Technical Support Document presents information that is

current at the time of publication, and its analyses are works in progress. The EPA

expects Chesapeake Bay jurisdictions with Bay tidal waters to continue related

analyses and to seek assistance from the EPA and their Chesapeake Bay Program

partners during their tributary strategy development and water quality standards

adoption processes. 

▼5

chapter i • Introduction
Resource constraints prevented a full evaluation of many issues such as local cost

and impact assessments, physical implementation constraints for technologies and

potential cap load impacts. However, the EPA anticipates that the four jurisdictions

with Chesapeake Bay tidal waters will explore such issues in greater detail, where

appropriate, during their respective water quality standards development processes.

APPROACH TO REFINING TIDAL-WATER DESIGNATED USES

The Chesapeake 2000 agreement and the subsequent six-state, District of Columbia

and EPA memoranda of understanding challenged the Chesapeake Bay watershed

jurisdictions to “define the water quality conditions necessary to protect aquatic

living resources” and to have the jurisdictions with tidal waters “use their best efforts

to adopt new or revised water quality standards consistent with the defined water

quality conditions.” Against this backdrop of a renewed commitment to restore

Chesapeake Bay water quality, the Chesapeake Bay Program partners determined

that the current underlying tidal-water designated uses must be refined to better

reflect desired Chesapeake Bay water quality conditions.

The federal water quality standards regulation establishes that states must specify

appropriate water uses to be achieved and protected. Current designated uses applied

to the waters of the Chesapeake Bay and its tidal tributaries do not fully reflect

natural conditions and are too broad in their definition of ‘use’ to support the adoption of more habitat-specific aquatic life criteria. Furthermore, they change across

jurisdictional borders in the same body of water.

Under the federal water quality standards regulation, states may adopt subcategories

of uses, seasonal uses and may remove uses under certain conditions (including

natural, physical and socio-economic conditions). If a state wishes to remove or establish a subcategory of a designated use that requires less stringent water quality

criteria, it must conduct a use attainability study. States must also demonstrate that all

water uses present on or after November 28, 1975, will always be protected. With

publication of the Technical Support Document, the EPA encourages states to

consider refining and subcategorizing their general aquatic life protection use applied

to Chesapeake Bay tidal waters, found in current state water quality standards. 

The EPA, in close collaboration with the Chesapeake Bay Water Quality Steering

Committee, published new Chesapeake Bay regional water quality criteria for

dissolved oxygen, water clarity and chlorophyll a (U.S. EPA 2003a). Portions of the

Chesapeake Bay criteria are either equal, more, or less stringent than the current

dissolved oxygen criteria adopted by the Chesapeake Bay jurisdictions in their water

quality standards. Each jurisdiction that currently lists Chesapeake Bay tidal waters as

state waters (Maryland, Virginia, Delaware and the District of Columbia) is responsible

for submitting its own UAA to justify changes to state water quality standards for the

Chesapeake Bay tidal waters. This Technical Support Document provides the jurisdictions with key information for conducting their own UAAs.

▼6

chapter i • Introduction
DETERMINING ATTAINMENT OF CURRENT DESIGNATED USES 

IS NOT FEASIBLE

The EPA Water Quality Standards Regulation (40 CFR 131.3) defines a UAA as:

A structured scientific assessment of the factors affecting the attainment of a

use which may include physical, chemical, biological and economic factors as

described in Section 131.10(g).

A UAA is required, according to Section 131.10 (j) of the EPA Water Quality Standards Regulation, when:

1. The state designates or has designated uses that do not include the uses specified in Section 101(a)(2) of the Act; or

2. The state wishes to remove a designated use that is specified in Section

101(a)(2) of the Act or to adopt subcategories of uses specified in Section

101(a)(2) that require less stringent criteria.5

In conducting a UAA, a state must be able to demonstrate that attaining the designated use is not feasible due to one or more of the six factors in Section 131.10(g)

listed below:

1. Naturally occurring pollutant concentrations prevent the attainment of the use;

2. Natural, ephemeral, intermittent or low-flow conditions or water levels prevent

the attainment of the use, unless these conditions may be compensated for by

the discharge of a sufficient volume of effluent without violating state water

conservation requirements to enable uses to be met;

3. Human-caused conditions or sources of pollution prevent the attainment of the

use and cannot be remedied or would cause more environmental damage to

correct than to leave in place;

4. Dams, diversions or other types of hydrologic modifications preclude the

attainment of the use, and it is not feasible to restore the water body to its original condition or to operate such modification in a way that would result in the

attainment of the use;

5. Physical conditions related to the natural features of the water body, such as the

lack of a proper substrate, cover, flow, depth, pools, riffles and the like, unrelated to chemical water quality, preclude attainment of aquatic life protection

uses; and 

6. Controls more stringent than those required by sections 301(b)(1)(A) and (B)

and Section 306 of the Act would result in substantial and widespread

economic and social impacts.

▼7

chapter i • Introduction

5Section 101(a)(2) Federal Water Pollution Control Act states that “...it is the national goal that wherever

attainable, an interim goal of water quality which provides for the protection and propagation of fish,

shellfish, and wildlife and provides for recreation in and on the water be achieved by July 1, 1983.”
The Technical Support Document focuses on the current designated uses in Chesapeake Bay tidal waters for the protection of aquatic life.6 Chapter III provides

scientific information that the states may use in determining whether current tidalwater designated uses in Maryland, Virginia, Delaware and the District of Columbia,

with corresponding dissolved oxygen criteria of 4 mg/l and 5 mg/l, are not achievable in all portions of the Chesapeake Bay and tidal tributaries. 

Factors 1 and 3, above, are applied in demonstrating why it appears that the current

uses may not be met in certain portions of the Chesapeake Bay and its tidal tributaries. States may rely on one or more of the factors to demonstrate that attaining the

current designated use is not feasible. Factors 4 and 5 concerning unalterable hydrologic modifications and natural physical conditions that would preclude attainment

may also explain why the current designated uses are unattainable in certain tidalwater habitats of the Chesapeake Bay. The Technical Support Document does not

explore these two factors in as great of detail as factors 1 and 3; however, the jurisdictions may choose any of the preceding six factors in conducting their

state-specific UAAs. 

JUSTIFYING THE REFINED TIDAL-WATER DESIGNATED USES

A UAA is not required to justify application of the refined designated uses, particularly for areas in which the uses (criteria) will be more stringent than current ones.

The Chesapeake Bay Program’s Water Quality Steering Committee decided,

however, that it was as important to document attainability of the more protective

refined designated uses as it was to justify changes to current designated uses.

Due to the shortcomings of current designated uses applied to the Chesapeake Bay

and its tidal tributaries, the Chesapeake Bay Program watershed partners concluded

that the underlying tidal-water designated uses need to be refined to reflect a greater

understanding of the complex Chesapeake Bay system and the needs of its living

resources. Specifically, the partners recommend that the following five refined

aquatic life designated uses be applied to the appropriate habitats in the Chesapeake

Bay and its tidal tributaries:

• Migratory fish spawning and nursery;

• Open-water fish and shellfish;

• Deep-water seasonal fish and shellfish;

• Deep-channel seasonal refuge; and

• Shallow-water bay grass.

▼8

chapter i • Introduction

6Specifically, all state waters in Maryland are protected for Use I or water contact recreation and protection of aquatic life. All state waters in Virginia are designated for the following uses: “ . . . recreational

uses, e.g., swimming and boating; the propagation and growth of a balanced, indigenous population of

aquatic life, including game fish which might reasonably be expected to inhabit them; wildlife; and the

production of edible and marketable natural resources, e.g., fish and shellfish.” Delaware state waters

are designated for protection of “fish, aquatic life and wildlife” with similar provisions for “protection

and propagation of fish, shellfish and wildlife” in District of Columbia’s waters.
The first four designated use subcategories were derived chiefly to address seasonally distinct habitats and living resource communities with widely varying dissolved

oxygen requirements. The shallow-water bay grass designated use would occur

seasonally in conjunction with the part of the year-round open-water use habitat for

waters that border the land along the tidal portions of the Chesapeake Bay and its

tributaries. It is intended to protect underwater bay grasses where the water clarity

criteria will apply. 

The same factors used to show why it appears the current designated uses are unattainable can also be applied in the development of the refined designated uses.

Factors 1 (natural conditions) and 3 (irremediable human-generated conditions)

were used to determine appropriate boundaries for the refined designated uses. The

Chesapeake Bay Program partners also took into consideration factors 4 and 5 as

part of the analysis for delineating the boundaries for the refined designated uses.

The monitoring data and model-simulated outputs described in Chapter IV show that

there are certain hydrologic and physical features that exist in the Chesapeake Bay

tidal waters today—some natural and some man-made, such as the shipping channels—which directly influence the horizontal as well as vertical extent of the

designated use boundaries.

ASSESSING ATTAINABILITY OF THE 

REFINED TIDAL-WATER DESIGNATED USES

The question of whether the refined designated uses are attainable is a challenging

one. There is no precise approach or existing guidance for answering this question.

The challenge is particularly daunting for an area as large and complex as the Chesapeake Bay and its watershed, with its heterogeneous habitats and its vulnerability to

pollutants from point and nonpoint sources. The concept of attainability encompasses technological, economic and even political and legal perspectives. The

Technical Support Document addresses these viewpoints to a limited extent. The

states ultimately need to make their final determinations by applying information

tailored to their respective jurisdictions. This document specifically addresses technological attainability of the migratory spawning and nursery, open-water,

deep-water, deep-channel (based on dissolved oxygen criteria attainment) and

shallow-water designated uses (based on past and recently observed underwater bay

grass distributions). Because the Chesapeake Bay chlorophyll a criteria were

published in narrative form, attainability of the open-water designated use was not

assessed for this parameter.

From a legal perspective, ‘existing uses’ are, by definition, attainable. By regulation,

they must be protected by designated uses in water quality standards (40 CFR

131.10[g], 131.10[h][1] and 131.10[i]). Further, at a minimum, uses are considered

attainable if they can be achieved by implementing effluent limits (referred to as best

available technology or BAT) required under sections 301(b) and 306 of the Clean

Water Act and by implementing cost-effective and reasonable best management

practices (40 CFR 131.10[d] and 131.10[h][2]).

▼9

chapter i • Introduction
Once a use is designated (as in the case of the Chesapeake Bay), it is presumed to be

attainable and may not be removed unless the state conducts a UAA and can demonstrate that attaining the designated use is not feasible based on one of the six use

removal factors (40 CFR 131.10[g][1][6]). If a state conducts a UAA and demonstrates that one or more of the six use removal factors are met for a particular

designated use, the state may remove the use. However, the state may not remove an

existing use and must revise water quality standards to reflect uses actually attained

(40 CFR 131.10[i]). In addition, designated uses not satisfying any of the six use

removal factors may not be removed.

As 40 CFR 131.2 states:

. . . water quality standards should, wherever attainable, provide water quality

for the protection and propagation of fish, shellfish, and wildlife and for recreation in and on the water and take into consideration their use and value of

public water supplies, propagation of fish, shellfish, and wildlife, recreation in

and on the water . . .

If the use removal factors are cited to remove a designated use, the state must adopt

an ‘appropriate’ use or uses in place of the one removed (40 CFR 131.10[a]). Attainable uses are appropriate uses and may be expressed as subcategories of use.

Because the use removal factors are designed to determine whether to remove a

designated use when it is not attainable, they serve the purpose equally effectively

when considering whether a use is attainable and should be designated. 

The Chesapeake Bay Program partners have devised a valuable tool for exploring

attainability from a technological perspective–a range of level-of-effort scenarios

that represent degrees of nutrient and sediment load reduction through simulated

implementation of best management practices and wastewater treatment upgrades.

These scenarios begin with Tier 1, which represents the current level of implementation in the watershed, including regulatory requirements implemented through the

year 2010, up to a scenario representing ‘limits of technology’ referred to as the E3

scenario or ‘everything, everywhere by everybody,’ which is acknowledged to be

physically implausible. Tier 2 and Tier 3 scenarios also were developed to represent

intermediate levels between the Tier 1 and E3 scenarios.

Each tier represents a nitrogen, phosphorus and sediment load reduction determined

by the technologies and levels of implementation assigned to it.7 These tiers are artificial constructs of technological levels of effort and do not represent actual

programs that the jurisdictions will eventually implement to meet the water quality

standards. These tiers are an assessment tool to determine potential load reductions

achievable by various levels of technological effort and were modeled to determine

water quality responses. Chapter V provides the results of the water quality model

▼10

chapter i • Introduction

7Sediment reduction is only estimated where it is incidental to implementation of BMPs directed toward

nutrient loading reductions. 
analyses for dissolved oxygen by tier, presented in a series of ‘attainability tables,’

that estimate the level of attainment achieved within the designated use boundaries.

These analyses shows that most segments of the Chesapeake Bay and its tidal tributaries realize attainment at the E3 levels. This attainment is also true for Tier 3 where,

if nonattainment does exist, it is generally at levels less than one percent, except for

Chesapeake Bay Program segment CB4MH or Middle Central Chesapeake Bay (see

Table V-6) where 8.51 percent nonattainment in deep-water remains. 

Chesapeake Bay Program partners have used the E3 scenario to represent humancaused conditions that cannot be remedied. The partners agree that reductions at E3

levels are not achievable and that the load reductions represented by Tier 3 are technologically achievable. Therefore, if a proposed use can be attained at load

reductions equal to or greater than Tier 3, but less than the E3 scenario, that use

should be designated. The jurisdictions may still, through their own analyses, show

that irremediable human-caused conditions prevent use attainment, or explain why

the uses cannot be attained based on substantial and widespread economic or social

impacts, or other factors in 40 CFR 131.10(g). However, the analyses published in

this Technical Support Document show that the refined designated uses can potentially be attained in the Chesapeake Bay and its tidal tributaries.

Chapter V also addresses the attainability of the shallow-water designated use.

Restoration of underwater bay grasses to areas supporting “the propagation and growth

of balanced, indigenous populations of ecologically, recreationally and commercially

important fish and shellfish inhabiting vegetated shallow-water habitats” is ultimately

the best measure of attaining the shallow-water bay grass designated use. This document provides the states with two means by which to determine the return of water

clarity conditions necessary to support restoration of underwater bay grasses and,

therefore, attainment of the shallow-water designated use. 

CONSIDERATION OF ECONOMIC AND SOCIAL IMPACTS

The sixth factor to consider when conducting a UAA listed under Section 131.10(g)

(“Controls more stringent than those required by Sections 301[b] and 306 of the Act

would result in substantial and widespread economic and social impact”) also has

been addressed to a limited extent in the Technical Support Document. The information presented in Chapter III justifying why current designated uses cannot be met

does not require reliance on the substantial and widespread economic and social

impact factors as part of the justification to change the uses. Furthermore, the Chesapeake Bay Program partners delineated the use boundaries for the Chesapeake Bay

and its tidal tributaries based on estuarine living resources and their habitats, not on

economic impact information.

Conversely, it is logical to ask if the designated uses are affordable. The Technical

Support Document does not attempt to provide conclusions on affordability because

the Chesapeake Bay Program partners judged it premature to specify thresholds for

substantial and widespread economic and social impacts. On a regional, state or

▼11

chapter i • Introduction
large watershed scale, economic impacts can be mitigated by cost-share, loans or

new federal or state funding programs. Cost and economic analyses to show impacts

that would preclude attainment of these refined uses must be more comprehensive

and rigorous than the present analyses.

JURISDICTION WATER QUALITY STANDARDS AND

TRIBUTARY STRATEGY DEVELOPMENT PROCESS

Upon publication of the Regional Criteria Guidance, the Chesapeake Bay tidalwater jurisdictions of Maryland, Virginia, Delaware and the District of Columbia

began their respective water quality standards development and adoption processes.

At the same time, all Chesapeake Bay watershed jurisdictions, including Pennsylvania, West Virginia and New York collaboratively allocated caps on nutrient and

sediment loads necessary to meet these anticipated water quality standards (i.e.,

Chesapeake Bay regional criteria and refined designated uses) (U.S. EPA 2003b).

States are scheduled to adopt water quality standards by 2005. Local watershed load

reduction action plans (referred to as ‘tributary strategies’), based on achieving the

Chesapeake 2000 nutrient and sediment cap load allocations, will be completed by

April 2004. The development of tributary strategies will provide area-specific information that jurisdictions can use in their water quality standards adoption process.

To promote consistency, jurisdictions will need to work cooperatively during their

tributary strategy development and water quality standards adoption processes,

particularly where tributary basins include more than one state in the Chesapeake

Bay watershed, such as the Potomac River basin.

LITERATURE CITED

Chesapeake Bay Watershed Partners. 2001. Memorandum of understanding among the state

of Delaware, the District of Columbia, the State of Maryland, the State of New York, the

Commonwealth of Virginia, the State of West Virginia and the U.S. Environmental Protection Agency regarding cooperative efforts for the protection of the Chesapeake Bay and its

rivers. Chesapeake Bay Program, Annapolis, Maryland.

Chesapeake Executive Council. 1987. 1987 Chesapeake Bay Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

Chesapeake Executive Council. 2000. Chesapeake 2000 Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved

Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.

U.S. EPA, Region 3. EPA 903-R-03-002. 

U.S. EPA. 2003b. Nutrient and Sediment Allocations for the Chesapeake Bay. U.S. EPA

Chesapeake Bay Program Office, Annapolis, Maryland. CBP/TRS 267/03.

U.S. EPA. 1998. Water Quality Standards Regulation. EPA 823-Z-98-002.

▼12

chapter i • Introduction
BACKGROUND

The Chesapeake Bay is the nation’s largest estuary and one of its most valuable

natural treasures. Even after centuries of intensive use, the Chesapeake Bay remains

a highly productive natural resource. It supplies millions of pounds of seafood, functions as a major hub for shipping and commerce, provides habitat for an extensive

array of wildlife and offers a variety of recreational opportunities for residents and

visitors. The Chesapeake Bay supports 348 species of finfish, 173 species of

shellfish and more than 2,700 plant species. It is home to 29 species of waterfowl

and is a major resting ground along the Atlantic Migratory Bird Flyway. Every year,

1 million waterfowl winter in the Chesapeake Bay’s basin.

The Chesapeake Bay proper is approximately 200 miles long, stretching from Havre

de Grace, Maryland, to Norfolk, Virginia. It varies in width from about 3.4 miles

near Aberdeen, Maryland, to 35 miles at its widest point, near the mouth of the

Potomac River. Including its tidal tributaries, the Chesapeake Bay encompasses

approximately 11,684 miles of shoreline.

On average, the Chesapeake Bay holds more than 15 trillion gallons of water.

Although the Bay’s length and width are dramatic, the average depth is only about

21 feet. The Bay is shaped like a shallow tray, except for a few deep troughs believed

to be remnants of the ancient Susquehanna River. The troughs, which in some areas

are maintained by dredging, form a deep channel along much of its length. This

channel allows passage of large commercial vessels. Because it is so shallow, the

Chesapeake Bay is far more sensitive to temperature fluctuations and wind than the

open ocean.

The Chesapeake Bay is an estuary, where freshwater and saltwater mix. About half

of the Bay’s water volume consists of saltwater from the Atlantic Ocean. The other

half drains into the Bay from an enormous 64,000-square-mile drainage basin or

watershed. Ninety percent of this freshwater is delivered from five major rivers: the

Susquehanna (which is responsible for about 50 percent), Potomac, James, Rappahannock and York rivers.

▼13

chapter ii • The Chesapeake Bay and Its Watershed

chapterii

The Chesapeake Bay 

and Its Watershed
The distribution and stability of such an estuarine ecosystem depends on three

important physical characteristics of the water: salinity, temperature and circulation.

Salinity is a key factor influencing the Bay’s morphology. Seawater from the Atlantic

Ocean enters the mouth of the Chesapeake Bay; salinity is highest at that point and

gradually decreases farther north. Saltwater is more dense than freshwater, thus

salinity increases at greater depths while freshwater tends to remain at the surface.

Salinity levels within the Chesapeake Bay vary widely, both seasonally and from

year to year, depending on the volume of incoming freshwater. 

Temperature dramatically changes the rate of chemical and biological reactions within

the water. Because the Chesapeake Bay is so shallow, its capacity to store heat over

time is relatively small. As a result, water temperature fluctuates throughout the year,

ranging from 34° to 84° Fahrenheit (2° to 52° Celsius). These changes in water temperature influence the cycles in which plants and animals feed, reproduce, move locally

or migrate. The temperature profile of the Chesapeake Bay is fairly predictable. 

The circulation of water transports plankton, fish eggs, shellfish larvae, sediment,

dissolved oxygen, minerals and nutrients throughout the Chesapeake Bay. Circulation is driven primarily by the movements of freshwater from the north and saltwater

from the south. Circulation causes nutrients and sediments to be mixed and resuspended. This mixing creates a zone of maximum turbidity that, due to the amount of

available nutrients, fish and other organisms often use as nursery areas.

Salinity, temperature and circulation dictate the physical characteristics of water. The

warmer, lighter freshwater flows seaward over a layer of saltier and denser water

flowing upstream. The opposing movement of these two flows forms saltwater fronts

or gradients that move up and down the Chesapeake Bay in response to the input of

freshwater. These fronts are characterized by intensive mixing. A layer separating

water of different densities, known as a pycnocline, is formed. This stratification

varies within seasons, depending on river flow. 

In autumn, the fresher surface waters cool faster than deeper waters and sink.

Vertical mixing of the two layers occurs rapidly. In the process nutrients are moved

up from the bottom, making them available to phytoplankton and other surface

organisms. This turnover also distributes much-needed dissolved oxygen to deeper

waters. In winter, water temperature and salinity are relatively constant from the

surface to the bottom. During spring and summer, surface and shallow waters are

warmer than deeper waters with the coldest water found at the bottom. This layering

of warmer waters over deeper waters is often broken down by turbulence. 

The water’s chemical composition also helps determine the distribution and abundance of plant and animal life in the Chesapeake Bay. The Bay’s waters contain

organic and inorganic materials, including dissolved gases, nutrients, inorganic salts,

trace elements, heavy metals and other chemicals.

Dissolved oxygen is essential for most aquatic animals. The amount of available

oxygen is affected by salinity and temperature. Cold water can hold more dissolved

▼14

chapter ii • The Chesapeake Bay and Its Watershed
oxygen than warmer water, and freshwater holds more than saltwater. Thus, concentrations of dissolved oxygen vary, in part, with both location and time. Oxygen is

transferred from the atmosphere into surface waters by diffusion and the aerating

action of the wind. It also is released by aquatic plants in the process of photosynthesis. Since photosynthesis requires light, the production of oxygen by rooted

aquatic plants is limited to waters that are usually no more than six feet deep. Surface

water is nearly saturated with oxygen most of the year, while deep bottom waters

range from saturated to anoxic (without oxygen). 

In winter respiration levels of organisms are relatively low. Vertical mixing is good,

and there is little salinity or temperature stratification. As a result, dissolved oxygen is

plentiful throughout the water column. During the spring and summer, increased

levels of animal and microbial respiration and greater stratification may reduce

vertical mixing, resulting in low levels of dissolved oxygen in deep water. In fact, deep

parts of some tributaries like the Patuxent, Potomac and Rappahannock rivers and the

Chesapeake Bay’s mainstem can become anoxic in summer. In the autumn when

surface waters cool, vertical mixing occurs and the deeper waters are re-oxygenated.

CHESAPEAKE BAY WATERSHED

The Chesapeake Bay receives about half its water volume from the Atlantic Ocean.

The rest drains into the Bay from its 64,000-square-mile drainage basin or watershed. Runoff from this enormous watershed flows into an estuary with a surface area

of 4,500 square miles resulting in a land-to-water ratio of 14 to 1. This ratio is one

of the key factors in explaining why the drainage area has such a significant influence on water quality. The watershed includes parts of six states—New York,

Pennsylvania, West Virginia, Delaware, Maryland and Virginia—and the entire

District of Columbia (Figure II-1). Threading through the Chesapeake Bay watershed are more than 100,000 streams and rivers that eventually flow into the Bay. 

Although the Chesapeake Bay lies entirely within the Atlantic Coastal Plain, its

watershed includes parts of the Piedmont and Appalachian provinces. The waters

that flow into the Bay have different chemical identities, depending on the geology

where they originate. In turn, the nature of the Bay itself depends on the characteristics and relative volumes of these contributing waters. 

The Atlantic Coastal Plain is a flat, lowland area with a maximum elevation of about

300 feet. It is supported by a bed of crystalline rock, covered with southeasterly

dipping wedge-shaped layers of relatively unconsolidated sand, clay and gravel.

Water passing through this loosely compacted mixture dissolves many of the

minerals. The most soluble elements are iron, calcium and magnesium. The coastal

plain extends from the edge of the continental shelf, to the east, to a fall line that

ranges from 15 to 90 miles west of the Chesapeake Bay. This fall line forms the

boundary between the Piedmont Plateau and the coastal plain. Waterfalls and rapids

clearly mark this line, which is close to Interstate Highway 95. Here, the elevation

▼15

chapter ii • The Chesapeake Bay and Its Watershed
rises to 1,100 feet. Cities such as Fredericksburg and Richmond in Virginia, Baltimore in Maryland, and Washington, D.C., developed along the fall line taking

advantage of the potential water power generated by the falls. Since colonial ships

could not sail past the fall line, cargo was transferred to canals or overland shipping.

Cities along the fall line became important areas for commerce.

The Piedmont Plateau extends from the fall line in the east to the Appalachian

Mountains in the west. This area is divided into two geologically distinct regions by

Parrs Ridge, which traverses Carroll, Howard and Montgomery counties in Maryland and adjacent counties in Pennsylvania. 

▼16

chapter ii • The Chesapeake Bay and Its Watershed

West Virginia

Virginia

Pennsylvania

New York

Maryland

DC Delaware

Figure II-1. The Chesapeake Bay watershed crosses the boundaries of six states—

Maryland, Virginia, Delaware, Pennsylvania, New York and West Virginia—and the 

District of Columbia.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
Several types of dense crystalline rock, including slates, schists, marble and granite,

compose the eastern side. This variety results in a very diverse topography. Rocks of

the Piedmont tend to be impermeable, and water from the eastern side is low in the

calcium and magnesium salts.

The western side of the Piedmont consists of sandstones, shales and siltstones,

layered over by limestone. This limestone bedrock contributes calcium and magnesium to its water, making it ‘hard.’ Waters from the western side of Parrs Ridge flow

into the Potomac River, one of the Chesapeake Bay’s largest tributaries.

The Appalachian Province covers the western and northern part of the watershed and

is rich in coal and natural gas deposits. Sandstone, siltstone, shale and limestone

form the bedrock. Water from this province flows to the Chesapeake Bay mainly via

the Susquehanna River.

The hospitable climate, lush vegetation and natural beauty of the Chesapeake Bay

watershed have attracted people for thousands of years. Hunters and gatherers first

arrived about 10,000 years ago. Native Americans began cultivating crops and

settling in villages throughout the area around a thousand years ago. Arriving less

than 500 years ago, Europeans and later Africans (brought forcibly to the region

beginning in 1619) struggled to transform forests into farmland during the colonial

era between 1607 and 1775.

Since then, social, political, economic, and technological developments in metallurgy, steam power, internal combustion engines, chemical engineering and, most

recently, electronics, have enabled people to transform regional environments in

dramatic ways. Excessive forest clearing and poor land management have increased

erosion, sending tons of sediment downstream. As a result, communities that once

served as important ports are now landlocked, and elsewhere, the construction of sea

walls and breakwaters has interfered with the natural flow of sand, causing beaches

to erode too rapidly.

The changes brought about during hundreds of years of forest clearing and urban

development have resulted in the following breakdown of current landuse in the

watershed: 58 percent forest, 23 percent agriculture, 9 percent urban/suburban and

10 percent mixed open (herbaceous lands that are not agricultural such as golf

courses or institutional grounds).

Today, nearly 16 million people live in the Chesapeake Bay watershed. Table II-1

provides a demographic summary of this population. Each resident lives just a few

minutes from one of the more than 100,000 rivers, streams and creeks that drain into

the Chesapeake Bay. Each tributary can be considered a pipeline from individual

communities into the Chesapeake Bay and its rivers. Because materials on land are

easily washed into streams and rivers, individual actions on the land ultimately affect

the quality of Chesapeake Bay. These activities even include the use of automobiles,

fertilizers, pesticides, toilets, water and electricity.

▼17

chapter ii • The Chesapeake Bay and Its Watershed
CHESAPEAKE BAY TIDAL-WATER QUALITY PROBLEMS

Water quality problems in the Chesapeake Bay and its tidal tributaries are illustrated

by the following environmental indicators which reveal the effects of excessive

nutrients and sediments in the water column.

A significant proportion of living resource habitats are currently unsuitable due to

low dissolved oxygen concentration during the summer months (Figure II-2). In

2001, half of the Chesapeake Bay’s deeper waters had reduced dissolved oxygen

▼18

chapter ii • The Chesapeake Bay and Its Watershed

Table II-1. Chesapeake Bay watershed demographics

Race (%)

White . . 78.1

Black . . 18.5

Asian . . . 2.3

American 

Indian . . . 0.3

Other . . . . . 1

Educational Attainment (%)

No High School Diploma . . 23.1

High School Diploma . . . . . 47.7

Associate Degree . . . . . . . . . 5.3

Bachelor Degree . . . . . . . . . 14.4

Graduate Degree . . . . . . . . . . 9.5

Housing

Location (%)

Urban . . 71.7

Rural . . . 27.4

Farm . . . . 0.9

Other . . . . . 1

Means of Sewage

Disposal (%)

Public . . . . 74.1

Septic . . . . 24.6

Other . . . . . 1.3 

Source

of Water (%)

Public . . . 77.6

Well . . . . 20.8

Other . . . . . 1.6 

Transportation

to Work (%)

Drive Alone . . . 70.3

Car Pool . . . . . . . 15

Public Trans. . . . 6.4

Bike/Walk . . . . . 4.5

Work Home . . . . 3.2 

Source: 1990 U.S. Census.

198519861987198819891990199119921993199419951996199719981999200020012002

Better

Worse Hypoxia

Severe Hypoxia

Anoxia

2.0 –<5 mg/L

2.0 –<2 mg/L

0 –<2 mg/L

Volume (1012 liters) below 5 mg/L

20

15

10

5

0

Figure II-2. Volume of the mainstem Chesapeake Bay lower layer waters with reduced

dissolved oxygen concentrations–June through September average 1985-2002.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
concentrations, a condition known as hypoxia. Hypoxic conditions stress aquatic life

and severely hypoxic waters may be lethal to aquatic plants and animals. If bottom

waters become completely without oxygen or anoxic, nutrients tied up in sediments

are released into the overlying waters, further fueling algal growth. Recent indications show an improving trend in dissolved oxygen since 1985, the year the

Chesapeake Bay Program’s complete data collection efforts were initiated.

Chlorophyll a is an indicator of algal biomass. Algae serve as a crucial link in the

food chain; they reduce water clarity, and, left uneaten, fuel the loss of dissolved

oxygen from tidal waters. Measured as chlorophyll a, algae are the first to respond

to changes in nutrient levels. Recent trends in the Middle, Wicomico and Manokin

rivers show improvements in the level of algal biomass. Most areas show no significant change, although the Rappahannock River, Tangier Sound and the mouth of the

James River show degrading trends in terms of chlorophyll a (Figure II-3). 

Water clarity is degrading in many parts of the basin (Figure II-4). Water clarity

criteria are not attained in many shallow-water designated use habitats. In portions

of the upper Chesapeake Bay, in the Elk and Middle rivers, in upper regions of the

Choptank River, in Piscataway and Mattawoman creeks, and in the South Branch

Elizabeth River, water clarity is improving. 

CAUSES OF CHESAPEAKE BAY WATER QUALITY PROBLEMS

The Chesapeake Bay is part of an extremely productive and complex ecosystem that

consists not only of the Bay and its tributaries, but of the plant, animal and human

life they support. Through a significant investment in scientific research and coordinated monitoring and modeling programs, the Chesapeake Bay Program partners

have gained deep understanding of how human activities affect the Bay’s ecology

and have led to declines in water quality. Using modeling tools such as the Chesapeake Bay Watershed Model and the Water Quality Model, the partners have learned

a great deal about this unique resource by allowing for, among other things, the

calculation and projection of changes in loads and the resultant responses in water

quality. These models provide an estimate of management actions (such as air

controls and point source controls) which will reduce nutrient or sediment loads to

the tidal waters and lead to attainment of the Chesapeake Bay dissolved oxygen,

water clarity and chlorophyll a criteria.

HUMAN POPULATION INCREASE

The relentless encroachment of the human population threatens the ecological

balance of the Chesapeake Bay. Population in the Chesapeake Bay watershed has

doubled since the 1950s with population levels projected to reach almost 18 million

people by 2020 (Figure II-5). Each individual directly affects the Chesapeake Bay

by adding waste, consuming resources, and changing the character of the land, water

and air that surround it.

▼19

chapter ii • The Chesapeake Bay and Its Watershed
▼20

chapter ii • The Chesapeake Bay and Its Watershed

Figure II-3. Status and trends in summer Chesapeake Bay and tidal tributary chlorophyll

a concentrations relative to concentrations characteristic of mesotrophic conditions. 

* ‘Meets’ means equal to or less than and ‘fails’ means above the following chlorophyll a

concentrations during the July through September timeframe:

25 ug/l tidal freshwaters

25 ug/l oligohaline waters

20 ug/l mesohaline waters

15 ug/l polyhaline waters.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼21

chapter ii • The Chesapeake Bay and Its Watershed

Figure II-4. Status and trends in underwater bay grass growing season water clarity in

Chesapeake Bay and tidal tributaries.

* ‘Meets’ equals nonexceedance; ‘fails’ equals exceedance of the water clarity criteria during

underwater bay grasses growing season applied in locations and depths where such grasses have

occurred since the 1930s (however, if the single best year of underwater bay grasses, measured

2000–2002, achieves the acreage goal for a segment, there is no need to meet the clarity criteria).

Application depths were based on: single best year percent of total potential habitat is >=20% 

or percent of total potential habitat is 10–19.9% and underwater bay grasses are persistent 

(1978–2000).

NOTE: The criteria attainment status covers the entire segment only for purposes of illustration. The

water clarity criteria apply with the shallow-water designated use habitat which can extend as far out

as the 2-meter depth contour depending on the segment.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
LOSS OF HABITAT

Historically, habitat provided by oyster bars, underwater bay grasses, wetlands and

forests enabled the Chesapeake Bay ecosystem to recycle nutrients and sediments

efficiently, resulting in one of the most productive ecosystems in the world. Dramatic

loss of these habitats has not only led to declines in the creatures that rely on them

for food and shelter; their loss also has reduced the ecosystem’s capacity to fully

utilize nutrients and sediments leading to poor water quality in the Chesapeake Bay

and its tidal tributaries. Restoration, conservation, and preservation of the habitat

provided by oysters, underwater bay grasses, wetlands and forests are critical for

restoring living resources and for improving Chesapeake Bay water quality.

In addition to the aquatic reef habitat they provide, oysters are voracious feeders, and

each is capable of filtering up to 50 gallons of water per day. It is estimated that at

their peak abundance, the total population of oysters in the Chesapeake Bay could

filter an amount of water equal to all the water in the Chesapeake Bay in three days.

Today, due to decreased abundance, it takes a year for these animals to filter the same

volume of water. Oyster harvests in the Chesapeake Bay have declined due to overharvesting, disease, pollution and loss of oyster reef habitat. Two diseases,

discovered in the 1950s and caused by the parasites MSX and Dermo, have been a

major cause of the oyster’s decline during recent times (Figure II-6).

Underwater bay grasses are important because they produce oxygen, provide food

for a variety of animals (especially waterfowl), serve as shelter and nursery areas for

many fish and shellfish, reduce wave action and shoreline erosion, absorb nutrients

such as phosphorus and nitrogen and trap sediments. Although underwater bay

▼22

chapter ii • The Chesapeake Bay and Its Watershed Chesapeake Basin Population (millions)

25

20

15

10

5

0

195019601970198019851990199520002005201020152020

Figure II-5. Chesapeake Bay watershed human population trends since 1950 and

projected through 2020.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
grasses increased from a low point of 37,000 acres in 1984 to 85,000 acres in 2001,

the Chesapeake Bay Program watershed partners have adopted a new restoration

goal of 185,000 acres (Figure II-7).

Wetlands and forests (especially those buffering streambanks and shorelines)

provide critical habitat and also act as natural filters to minimize sediment loads and

absorb nutrients. Approximately 1.5 million acres of wetlands remain in the Chesapeake Bay watershed, less than half of the wetlands that were here during colonial

times. Forests that once covered 90 to 95 percent of the watershed now cover only

58 percent (Figure II-8). 

EXCESS NUTRIENTS

Nutrients are essential; they provide crucial ingredients to help living things grow.

However, there is a delicate balance between what is needed for organisms to thrive,

and what is excessively harmful. The amount of nutrients that would naturally enter

the Chesapeake Bay has been adversely multiplied by anthropogenic sources over the

course of history. Runoff from fertilizers applied to agriculture and lawns, sewage and

industrial discharges, automobile emissions and power generation, are all sources that

create excessive amounts of nutrient pollution delivered to the Chesapeake Bay and

▼23

chapter ii • The Chesapeake Bay and Its Watershed

53 56 59 62

Virginia

Maryland

65 68 71 74 77 80 83 86 89 92 95 98 2001

40

35

30

25

20

15

10

5

0

Commercial Landings (millions of pounds)

Figure II-6. Trends in Maryland and Virginia commercial harvest landings of oysters 1953–2001.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼24

chapter ii • The Chesapeake Bay and Its Watershed

Restoration Goal (185,000 acres by 2010)

Bay Grasses (x 1,000 acres)

200

180

160

140

120

100

80

60

40

20

0

198419851986198719881989199019911992199319941995199619971998199920002001

Figure II-7. Trends in the acreages of Chesapeake Bay and tidal tributary underwater

bay grasses compared to the new 185,000 acre restoration goal. Light blue area of 

bar includes estimated additional acreage when flight restrictions or weather conditions

prevented collection of a complete set of aerial photographs.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net. Percentage of Watershed Forested

Early

Colonies

Land

cleared for

agriculture

and timber

Land

abandoned

after Civil

War and

Depression

2000

D

e

v

e

l

o

p

m

e

n

t

1650 1700 1750 1800 1850 1900 1950

100

80

60

40

20

0

Figure II-8. Trends in Chesapeake Bay basin forests expressed as percentage of the

watershed that was forested since 1650.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
its tidal tributaries. These anthropogenic sources of nutrients, together with a decline

in the Chesapeake Bay’s own natural capacity to assimilate these pollutants due to

loss of habitats and living resources, have created overwhelming stresses.

Excess amounts of nitrogen and phosphorus cause rapid growth of phytoplankton,

creating dense algal populations or blooms. These blooms become so dense that they

reduce the amount of sunlight available to underwater bay grasses. Without sufficient

light, these underwater plants cannot photosynthesize and produce the food they

need to survive. Algae also may grow directly on the surface of underwater bay

grasses, further blocking light. Another hazard of nutrient-enriched algal blooms

comes after the algae die. As the algal blooms decay, oxygen is consumed via

bacterial decomposition which can lead to dangerously low oxygen levels available

for aquatic organisms. Known as eutrophication, this nutrient over-enrichment,

ultimately leading to low dissolved oxygen levels in ambient waters, is a widespread

problem throughout the tidal waters.

EXCESS SEDIMENTS

The surrounding watershed and the tidal waters of the Chesapeake Bay and its tidal

tributaries transport huge quantities of sediments. Although sediments are a natural

part of the Chesapeake Bay ecosystem, accumulation of excessive amounts is undesirable. As sediments settle to the bottom of the Chesapeake Bay, they can smother

bottom-dwelling plants and animals, such as oysters and clams. Sediments

suspended in the water column cause the water to become cloudy, decreasing the

light available for underwater bay grasses. Sediment-related water quality problems,

however, tend to be more of a localized problem.

Individual sediment particles have a large surface area, and many molecules easily

adsorb or attach to them. As a result, sediments can act as chemical sinks by

adsorbing nutrients and other pollutants. Thus, areas of high sediment deposition

sometimes have high concentrations of nutrients which may later be released.

Reducing sediment loads to the Chesapeake Bay and its tidal tributaries is critical for

restoring water quality.

SOURCES OF NUTRIENT LOADS TO THE 

CHESAPEAKE BAY TIDAL WATERS

When accounting for all the nutrients that enter the Chesapeake Bay from its watershed, the two largest anthropogenic contributors of both nitrogen and phosphorus are

nonpoint source runoff from agriculture and point sources. Forests are a natural

source of nutrients, but relative to anthropogenic sources, are a relatively small

percentage of the total nutrient load entering the Chesapeake Bay. The largest source

of sediments in the Bay is agriculture, followed by forest, urban runoff and mixed

open lands. Figures II-9 through II-14 provide a breakdown of the nitrogen,

phosphorus, and sediment loads delivered to the Chesapeake Bay and its tidal tributaries as well as estimated reductions achieved in these loads from 1985 to 2000

from each source. These loads do not include atmosphere deposition directly to tidal

waters—see “Atmospheric Sources” below.

▼25

chapter ii • The Chesapeake Bay and Its Watershed
▼26

chapter ii • The Chesapeake Bay and Its Watershed

Figure II-9. Chesapeake Bay

Watershed Model-estimated nitrogen

loads by source delivered to the

Chesapeake Bay and its tidal tributaries excluding direct atmospheric deposition to tidal waters and shoreline

erosion. A total of 285 million

pounds/year were delivered to the

tidal waters based on the Watershed

Model’s 2000 Progress scenario.

Source: Chesapeake Bay Program website

http://www.chesapeakebay.net.

Non-Tidal Water

Deposition

1% 

Septic

4%

Mixed Open

6%

Urban Runoff

11%

Forest

15%

Point Source

22%

Agriculture

41%

149.4

30.6

17.6

10.1

116.3 (41%)

41.5 (15%)

38.7

30.3 (11%)

18.4 (6%)

11.9 (4%)

3.5

3.6 (1%)

0

30

60

90

120

150

180

210

240

270

300

330

360

1985 2000 Progress

Total Nitrogen Load

(million lbs/year)

Non-Tidal

Water

Deposition

Septic

Mixed Open

Urban

Runoff

Forest

Point

Source

Agriculture

87.7

62.8 (22%)

Figure II-10. 1985 and 2000 Chesapeake Bay Watershed Model-estimated nitrogen loads

by source delivered to the Chesapeake Bay and its tidal tributaries excluding 

direct atmospheric deposition to tidal waters and shoreline erosion.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼27

chapter ii • The Chesapeake Bay and Its Watershed

Figure II-11. Chesapeake Bay

Watershed Model-estimated

phosphorus loads by source 

delivered to the Chesapeake Bay and

its tidal tributaries excluding direct

atmospheric deposition to tidal

waters and shoreline erosion. A 

total of 19.1 million pounds/year

were delivered to the tidal waters

based on the Watershed Model’s

2000 Progress scenario. 

Source: Chesapeake Bay Program website

http://www.chesapeakebay.net.

Agriculture

48%

Point Source

22%

Forest

2%

Urban Runoff

16%

Non-Tidal Water

Deposition

1% 

Mixed Open

11%

11.57

3.73

2.12

8.99 (47%)

0.41 (2%)

0.38

3.12 (16%)

2.18 (11%)

0.16 (1%)

0.16

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

1985 2000 Progress

Total Phosphorus Loas

(million lbs/year)

Non-Tidal

Water

Deposition

Mixed Open

Urban

Runoff

Forest

Point

Source

Agriculture

9.17

4.26 (22%)

Figure II-12. 1985 and 2000 Chesapeake Bay Watershed Model-estimated phosphorus

loads by source delivered to the Chesapeake Bay and its tidal tributaries excluding direct

atmospheric deposition to tidal waters and shoreline erosion.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼28

chapter ii • The Chesapeake Bay and Its Watershed

Figure II-13. Chesapeake Bay

Watershed Model-estimated 

sediment loads by source delivered 

to the Chesapeake Bay and its 

tidal tributaries excluding direct

atmospheric deposition to tidal

waters and shoreline erosion. A 

total of 5.04 million pounds/year

were delivered to the tidal waters

based on the Watershed Model’s

2000 Progress scenario.

Source: Chesapeake Bay Program website

http://www.chesapeakebay.net.

Agriculture

63%

Forest

20%

Urban Runoff

9%

Mixed Open

8%

4.074

0.377

3.188 (63%)

0.969

0.386 (8%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

1985 2000 Progress

Sediment Load

(million tons/year)

Mixed Open

Urban

Runoff

Forest

Agriculture

0.995 (20%)

0.475 (9%)

0.413

Figure II-14. 1985 and 2000 Chesapeake Bay Watershed Model-estimated sediment 

loads delivered to the Chesapeake Bay and its tidal tributaries excluding direct 

atmospheric deposition to tidal waters and shoreline erosion.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
NONPOINT SOURCES

Nonpoint source pollution, unlike pollution from industrial and sewage treatment

plants, comes from many diffuse sources. Rainfall or melted snow moving over and

through the ground is one such source. As the runoff moves, it picks up and carries

away natural and anthropogenic pollutants, some of which are deposited into the

Chesapeake Bay and its tidal tributaries. Animal manure or chemical fertilizers

applied to lawns, gardens and farm fields can wash off the land into streams and rivers

or seep into the ground where they can be delivered to streams via groundwater.

Nonpoint source pollution in the Chesapeake Bay watershed emanates from six

sources: agriculture, forest, urban, mixed open, septic and atmospheric deposition.

As noted earlier, agriculture accounts for the largest percentage of nonpoint source

nitrogen pollution. 

Agricultural runoff includes nutrients from chemical fertilizers and animal manure

applied to land, as well as eroded soil particles and organic matter. Improper storage

of animal wastes and mortality can result in additional nutrients being leaked into the

groundwater or carried off in rainwater. Animals pastured near streams and other

water bodies also contribute to the nutrient load delivered to the tributaries of the

Chesapeake Bay. 

Septic systems leak nutrients into the groundwater since most systems currently do

not incorporate technologies to remove nitrogen from the wastewater they treat then

discharge. Such systems are a source of nitrogen to the watershed not only from the

treated effluent, but from systems that are not functioning properly due to age,

neglect in operation and maintenance, or improper siting and installation. 

Increases in nutrient runoff from urban areas are expected to occur in the future due

to increasing development of forested and agricultural lands. Nitrogen loads from

septic systems are expected to increase as population increases, however, if people

continue to move away from the urban and suburban areas that are currently 

serviced by public sewer facilities, projected loads may be even higher. Runoff from

farms is generally declining as farmers adopt nutrient management and runoff

control techniques, but also because the overall amount of farmland is declining.

POINT SOURCES

A point source is an outfall pipe associated with a point of entry, such as the end of a

pipe, where nutrients enter waterways. Industrial sites and wastewater treatment

plants are examples of point sources. As of 2000, point sources were estimated to

account for 22 percent of the total load of nitrogen and phosphorus to the Chesapeake

Bay and its tidal tributaries. The Chesapeake Bay Program, working with its partner

states and jurisdictions, assimilated a database on all of the point sources with significant contributions of nutrients to the watershed. (Sediments are not currently counted

as a component of point source effluents.) The point source database consists of

▼29

chapter ii • The Chesapeake Bay and Its Watershed
▼30

chapter ii • The Chesapeake Bay and Its Watershed

facilities located in all the states and jurisdictions in the Chesapeake Bay watershed 

(Table II-2). These point sources are divided into four principal categories.

• Significant municipal facilities, which are generally municipal wastewater

treatment plants that discharge flows of equal to or greater than 0.5 millions of

gallons per day (MGD). More specifically, significant municipal facilities are

defined slightly differently for each jurisdiction. For Virginia, these facilities

are those that have a design flow of 0.5 MGD or greater, and all facilities

located below the fall line, regardless of flow. For Maryland, significant facilities are those having a current flow of 0.5 MGD or greater. For Pennsylvania,

significant facilities are those having average annual 1985 flows of 0.4 MGD

or greater. For Delaware, West Virginia, and New York, the Chesapeake Bay

Program selected as significant municipal facilities those in the EPA Permit

Compliance System database with current flows of 0.5 MGD or greater.

• Significant industrial facilities have been identified as those that discharge the

equivalent or greater amounts of nutrients as compared to a municipal wastewater treatment facility’s discharge of 0.5 MGD. These discharge loads would

roughly be equivalent to those of municipalities with flows of 0.5 MGD or

greater, or a total nitrogen load of 75 pounds per day, and a phosphorus load of

25 pounds per day or greater (based on a municipal facility effluent discharge

of 2.5 mg/l total phosphorus and 18 mg/l total nitrogen).

• Nonsignificant municipal facilities are those that are generally smaller than

discharge flows of 0.5 MGD. Only nonsignificant municipal facilities in Maryland and Virginia are included in the database due to the availability of data.

While there are approximately 185 nonsignificant municipal facilities across

the Chesapeake Bay watershed, the flow and corresponding nutrient loads from

these facilities are less than 5 percent of the total for all point sources.

• Combined sewer overflow loads only for the District of Colombia are included

in the database because it is the only location for which the Chesapeake Bay

Program has nutrient load data. Certainly other combined sewer overflows

exist in the watershed, however, to date these have not been quantified in terms

of nitrogen and phosphorus load discharges. 

Table II-2. Summary of point source facilities within the Chesapeake Bay watershed.

Point Source Number of Total 2000

Category Description Facilities Flow (MGD)

Significant Municipals* Generally > 0.5 MGD 304 1,554.4 

Significant Industrials Discharge loads generally 49 524.7 

> 75 lb/day TN & 25 lb/day TP 

Non-significant Municipals Generally < 0.5 MGD 185 10.8 

Combined Sewer Overflows Only for Blue Plains 1 7.6 

Total 540 2,097.5 

*Including the six Virginia plants to be built by 2010. 

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
Today, 83 of the 304 significant municipal wastewater treatment plants and many

industrial facilities as well, are using nutrient removal technology (NRT). By 2010,

that number is likely to increase to 156. Exponential advances in the development of

NRT in recent years, along with performance levels beyond what was traditionally

expected, have clearly shown the potential for this technology to achieve much lower

levels of nitrogen in discharges than the traditionally accepted performance levels. It

must be recognized that the enhanced performance seen to date is partly due to the

fact that some treatment plants are operating below their design capacity, and this

level of nutrient reduction may be difficult to maintain as flows increase. To date, 12

of the 49 significant industrial nutrient dischargers located in the Chesapeake Bay

watershed are practicing some form of nutrient removal, and that number is expected

to increase to 16 by 2010.

The nutrient load discharged from municipal point sources is directly linked to population. Because of the implementation of NRT to date, these point sources

collectively have achieved a 53 percent reduction in phosphorus loads and a 28

percent reduction in nitrogen loads since 1985, despite the 15 percent increase in

population since then. But because the watershed’s population is expected to

increase by an additional 14 percent by 2010, it will be increasingly more challenging to achieve nutrient reductions from point sources. Figures II-15 and II-16

illustrate the nitrogen and phosphorus loads, respectively, from point sources in the

▼31

chapter ii • The Chesapeake Bay and Its Watershed

0

10

20

30

40

50

60

70

80

90

100

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 2000 2010 2015 2020

Year

Total Nitrogen Delivered Loads

(million pounds/year)

0

2

4

8

10

12

14

16

18

20

Human Population (Million)

Figure II-15. Total nitrogen loads delivered to the Chesapeake Bay and its tidal tributaries from all

point source facilities in the watershed ( ) compared with human population trends ( ) in the

Chesapeake Bay watershed projected through 2020.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
past, present and for future projections based on NRT implementation plans by 2010,

and for the year 2020 if no more facilities than currently planned implement NRT.

Significant progress has been made since 1985 in achieving reductions, but population growth will diminish these successes unless NRT is implemented in more of the

facilities, while simultaneously reaching far greater performance levels. 

ATMOSPHERIC SOURCES

The sources of nitrogen emissions which contribute to atmospheric nitrogen deposition to the Chesapeake Bay and its watershed are primarily fossil fuels combustion

(e.g., electric power generation, on-road vehicles, and industry) which emit nitrogen

oxides (NOx) and agricultural activities (such as commercial fertilizers and animal

manure), which release ammonia into the air. Much of the atmospheric nitrogen that

deposits to the watershed and makes it way to the tidal waters originates from states

located in the nitrogen (NOx and ammonia) airsheds (Figure II-17). The NOx airshed

is roughly 1,081,600 km2 in size and the ammonia airshed is roughly 688,000 km2

in size. 

Atmospheric nutrient pollution that falls directly on the water is displayed as a separate category and accounts for 8 percent of the total nitrogen load. Ultimately,

▼32

chapter ii • The Chesapeake Bay and Its Watershed

0

1

2

3

4

5

8

9

10

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 2000 2010 2015 2020

Year

Total Phosphorus Delivered Loads 

(million pounds/year)

0

2

4

8

10

12

14

16

18

20

Human Population (Million)

Figure II-16. Total phosphorus loads delivered to the Chesapeake Bay and its tidal tributaries from all

point source facilities in the watershed ( ) compared with human population trends ( ) in the

Chesapeake Bay watershed projected through 2020.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼33

chapter ii • The Chesapeake Bay and Its Watershed

atmospheric nitrogen emissions can be viewed as a nonpoint source when they are

deposited on the land and reach the Chesapeake Bay as runoff. Atmospheric nitrogen

that falls on the land accounts for an additional 24 percent of the total nitrogen load

and is included as part of the agriculture, forest and urban and mixed open sources

in Figures II-9 and II-10. 

REDUCED

OXIDIZED

Figure II-17. Principal nitrogen airsheds for the Chesapeake Bay.

Source: Chesapeake Bay Program website http://www.chesapeakebay.net/air/air.htm.
ANTHROPOGENIC SOURCE INPUTS

Table II-3 was developed by estimating the relative nitrogen and phosphorus source

contributions from the perspective of anthropogenic inputs–atmospheric emissions,

chemical fertilizers and manure. This table includes atmospheric deposition directly

to tidal waters (20 million pounds), thus totaling a model-estimated 305 million

pounds/year of nitrogen delivered to the Chesapeake Bay and its tidal waters instead

of 285 million pounds/year as portrayed in Figures II-9 and II-10. As also shown in

Table II-3, the combined atmospheric deposition directly to non-tidal and tidal

surface waters is 8 percent (7 percent plus 1 percent) of the total load. 

Table II-3 provides estimates based solely on proportions of anthropogenic inputs.

There are three key inputs to the land surfaces–atmospheric deposition, chemical

fertilizer applications, and manure applications–from which the relative contribution

in delivered nitrogen loads is depicted based on their relative proportions. There are

natural sources of nitrogen loads to Chesapeake Bay tidal waters that cannot be

extracted and are, therefore, included in these source contributions.

▼34

chapter ii • The Chesapeake Bay and Its Watershed

Table II-3. Chesapeake Bay Airshed and Watershed Model-estimated 2000 Progress scenario sources

of nitrogen and phosphorus loads (million pounds/year) delivered to the Chesapeake Bay and its

tidal tributaries based on anthropogenic inputs of atmospheric deposition, chemical fertilizers,

manure, point sources and septics, excluding shoreline erosion.

Total Total

Total Nitrogen Total Phosphorus

Nitrogen (% of Total) Phosphorus (% of Total)

2000 2000 2000 2000

Source Loading Category Progress Progress Progress Progress

Atmospheric Deposition to Land 75,003,697 25% 5,900,372 29%

Atmospheric Deposition to Non-Tidal Water 3,559,840 1% 162,471 1% 

Atmospheric Deposition to Tidal Water 20,467,458 7% 1,550,081 7% 

Chemical Fertilizer Applications 

to Agricultural Land 49,353,664 16% 3,456,104 17% 

Chemical Fertilizer Applications 

to Urban Land 18,146,154 6% 0 0% 

Chemical Fertilizer Applications to 

Mixed Open Land 9,872,122 3% 0 0% 

Manure Applications to Agricultural Land 46,048,616 15% 4,646,036 22% 

Animal Feeding Operation Runoff 8,026,157 3% 696,297 3% 

Point Source 62,841,812 21% 4,257,314 21% 

Septic 11,904,029 4% 0 0% 

Bay-Wide Total 305,223,54 100% 20,668,675 100% 

Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
BACKGROUND

Many natural biological, physical and chemical processes and interactions influence

water quality conditions and physical habitats in the Chesapeake Bay and its tidal

tributaries. In addition, the watershed and estuary have changed dramatically, and in

many ways, irreversibly, over the last four centuries as the population has grown to

nearly 16 million people. The current state designated uses cannot be met in the

deeper waters of the Chesapeake Bay mainstem and portions of the major lower tributaries due to natural and human-caused conditions that cannot be remedied. The

current dissolved oxygen criteria adopted by Maryland and Virginia into their water

quality standards—≥5 mg/l at all times and ≥4 mg/l minimum/≥5 mg/l daily

average, respectively—are unlikely to be achieved in deeper Chesapeake Bay tidal

waters during the summer season where physical processes (such as water-column

stratification and water circulation) and bottom bathymetry-related barriers prevent

the replenishment with oxygenated waters. 

As described below, a combination of natural and human-caused conditions prevents

attainment of the dissolved oxygen concentrations necessary to meet the states’

current aquatic life designated uses in portions of the Chesapeake Bay and its tidal

tributaries. It should be noted that any of the six designated use removal factors specified in the EPA Water Quality Standards regulations (40 CFR 131.10[g]) and

described in Chapter I can be employed, where appropriate, to justify changing a

designated use. This chapter relies on two of those factors, but that reliance does not

prevent the states from using one or more additional factors in justifying refinements

to their tidal-water designated uses.

The model simulation of all-forested and pristine watersheds and findings from

scientific paleoecological records indicate that dissolved oxygen levels less than 

5 mg/l are a natural condition in some deeper waters of the Chesapeake Bay and its

tidal tributaries during the summer. Furthermore, even where natural conditions

could support a dissolved oxygen concentration of 5 mg/l, model simulations show

▼35

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

chapteriii

Why Attaining the Current 

Tidal-Water Designated Uses

Appears Not to be Feasible
that areas exist where current state standards are unlikely to be met due to irremediable human-caused conditions.

NATURAL CONDITIONS THAT MAY PREVENT

ATTAINMENT OF CURRENT DESIGNATED USES

Evidence from the paleoecological record of the Chesapeake Bay Watershed and

Water Quality models’ simulations of a pristine and all-forested Chesapeake Bay

system indicates that natural conditions alone may prevent attainment of current

uses. In the absence of monitoring data from periods before human settlement

occurred, these findings and simulations provide the best available descriptions and

estimates of the Bay’s tidal-water quality under natural conditions.

PALEOECOLOGICAL RECORD OF NATURAL CONDITIONS

Dissolved oxygen levels vary naturally in lakes, estuaries and oceans over temporal

and spatial scales due to many different biological, chemical and physical processes.

In estuaries such as the Chesapeake Bay, freshwater inflow that influences watercolumn stratification; nutrient input and cycling; physical processes such as

density-driven circulation; and tides, winds, water temperature and bacterial activity

are among the most important factors. These processes can lead to large natural

seasonal and interannual variability in oxygen levels in many parts of the Chesapeake Bay and its tidal tributaries. 

Superimposed on this natural dissolved oxygen variability is a progressive increase

in the intensity and frequency of hypoxia and anoxia over the past 100 to 150 years,

most notably since the 1960s. This human-induced eutrophication is evident both

from instrumental data and geochemical and faunal/floral ‘proxies’ of dissolved

oxygen conditions obtained from the sedimentary record. 

The instrumental record, while incomplete prior to the inception of the multi-agency

Chesapeake Bay Monitoring Program in 1984, suggests that as early as the 1930s

(Newcombe and Horne 1938) and especially since the 1960s (Taft et al. 1980),

summer oxygen depletion has been recorded in the Chesapeake Bay. Officer et al.

(1984), Malone (1992), Harding and Perry (1997) and Hagy (2002) provide useful

discussions of the instrumental record of dissolved oxygen and related parameters

such as chlorophyll a across this multi-decadal data record. 

At issue is whether, and to what degree, dissolved oxygen reductions are a naturally

occurring phenomenon in the Chesapeake Bay. Long sediment core records 

(17 meters to greater than 21 meters in length) indicate that the Chesapeake Bay

formed about 7,500 years ago (Cronin et al. 2000; Colman et al. 2002) when the

rising sea level after the final stage of Pleistocene deglaciation flooded the Susquehanna channel. The modern estuarine circulation and salinity regime probably began

in the mid- to late Holocene epoch, about 4,000-5,000 years ago (in the regional

▼36

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
climate of the early Holocene, Chesapeake Bay’s salinity differed from that of the

late Holocene). This theory is based on the appearance of ‘pre-colonial’ benthic

foraminiferal, ostracode and dinoflagellate assemblages. It is against this mid- to late

Holocene baseline that the post-European settlement and modern dissolved oxygen

regime of the Chesapeake Bay can be viewed.

During the past decade, studies of the Chesapeake Bay’s late Holocene dissolved

oxygen record have been carried out using several proxies of past dissolved oxygen

conditions, which are preserved in sediment cores that have been dated using the

most advanced geochronological methods. These studies, using various indicators of

past dissolved oxygen conditions, are reviewed in Cronin and Vann (2003) and

provide information that puts the monitoring record of the modern Chesapeake Bay

into a long-term perspective and permits an evaluation of natural variability in the

context of restoration targets. The following types of measurements of oxygensensitive chemical and biological indicators have been used: nitrogen isotopes

(Bratton et al. 2003); biogenic silica and diatom communities (Cooper and Brush

1991; Cooper 1995; Colman and Bratton 2003); molybdenum and other metals

(Adelson et al. 2000; Zheng et al. 2003); lipid biomarkers; acid volatile sulfur

(AVS)/chromium reducible sulfur (CRS) ratios; total nitrogen and total organic

carbon (Zimmerman and Canuel 2000); elemental analyses (Cornwell et al. 1996)

and paleoecological reconstructions based on dinoflagellate cysts (Willard et al.

2003); and benthic foraminiferal assemblages (Karlsen et al. 2000). Although space

precludes a comprehensive review of these studies, and the time period studied and

level of quantification vary, several major themes emerge, summarized below.

First, the 20th century sedimentary record confirms the limited monitoring record of

dissolved oxygen, documenting that there has been a progressive decrease in

dissolved oxygen levels, including the periods of extensive anoxia in the deepchannel region of the Chesapeake Bay that have been prominent during the past 40

years. Most studies provide strong evidence that there was a greater frequency or

duration of seasonal anoxia beginning in the late 1930s and 1940s and again around

1970, reaching unprecedented frequencies or duration in the past few decades in the

mesohaline Chesapeake Bay and the lower reaches of several tidal tributaries

(Zimmerman and Canuel 2000; Hagy 2002). Clear evidence of these low dissolved

oxygen conditions has been found in all geochemical and paleoecological indicators

studied principally through their great impact on benthic and phytoplankton (both

diatom and dinoflagellate) communities.

Second, extensive late 18th and 19th century land clearance also led to oxygen reduction and hypoxia, which exceeded levels characteristic of the previous 2,000 years.

Best estimates for deep-channel mid-bay seasonal oxygen minima from 1750 to

around 1950 are 0.3 to 1.4-2.8 mg/l and are based on a shift to dinoflagellate cyst

assemblages of species tolerant of low dissolved oxygen conditions. This shift is

characterized by a four- to fivefold increase in the flux of biogenic silica, a greater

than twofold (5-10 milliliter-1) increase in nitrogen isotope ratios (15N) and periods

of common (though not dominant) Ammonia parkinsoniana, a facultative anaerobic

▼37

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
foraminifer. These patterns are likely the result of increased sediment influx and

nitrogen and phosphorous runoff due to extensive land clearance and agriculture. 

Third, before the 17th century, dissolved oxygen proxy data suggest that dissolved

oxygen levels in the deep channel of the Chesapeake Bay varied over decadal and

interannual time scales. Although it is difficult to quantify the extremes, dissolved

oxygen probably fell to 3 to 6 mg/l, but rarely if ever fell below 1.4 to 2.8 mg/l.

These paleo-dissolved oxygen reconstructions are consistent with the Chesapeake

Bay’s natural tendency to experience seasonal oxygen reductions due to its bathymetry, freshwater-driven salinity stratification, high primary productivity and organic

matter and nutrient regeneration (Boicourt 1992; Malone 1992; Boynton et al. 1995).

In summary, the main channel of the Chesapeake Bay most likely experienced

reductions in dissolved oxygen before large-scale post-colonial land clearance took

place, due to natural factors such as climate-driven variability in freshwater inflow

(Table III-1). However, this progressive decline in summer oxygen minima, beginning in the 18th century and accelerating during the second half of the 20th century,

is superimposed on interannual and decadal patterns of dissolved oxygen variability.

Human activity during the post-colonial period has caused the trend towards hypoxia

and most recently (especially after the 1960s) anoxia in the main channel of the

Chesapeake Bay and some of its larger tidal tributaries. The impact of these patterns

has been observed in large-scale changes in benthos and phytoplankton communities, which are manifestations of habitat loss and degradation. 

WATER QUALITY CONDITIONS UNDER ALL-FORESTED 

AND PRISTINE WATERSHEDS

The natural relationships between processes on the land and in the water have been

altered to such a degree that it is now difficult to discern natural conditions in this

complex estuarine ecosystem. A ‘natural’ system is often considered to be the state

prior to European settlement, although pre-contact Native American activities had an

effect on the watershed and the Chesapeake Bay ecosystem as well. Pristine estuarine ecosystems no longer exist from which to reference water quality conditions

since human-induced changes now affect even the most remote regions of the planet.

Given the research and monitoring data limitations for measuring natural water

quality conditions, the Chesapeake Bay Program developed a paired set of model

scenarios that represent its best effort to simulate water quality conditions prior to

European settlement. By using the same model simulation tools to estimate presettlement water quality conditions as those used in other aspects of the attainability

analyses presented in the Technical Support Document, reasonable comparisons 

can be made among estimated nutrient and sediment loading results and resulting

simulated tidal-water quality responses.

The ‘all-forest’ scenario is a model simulation of what nutrient and sediment loads

might occur if the entire Chesapeake Bay watershed was forested and atmospheric

▼38

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
▼39

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-1. Synthesis of five scientific experts’ individual and collective findings

on the history of anoxia and hypoxic conditions in Chesapeake Bay tidal waters.

Chesapeake Bay Dissolved Oxygen Criteria

Team member Dr. Thomas Cronin, of the

U.S. Geological Survey (USGS), surveyed

five scientists8 who have studied the history

of anoxia and hypoxia in the Chesapeake

Bay over decadal and centennial time

scales, using geochemical and biological

proxies from sediment cores and instrumental and historical records. The

consensus of the five scientists is that the

Chesapeake Bay was seasonally anoxic

between 1900 and 1960. The seasonal

anoxia was extensive in the deep channel

and probably lasted several months.

Similarly, between 1600 and 1900, the 

near-unanimous consensus is that the

Chesapeake Bay was seasonally anoxic for

probably weeks to months in the deep

channel. One researcher had reservations

about his group’s earlier conclusion on

definitive evidence of anoxia prior to 1900,

but cannot exclude the possibility of anoxia

during this period. Anoxia during the 1900–

1960 period was probably geographically

less extensive in the Chesapeake Bay and

perhaps occurred less frequently (i.e., not

every year) than after the 1960s. In addition

to the geochemical and faunal proxies of

past trends in oxygen depletion, experts cite

the Sale and Skinner (1917) instrumental

documentation of hypoxia and probable

anoxia in the lower Potomac River in 1912.

For the period prior to European colonization (approximately 1600 AD), the

consensus is that the deep channel of the

Bay may have been briefly hypoxic (less

than 2 mg/l), especially during relatively

wet periods (which did occur, based on the

paleo-climate record). Anoxia probably

occurred only during exceptional conditions. It should be noted that the late 

16th century and much of the 17th century

were extremely dry periods, not conducive

to oxygen depletion. 

In sum, hypoxia, and probably periodic

spatially limited anoxia, occurred in the

Chesapeake Bay prior to the large-scale

application of fertilizer, but since the 

1960s oxygen depletion has become 

much more severe.

These experts also unanimously believe that

restoring the Chesapeake Bay to mid-20th

century, pre-1960 conditions might be

possible but very difficult (one expert

suggested an 80 percent nitrogen reduction

was necessary), in light of remnant nutrients

in sediment in the Chesapeake Bay and

behind dams, likely increased precipitation

as the climate changes, population growth

and other factors. Most researchers believe

that restoring the Chesapeake Bay to conditions prior to 1900 is either impossible,

or not realistic, simply due to the fact that

the temporal variability (year-to-year and

decadal) in ‘naturally occurring’ hypoxia

renders a single target dissolved oxygen

level impossible to define. 

Source: U.S. EPA 2003. 

8T. M. Cronin (USGS, Reston, Virginia), S. Cooper (Bryn Athyn College), J. F. Bratton (USGS, Woods

Hole, Massachusetts), A. Zimmerman (Pennsylvania State University), G. Helz (University of Maryland, College Park).
deposition reduced to 10 percent of the current loading rates. The storage of nutrients in the soil is still somewhat elevated under this scenario, and the nitrogen

delivered to the Bay’s tidal waters is actually greater than the atmospheric inputs to

the watershed, owing to a ‘draw-down’ of nutrients in the soil. Shoreline erosion

loading rates are maintained at current levels.

The ‘pristine’ scenario is a model simulation of what may have occurred under presettlement conditions. Atmospheric deposition is reduced to 10 percent of the current

loading rates as in the all-forest scenario, but the soil storage of nutrients is also

reduced, so that there is no ‘draw-down’ of nutrients during the simulation. In addition, steps were taken to restrict the conversion of particulate organic nitrogen to

solution organic nitrogen. Shoreline erosion was set to only 10 percent of current

levels to account for the pre-settlement presence of vast underwater grass beds and

intertidal oyster bar breakwaters. Unlike most model simulations, no fertilizer

applications to agricultural land, implementation of best management practices,

septic loads or discharges from point sources are shown in either the all-forest or

pristine scenarios.

STRENGTHS AND LIMITATIONS OF THE ALL-FOREST 

AND PRISTINE SCENARIOS

It is extremely difficult to determine the accuracy of the predictions at one-tenth the

calibrated nitrogen loads for both the Chesapeake Bay Watershed and Water Quality

models. Overall, the extremes of the all-forest and pristine scenarios push all three

Chesapeake Bay models, including the Bay airshed model, to their limits since they

are calibrated to relatively current conditions.

The biological filtering capacities of a pristine Chesapeake Bay ecosystem are not

factored into the current Bay models. One of these processes involved the vast extent

of filter feeders, such as oysters, that consumed water-borne nutrients. In addition,

oyster reefs provided habitat for an enormous range of other animals such as worms,

snails, sea squirts, sponges, small crabs, and fishes, all of which are important

components of the estuarine food web.

Existing reservoirs, dams, and shipping channels are present in the all-forest and

pristine scenario landscapes and tidal waters because the Chesapeake Bay Watershed

and Water Quality models were calibrated with these human alterations in place. As

described in Chapter IV, these physical alterations can directly influence Chesapeake

Bay tidal-water quality conditions.

MODEL-SIMULATED NATURAL DISSOLVED OXYGEN CONDITIONS

By anticipating these limitations when characterizing pre-European settlement

effects on watershed loadings and tidal-water quality conditions, the paired all-forest

and pristine scenarios present the best quantitative estimate of where and when

“naturally occurring pollutant concentrations prevent the attainment of the use”

▼40

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
▼41

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

(40 CFR 131.10[g]). The range of nutrient and sediment loads from these two

scenarios yields the watershed partners’ current best estimated range of “naturally

occurring pollutant concentrations” and resulting Chesapeake Bay tidal-water

quality conditions. Like all model results, the loads and water quality responses are

most useful when compared to other scenarios. In this case, adequate comparisons

can be made between the all-forest scenario results and those containing established

levels of anthropogenic effects.

Figure III-1 illustrates the results of outputs from three scenarios of the Chesapeake

Bay Water Quality Model–the pristine, all-forest, and E3 scenarios. The outputs

provide the percent nonattainment of a 5 mg/l monthly average dissolved oxygen

concentrations over 10 years of hydrology for the deep-channel, deep-water, openwater and migratory designated uses as discussed in Chapter IV. These dissolved

oxygen concentrations are displayed over time (June 1 through September 30) and

volume of each respective designated use. Given the integration of the Chesapeake

Bay Water Quality Model with water quality monitoring data, the outputs are

currently generated as monthly averages although the water quality model operates

on hourly time scales (Table III-2).

0%

10%

20%

30%

40%

50%

60%

70%

Deep-Channel Deep-Water Open-Water Migratory

Refined Tidal-Water Designated Uses

Percent Nonattainment of 5 mg/l Monthly Average

Dissolved Oxygen Concentration Over Time and Volume

Figure III-1. Percent nonattainment of a 5 mg/l monthly average dissolved oxygen concentration over

the June through September period for the E3 (physically implausible) ( ), all-forest ( ) and pristine 

( ) model scenarios by the refined tidal-water designated uses.
▼42

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-2. Chesapeake Bay Watershed and Water Quality models.

The watershed and airshed models are

loading models. As such, they provide an

estimate of management actions through air

controls, agricultural best management

practices, or point source controls which

will reduce nutrient or sediment loads to 

the Chesapeake. The advantage of using

loading models is that the full simulation

through different hydrologies of wet, dry,

and average periods can be simulated on

existing or hypothetical landuse patterns.

All of the Chesapeake Bay Program models

used in the attainability analyses simulate

the 10-year period of 1985 to 1994 (Linker

et al. 2000). 

Chesapeake Bay Watershed Model

The Chesapeake Bay Watershed Model is

designed to simulate nutrient and sediment

loads delivered to the Chesapeake Bay under

different management scenarios (Donigian

et al. 1994; Linker et al. 1996; Linker 1996).

The simulation is an overall mass balance of

nitrogen and phosphorus in the basin, so that

the ultimate fate of the input nutrients is

incorporation into crop or forest plant material, incorporation into soil, or loss through

river runoff. The Chesapeake Bay Watershed

Model has been in continuous operation

within the Chesapeake Bay Program since

1982, and has had many upgrades and

refinements since that time. The current

version of the Watershed Model, Phase 4.3,

is a comprehensive package for the simulation of watershed hydrology, nutrient and

sediment export from pervious and impervious landuses and the transport of these

loads in rivers and reservoirs.

Chesapeake Bay Water Quality Model

The complex movement of water within the

Chesapeake Bay, particularly the densitydriven vertical estuarine stratification, is

simulated with a Chesapeake Bay hydrodynamic model of more than 13,000 cells

(Wang and Johnson 2000). The Water

Quality Model is linked to the hydrodynamic model and uses complex 

nonlinear equations describing 26 state

variables of relevance to the simulation of

dissolved oxygen, water clarity and chlorophyll a (Cerco 1993, 1995a, 1995b, 2000;

Thomann et al. 1994; Cerco and Meyers

2000). Coupled with the Water Quality

Model are simulations of settling organic

material sediment and its subsequent decay

and flux of inorganic nutrients from the

sediment (Di Toro 2001), as well as a

coupled simulation of underwater bay

grasses in the shallows (Cerco and 

Moore 2001).

Integration of Monitoring and 

Modeling for Criteria Assessment 

The observed data is used to assess 

criteria attainment during a ‘base’ period

corresponding to the years of calibration 

for the Chesapeake Bay Water Quality

Model, 1985–1994. The Chesapeake Bay

Water Quality Model is used in scenario

mode to determine the effect of changes in

nutrient and sediment loads on water

quality concentrations. A modified

1985–1994 observed data set is generated

for each scenario using both the model and

the observations. The same criteria attainment assessment process applied to the

observed data is then applied to this

‘scenario’ data to determine likely criteria

attainment under modified loading

scenarios. For a full discussion of this

procedure, see A Comparison of Chesapeake Bay Estuary Model Calibration with

1985–1994 Observed Data and Method 

of Application to Water Quality Criteria

(Linker et al. 2002). 
Under existing state water quality standards (see Chapter IV), the current dissolved

oxygen criteria for Chesapeake Bay tidal waters in Maryland is “greater than or

equal to 5 mg/l at all times,” and in Virginia the Chesapeake Bay tidal-water criteria

are “greater than or equal to 4 mg/l minimum, and greater than or equal to 5 mg/l

daily average [see Table IV-1].” The analysis illustrated here for monthly average

dissolved oxygen concentrations is less stringent of an averaging period than the

current criteria in the states’ water quality standards, given the monthly model output

limitation.

Results from the all-forest and pristine scenarios indicate that water quality in those

portions of the Chesapeake Bay that currently have deep-water and deep-channel

designated uses are unlikely to meet existing Maryland and Virginia state dissolved

oxygen water quality standards under natural conditions. Baywide, between 3

percent (pristine) and 28 percent (all-forest) of the volume and time over the summer

months of the 10-year simulation period would likely not attain the current designated uses in the deep channel (Figure III-1). The current designated uses would

likely not be attained up to 7 percent of the volume and time during the summer

months under natural conditions in the deep-water habitats.

An examination of all-forest and pristine scenario results on a segment-by-segment

scale documents similar findings. Table III-3 provides model-simulated results for

the summer months–June through September–which have the lowest ambient

dissolved oxygen concentrations. Results are presented for the 35 major Chesapeake

Bay Program segments. In the upper, middle and lower central Chesapeake Bay,

lower Potomac River, lower Rappahannock River and Eastern Bay segments there

are natural barriers (e.g., water-column stratification, bottom bathymetry) preventing

replenishment of dissolved oxygen to the deeper portions of the tidal waters under

the all-forest scenario. For these segments under the all-forest scenario, nonattainment of the current state-adopted dissolved oxygen criteria assessed by the refined

deep-water and deep-channel designated use habitats ranged up to 41 percent of the

possible volume and time during the summer over the 10-year simulation period

(Table III-3). Nonattainment values were down in the range of 4 percent to 5 percent

under the pristine scenario.

These all-forest and pristine scenario findings are consistent with the conclusions

reached through analysis of the Paleoecological Records of Natural Conditions

described above. 

▼43

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
▼44

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-3. Percent nonattainment of 5 mg/l monthly averaged dissolved 

oxygen concentrations over the June through September period from the E3, 

all-forest and pristine model scenarios for the 35 major Chesapeake Bay 

Program segments by the refined tidal-water designated uses.

Refined

Tidal-Water Scenario

Chesapeake Bay Program Segment Designated Use E3 All-Forest Pristine

Northern Chesapeake Bay (CB1TF) MIG A A A 

OW A A A 

Upper Chesapeake Bay (CB2OH) MIG A A A 

OW A A A 

Upper Central Chesapeake Bay (CB3MH) MIG A A A 

OW A A A 

DW 6 A A 

DC 44 10 A 

Middle Central Chesapeake Bay (CB4MH) OW A A A 

DW 25 2 A 

DC 81 41 4 

Upper Central Chesapeake Bay (CB5MH) OW A A A 

DW 8 1 A 

DC 54 28 4 

Western Lower Chesapeake Bay (CB6PH) OW A A A 

DW 4 A A 

Eastern Lower Chesapeake Bay (CB7PH) OW A A A 

DW 1 A A 

Mouth of Chesapeake Bay (CB8PH) OW A A A 

Upper Patuxent River (PAXTF) MIG A A A 

OW A 5 5 

Middle Patuxent River (PAXOH) MIG A A A 

OW A A A 

Lower Patuxent River (PAXMH) MIG A A A 

OW A A A 

DW 9 A A 

Upper Potomac River (POTTF) MIG A A A 

OW A A A 

Middle Potomac River (POTOH) MIG A A A 

OW A A A 

Lower Potomac River (POTMH) MIG A A A 

OW A A A 

DW 8 A A 

DC 50 11 A 

Upper Rappahannock River (RPPTF) MIG A A A 

OW A A A 

Middle Rappahannock River (RPPOH) MIG A A A 

OW A A A 

continued
▼45

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-3. Percent nonattainment of 5 mg/l monthly averaged dissolved 

oxygen concentrations over the June through September period from the E3, 

all-forest and pristine model scenarios for the 35 major Chesapeake Bay 

Program segments by the refined tidal-water designated uses (cont.).

Refined

Tidal-Water Scenario

Chesapeake Bay Program Segment Designated Use E3 All-Forest Pristine

Lower Rappahannock River (RPPMH) MIG A A A 

OW A A A 

DW 6 A A 

DC 39 11 A 

Piankatank River (PIAMH) OW A A A 

Upper Mattaponi River (MPNTF) MIG A A A 

OW 25 45 54 

Lower Mattaponi River (MPNOH) MIG A A A 

OW 48 56 59

Upper Pamunkey River (PMKTF) MIG A A A 

OW 13 50 62

Lower Pamunkey River (PMKOH) MIG A A A 

Middle York River (YRKMH) MIG A A A 

OW A A A 

Lower York River (YRKPH) OW A A A 

DW 2 A A 

Mobjack Bay (MOBPH) OW A A A 

Upper James River (JMSTF) MIG A A A 

OW A A A

Middle James River (JMSOH) MIG A A A 

OW A A A 

Lower James River (JMSMH) MIG A A A 

OW A A A 

Mouth of the James River (JMSPH) OW A A A 

Eastern Bay (EASMH) MIG A A A 

OW A A A 

DW 10 A A 

DC 61 22 A 

Middle Choptank River (CHOOH) MIG A A A 

OW A A A 

Lower Choptank River (CHOMH2) MIG A A A 

OW A A A 

Mouth of the Choptank River (CHOMH1) MIG A A A 

OW A A A 

Tangier Sound (TANMH) OW A A A 

Lower Pocomoke River (POCMH) OW A A A 

A = Applicable dissolved oxygen criteria fully attained; analysis based on monthly averaged dissolved oxygen

concentrations 5 mg/l, 3 mg/l and 1 mg/l for open-water, deep-water and deep-channel designated uses. 

DU = designated use; OW = open-water; DW = deep-water; DC = deep-channel.
HUMAN-CAUSED CONDITIONS THAT CANNOT BE

REMEDIED WHICH APPEAR TO PREVENT ATTAINMENT

OF CURRENT DESIGNATED USES

Beyond natural conditions, some human-related conditions and alterations of the

watershed and tidal-water habitats must be considered in determining attainability of

the current designated uses. To conduct this component of the UAA, where and when

“human-caused conditions or source of pollution prevent the attainment of the use

and cannot be remedied” (CFR 131.10[g]) must be defined. 

The Chesapeake Bay Program developed a series of level-of-effort scenarios as a

tool for assessing the Chesapeake Bay watershed’s potential for nutrient and sediment reductions (Appendix A). These scenarios range from a Tier 1 level, which will

be in place by 2010 under current voluntary and regulatory programs, up to the

fourth, ‘everything, everywhere by everybody,’ or the E3 scenario. Each scenario

was based on 2010 projections of landuses, human population, agricultural animal

populations, point source flows and septic systems. 

Reduction actions defined in the E3 scenario were simulated using the Chesapeake

Bay Program’s Phase 4.3 Watershed Model and the EPA’s Regional Acid Deposition

Model (RADM), resulting in estimated airshed and watershed loads for nitrogen,

phosphorus and sediment. The loading inputs from the airshed and watershed

models were then fed into the Chesapeake Bay Water Quality Model to simulate the

resulting dissolved oxygen concentrations.

The E3 scenario represents the limits of technology as known at the time of this

analysis (Table III-4) and is acknowledged not to be physically plausible in all cases

(Table III-5). This analysis assumes that any nutrient or sediment reductions equal

to or beyond the levels defined through the E3 scenario can be considered to represent human-caused conditions that cannot be remedied and can be used for justifying

why current designated uses cannot be met. 

It is not possible to determine definitively human-caused conditions that cannot be

remedied. However, the E3 scenario represents the Chesapeake Bay Program partners’ best effort to capture those conditions by removing as much subjectivity as

possible in developing the scenario. Reported E3 scenario loading results from the

Chesapeake Bay watershed’s land area, as a whole, represent theoretical minimum

loads equal to or beyond which it would be extremely difficult, if not impossible, in

many cases to achieve at this time. However, the reported E3 scenario-simulated

water quality response can be improved if opportunities for further controls on

shoreline erosion are incorporated.

It appears unlikely that current state water quality standards for dissolved oxygen

can be achieved in significant portions of the Chesapeake Bay and tidal tributaries’

deep-water and deep-channel habitats (see Table III-3). As approximated by a 5 mg/l

monthly average dissolved oxygen concentration, the existing state dissolved oxygen

▼46

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
▼47

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-4. E3 scenario description.

The defined levels for technology and best

management practices implementation in

the ‘everything, everywhere by everybody,’

or the E3 scenario, are theoretical. There are

no cost and few physical limitations applied

to implementing BMPs for point and

nonpoint sources. In addition, the E3

scenario includes new technologies,

management practices and programs that

are not currently part of Bay watershed

jurisdictional pollutant control strategies.

Appendix A details the assumptions and

methodologies used in developing each

technology and BMP-based implementation

level in the three tier and E3 scenarios for

all nutrient and sediment source categories.

Agricultural Nonpoint Source Controls

In the E3 scenario, it was assumed that the

load from every available acre of the relevant land area was being controlled by a

full suite of existing or innovative practices

for most applied BMPs. In addition,

management programs converted landuses

from those with high-yielding nutrient and

sediment loads to those with lower loads

without regard to the economic viability of

such changes. Every acre of cropland is

conservation-tilled. Applications of fertilizers are set so that the crops do not receive

more than 98 percent of their need, well

below current recommended nutrient

management rates. All other components of

farm plans are fully implemented and the

cropland is planted in cover crops to maximize nutrient reduction benefits.

The E3 scenario designates 100-foot

riparian forest buffers on all unbuffered

stream miles in the Chesapeake Bay watershed. A total of 25,000 acres of cropland

are restored to wetlands. A quarter of the

crop and hay areas not converted to riparian

forest buffers or restored to wetlands are

retired to grass conditions. The E3 scenario

assumes there is rotational grazing on all

pasture land and that all unbuffered streams

through pastures are fully protected through

both riparian buffers and fencing to exclude

animals. The waste in animal feeding

operations is controlled to a degree that

there is no runoff. Another quarter of crop

acreage in the Chesapeake Bay basin is

replaced with long-term grasses that serve

as a carbon bank and could be converted to

energy through combustion.

Urban/Suburban Nonpoint Source

Controls

To minimize storm water runoff from urban

and suburban areas in the E3 scenario, all

land projected to be developed in the next

decade is employing environmental site

design or low-impact development practices. In addition, all existing urban areas

are retrofitted with a suite of practices to

significantly reduce nutrient and sediment

loads. Fifty-foot riparian forest buffers are

placed along all currently unbuffered urban

stream miles, while 100-foot buffers are

found on all herbaceous lands that are not

in agriculture. Also, all urban and nonagricultural grass acres do not receive nutrient

applications from chemical fertilizers.

The E3 scenario calls for a 30 percent

reduction in projected urban growth in

Pennsylvania, Maryland, Virginia and the

District of Columbia over the next decade

to conform to commitments of the Chesapeake 2000 agreement. Specifically for this

model scenario, more urban areas are built

up rather than out, and 30 percent of the

forests are protected from development.

Point Source Controls

In the E3 scenario, all significant municipal

dischargers maintain annual averaged

effluent concentrations of 3 mg/l total

nitrogen and 0.1 mg/l total phosphorus. All

new septic systems employ denitrification

technologies and are maintained through

regular pumping to meet edge-of-septicfield nitrogen loadings that are one-quarter

of typical loads. In addition, E3 atmospheric deposition assumes emission controls

on utilities, industry and mobile sources

beyond what the Clean Air Act requires. 
▼48

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible

Table III-5. E3 scenario possible over- and underestimations of attainable load

reductions.

Physical Limitations

In all appropriate circumstances, BMP

implementation levels in the E3 scenario

were applied to all relevant landuse areas 

or current limits of technology. In many

cases and to remove the subjectivity in

determining human-caused conditions that

cannot be remedied, there were no physical

limitations to employing the practices or

programs.

For many BMPs, the E3 implementation

levels could not physically be achieved. For

example, space may not be available for 50-

foot riparian buffers in urban areas or

certain developed lands may not allow for

retrofitting with practices that attain pollutant reduction efficiencies used in the E3

scenario. In addition, certain crop types

cannot be conservation-tilled and it may be

physically impossible to completely eliminate runoff from animal feeding operations. 

It is also unlikely that every homeowner and

farmer would efficiently apply fertilizers so

that only the needs of the vegetation are met

and that waterfront property owners would

plant 50-foot buffers even if it were physically possible. As a whole, ‘feasible’

participation levels are not built into the E3

scenario. All of these instances are examples of where the E3 scenario may

overestimate reductions.

Underestimations of Load Reductions

Attainable under the E3 Scenario

By contrast, some BMP implementation

levels physically could be even higher than

those currently defined in the E3 scenario.

For example, it is physically possible that

more than 25,000 acres of cropland and hay

in Chesapeake Bay watershed could be

restored to wetlands. This limitation on

wetland acres restored in the E3 scenario for

Pennsylvania, Maryland and Virginia was

used to reflect the Chesapeake 2000 goal. 

As another example, 25 percent of cropland

was replaced with long-term grasses that

serve as a carbon bank and could be

converted to energy through combustion.

Benefits of a carbon sequestration program,

in terms of lower pollutant loads, would

increase as more agricultural land is

converted. Conversion of more than 25

percent of cropland is physically possible.

In addition, the 30 percent reduction in

urban sprawl over a decade could be set at a

higher level. This rate was employed in the

E3 scenario to adhere to a Chesapeake 2000

goal.

The E3 scenario only includes shoreline

erosion controls at current levels due to a

current inability to define a ‘maximum’

limit that would not be entirely subjective.

It has been demonstrated through modeling

efforts that additional controls of shoreline

erosion can significantly improve tidalwater quality. In general, much opportunity

exists for reducing sediment and nutrient

loads from eroding shorelines that is not

reflected in the E3 scenario water quality

model results.

If greater BMP implementation levels than

those designated in the E3 scenario could

be physically achieved for any BMPs,

pollutant loadings would decrease and there

would be corresponding improved

responses in water quality. For the most

part, however, the E3 scenario did not

consider real physical limitations to BMP

implementation or participation levels. 
criteria protecting the current designated uses could not be attained in these habitats

even after implementation of technologies and management practices at levels

defined in the E3 scenario (see Figure III-1).

FINDINGS AND CONCLUSIONS

The combined results of the E3, all-forest and pristine scenarios (see Figure III-1 and

Table III-3) along with the scientific conclusions from the paleoecological record,

strongly indicate that current state aquatic life designated uses cannot be achieved in

the Chesapeake Bay’s and tidal tributaries’ deep-water and deep-channel habitats

where natural physical processes and bottom bathymetry-related barriers prevent

oxygen replenishment (see Chapter IV). Natural conditions, as well as humancaused conditions that cannot be remedied, would result in even higher levels of

nonattainment of the states’ existing 4 mg/l daily minimum and 5 mg/l daily averaged dissolved oxygen criteria than illustrated in Figure III-1 and summarized in

Table III-3, given the application of a 5 mg/l monthly average dissolved oxygen

concentration for this analysis.

LITERATURE CITED

Adelson, J. M., G. R. Helz and C. V. Miller. 2000. Reconstructing the rise of recent coastal

anoxia; molybdenum in Chesapeake Bay sediments. Geochemica et Cosmochemica Acta

65:237- 252.

Boicourt, W. C. 1992. Influences of circulation processes on dissolved oxygen in Chesapeake

Bay. In Smith, D., M. Leffler and G. Mackiernan (eds.). Oxygen dynamics in Chesapeake

Bay: A Synthesis of Research. University of Maryland Sea Grant College Publications,

College Park, Maryland. Pp. 7-59.

Boynton, W. R., J. H. Garber, R. Summers and W. M. Kemp. 1995. Inputs, transformations,

and transport of nitrogen and phosphorous in Chesapeake Bay and selected tributaries. Estuaries 18:285-314.

Bratton, J. F., S. M. Colman, R. R. Sea and P. C. Baucom. In press. Isotopic record of

nitrogen and carbon cycling in Chesapeake Bay over the last 2,700 years and implications for

modern oxygen depletion. Limnology and Oceanography.

Cerco, C. F., L. Linker, J. Sweeney, G. Shenk and A. J. Butt. 2002. Nutrient and solids

controls in Virginia’s Chesapeake Bay tributaries. Journal of Water Resources Planning and

Management May/June: 179-189.

Cerco, C. F. and K. Moore. 2001. System-wide submerged aquatic vegetation model for

Chesapeake Bay. Estuaries 24(4):522-534.

Cerco, C. and M. Meyers. 2000. Tributary Refinements to Chesapeake Bay Model. Journal

of Environmental Engineering 126(2):164-174.

▼49

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
Cerco, C. F. 2000. Phytoplankton kinetics in the Chesapeake Bay Eutrophication Model.

Journal of Water Quality and Ecosystem Modeling 1(1-4):5-49.

Cerco, C. F. 1995. Response of Chesapeake Bay to nutrient load reductions. Journal of Environmental Engineering 121(8): 549-556.

Cerco, C. F. 1995. Simulation of Long-Term Trends in Chesapeake Bay Eutrophication.

Journal of Environmental Engineering 121(4):298-310.

Cerco, C. F. 1993. Three-Dimensional Eutrophication Model of Chesapeake Bay. Journal of

Environmental Engineering 119(6):1006-1025.

Colman, S. M. and J. F. Bratton. 2003. Anthropogenically induced changes in sediment and

biogenic silica fluxes in Chesapeake Bay. Geology 31(1):71-74.

Colman, S. M., P. C. Baucom, J. Bratton, T. M. Cronin, J. P. McGeehin, D. A. Willard, A.

Zimmerman and P. R. Vogt. 2002. Radiocarbon dating of Holocene sediments in Chesapeake

Bay. Quaternary Research 57:58-70.

Cooper, S. R. 1995. Chesapeake Bay watershed historical land use: Impact on water quality

and diatom communities. Ecological Applications 5:703-723.

Cooper, S. R. and G. S. Brush. 1991. Long-term history of Chesapeake Bay anoxia. Science

254:992-996.

Cornwell, J. C., D. J. Conley, M. Owens and J. C. Stevenson. 1996. A sediment chronology

of the eutrophication of Chesapeake Bay. Estuaries 19:488-499.

Cronin, T. M., ed. 2000. Initial Report on IMAGES V Cruise of the Marion-Dufresne to

Chesapeake Bay June 20-22, 1999. USGS Open-file report 00-306.

Cronin, T. M. and C. Vann. 2003. The sedimentary record of anthropogenic and climatic

influence on the Patuxent estuary and Chesapeake Bay ecosystems. Estuaries 26(2A):196-

209.

Di Toro, D. M. 2001. Sediment Flux Modeling. John Wiley and Sons, Inc. New York. 624p.

Donigian, J. A., B. R. Bicknell, A.S. Patwardhan, L.C. Linker, C.H. Chang and R. Reynolds.

1994. Watershed Model Application to Calculate Bay Nutrient Loadings: Final Findings and

Recommendations. U. S. EPA Chesapeake Bay Program, Annapolis, Maryland.

Hagy, J. D. 2002. Eutrophication, hypoxia and trophic transfer efficiency in Chesapeake Bay.

Ph.D. dissertation, University of Maryland, College Park, Maryland.

Harding, L. W. and E. S. Perry. 1997. Long-term increase of phytoplankton biomass in

Chesapeake Bay, 1950-1994. Marine Ecology Progress Series 157:39-52

Karlsen, A. W., T. M. Cronin, S. E. Ishman, D. A. Willard, R. Kerhin, C. W. Holmes and M.

Marot. 2000. Historical trends in Chesapeake Bay dissolved oxygen based on benthic

foraminifera from sediment cores. Estuaries 23:488-508.

Linker, L. C., G. W. Shenk, P. Wang, C. F. Cerco, A. J. Butt, P. J. Tango and R. W. Savidge.

2002. A Comparison of Chesapeake Bay Estuary Model Calibration with 1985–1994

Observed Data and Method of Application to Water Quality Criteria. Modeling Subcommittee, Chesapeake Bay Program Office, Annapolis, Maryland.

Linker, L. C., G. W. Shenk, D. L. Dennis and J. S. Sweeney. 2000. Cross-Media Models 

of the Chesapeake Bay Watershed and Airshed. Water Quality and Ecosystem Modeling 1(1-

4):91-122.

▼50

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
Linker, L. C., 1996. Models of the Chesapeake Bay. Sea Technology 37(9):49-55.

Linker, L. C., C. G. Stigall, C. H. Chang and A. S. Donigian, Jr. 1996. Aquatic accounting:

Chesapeake Bay Watershed Model quantifies nutrient loads. Water Environment and

Technology 8(1):48-52.

Malone, T. C. 1992. Effects of water-column processes on dissolved oxygen: Nutrients,

phytoplankton and zooplankton. In: Smith, D., M. Leffler and G. Mackiernan (eds.). Oxygen

Dynamics in Chesapeake Bay: A Synthesis of Research. University of Maryland Sea Grant

College Publications, College Park, Maryland. Pp. 61-112.

Newcombe, C. L. and W. A. Horne. 1938. Oxygen-poor waters of the Chesapeake Bay.

Science 88:80-81.

Officer, C. B., R. B. Biggs, J. L. Taft, L. E. Cronin, M. A. Tyler and W. R. Boynton. 1984.

Chesapeake Bay anoxia: Origin, development, and significance. Science 223:22-27.

Taft, J. L., W. R. Taylor, E. O. Hartwig and R. Loftus. 1980. Seasonal oxygen depletion in

Chesapeake Bay. Estuaries 3:242-247.

Thomann, R. V., J. R. Collier, A. Butt, E. Casman and L. C. Linker. 1994. Response of the

Chesapeake Bay Water Quality Model to Loading Scenarios. Chesapeake Bay Program

Office, Annapolis, Maryland.

Wang, H. V. and B. H. Johnson. 2000. Validation and application of the second generation

three- dimensional hydrodynamic model of Chesapeake Bay. Journal of Water Quality and

Ecosystem Modeling 1(1-4):51-90.

Willard, D. A., T. M. Cronin, S. Verardo. 2003. Late-Holocene climate and ecosystem history

from Chesapeake Bay sediment cores, USA. The Holocene Vol. 13.

Zheng, Y., B. Weinman, T. M. Cronin, M. Q. Fleisher and R. F. Anderson. In press. A rapid

procedure for thorium, uranium, cadmium and molybdenum in small sediment samples by

inductively coupled plasma-mass spectrometry: Application in Chesapeake Bay. Applied

Geochemistry.

Zimmerman, A. R. and E. A. Canuel. 2000. A geochemical record of eutrophication and

anoxia in Chesapeake Bay sediments: Anthropogenic influence on organic matter composition. Marine Chemistry 69:117-137.

▼51

chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
▼53

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

chapteriv

Refined Designated Uses 

for the Chesapeake Bay and

Tidal Tributaries

BACKGROUND

RENEWED COMMITMENT TO RESTORE 

CHESAPEAKE BAY WATER QUALITY

The Chesapeake 2000 agreement and the subsequent six-state, District of Columbia

and EPA memoranda of understanding challenged the Bay watershed jurisdictions

to, “by 2010, correct the nutrient- and sediment-related problems in the Chesapeake

Bay and its tidal tributaries sufficiently to remove the Bay and the tidal portions of

its tributaries from the list of impaired waters under the Clean Water Act.” (Chesapeake Executive Council 2000; Chesapeake Bay Watershed Partners 2001.)

These agreements included commitments to “define the water quality conditions

necessary to protect aquatic living resources” and to have the jurisdictions with tidal

waters “use their best efforts to adopt new or revised water quality standards consistent with the defined water quality conditions.” Against this backdrop of a renewed

commitment to restore Bay water quality (in part through the adoption of a consistent set of Chesapeake Bay water quality criteria as state standards), the Chesapeake

Bay watershed partners recognized that the underlying tidal-water designated uses

must be refined to better reflect desired Bay water quality conditions.

CURRENT STATE TIDAL-WATER DESIGNATED USES

Virginia, Maryland, Delaware and the District of Columbia have identified parts of

the Chesapeake Bay and its tidal tributaries as ‘state waters.’ The current designated

uses for these state waters are for the protection of aquatic life (Table IV-1; figures

IV-1 through IV-4). The accompanying current criteria addressing nutrient and sediment enrichment impairments are limited to different dissolved oxygen

concentrations, which apply separately to each jurisdiction’s tidal waters. 
▼54

chapter i • Introduction

Current Designated Use for Chesapeake Bay and 

State Tidal Tributary Waters 

Maryland • Use II (shellfish harvesting waters)—Chesapeake Bay proper

• Use I (water contact recreation, protection of aquatic life)—

All surface waters 

Virginia • Class II (estuarine waters) for tidal water—Coastal zone to fall

line—Primary and secondary contact recreation, fish and shellfish

consumption, aquatic life and wildlife

“All state waters, including wetlands, are designated for the

following uses: recreational uses, e.g., swimming and

boating; the propagation and growth of a balanced,

indigenous population of aquatic life, including game fish

which might reasonably be expected to inhabit them; wildlife;

and the production of edible and marketable natural resources,

e.g., fish and shellfish.”

Delaware • Broad Creek, Nanticoke River—Industrial water supply, primary

contact recreation, secondary contact recreation, fish and aquatic

life and wildlife, agriculture water supply with additional

classification as “waters of exceptional recreational and

ecological significance” (ERES waters).

District of Columbia • Potomac River Class A (primary contact recreation), B (primary

contact recreation and aesthetics), C (protection and propagation

of fish, shellfish, and wildlife), D (consumption of fish and

shellfish) and E (navigation). 

Table IV-1. Summary of current designated uses for states’ Chesapeake Bay 

and tidal tributary waters. 
▼55

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-1. Current designated uses for Chesapeake Bay and tidal tributary waters

located in Maryland.

Source: Code of Maryland Regulations 26.08.02 for water quality dated November 1, 1993.
▼56

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-2. Current designated uses for Chesapeake Bay and tidal tributary waters

located in Virginia.

Source: Virginia State Water Control Board Regulation 9 VAC 25-260-5-et. seq. Water Quality

Standards dated December 10, 1997.

All state waters are designed for the following uses:

recreational uses, e.g. swimming and boating; the propagation and growth of a balanced, indigenous population 

or aquatic life, including game fish, which might reasonably

be expected to inhabit them; and the production of edible

and marketable natural resources, e.g. fish and shellfish.

Boundaries for Class II Waters are established for determining application of the appropriate aquatic life criteria.

Freshwater criteria apply in the tidal freshwaters. The 

more stringent of either the freshwater or saltwater criteria

apply in transition zone waters. Saltwater criteria apply in

estuarine waters.

The Class II waters are Tidal Water—coastal zone to fall line.

Designated Uses

Class II Tidal Freshwater

Class II Transition Zone

Class II Estuarine
▼57

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-3. Current designated uses for Chesapeake Bay tidal tributary waters located 

in Delaware.

Source: State of Delaware Water Quality Regulations.

Designated Uses

1. Industrial Water Supply

2. Agricultural Water Supply

3. Primary Contact Recreation

4. Secondary Contact Recreation

5. Fish, Aquatic Life, and Wildlife

6. Waters of Exception Recreational

or Ecological Significance
▼58

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-4. Current designated uses for Chesapeake Bay tidal tributary waters located 

in the District of Columbia.

Source: District of Columbia Department of Consumer and Regulatory Affairs Notice of Final

Rulemaking.

Designated Uses

A. Primary contact recreation.

B. Secondary contact recreation and aesthetic enjoyment.

C. Protection and propagation of fish, shellfish, and wildlife.

D. Protection of human health related to consumption of fish

and shellfish.

E. Navigation.

Rivers and streams either outside of DC or

non-tidal sections are a lighter gray.
REFINING TIDAL-WATER DESIGNATED USES

The Chesapeake Bay Program watershed partners determined that the underlying

tidal-water designated uses must be refined to better reflect the desired and attainable Chesapeake Bay water quality conditions called for in the Chesapeake 2000

agreement. In refining the current tidal-water designated uses, the six Chesapeake

Bay watershed states and the District of Columbia took into account five principal

considerations:

• Habitats used in common by sets of species and during particular life stages

should be delineated as separate designated uses;

• Natural variations in water quality should be accounted for by the designated

uses;

• Seasonal uses of different habitats should be factored into the designated uses;

• The Chesapeake Bay criteria for dissolved oxygen, water clarity and chlorophyll a should be tailored to support each designated use; and

• The refined designated uses applied to the Chesapeake Bay and its tidal tributary waters will support the federal Clean Water Act goals and state goals for

uses existing in these water since 1975.

The Chesapeake Bay watershed partners are proposing five refined subcategories of

the current broad aquatic life designated uses contained in the existing state water

quality standards of the four jurisdictions bordering directly on Chesapeake Bay and

its tidal tributaries. Figure IV-5 illustrates the conceptual framework of the refined

tidal-water designated uses; Table IV-2 provides general descriptions of the five

designated uses and the aquatic communities they were established to protect.9 Four

of the refined designated uses were derived largely to address seasonally distinct

habitats and living resource communities with widely varying dissolved oxygen

requirements:

• Migratory fish spawning and nursery;

• Open-water fish and shellfish;

• Deep-water seasonal fish and shellfish; and

• Deep-channel seasonal refuge.

The fifth refined designated use, the shallow-water bay grass designated use, occurs

seasonally in conjunction with that part of the year-round open-water use which

borders the land along the tidal portions of the Chesapeake Bay and its tributaries

(Figure IV-5).

▼59

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

9Note that for brevity, these refined designated uses may be referred to as migratory spawning and

nursery, shallow-water, open-water, deep-water and deep-channel.
LIVING RESOURCE-BASED REFINED DESIGNATED USES AND

PROTECTIVE CRITERIA

The five refined designated uses were derived to reflect the habitats of an array of

recreationally, commercially and ecologically important species. The supporting

prey communities were given full consideration along with the ‘target species’ in

defining the designated uses. 

Two extensive syntheses of habitat requirements for important target species and

communities in the Chesapeake Bay and its tidal tributaries formed the basis from

which these refined designated uses were conceived and developed (Chesapeake Bay

▼60

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep-Channel

Seasonal Refuge Use

Deep-Channel

Seasonal Refuge Use

A. Cross-Section of Chesapeake Bay or Tidal Tributary

B. Oblique View of the Chesapeake Bay and its Tidal Tributaries

Shallow-Water

Bay Grass Use Open-Water

Deep-Water Fish and Shellfish Use

Seasonal Fish and

Shellfish Use

Deep-Water

Seasonal Fish and

Shellfish Use

Migratory Fish

Spawning and

Nursery Use

Shallow-Water

Bay Grass Use Open-Water

Fish and Shellfish Use

Figure IV-5. Conceptual illustration of the five Chesapeake Bay tidal-water designated

use zones.
Living Resource Task Force 1987; Funderburk et al. 1991). Only when coupled with

analyses of the extensive Chesapeake Bay Monitoring Program’s water quality,

biological and living resource databases, now spanning 19 years, could the refined

tidal-water designated uses described below be documented and delineated across all

tidal-water habitats without constraints by jurisdictional borders. 

The five tidal-water designated uses, in turn, provided the context for deriving

dissolved oxygen, water clarity and chlorophyll a water quality criteria for the

Chesapeake Bay and its tidal tributaries. These criteria, derived to protect each of the

five refined designated uses, were based on effects data from a wide array of biological communities to capture the range of sensitivity of the thousands of aquatic

species inhabiting the Chesapeake Bay and tidal tributary estuarine habitats (U.S.

EPA 2003). Table IV-3 shows the proposed refined designated uses by Chesapeake

Bay Program segment.

▼61

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-2. General descriptions of the five proposed Chesapeake Bay tidal-water

designated uses. 

Migratory Fish Spawning and Nursery Designated Use: Aims to protect migratory

finfish during the late winter/spring spawning and nursery season in tidal freshwater to 

low-salinity habitats. This habitat zone is primarily found in the upper reaches of many 

Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay and will benefit 

several species, including striped bass, perch, shad, herring and sturgeon.

Shallow-Water Designated Use: Designed to protect underwater bay grasses and the 

many fish and crab species that depend on the shallow-water habitat provided by 

underwater bay grass beds.

Open-Water Fish and Shellfish Designated Use: Aims to improve water quality in the

surface water habitats within tidal creeks, rivers, embayments and the mainstem Chesapeake

Bay year-round. This use protects diverse populations of sport fish including striped bass,

bluefish, mackerel and sea trout, bait fish such as menhaden and silversides, as well as the

listed shortnose sturgeon.

Deep-Water Seasonal Fish and Shellfish Designated Use: Aims to protect living

resources inhabiting the deeper transitional water column and bottom habitats between 

the well-mixed surface waters and the very deep channels during the summer months. 

This use protects many bottom-feeding fish, crabs and oysters, as well as other important

species, including the bay anchovy.

Deep-Channel Seasonal Refuge Designated Use: Designed to protect bottom sedimentdwelling worms and small clams that act as food for bottom-feeding fish and crabs in 

the very deep channel in summer. The deep-channel designated use recognizes that low

dissolved oxygen conditions prevail in the deepest portions of this habitat zone and will

naturally have very low to no oxygen during the summer. 
▼62

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment. 

Migratory

Spawning

and Nursery Deep-Water Deep-Channel Shallow-Water

Chesapeake Bay Program (CBP) CBP (Feb. 1– Open-Water (June 1– (June 1– (April 1–

Segment Name Segment May 31) (Year-Round) Sept. 30) Sept. 30) Oct. 30)

Northern Chesapeake Bay CB1TF x x x 

Upper Chesapeake Bay CB2OH x x x 

Upper Central Chesapeake Bay CB3MH x x x x x 

Middle Central Chesapeake Bay CB4MH x x x x 

Lower Central Chesapeake Bay CB5MH x x x x 

Western Lower Chesapeake Bay CB6PH x x x 

Eastern Lower Chesapeake Bay CB7PH x x x 

Mouth of the Chesapeake Bay CB8PH x x 

Bush River BSHOH x x x 

Gunpowder River GUNOH x x x 

Middle River MIDOH x x x 

Back River BACOH x x x 

Patapsco River PATMH x x x x 

Magothy River MAGMH x x x 

Severn River SEVMH x x x 

South River SOUMH x x x 

Rhode River RHDMH x x x 

West River WSTMH x x x 

Upper Patuxent River PAXTF x x x 

Western Branch (Patuxent River) WBRTF x x x 

Middle Patuxent River PAXOH x x x 

Lower Patuxent River PAXMH x x x x 

Upper Potomac River POTTF x x x 

Anacostia River ANATF x x x 

Piscataway Creek PISTF x x x 

Mattawoman Creek MATTF x x x 

Middle Potomac River POTOH x x x 

Lower Potomac River POTMH x x x x x 

Upper Rappahannock River RPPTF x x x 

Middle Rappahannock River RPPOH x x x 

Lower Rappahannock River RPPMH x x x x x 

Corrotoman River CRRMH x x x 

Piankatank River PIAMH x x x 

Upper Mattaponi River MPNTF x x x 

Lower Mattaponi River MPNOH x x x 

Upper Pamunkey River PMKTF x x x 

Lower Pamunkey River PMKOH x x x 

Middle York River YRKMH x x x 

Lower York River YRKPH x x x 

continued
▼63

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment (cont.). 

Migratory

Spawning

and Nursery Deep-Water Deep-Channel Shallow-Water

Chesapeake Bay Program (CBP) CBP (Feb. 1– Open-Water (June 1– (June 1– (April 1–

Segment Name Segment May 31) (Year-Round) Sept. 30) Sept. 30) Oct. 30)

Mobjack Bay MOBPH x x x 

Upper James River JMSTF x x x 

Appomattox River APPTF x x x 

Middle James River JMSOH x x x 

Chickahominy River CHKOH x x x 

Lower James River JMSMH x x x 

Mouth of the James River JMSPH x x 

Western Branch Elizabeth River WBEMH x 

Southern Branch Elizabeth River SBEMH x 

Eastern Branch Elizabeth River EBEMH x 

Mouth to mid-Elizabeth River ELIMH x 

Lafayette River LAFMH x 

Mouth of the Elizabeth River ELIPH x x x 

Lynnhaven River LYNPH x x 

Northeast River NORTF x x x 

C&D Canal C&DOH x x x 

Bohemia River BOHOH x x x 

Elk River ELKOH x x x 

Sassafras River SASOH x x x 

Upper Chester River CHSTF x x x 

Middle Chester River CHSOH x x x 

Lower Chester River CHSMH x x x x x 

Eastern Bay EASMH x x x x 

Upper Choptank River CHOTF x x 

Middle Choptank River CHOOH x x x 

Lower Choptank River CHOMH2 x x x 

Mouth of the Choptank River CHOMH1 x x x 

Little Choptank River LCHMH x x 

Honga River HNGMH x x 

Fishing Bay FSBMH x x x 

Upper Nanticoke River NANTF x x x 

Middle Nanticoke River NANOH x x x 

Lower Nanticoke River NANMH x x x 

Wicomico River WICMH x x x 

Manokin River MANMH x x x 

Big Annemessex River BIGMH x x x 

Upper Pocomoke River POCTF x x 

Middle Pocomoke River POCOH x x x 

Lower Pocomoke River POCMH x x x 

Tangier Sound TANMH x x 
▼64

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

CHESAPEAKE BAY TIDAL-WATER DESIGNATED USES

The migratory fish spawning and nursery designated use is described first, given its

unique seasonal role in protecting the spawning and nursery grounds of Chesapeake

Bay and East Coast anadromous fish species. The shallow-water bay grass designated use is then described, as it protects the vegetated shallow-water habitats that

are so critical to many individual estuarine species and living resource communities.

Next, the open-water, deep-water and deep-channel designated uses are described as

a series of year-round and seasonal subcategory designated uses formed around

unique habitats defined largely by natural conditions (e.g., stratification of the water

column, water circulation patterns) and physical barriers (Bay and tidal-water

bottom bathymetry) in the tidal waters.

The watershed states with tidally influenced Chesapeake Bay waters (Maryland,

Virginia and Delaware) and the District of Columbia ultimately are responsible for

defining and adopting the designated uses into their state water quality standards.

These uses will be adopted as subcategories of current state tidal-water designated

uses, which are designed to protect aquatic life. The formal process for refining

designated uses will meet the requirements of the Clean Water Act and any applicable jurisdiction-specific environmental laws or regulations.

The adopted designated uses will protect existing aquatic and human uses of the tidal

waters that have been present since 1975. These designations go beyond minimum

requirements (131.10[d] and [h][2]) and satisfy all requirements for meeting Clean

Water Act goals (131.10 [a]), downstream waters maintenance and protection

(131.10[b]) and for subcategorization as allowed by 131.10(g). The specific use definitions and the spatial application of the final designated uses will undergo public

review through the four jurisdictions’ respective regulatory adoption processes prior

to EPA approval of the states’ water quality standards.

MIGRATORY FISH SPAWNING AND NURSERY DESIGNATED USE

Waters with this designated use shall support the survival, growth and propagation

of balanced indigenous populations of ecologically, recreationally and commercially

important anadromous, semi-anadromous and tidal freshwater resident fish 

species inhabiting spawning and nursery grounds from February 1 through May 31

(Table IV-4). 

Designated Use Rationale

Based on a commitment within the 1987 Chesapeake Bay Agreement (Chesapeake

Executive Council 1987), a list of target anadromous and semi-anadromous species

was identified, including striped bass, American shad, hickory shad, alewife, blueback herring, white perch and yellow perch, based on their commercial, recreational

and ecological value and “the threat to sustained production due to population
▼65

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-4. Migratory fish spawning and nursery designated use summary. 

Applicable Criteria: Dissolved Oxygen:

6.0 mg/l 7-day mean (only tidal habitats with 0–0.5 ppt salinity) 

5.0 mg/l instantaneous minimum 

Application: February 1 through May 31 

Designated Use: This designated use supports the survival, growth and

propagation of balanced, indigenous populations of

ecologically, recreationally and commercially important

anadromous, semi-anadromous and tidal freshwater resident

fish species inhabiting spawning and nursery grounds. 

Designated Use Boundary: The boundaries of this use extend from the upriver extent 

of tidally influenced waters to the downriver and upper

Chesapeake Bay end of spawning and nursery habitats that

have been determined through a composite of all targeted

anadromous and semi-anadromous fish species’ spawning

and nursery habitats. The use extends horizontally from the

shoreline of the body of water to the adjacent shoreline, and

extends down through the water column to the bottom

sediment-water interface. 

Source for the Applicable Criteria: U.S. EPA 2003.

decline or serious habitat degradation” (Chesapeake Bay Living Resources Task

Force 1987). These species form a representative subset of species comprising a

“balanced, indigenous population.” Other ecologically important anadromous and

semi-anadromous fish species also will be protected under this designated use.

Chesapeake Bay tidal waters support spawning and nursery areas that are important

not only to Bay fishery populations, but also to populations that inhabit the entire East

Coast, such as striped bass. The eggs, larvae and early juveniles of anadromous and

semi-anadromous species often have more sensitive habitat quality requirements than

other species and life stages (Funderburk et al. 1991; Jordan et al. 1992). These same

habitats are critical spawning and nursery grounds for tidal freshwater resident fish

species from February 1 to May 31 (U.S. EPA 2003). Thus, the combined migratory

and tidal freshwater resident fish spawning and nursery habitats were delineated as a

refined tidal-water designated use for the Chesapeake Bay and its tidal tributaries.

Designated Use Boundary Delineation

The boundaries of the migratory fish spawning and nursery designated use were

delineated from the upriver extent of tidally influenced waters to the downriver and

upper Chesapeake Bay end of spawning and nursery habitats that have been

determined through a composite of all targeted anadromous and semi-anadromous

fish species’ spawning and nursery habitats (Figure IV-6).
Critical Support Communities—Food and Shelter

In this designated use, spawning adults and the resulting larvae and early juvenile

fish depend on phytoplankton, zooplankton, bottom-dwelling worms and clams and

forage fish as prey (Funderburk et al. 1991). The presence of underwater bay grasses

in the shallows of the designated use habitat provides essential shelter for young

juveniles as well as many prey species.

Seasonal Use Application

The migratory fish spawning and nursery designated use applies from February 1

through May 31. The defined season for applying this use is based on a composite

of the full range of spawning and nursery periods of all the target anadromous and

semi-anadromous species.

Striped bass and juveniles of other migratory spawners are passively dispersed as

eggs and larvae and move farther downstream as they grow. Most juveniles do not

leave the boundaries of their respective spawning and nursery areas. Adult yellow

perch migrate from downstream to their spawning areas in the lower-salinity upper

reaches of the tidal tributaries from mid-February through March (Richkus and

Stroup 1987; Tsai and Gibson 1971). By early June, young-of-the-year juvenile

striped bass begin to move shoreward, spending the summer and early fall in shoal

waters less than six feet deep (Setzler-Hamilton et al. 1981). As juveniles grow, they

▼66

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Migratory Fish

Spawning and Nursery

Designated Use

Figure IV-6. Illustration of the boundaries of the migratory fish spawning and nursery

designated use.
move progressively downriver (Boreman and Klauda 1988; Dey 1981; SetzlerHamilton et al. 1981). The February 1 beginning date reflects the initiation of the

yellow perch spawning season; the May 31 end date reflects when the eggs and

larvae have finished their transition to the juvenile life stage for all the target anadromous and semi-anadromous species.

Applicable Chesapeake Bay Water Quality Criteria10

The migratory fish spawning and nursery designated use is seasonally defined and

occurs in conjunction with the year-round open-water designated uses and the

seasonal shallow-water designated uses (see Figure IV-5). The migratory fish

spawning and nursery designated use provides for the protection of the early life

stages of anadromous, semi-anadromous and resident tidal-fresh species through the

application of dissolved oxygen criteria derived for that purpose (U.S. EPA 2003).

From February 1 through May 31, the migratory fish spawning and nursery

dissolved oxygen criteria ensure protection of the egg, larval and early juvenile life

stages (Table IV-4). Free-flowing streams and rivers, where several of the target

species (e.g., shad, river herring) migrate for spawning, are protected through other

existing state water quality standards.

The open-water fish and shellfish designated use dissolved oxygen criteria were

derived to be protective of juvenile and adult life stages of anadromous and semianadromous species after May 31 (see Table IV-6; U.S. EPA 2003). The overlapping

nature of these discrete designated uses will thus ensure that water quality conditions

protective of different species’ life stages are present in those designated use habitats. See chapters 3 and 6, respectively, in U.S. EPA 2003 for more details on the

individual dissolved oxygen criteria and criteria implementation procedures.

SHALLOW-WATER BAY GRASS DESIGNATED USE

Waters with this designated use support the survival, growth and propagation of

rooted, underwater bay grasses necessary for the propagation and growth of

balanced, indigenous populations of ecologically, recreationally and commercially

important fish and shellfish inhabiting vegetated shallow-water habitats (Table IV-5).

Designated Use Rationale

The shallow-water bay grass designated use protects a wide variety of species, such

as largemouth bass and pickerel, which inhabit vegetated tidal-fresh and low-salinity

habitats; juvenile speckled sea trout in vegetated higher salinity areas; and blue crabs

that inhabit vegetated shallow-water habitats covering the full range of salinities

encountered in the Chesapeake Bay and its tidal tributaries. Underwater bay grasses,

▼67

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

10Maryland, Virginia, Delaware and the District of Columbia currently have water quality standards in

place that address pH conditions within the migratory fish spawning and nursery habitats.
the critical community that the designated use protects, provide the shelter and food

that make shallow-water habitats so unique and integral to the productivity of the

Chesapeake Bay ecosystem. Many Chesapeake Bay species depend on vegetated

shallow-water habitats at some point during their life cycle (Funderburk et al. 1991).

Given the unique nature of this habitat and its critical importance to the Chesapeake

Bay ecosystem, shallow waters were delineated as a refined tidal-water designated

use for the Chesapeake Bay and its tidal tributaries.

The shallow-water bay grass designated use is intended specifically to delineate the

habitats where the water clarity criteria would apply. The open-water fish and

shellfish designated use and the accompanying dissolved oxygen criteria will fully

protect the biological communities inhabiting shallow-water habitats. The 

open-water designated use extends into the intertidal zone and protects shallowwater organisms beyond underwater bay grasses. The seasonal shallow-water bay

grass designated use, similar to the migratory fish spawning and nursery use,

actually occurs in conjunction with the year-round open-water designated use (see

Figure IV-5) and provides specific protection for underwater bay grasses through the

application of water clarity criteria.

Designated Use Boundary Delineation

The shallow-water bay grass designated use covers tidally influenced waters, from

the intertidal zone out to a Chesapeake Bay Program segment-specific depth contour

▼68

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-5. Shallow-water bay grass designated use summary. 

Applicable Criteria: Water Clarity:

13 percent ambient light through water (tidal habitats with

0–5 ppt salinity)

22 percent ambient light through water (tidal habitats with

greater than 5 ppt salinity)

Application: April 1 through October 31 for tidal-fresh, oligohaline and

mesohaline habitats (0–18 ppt salinity); March 1 through 

May 31 and September 1 through November 30 for

polyhaline habitats (>18 ppt salinity)

Designated Use: Waters with this designated use support the survival, growth

and propagation of rooted underwater bay grasses necessary

for the propagation and growth of balanced, indigenous

populations of ecologically, recreationally and commercially

important fish and shellfish inhabiting vegetated shallowwater habitats.

Designated Use Boundary: Tidally influenced waters from the intertidal zone out to a

Chesapeake Bay Program segment-specific depth contour

that varies from 0.5 to 2 meters. 

Source for the Applicable Criteria: U.S. EPA 2003.
that varies from 0.5 to 2 meters (Figure IV-7). The segment-specific depths were

based on rules described in detail in “Shallow-Water Bay Grass Designated Use

Boundaries” (see page 105) along with two other approaches to defining shallowwater use boundaries.

Critical Support Communities—Food and Shelter

Phytoplankton, zooplankton, forage fish and bottom-dwelling worms and clams feed

many fish, crab and mollusk species that inhabit shallow-water habitats for part or

all of their life stages (Funderburk et al. 1991). Water quality criteria necessary to

fully support the shallow-water designated use must provide for the survival, growth

and successful propagation of prey communities in sufficient quantities.

Applicable Bay Water Quality Criteria

The shallow-water bay grass designated use is a seasonal use designation that occurs

in conjunction with the year-round open-water use and the seasonal migratory

spawning and nursery designated uses (see Figure IV-5). The shallow-water bay

grass designated use boundary delineates where specific levels of water clarity must

be restored to support restoration of underwater bay grasses. The applicable salinity

regime-based water clarity criteria apply during the appropriate underwater bay

grass growing season: April 1 through October 31 for tidal-fresh, oligohaline and

mesohaline habitats and March 1 through May 31 and September 1 through

November 30 for polyhaline habitats (see Table IV-5; U.S. EPA 2003).

▼69

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Shallow-Water

Designated Use

Figure IV-7. Illustration of the boundaries of the shallow-water bay grass designated use. 
Underlying the seasonal shallow-water bay grass designated use is the year-round

open-water fish and shellfish designated use to support grass living resource communities inhabiting these shallow-water areas (see Table IV-6; U.S. EPA 2003). The

open-water fish and shellfish dissolved oxygen criteria apply into the shallows to the

intertidal zone. Therefore, nonvegetated shallow-water habitats and the living

resource communities that depend on those habitats will receive protection under the

open-water designated use. See chapters 3, 4 and 6, respectively, in U.S. EPA 2003

for more details on the individual dissolved oxygen criteria, water clarity criteria and

criteria implementation guidelines.

OPEN-WATER FISH AND SHELLFISH DESIGNATED USE

Waters with this designated use support the survival, growth and propagation of

balanced, indigenous populations of ecologically, recreationally and commercially

important fish and shellfish species inhabiting open-water habitats (Table IV-6).

Designated Use Rationale

The natural temperature and salinity stratification of open waters influences

dissolved oxygen concentrations and, thus, the distribution of Chesapeake Bay

species. Surface mixed-layer waters with higher oxygen levels located above the

pycnocline support a different community of species than deeper waters from late

spring to early fall. Several well-known species that inhabit these open waters are

menhaden, striped bass and bluefish. Their habitat requirements and prey needs

differ from those of species and communities inhabiting deeper water habitats during

the summer months. See the deep-water “Designated Use Rationale” on page 74 for

more detailed documentation.

Clear evidence from the Chesapeake Bay as well as other estuarine and coastal

systems, including Long Island Sound (Howell and Simpson 1994), AlbemarlePamlico Sound (Eby 2001) and the Gulf of Mexico (Craig et al. 2001), indicates that

the fish and other organisms inhabiting open-water habitats will use deeper withinpycnocline and below-pycnocline habitats, given suitable dissolved oxygen

conditions. It is the lack of sufficient oxygen, not the presence of stratification, that

limits the use of these deeper habitats. Therefore, the open-water designated use

applies to transitional pycnocline and bottom mixed-layer below-pycnocline habitats

where these below-pycnocline and pycnocline waters are sufficiently reoxygenated

by oceanic or riverine waters.

During their first winter of life, members of five important Chesapeake Bay species—

white perch, striped bass, Atlantic croaker, shortnose sturgeon and Atlantic

sturgeon—are constrained to oligohaline and mesohaline regions (< 20 ppt) in the

upper Chesapeake Bay mainstem, and seek out warmer temperatures that occur in

deeper channel waters below the thermocline. From October through May, the deepchannel habitats in the upper Bay adjacent to shallower summer and fall habitats

should be considered important nursery habitats for young-of-the-year juvenile white

▼70

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼71

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-6. Open-water fish and shellfish designated use summary. 

Applicable Criteria: Dissolved Oxygen

5.5 mg/l 30-day mean (tidal habitats with 0–0.5 ppt salinity)

5.0 mg/l 30-day mean (tidal habitats with greater 

than 0.5 ppt salinity)

4.0 mg/l 7-day mean

3.2 mg/l instantaneous minimum

Chlorophyll a:

Concentrations of chlorophyll a in free-floating microscopic

aquatic plants (algae) shall not exceed levels that result in

ecologically undesirable consequences–such as reduced water

clarity, low dissolved oxygen, food supply imbalances, proliferation of species deemed potentially harmful to aquatic life or

humans or aesthetically objectionable conditions–or otherwise

render tidal waters unsuitable for designated uses.

Application: Year-round: open-water designated use and dissolved 

oxygen criteria. 

March 1 through May 31 and July 1 through September 30:

chlorophyll a criteria.

Designated Use: Waters with this designated use support the survival, growth

and propagation of balanced, indigenous populations of

ecologically, recreationally and commercially important fish

and shellfish species inhabiting open-water habitats.

Designated Use Boundary: From June 1 through September 30 the open-water

designated use includes tidally influenced waters extending

horizontally from the shoreline to the adjacent shoreline. 

If a pycnocline is present and, in combination with bottom

bathymetry and water-column circulation patterns, presents a

barrier to oxygen replenishment of deeper waters, the openwater fish and shellfish designated use extends down into the

water column only as far as the measured upper boundary of

the pycnocline. If a pycnocline is present but other physical

circulation patterns (such as influx of oxygen rich oceanic

bottom waters) provide for oxygen replenishment of deeper

waters, the open-water fish and shellfish designated use

extends down into the water column to the bottom watersediment interface. 

From October 1 through May 31, the open-water designated

use includes all tidally influenced waters extending

horizontally from the shoreline to the adjacent shoreline,

extending down through the water column to the bottom

water-sediment interface. 

Source for the Applicable Criteria: U.S. EPA 2003.
▼72

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

perch, striped bass, and Atlantic croaker (Pothoven et al. 1997) as well as Atlantic and

shortnose sturgeon (Miller et al. 1997; Secor et al. 2000; Welsh et al. 2000).

During the coldest months, the interaction between temperatures and salinity tolerances may result in a ‘habitat squeeze’ or bottleneck, forcing juveniles into

deep-channel habitats seeking preferred temperatures. Unpublished data from the

Maryland Environmental Service indicate that a thermocline, separating the warmer

deep waters from colder overlaying waters, typically occurs at a 10-to 20-meter

depth in the deep channel from October through February. Therefore, from fall

through late spring when the open-water designated use applies to these natural

channel habitats, it also protects indigenous populations of important fish species

that depend on deep-channel habitats for overwintering.

Based on these natural conditions and their influence on oxygen levels and the

seasonal distributions of Chesapeake Bay species, open waters were delineated as a

refined tidal-water designated use in the Chesapeake Bay.

Designated Use Boundary Delineation

From June 1 through September 30 the open-water designated use includes tidally

influenced waters extending horizontally from the shoreline to the adjacent shoreline

(Figure IV-8). If a pycnocline is present and, in combination with bottom bathymetry

and water-column circulation patterns, presents a barrier to oxygen replenishment of

deeper waters, the open-water fish and shellfish designated use extends down into

the water column only as far as the measured upper boundary of the pycnocline

Open-Water

Designated Use

Figure IV-8. Illustration of the boundaries of the open-water fish and shellfish

designated use.
(Figure IV-9). If a pycnocline is present but other physical circulation patterns (such

as influx of oxygen rich oceanic bottom waters) provide for oxygen replenishment

of deeper waters, the open-water fish and shellfish designated use extends down

through the water column to the bottom water-sediment interface.

From October 1 through May 31, the boundaries of the open-water designated use

includes all tidally influenced waters extending horizontally from the shoreline to the

adjacent shoreline, extending down through the water column to the bottom watersediment interface. 

Critical Support Communities—Food and Shelter

Water column-dwelling phytoplankton, zooplankton and forage fish constitute the

major prey for other species in the Chesapeake Bay’s open waters (Funderburk et al.

1991). Water quality criteria to support the open-water designated use fully must

provide for the survival, growth and successful propagation of quality prey communities in sufficient quantities.

Applicable Bay Water Quality Criteria

The open-water dissolved oxygen criteria apply year-round (see Table IV-6). The

applicable salinity regime-based chlorophyll a criteria apply only in spring (March

1 through May 31) and summer (July 1 through September 30) to the open-water

designated use habitats. See chapters 3 and 5, respectively, in U.S. EPA (2003) for

more details on the individual dissolved oxygen and chlorophyll a criteria and

chapter 6 for detailed criteria implementation procedures.

DEEP-WATER SEASONAL FISH AND SHELLFISH DESIGNATED USE

Waters with this designated use protect the survival, growth and propagation of

balanced, indigenous populations of important fish and shellfish species inhabiting

deep-water habitats (Table IV-7).

▼73

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Open-Water Shallow

Water

Shallow

Water

Upper Pycnocline

Boundary

Figure IV-9. Illustration of the vertical boundaries for the refined open-water fish

and shellfish designated use.
Designated Use Rationale

In an eutrophic system such as the Chesapeake Bay, excess organic matter settles to

the bottom, where it fuels microbial activity (e.g., Malone et al. 1986; Tuttle et al.

1987). With more fuel, more oxygen is consumed and, where replenishment with

oxygen-saturated waters is restricted, the water becomes more severely oxygendepleted. There is evidence that hypoxic and anoxic conditions existed in the deeper

waters of the Chesapeake Bay prior to European settlement (Cooper and Brush

1991). These same data indicate that anthropogenic activity has increased the extent,

frequency and severity of oxygen depletion in the Chesapeake Bay (Zimmerman and

Canuel 2000; Hagy 2002).

Many parts of the Chesapeake Bay become, on a seasonal basis, vertically stratified

because of depth-related density differences in the water column, caused primarily

by variations in salinity and, to a lesser degree, temperature. Warmer, freshwater

from the rivers floats on top of the cooler, denser saltwater at the bottom that enters

the Bay from the ocean. The gravitational force of the downriver flow of freshwater

causes a wedge of deeper, saltier water to move up the Bay and upriver. Vertically,

at some point in the water column, a zone of maximum density difference is reached,

which inhibits or prevents the exchange between water above and below it. This

region is called the pycnocline. In the summer months, respiration by organisms

living below the pycnocline can deplete concentrations of dissolved oxygen.

▼74

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-7. Deep-water seasonal fish and shellfish designated use summary. 

Applicable Criteria: Dissolved Oxygen:

3 mg liter-1 30-day mean

2.3 mg liter-1 1-day mean

1.7 mg liter-1 instantaneous minimum

Application: June 1 through September 30

Designated Use: Waters with this designated use protect the survival, growth 

and propagation of balanced, indigenous populations of 

ecologically, recreationally, and commercially important 

fish and shellfish species inhabiting deep-water habitats.

Designated Use Boundary: Tidally influenced waters located between the measured depths

of the upper and lower boundaries of the pycnocline in areas

where the measured pycnocline, in combination with bottom

bathymetry and water circulation patterns, presents a barrier to

oxygen replenishment of deeper waters. In some areas where a

lower boundary of the pycnocline is not calculated, the deepwater designated use extends from the measured depth of the

upper boundary of the pycnocline down through the water

column to the bottom sediment-water interface. 

Source for the Applicable Criteria: U.S. EPA 2003.
Because waters in and below the pycnocline are isolated from well-mixed surface

waters, dissolved oxygen concentrations can decrease until they are stressful or

lethal to higher organisms.

The formation of the pycnocline is a natural process. In areas where stratification is

common, the pycnocline generally forms at about the same depth range, but is

subject to seasonal and annual variations in depth due to river flow, temperature and

salinity patterns. It is generally shallower at the mouths of rivers and the Chesapeake

Bay and deeper at the heads of rivers. The effect of the pycnocline also is not the

same everywhere in the Chesapeake Bay and is influenced by local characteristics

such as bathymetry, vertical and horizontal water circulation patterns, and proximity

to the ocean and major river fall-lines. In some parts of the Bay and its tidal rivers,

these factors create a more complex stratification pattern: a second pycnocline is

formed lower in the water column, dividing it into three layers. If a region is

contained by the pycnocline above and by bottom bathymetry laterally, it is even

more isolated from oxygen-replenishing waters.

Bay anchovy is a target species whose egg and larval life stages are spent in pycnocline waters (Keister et al. 2000; Rilling and Houde 1999; MacGregor and Houde

1996). Blue crabs, oysters, softshell clams, hard clams, spot, croaker, flounder and

catfish inhabit the near-bottom waters in the deep-water habitats (Funderburk et al.

1991). The oxygen requirements of these species differ from those of species inhabiting shallow-water, open-water and deep-channel habitats. Their feeding patterns

and distribution of eggs and larvae are greatly influenced by natural features of the

water column such as the pycnocline.

Deep waters were delineated as a refined tidal-water designated use for the Chesapeake Bay and its tidal tributaries based on the unique nature of the pycnocline

region as an important living resource habitat and the transitional nature of its water

quality conditions.

Designated Use Boundary Delineation

The deep-water designated use includes the tidally influenced waters between the

measured upper and lower boundaries of the pycnocline where, in combination with

bottom bathymetry and water circulation patterns, the pycnocline limits oxygen

replenishment of deeper waters (Figure IV-10). In some areas where a lower

boundary of the pycnocline is not calculated, the deep-water designated use extends

from the measured depth of the upper boundary of the pycnocline down through the

water column to the bottom sediment-water interface.

Critical Support Communities—Food and Shelter

Bottom-dwelling worms and clams and reef-dwelling forage fish are important food

sources for the fish and crabs in deep-water habitats (Funderburk et al. 1991). Water

quality criteria to support the deep-water designated use must provide for the

survival, growth and successful propagation of quality prey communities in sufficient quantities.

▼75

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Seasonal Use Application

The deep-water seasonal fish and shellfish designated use applies from June 1

through September 30. By June, a combination of natural water-column stratification

and increased biological oxygen consumption driven by higher water temperatures

prevents the Chesapeake Bay’s deep waters from retaining high concentrations of

dissolved oxygen. These natural conditions generally persist into September. From

October 1 through May 31 the open-water fish and shellfish designated use applies

to these same waters.

Applicable Bay Water Quality Criteria

The deep-water dissolved oxygen criteria apply from June 1 through September 30

(see Table IV-7). See chapters 3 and 6, respectively, in U.S. EPA 2003 for more

details on the deep-water dissolved oxygen criteria and criteria implementation

procedures.

DEEP-CHANNEL SEASONAL REFUGE DESIGNATED USE

Waters with this designated use must protect the survival of balanced, indigenous

populations of ecologically important benthic infaunal and epifaunal worms and

clams, which provide food for bottom-feeding fish and crabs (Table IV-8).

Designated Use Rationale

In the Chesapeake Bay, researchers have determined the oxygen minimum to be in

the below-pycnocline waters throughout the deep trough in the mainstem Chesapeake Bay in the late spring to early fall (Smith et al. 1992). Isolated from aerated

surface waters, low dissolved oxygen concentrations in this region are due to excess

oxygen consumption from bacterial breakdown of organic material over oxygen

additions from ocean waters flowing in from far down-Bay. North of this region, the

▼76

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep-Water

Upper Pycnocline

Boundary

Lower Pycnocline

Boundary

Figure IV-10. Illustration of the vertical boundaries for the refined deep-water

designated use. 
trough quickly becomes shallow and bottom waters are oxygenated as they mix with

aerated waters in the shoals. Below-pycnocline waters to the south are reoxygenated

through mixing with oxygenated oceanic waters entering the Chesapeake Bay mouth.

These deep channels are sinks for excess organic material which, in the process of

decaying, increase oxygen consumption. They are isolated from surface and oceanic

sources of oxygen replenishment. Vertical stratification and gravitational and horizontal circulation often cause severe, sudden oxygen depletion beginning just below

the lower boundary of the pycnocline and extending to the bottom (Smith et al.

1992). Given the physical nature of the deep trough leading to naturally severe

oxygen depletion during the summer, the deep-channel was delineated as a refined

tidal-water designated use for Chesapeake Bay.

Designated Use Boundary Delineation

Deep-channel designated use waters are defined as tidally influenced waters at

depths greater than the measured lower boundary of the pycnocline in areas where

the pycnocline, in combination with bottom bathymetry and water circulation

patterns, presents a barrier to oxygen replenishment of deeper waters (Figure IV-11).

The deep-channel designated use is defined laterally by bathymetry of the trough and

vertically by the lower boundary of the pycnocline above, and below, at the bottom

sediment-water interface.

▼77

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-8. Deep-channel seasonal refuge designated use summary. 

Applicable Criteria: Dissolved Oxygen:

1.0 mg/l instantaneous minimum

Application: June 1 through September 30

Designated Use: Waters with this designated use must protect the survival of

balanced, indigenous populations of ecologically important

benthic infaunal and epifaunal worms and clams, which

provide food for bottom-feeding fish and crabs.

Designated Use Boundary: Deep-channel designated use waters are defined as tidally

influenced waters at depths greater than the measured lower

boundary of the pycnocline in areas where, in combination

with bottom bathymetry and water circulation patterns, the

pycnocline presents a barrier to oxygen replenishment of

deeper waters. The deep-channel designated use is defined

laterally by bathymetry of the trough and vertically by the

lower boundary of the pycnocline above, and below, at the

bottom sediment-water interface.

Source for the Applicable Criteria: U.S. EPA 2003.
Critical Support Communities—Food and Shelter

Bottom-dwelling worms and clams are the principal food source of bottom-feeding

fish and crabs in the deep-channel (Funderburk et al. 1991). Water quality criteria 

for the deep-channel designated use must provide for the survival of these prey

communities.

Seasonal Use Application

The deep-channel designated use applies from June 1 through September 30. By

June, a combination of natural water-column stratification and increased water

temperature prevents the Chesapeake Bay’s deep-channel waters from retaining high

concentrations of dissolved oxygen. These natural conditions generally persist

through September. From October 1 through May 31 the open-water designated use

applies to these same habitats.

Applicable Bay Water Quality Criteria

The deep-channel dissolved oxygen criteria apply from June 1 through September

30 (see Table IV-8). See chapters 3 and 6, respectively, in U.S. EPA 2003 for more

details on the deep-channel dissolved oxygen criteria and criteria implementation

procedures.

CHESAPEAKE BAY TIDAL-WATER 

DESIGNATED USE BOUNDARIES

Correct application of the Chesapeake Bay water quality criteria depends on the

accurate delineation of the five tidal-water designated uses. Each of the designated

uses has different dissolved oxygen criteria derived to match the respective level of

protection required by different living resource communities. In case of the shallow-

▼78

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep Channel Lower Pycnocline

Boundary

Figure IV-11. Illustration of the vertical boundaries of the refined deep-channel

seasonal refuge designated use. 
water bay grass designated use, the location of the boundaries is critical to providing

sufficient suitable habitat for the restoration of the desired number of acres of underwater bay grasses.

The vertical depth and horizontal breadth of the designated use boundaries are based

on a combination of factors: natural water-column stratification, bottom bathymetric

features and circulation patterns, among other considerations. It is important to note

that these boundaries have been developed without consideration of attainability

from the perspective of potentially widespread social and economic impacts. The

states may find they need to adjust these boundaries according to such impacts

(131.19[g][6]), which may prevent attainment of the designated use, and must justify

these adjustments during their water quality standards adoption processes. The technology-based attainability of these refined tidal-water designated uses and their

boundaries is documented in Chapter V.

Four of the six factors defined in 40 CFR 101.10(g) justify deriving the boundaries

described in this chapter for the refined tidal-water designated uses:

• Natural, ephemeral, intermittent or low-flow conditions or water levels (e.g.,

application of a 10-year water quality data record (1985-1994) reflecting a

wide range of watershed hydrologic and tidal bay hydrodynamic conditions);

• Dams, diversion or other types of hydrologic modifications (e.g., dredged

shipping channels);

• Physical conditions related to the natural features of the water body, such as the

lack of a proper substrate, cover, flow, depth, pools, riffles and the like (e.g.,

water-column stratification, bottom bathymetry); and

• Naturally occurring pollutant concentrations (see Chapter III).

MIGRATORY FISH SPAWNING AND NURSERY 

DESIGNATED USE BOUNDARIES

The boundaries of the migratory fish spawning and nursery designated use were

delineated from the upriver extent of tidally influenced waters to the downriver and

upper Chesapeake Bay end of spawning and nursery habitats that have been determined through a composite of all targeted anadromous and semi-anadromous fish

species’ spawning and nursery habitats (Figure IV-12). Free-flowing streams and

rivers, where several of the target species (e.g., shad and river herring) migrate for

spawning, are protected through other existing state water quality standards.

To generate these boundaries, habitat distribution maps, drawn from the Habitat

Requirements for Chesapeake Bay Living Resources–Second Edition (Funderburk et

al. 1991), were used. The distribution maps used during delineation of the migratory

spawning and nursery designated use included:

• Alewife spawning and nursery;

• Alewife nursery;

▼79

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼80

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-12. Map showing the migratory spawning and nursery designated use for the

Chesapeake Bay and its tidal tributaries (black areas).
• American shad spawning and nursery;

• American shad nursery;

• Hickory shad spawning and nursery;

• Herring spawning and nursery;

• Herring nursery;

• Striped bass spawning reaches;

• Striped bass spawning rivers;

• White perch nursery;

• White perch spawning; and

• Yellow perch spawning and nursery.

For those species that had multiple habitat distribution maps for related life stages,

the maps were merged into a single coverage. Then individual species maps were

superimposed on a composite spawning and nursery habitat map.

The striped bass habitat distribution maps used in this process were originally titled

“Striped Bass Chesapeake Bay Spawning Reaches and Spawning Rivers” by

Funderburk et al. (1991). The sources of the spawning reach distributions were

research and monitoring findings synthesized by Setzler-Hamilton and Hall (1991).

However, the mapped extent of the nursery areas, referred to as spawning rivers in

the original map, was based on Maryland and Virginia legislative definitions,11 not

on fisheries survey findings.

Those regulations, which define “spawning rivers and areas,” did not attempt to

define “early juvenile nursery habitat” but rather those rivers in which striped bass

spawn. The spawning reach designation in the regulation was used to describe areas

where striped bass eggs and larvae had been found. This justification was based on

icthyoplankton collections done in the 1950s in Maryland (Mansueti and Hollis

1963). Tresselt (1952) defined spawning reaches in Virginia.

To further enhance understanding of nursery areas, discussions were held with

fishery scientists Herb Austin and Deane Este of the College of William and Mary’s

Virginia Institute of Marine Science, and Eric Durell, Maryland Department of

Natural Resources, who are responsible for their respective states’ juvenile striped

bass seine surveys. The primary nursery areas for young-of-the-year striped bass

were delineated based on a comparison of long-term Maryland and Virginia seine

survey data with the legislatively-defined extent of early juvenile nursery habitat. In

any given year, juvenile striped bass can be found throughout a broader range of

Chesapeake Bay tidal waters. The primary nursery areas where the highest concentrations of early juvenile life-stage striped bass are almost always found in the spring

▼81

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

11Code of Maryland Regulations 08.02.05.02 and Virginia Marine Resources Commission Regulation

450-01-0034 as cited inChesapeake Bay Living Resources Task Force (1987).
were identified and incorporated into the composite map described above (e.g.,

Austin et al. 2000). The striped bass nursery areas were supplemented to ensure that

shad and river herring spawning and nursery areas were fully represented within the

migratory fish spawning and nursery designated use boundaries (Rulifson 1994;

Olney 2002).

From February 1 through May 31, the migratory fish spawning and nursery designated use occurs in conjunction with, and, therefore, encompasses specific portions

of the seasonal shallow-water bay grass and year-round open-water fish and shellfish

designated use habitats (see shaded sections in Figure IV-5). The designated use

extends horizontally from the shoreline across the body of water to the adjacent

shoreline, and extends down through the water column to the bottom sediment-water

interface.

The exact spatial and temporal extent of migratory fish spawning and nursery

designated use would vary annually due to regional climatic patterns if actual

observed salinity and temperature were used to define year-by-year boundaries.

Because use of year-by-year delineation of the exact boundaries of the migratory fish

spawning and nursery designated adds complexity, a fixed set of boundaries was

established. The migratory fish spawning and nursery designated use habitat shown

in Figure IV-12 reflects both long-term, decadal average salinity conditions and

decades’ worth of fisheries-independent beach seine and trawl monitoring data.

States can adopt an approach (to be defined) for defining migratory spawning and

nursery designated use boundaries on a year-to-year basis by directly factoring in the

influence of interannual climatic patterns on the use boundaries.

OPEN-WATER, DEEP-WATER AND DEEP-CHANNEL 

DESIGNATED USE BOUNDARIES 

Background

The open-water, deep-water and deep-channel designated uses, the habitats they

represent and the dissolved oxygen criteria for ensuring their protection are inextricably related to physical structure (water-column stratification, bottom bathymetry)

and to physical, chemical, meteorological and fluvial forces and processes. Understanding these factors will enhance understanding of the designated use delineation

process as well as the issues underlying application of the dissolved oxygen criteria.

The following section provides background on these three principal factors: bathymetry, flow and circulation, and vertical density gradients and pycnoclines.

Bathymetry

Although the Chesapeake Bay is a relatively shallow estuary, bathymetric features

play a large role both in defining the Bay’s habitats as well as the eutrophicationrelated water quality problems observed throughout most of the tidal waters. 

▼82

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
The most prominent bathymetric feature in the Bay is the deep trench that runs from

the Chesapeake Bay Bridge between Annapolis and Kent Island, Maryland, to an

area midway between the southern shore of the mouth of the Potomac River and the

northern shore of the mouth of the Rappahannock River (figures IV-13 and IV-14).

The trench ranges from 24 to 48 meters in depth and extends generally midchannel

between the western and eastern shores of the mainstem Chesapeake Bay. It is

thought to be a remnant of the ancient Susquehanna River. A shallower trench

extends down along the Virginia Eastern Shore (Figure IV-15). Similar, smaller

trenches and holes exist elsewhere in Bay tidal waters, generally in the larger tidal

tributary rivers near their mouths. These are described later in the more detailed

regional descriptions that follow. 

▼83

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-13. Major bathymetric trenches within the Chesapeake Bay and its tidal tributaries.
▼84

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-14. Three-dimensional view of the Chesapeake Bay mainstem trench as

viewed from the south looking north. The depth versus width relationship has been

enhanced to improve viewing.

Figure IV-15. Three-dimensional view of the ‘Virginian Sea’ as viewed from the south

looking north. The depth versus width relationship has been enhanced to improve 

viewing.
These deep regions contrast with the Chesapeake Bay as a whole, which has an

average depth of only 6 meters. They also figure prominently in the Chesapeake

Bay’s dissolved oxygen problems. When it is overlain by a stratified water column,

the bottom water in the trenches and holes is isolated from the oxygenated surface

water and can become oxygen-depleted. This situation generally occurs in the late

spring and summer when oxygen-consuming activity is high and discontinuity in

water density through the water column can act as a barrier, i.e., act as a ‘lid,’

capping off the exchange of oxygenated water with the oxygen-depleted waters in

the trenches and holes. However, some of the deep areas of the Chesapeake Bay,

although capped as described, do not suffer from chronically low dissolved oxygen.

These areas generally have their downstream or seaward end open so that deep-water

exchange with the oxygenated deep water from the ocean can occur. 

FLOW AND CIRCULATION

Processes within the Chesapeake Bay and its tidal tributaries are strongly influenced

by flow and circulation patterns. These factors affect the mixing of the Bay’s waters

and the distribution of salinity, dissolved compounds and planktonic organisms. Like

most estuaries, the Chesapeake Bay has a two-layer flow pattern. Net flow in the

upper layer moves down the Bay or downriver, while net flow in the bottom layer

moves up the Bay or upriver. 

This two-layer flow is caused primarily by the difference in density between the less

dense, low-salinity water that flows off the land and the more dense, high-salinity

water that flows in from the ocean. The less dense, more buoyant, low salinity water

floats on the surface of higher salinity water. The tendency of ocean water in summer

to be cooler than freshwater also contributes to its higher density. Interannual and

seasonal differences in freshwater inflow to the rivers and the Chesapeake Bay, due

largely to meteorological factors, affect the interaction of the two layers. 

Tidal forces move water into and out of the Chesapeake Bay and its rivers. Tidal

currents interact with the bathymetric surfaces of the bottom, with the seaward flow

of freshwater and with the air-water interface affecting internal turbulence and

mixing. Tied to lunar cycles, the daily, monthly and seasonal tidal rhythms are relatively predictable components of flow and circulation. 

The Coriolis force is another important physical circulation process in the Chesapeake Bay. The Coriolis force is related to the earth’s rotation and causes moving

objects such as fluids to veer to the right (clockwise) in the Northern Hemisphere

and to the left (counter-clockwise) in the Southern Hemisphere. This force increases

with proximity to the poles. Currents in the Northern Hemisphere tend to move

clockwise over their course unless they encounter a barrier such as a land mass. Thus

ocean water flowing into the Chesapeake Bay at the mouth is deflected north due to

the Coriolis force. The current continues around to the right until it encounters the

Eastern Shore, which directs the flow up the Bay. Water flowing down and out of the

Chesapeake Bay on the surface, flows primarily down the Western Shore as the

▼85

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼86

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Coriolis force tends to push it to the right. This same phenomenon of inflow on the

bottom on the right and outflow on the surface on the left occurs in the Bay’s tidal

tributaries as well. 

VERTICAL DENSITY GRADIENTS AND PYCNOCLINES

In many parts of the Chesapeake Bay, the water column becomes stratified because

of differences in water density. These differences are caused primarily by differences

in salinity and, to lesser degree, in temperature. The water column becomes vertically stratified when, at some depth, a difference in water density from one depth to

the next is large enough to inhibit or prevent exchange between water above and

below it. Fisher et al. (2003) found the density gradient for defining inhibition or

prevention of water exchange in the Chesapeake Bay to be 0.1 kg/m4. The depth

nearest the surface where this first occurs is referred to as the pycnocline. The

discontinuity may be gradual, as shown in Figure IV-16a, exhibiting a generally

uniform gradient of increasing density from one depth to the next through the water

column. In such cases, one refers to the region of the pycnocline. 

a. b.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

151050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

151050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

Figure IV-16. The figures illustrate a variety of water density and dissolved oxygen

profiles found in the Chesapeake Bay and its tidal tributaries. The black line represents

water density (kg/m 4), the blue line represents dissolved oxygen concentration (mg/l). 

The vertical axis indicates depth (meters) below the surface. The horizontal line crossing

the density line, when present, indicates upper and lower pycnocline depth using the

Fisher et al. 2003 method. Figure ‘a’ is an example of a sharp, upper pycnocline with

density gradually increasing with distance from the surface. Figure ‘b’ is an example 

of a more distinct three-layer structure.

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
In areas where stratification is common, the pycnocline typically forms at about the

same depth, but is subject to seasonal and annual variations in depth due to river

flow, temperature and salinity patterns. The pycnocline is generally shallower at the

mouths of tidal rivers and the Chesapeake Bay and deeper with distance upriver and

up-Bay. In the central, deepest part of the mainstem Chesapeake Bay, the pycnocline

tends to deepen and ‘tilt’ slightly on the east-west axis, depending on the strength

and direction of prevailing winds as well as the relative balance of the several forces

controlling Chesapeake Bay circulation. North of this area, where the Bay narrows

and grows shallow, and north-moving bottom water shoals up from the deep trench,

the pycnocline is generally found closer to the surface. In upriver areas of tidal tributaries, pycnoclines may occur occasionally depending on episodic intrusions of

saline waters. In other areas, such as the mouth of Tangier Sound in the lower Chesapeake Bay, pycnoclines are occasional or intermittent because fresh and saline

waters are typically well-mixed by tidal currents and bathymetric features. 

In some areas, the many factors acting on circulation create a more complex stratification structure. Below the surface mixed layer, there is a layer where density

continues to change with depth. Then a second, sharp density discontinuity is

encountered, creating a discrete bottom mixed layer (Figure IV-16b). A density

gradient of 0.2 kg/m4 was found to inhibit upward vertical exchange and form a

boundary for this lower mixed zone. (See Appendix D for a more thorough explanation of the methods for determining the pycnocline.)

For these reasons, the shape of a density profile can be highly variable within and

between locations. The profile in Figure IV-16b is common in medium-to-deep areas

of the mainstem Chesapeake Bay and lower tributaries during the summer months.

There is an upper mixed layer several meters thick, followed by a distinct change in

the density gradient. This change marks the upper depth of the pycnocline and the

lower depth of the upper mixed layer. The thickness of the inter-pycnocline region

in this example is 9 meters, about a third of the water column. The bottom mixed

layer is fairly thick in this case, extending approximately 13 meters to the bottom.

The figure illustrates the effect of the pycnocline and density gradient on oxygen

concentration in this part of the Chesapeake Bay. Oxygen in the surface mixed layer

is close to saturation. Below the upper pycnocline depth, oxygen levels fall with

increasing distance from the oxygenated upper layer. The bottom mixed layer is

consistent at about 1 mg/l through the entire thickness to the bottom. 

Figure IV-17a shows a pycnocline type that is common to shallow to medium-depth

areas of the mainstem Chesapeake Bay and mid-to-lower areas of the tidal tributaries. There is a well-defined surface mixed layer, marked by a sharp density

discontinuity, but no lower mixed layer. The pycnocline extends through the water

column to the bottom sediment-water interface, with dissolved oxygen concentrations decreasing with distance from the upper pycnocline boundary. Figure IV-17b

shows a different density structure at the same location on a different date. There is

no density discontinuity, the upper mixed layer extends through the entire water

column and dissolved oxygen levels greater than 5 mg/l are sustained through to the

bottom sediment-water interface. The vertical profiles in figures IV-17a and IV-17b

▼87

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
are typical of tidal-fresh and shallow areas of the mainstem Chesapeake Bay and

tidal tributaries and can frequently be observed in medium-depth regions of the

mainstem Bay and mid- to lower sections of the tidal tributaries.

The relationship of dissolved oxygen to the presence or absence of a pycnocline and

density gradient is different in the lower Chesapeake Bay mainstem (Figure IV-17c).

A sharp pycnocline exists, but the gradient in dissolved oxygen concentrations is not

as pronounced. Vertical mixing is still retarded by the pycnocline as in other areas of

the Chesapeake Bay, but bottom waters are not as low in oxygen due to the replenishment of oxygenated waters from the ocean. 

Figure IV-18 is a snapshot of water density and dissolved oxygen profiles at various

sites in the Chesapeake Bay during the summer of 1997. The lines depicting water

density demonstrate the layering and mingling of water masses of different sources

and histories within the confines of the trenches and on the shoals. The plots also

▼88

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

a.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

0 5 10

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

b.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

0 5 10

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

c.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

15 25201050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

Figure IV-17. The figures illustrate a variety of water density and dissolved oxygen profiles found in the

Chesapeake Bay and its tidal tributaries. The black represents water density (kg/m 4), the blue line represents

dissolved oxygen concentration (mg/l). The vertical axis is depth (meters) below the surface. The horizontal line

crossing the density line, when present, indicates upper and lower pycnocline depth using the Fisher et al. 2003

method. Figure ‘a’ represents vertical profiles of density and dissolved oxygen concentration at a relatively shallow site. A layer of homogenous, oxygenated low salinity water lies over water with a gradually increasing salinity/density gradient. Figure ‘b’ represents vertical profiles of density and dissolved oxygen at the same relatively

shallow site when the water column is fully mixed. Figure ‘c’ represents vertical profiles of density and dissolved

oxygen at a site in the lower mainstem Chesapeake Bay where dissolved oxygen levels are sustained throughout

the water column in the presence of a density gradient and pycnocline.

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼89

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-18. ‘Snapshot’ of water density and dissolved oxygen vertical depth profiles at various water quality

monitoring program stations in the Chesapeake Bay and its tidal tributaries in the summer of 1997. 

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼90

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

illustrate the difference small and large variations in density can have on dissolved

oxygen concentrations as described above. For example, at monitoring station EE3.2

in Tangier Sound, the decrease in dissolved oxygen concentration (about 2 mg/l) at 14

meters has a density difference just large enough to be considered a pycnocline.

Downstream, at station CB7.2, the change in density is much larger but induces about

the same magnitude of decrease in the dissolved oxygen concentration gradient.

DELINEATING THE DESIGNATED USE BOUNDARIES

Vertical stratification has direct implications for delineating the designated use

boundaries. Much of the water in the Chesapeake Bay and its tidal tributaries is

shallow and well-mixed or easily aerated. These areas plus the surface mixed layers

overlying stratified water in channels and holes constitute the open-water fish and

shellfish designated use. The upper layer mixes on time scales of minutes to hours

(Alldredge et al. 2002), which means that all of the water in this layer comes in close

contact with the atmosphere and should be able to attain the most protective surface

water dissolved oxygen criterion. The open-water designated use boundary is, therefore, defined as the upper mixed layer, extending from the water surface to the

bottom water-sediment interface, where no stratification occurs or to the measured

depth of the upper pycnocline where, in combination with bottom bathymetry and

water-column circulation, it presents a barrier to oxygen replenishment of deeper

waters. From June through September, the open-water designated use accounts for

approximately 70 percent of the total volume of the Chesapeake Bay and its tidal

tributaries, and many Chesapeake Bay Program segments have only this one designated use (Table IV-9).

Water in the bottom mixed layer is essentially trapped. The bottom mixed layer is

separated from the upper mixed layer by the pycnocline and receives very limited

oxygen from either mixing or diffusion. Biological respiration and decomposition

processes deplete the ambient dissolved oxygen, and bottom sediments exert additional oxygen demand. The shape of the bottom mixed layer or deep-channel

designated use is essentially a thin layer along the bottom in most areas, with thicker

sections in some deeper areas of the Chesapeake Bay. Water within the pycnocline

between the upper and lower mixed layers is defined as the deep-water designated use.

However, as noted and illustrated above, a pycnocline and density gradient do not

affect dissolved oxygen concentration conditions to the same degree in all areas of

the Chesapeake Bay and its tidal tributaries. There are regional peculiarities in

bathymetry and flow that strongly influence the effect of a pycnocline on dissolved

oxygen concentrations, and these must be taken into account. 

THE BOUNDARY DELINEATION PROCESS

The process of identifying and delineating the open-water, deep-water and deepchannel designated use boundaries employed observed and model-simulated

characterizations of dissolved oxygen concentrations and the theoretical effects of

the physical and chemical processes discussed above. The process first identified the
▼91

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay

Program segment. Calculations are based on the 1998-2000 summer (June

through September) mean depths of the upper and lower pycnoclines.

Volume (cubic kilometers) 

Chesapeake Bay 

Program Segment Migratory Open-Water Deep-Water Deep Channel 

CB1TF .35/4% .35/1% 

CB2OH 1.22/14% 1.23/2% 

CB3MH 2.27/27% 1.05/2% .87/6% .47/5%

CB4MH 4.26/9% 2.73/9% 2.25/26%

CB5MH 7.57/15% 3.17/15% 4.62/52%

CB6PH 5.03/10% 5.03/10%

CB7PH 10.29/21% 10.29/21%

CB8PH 3.16/6%

BSHOH .05/<1% .02/<1%

GUNOH .06/<1% .06/<1%

MIDOH .03/<1% .03/<1%

BACOH .02/<1% .02/<1%

PATMH .37/4% .06/<1% .02/<1%

MAGMH .06/1% .08/<1%

SEVMH .08/1% .11/<1%

SOUMH .05/<1% .07/<1%

RHDMH .01/<1% .02/<1%

WSTMH .01/<1% .02/<1%

PAXTF .01/<1% .01/<1%

PAXOH .03/<1% .03/<1%

PAXMH .39/5% .38/1% .38/1%

POTTF .48/6% .48/1%

PISTF .003/<1% .003/<1%

MATTF .01/<1% .01/<1%

POTOH .84/10% .84/2%

POTMH 1.16/14% 3.17/6% 1.25/9% 1.20/14%

RPPTF .10/1% .10/<1%

RPPOH .05/<1% .05/<1%

RPPMH .17/2% 1.00/2% .33/2% .13/1%

CRRMH .07/1% .07/<1%

PIAMH .20/2% .20/<1%

MPNTF .01/<1% .01/<1%

MPNOH .04/<1% .04/<1%

PMKTF .03/<1% .03/<1%

PMKOH .06/<1% .06/<1%

YRKMH .08/1% .28/1%

YRKPH .24/<1% .15/<1%

MOBPH 1.33/3%

continued
▼92

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Volume (cubic kilometers) 

Chesapeake Bay 

Program Segment Migratory Open-Water Deep-Water Deep Channel 

JMSTF .26/3% .27/<1%

APPTF .002/<1 .002/<1%

JMSOH .43/5% .43/1%

CHKOH .05/<1% .05/<1%

JMSMH .36/4% .97/2%

JMSPH .43/1%

WBEMH .01/<1%

SBEMH .03/<1%

EBEMH .01/<1%

LAFMH .003/<1%

ELIPH .04/<1% .02/<1% .002/<1%

LYNPH .02/<1%

NORTF .03<1% .03<1%

C&DOH .02/<1% .02/<1%

BOHOH .02/<1% .02/<1%

ELKOH .10/1% .10/<1%

SASOH .08/1 .08/<1%

CHSTF .003/<1% .003/<1%

CHSOH .03/<1% .03/<1%

CHSMH .41/5% .41/1% .01/<1% <1%

EASMH .78/2% .09/1% .12/1%

CHOTF .02/<1% .02/<1%

CHOOH .04/<1% .04/<1%

CHOMH2 .12/1% .26/1%

CHOMH1 .02/<1% .95/2%

LCHMH .21/1%

HNGMH .19/<1%

FSBMH .14/2% .14/<1%

NANTF .01/<1% .01/<1%

NANOH .05/<1% .05/<1%

NANMH .03/<1% .10/<1%

WICMH .02/<1% .06/<1%

MANMH .01/<1% .09/<1%

BIGMH .002/<1% .04/<1%

POCTF .004/<1% .004/<1%

POCOH .02/<1% .02/<1%

POCMH .01/<1% .35/1%

TANMH 3.98/8%

Total 8.54/100% 49.65/100% 13.41/100% 8.79/100%

Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay

Program segment. Calculations are based on the 1998-2000 summer (June

through September) mean depths of the upper and lower pycnoclines (cont.).
▼93

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

deep-channel designated use habitats: the areas of the Chesapeake Bay and its tidal

tributaries that suffer chronic low dissolved oxygen concentrations due to the natural

interplay of water-column stratification, bottom bathymetry and water circulation

patterns. These areas are so strongly isolated by these factors that they become

immune from remediation. The next step was to identify the deep-water designated

use habitats—areas with chronically low dissolved oxygen concentrations driven

largely by water-column stratification, bottom bathymetry and water circulation

patterns, but with hypoxic conditions (extent and severity) that are responsive to

change, including changes in anthropogenic inputs. The rest of the tidal Bay habitats

were identified as open-water designated use habitats.

First it was necessary to identify potential areas for delineation as deep-channel and

deep-water designated use habitats by examining empirical dissolved oxygen

concentration and distribution data under the ‘best’ observed conditions. The 17-year

dissolved oxygen record from the Chesapeake Bay Program’s Water Quality Monitoring Program, 1984-2000, was reviewed to find the best summer dissolved oxygen

conditions in this time period.12 Using hypoxic volume-days as the metric, 1997 was

chosen. The dissolved oxygen conditions of that year largely reflect the effect of low

freshwater inflow and lower nutrient and sediment inputs from reduced rain and

subsequent runoff. 

Maps of bottom-water dissolved oxygen concentrations in the summer of 1997

revealed the areas with the most recalcitrant low dissolved oxygen concentrations.

These maps also revealed areas with adequate dissolved oxygen concentrations, but

with episodic low dissolved oxygen concentrations under other flow and runoff loading

conditions. Maps of the spatial extent of waters

with concentrations of 1 mg/l and 3 mg/l over the

17-year period helped identify areas where physical processes strongly influence dissolved

oxygen concentrations and where low dissolved

oxygen persists over a wide range of flows and

associated nutrient loads. The regions identified

as having chronic low dissolved oxygen concentrations attributable to the combined affects of

pycnocline, bathymetry and flow were as follows:

• Upper, middle and lower central Chesapeake

Bay segments (CB3MH, CB4MH and

CB5MH);

• Northern reaches of the western and eastern

lower Chesapeake Bay (CB6PH and

CB7PH);

12Historical dissolved oxygen data were available from as early as the 1950s; however, the temporal and

spatial coverage prior to 1984 was uneven and too coarse for this analysis.

Dissolved Oxygen 

and Temperature

As the temperature of a liquid

increases, the ability of gases

to dissolve into it decreases. 

In other words, as water gets

warmer, the concentration 

of gases, such as oxygen,

within it decreases. This

change has implications for

the Chesapeake Bay in the

summer time because, as the

water’s temperature increases,

it can hold less and less

oxygen.The inability to hold

oxygen happens at a time

when overall metabolism in

the Bay is increasing with

temperature. Higher metabolism is coupled with increased

dissolved oxygen consumption.
• Patapsco River (PATMH);

• Mesohaline segments of the Chester, Eastern Bay, Patuxent, Potomac and Rappahannock rivers (CHSMH, EASMH, PXTMH, POTMH and RPPMH); and 

• Polyhaline segment of the York River (YRKPH) (Figure IV-19).

How water-column stratification, bottom bathymetry and water circulation patterns

affect dissolved oxygen conditions and, therefore, the designated use boundaries in

each of these regions are discussed and illustrated below.

Upper Central Chesapeake Bay 

The upper central Chesapeake Bay, or segment CB3MH, includes the ‘head’ of the

mainstem Chesapeake Bay trench at its northern border near the Chesapeake Bay

Bridge (Figure IV-19). In this segment the flow shifts from a single to a two-layer

flow. The exact point where this occurs shifts south and north as the flow from the

Susquehanna River increases and decreases with seasonal and interannual variation.

Its location in the center of this estuarine transition zone puts segment CB3MH at

the extreme end of oxygen dynamics in the Chesapeake Bay. As ocean water moves

up the Bay beneath the pycnocline, metabolic processes are consuming its reserve of

dissolved oxygen. By the time this water reaches segment CB3MH, it has traveled

approximately 220 kilometers and, depending on the time of year, it can be partly or

completely deprived of dissolved oxygen. Because of this, the very southern portion

of segment CB3MH is the first part of the Chesapeake Bay mainstem to show

oxygen depletion in the spring and the last to become reoxygenated in the fall. As

the northward-flowing bottom water encounters the head of the mainstem trench, it

spills into the shallower waters of the middle portion of segment CB3MH before

meeting and mixing with the south-flowing waters of the Susquehanna River (Figure

IV-20). Therefore, even though this middle portion of segment CB3MH is not

‘trench-like’ in depth, this area has deep-channel and deep-water designated uses. 

Middle Central Chesapeake Bay 

The middle central Chesapeake Bay, or segment CB4MH, encompasses the entire

northern half of the Chesapeake Bay mainstem trench with the exception of the head,

which lies in segment CB3MH (Figure IV-19). The trench runs 20 to 35 meters deep

along the eastern side of the segment. Once a pycnocline develops in this segment,

it acts as a lid over the trench and effectively isolates below-pycnocline waters from

the overlying waters. The source of the below-pycnocline water in segment CB4MH

is the already depleted below-pycnocline water of segment CB5MH (Figure IV-21).

Therefore, the only source of dissolved oxygen for below-pycnocline segment

CB4MH water is the occasional storm-induced downwelling event. Given the size of

this segment, these events are relatively localized and short-lived. Because the pycnocline so effectively isolates the deeper waters in this segment, along with bottom

bathymetry and water circulation patterns, these within-pycnocline waters are designated as deep-water and the below-pycnocline waters are designated as deep-channel

designated use habitats.

▼94

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼95

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Lower Central Chesapeake Bay

The lower central Chesapeake Bay, or segment CB5MH, encompasses the entire

southern half of the Bay’s mainstem trench (see Figure IV-19). As in segment

CB4MH, the pycnocline in this segment can ‘cap’ waters in the trench so that the

only significant source of exchange is water flowing into the southern end of the

trench, beneath the pycnocline. During most of the year, as this source water enters

Figure IV-19. Chesapeake Bay Program segments identified as having chronic low dissolved oxygen

attributable to the combined effects of pycnocline, bathymetry and flow.

Lower

Chester River

(CHSMH)
▼96

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Up-bay movement of oxygendepleted sub-pycnocline water 

from the mainstem trench mixes 

with down-bay flow from the 

Susquehanna and becomes 

re-oxygenated.

Oxygen depleted water flows 

up-bay under the pycnocline in 

the mainstem trench. Upon 

reaching the northern terminus 

of the trench, it flows up and 

into the shallower waters of 

northern CB3MH and into the 

Patapsco River via the 

shipping channel.

Pycnocline

Northern terminus of 

the mainstem trench.

Shipping channel to 

Baltimore Harbor in 

the Patapsco River.

Figure IV-20. Three-dimensional schematic of the northern terminus of the mainstem Chesapeake Bay

trench. Flow is depicted by thick arrows. Above and below pycnocline waters are shaded differently.

Region depicted is boxed on inset map. 

Pycnocline

Rappahannock

Potomac

Patuxent Patapsco

As ocean water moves up the 

bay, under the pycnocline, it 

becomes gradually depleted 

in dissolved oxygen until it is 

hypoxic/anoxic when it 

reaches the head of the 

Chesapeake Bay mainstem 

trench.

Figure IV-21. Three-dimensional schematic of the hydrodynamics of the Chesapeake Bay mainstem

trench. View is from the southeast looking northwest.
the trench, its dissolved oxygen concentration is still relatively undepleted, because

it is not far from its ocean source. However, during July and August, temperatures in

the southern mainstem Chesapeake Bay can be warm enough and benthic metabolism high enough for this source water to have depleted oxygen supplies (see

“Dissolved Oxygen and Temperature” sidebar, above). As this water moves up the

trench during the late spring and summer months, metabolic processes under the

pycnocline gradually consume the available dissolved oxygen until it is severely

depleted by the time it reaches the northern part of segment CB5MH (Figure IV-21).

The southern half of segment CB5MH is generally the last part of the Chesapeake

Bay mainstem to become oxygen-depleted and the first to become replenished.

Because the pycnocline so effectively isolates the bottom waters in this segment,

along with bottom bathymetry and water circulation patterns, the within-pycnocline

waters are designated as deep-water designated use habitat and the below-pycnocline

waters are designated as deep-channel designated use habitat.

Western and Eastern Lower Chesapeake Bay

The western and eastern lower Chesapeake Bay, segments CB6PH and CB7PH,

respectively, together make up the broadest region of the Chesapeake Bay mainstem.

The entire region is heavily influenced by the ocean. A 17- to 22-meter trench runs

along the axis of segment CB7PH, extending from the northern end of the segment

almost to its southern boundary (see Figure IV-19). The trench is approximately 

2.5 kilometers wide and deepens to an approximately 50-meter hole near its southern

terminus. Although the trench becomes capped by a pycnocline, below-pycnocline

dissolved oxygen concentrations within the trench are usually not affected. As ocean

water flows into the Chesapeake Bay mouth along the bottom, the Coriolis force

swings this flow northward along the lower eastern shore of the Chesapeake Bay. This

waterflow pattern carries ocean water directly into the trench in segment CB7PH and

provides a steady supply of oxygenated water to the below-pycnocline habitats.

Ocean water similarly replenishes the below-pycnocline waters of segment CB6PH. 

Only the very northern portions of segments CB6PH and CB7PH appear to have a

chronic dissolved oxygen depletion problem related to the pycnocline and local

bottom bathymetry. The northern boundary of these two segments forms a line,

inclining northeastward from the mouth of the Rappahannock River to a point at the

southern tip of the islands forming Tangier Sound (see Figure IV-19). The line

approximates the location of a broad shoal or sill on the Chesapeake Bay bottom.

The sill defines the southern terminus of the mainstem Chesapeake Bay deep trench

and functions as a ‘hydrologic control point’ for waters passing over it. 

A shipping channel cuts through the sill, connecting the trench in segment CB7PH

to the trench in the middle Chesapeake Bay (Figure IV-22). The channel enables an

exchange of oxygen-depleted bottom waters from the mainstem trench with water in

the northern portions of segments CB6PH and CB7PH. 

▼97

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Although the overall direction of flow in the bottom layer is northward in this region,

the smaller-scale actions of the outgoing tide can pulse bottom waters down-estuary

(Figure IV-22). Oxygen-deficient water intrudes on the bottom and as lenses into

mid-water depths. This effect can be intensified during a strong north-westerly wind

event (see sidebar, “Tides Affected by Moon and Sun” on page 100). 

The deep-water designated use, therefore, extends below the sill in these two segments.

Its lower boundary runs along a line more or less parallel to, but south of, the northern

segment line (Figure IV-23). The delineation of the boundary was determined by

examining maps of contemporary dissolved oxygen concentration distributions and the

anecdotal historical dissolved oxygen concentration data record. 

▼98

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Pycnocline

As ocean water encounters the sill 

that forms the southern terminus of 

the mainstem trench, it moves up 

and over the sill and into the trench. 

Ocean water also moves through 

the shipping channel in the sill and 

into Tangier Sound.

Subpycnocline water from the 

mainstem trench can move down 

bay through the shipping channel. 

This movement usually occurs 

due to the effects of wind and tide.

Shipping

Channel

Sill

To Tangler

Sound

Figure IV-22. Three-dimensional schematic of the hydrodynamics of the northern portion of segments

CB6PH and CB7PH. View is from the south. Area portrayed is boxed on the inset map.
▼99

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-23. Map showing the dissolved oxygen designated uses of the Chesapeake Bay and its

tidal tributaries.
Patapsco River

The Patapsco River, segment PATMH, is a highly urbanized tidal waterway, home to a large industrial center and

one of the largest shipping ports on the eastern seaboard.

It is heavily and routinely dredged, and a significant

portion of its shoreline has been hardened. Its shipping

channel is directly connected to the Chesapeake Bay

mainstem trench, allowing for the advection of oxygendepleted water to its below-pycnocline layer (figures

IV-20 and IV-24). The river has a complex three-layer

flow structure. The middle, pycnocline waters of the

Patapsco River are designated as a deep-water use, and

the below-pycnocline waters are designated as a deepchannel use.

Chester River

The downriver, mesohaline portion of the Chester River,

segment CHSMH, contains a trench that ranges in depth

from 20 to 25 meters (see Figure IV-19). The trench is

separated from the mainstem Chesapeake Bay by a sill.

This sill can potentially affect dissolved oxygen levels in

the deep waters of the trench that are chronically low in

the summer months. The pycnocline can form a ‘lid’ over

the trench, cutting off the exchange with surface waters.

Because of the sill at the mouth of the river, tidal flushing

by bottom waters can be restricted, reducing the replenishment of the bottom waters of the trench as well as the

▼100

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Tides Affected By Moon and Sun

Tides are controlled by the gravitational pull

of the sun as well as the moon. When the

moon and the sun are aligned, such as during

a full moon or a new moon, tides achieve

their highest highs and lowest lows. This

phenomenon is called a ‘spring’ tide. When

the pull of the sun and moon are at right

angles, they act to cancel each other out, and

tidal amplitude is at its lowest. This is called a

‘neap’ tide.

The higher amplitude tide that occurs during

‘spring’ tide results in increased tidal flow.

This can be beneficial as when this increased

flow advects oxygen rich water into an

estuary. Conversely, it can be detrimental if

the advected water is coming from deeper

waters with low dissolved oxygen.

Sun 

Earth 

Moon 

Gravitational 

Pull 

Diagram depicts

‘spring’ tide

alignment of

sun and moon.

Figure IV-24. The image on the left shows the bathymetry of the shipping channel

approach to Baltimore Harbor and how it is connected to the ‘head’ of the Chesapeake

Bay mainstem trench at the bottom of the picture (middle to right side). The image on

the right is of the bathymetry of Baltimore Harbor. To improve visualization, the depth

versus width relationship has been enhanced. 
potential mixing force that the inflow might have. It may also be the case that during

extreme (spring) tidal events (see sidebar, “Tides Affected by Moon and Sun,” on

previous page) low dissolved oxygen bottom water from the mainstem trench is

advected into the Chester River trench, where it is sequestered under the pycnocline

(Figure IV-25).

When a measurable pycnocline is observed (often due to these ‘spill-over events’),

the within-pycnocline waters of the lower Chester River (river mouth up to the sill

at Ringgold Point on Eastern Neck) have a deep-water designated use, and the

below-pycnocline waters have a deep-channel designated use. In the absence of

▼101

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Pycnocline

Water is pushed 

to the western shore

Easterly Wind

Mainstem Trench

Western Shore

Eastern Shore

A

B

C

{

Easterly Wind

Downward displacement of 

western pycnocline forces 

subpycnocline water out of 

trench and into the shallow 

waters of the eastern shore 

and into the eastern shore 

tributaries.

Pressure from water that 

‘piles up’ on western shore 

exerts a downward pressure 

on the pycnocline.

Figure IV-25. Panel A shows the 

‘normal’ state of the pycnocline over 

the Chesapeake Bay mainstem trench. 

In Panel B, a strong easterly wind pushes

water from the eastern shore to the

western shore. As water ‘piles up’ on 

the western shore in Panel C, it exerts a

downward pressure on the pycnocline

there. As the pycnocline is pushed down

on the western shore, a pressure differential is created between the west and east

shores causing water to be displaced up

and out of the Chesapeake Bay mainstem

trench and into the shallow waters of the

eastern shore and into the eastern shore

tributaries. Strong westerly winds result 

in the opposite phenomena, where the

pycnocline tilts in the opposite direction

and subpycnocline water is advected to

the western shore. 
water-column stratification, the open-water designated use will apply throughout the

water column to the bottom sediment-water interface in the lower Chester River. 

Eastern Bay 

In the Eastern Bay, segment EASMH, a trench extends from the river mouth, where

it connects with the mainstem trench to a point halfway up the Bay (see Figure IV19). This connection with the mainstem Chesapeake Bay trench has implications for

dissolved oxygen in the bottom waters of lower Eastern Bay, since the belowpycnocline waters of this portion of Eastern Bay and the mainstem Chesapeake Bay

trench exchange freely. This region of the mainstem trench has some of the worst

dissolved oxygen conditions in the entire Chesapeake Bay. Because of this, belowpycnocline waters in lower Eastern Bay are chronically low in dissolved oxygen in

summer. When a measurable pycnocline is observed, the within-pycnocline waters

of Eastern Bay have a deep-water designated use and the below-pycnocline waters

have a deep-channel designated use (see Figure IV-23). In the absence of watercolumn stratification, the open-water designated use will apply throughout the water

column to the bottom sediment-water interface in Eastern Bay. 

Patuxent River 

The trench in the lower Patuxent River, segment PXTMH, contains one of the

deepest points in the Chesapeake Bay just off of Point Patience. The Patuxent River

trench terminates at a sill at the mouth of the river (Figure IV-26). Dissolved oxygen

concentrations become depressed beneath the pycnocline in the summer, but not to

the degree they do in the mainstem Chesapeake Bay trench. These depressed

dissolved oxygen concentrations may be due to pycnocline-disrupting turbulence as

the river flows through the constriction at Point Patience. Below-pycnocline

dissolved oxygen does not become completely replenished, but these waters do naturally reoxygenate enough to maintain levels high enough for a deep-water designated

use (see Figure IV-23). Given the depth of this trench, it is likely that hypoxia is a

natural condition below the pycnocline in the summer. 

Potomac River

The lower Potomac River trench, located in segment POTMH, extends from the

mouth of the river up to Ragged Point and averages 15 to 25 meters deep (see Figure

IV-19). A 10- to 15-meter shelf extends from the sides of the trench and connects

with a similar region in the mainstem Chesapeake Bay (Figure IV-27). Although the

Potomac trench is not connected to the mainstem Bay trench there is not a sill across

the mouth of the Potomac. The pycnocline effectively isolates the water volume in

the trench from the surface waters. In addition, given the size of the Potomac River

watershed, a relatively large amount of organic matter could be delivered to the

below-pycnocline waters of the Potomac trench. It is very likely that, due to the size

and depth of this deep-water area coupled with strong water-column stratification,

low dissolved oxygen conditions are a natural feature of the Potomac trench. The

▼102

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
pycnocline waters of the lower Potomac River (POTMH) have a deep-water

designated use and the below-pycnocline waters have a deep-channel designated use

(see Figure IV-23). 

Rappahannock River

The Rappahannock trench, located in segment RPPMH, extends from the mouth of

the Rappahannock River to Belle Isle (see Figure IV-19). The downriver end of the

trench terminates in a sill that extends across the mouth of the river. Dissolved

oxygen concentrations in the bottom waters of the trench are affected by the formation of the pycnocline. However, bottom water in the upriver half of the trench is

more affected than the downriver half. This phenomenon may be related to strong

currents flowing in the Rappahannock River along the bottom and over the sill. Chao

and Paluskiewicz (1991) found that lower-layer density currents flowing over a sill

cause downward mixing upriver of the sill (Figure IV-28). If this downward mixing

is occurring in the downriver half of the Rappahannock trench, it would explain why

▼103

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-26. Bathymetry at 

the mouth of the Patuxent River. 

To improve visualization, the 

depth relative to the width 

has been enhanced.

Figure IV-27. Bathymetry at 

the mouth of the Potomac River. 

To improve visualization, the 

depth relative to width has 

been enhanced. 
bottom water dissolved oxygen is less affected by the pycnocline in this region. In

the Virginia rivers, bottom layer, upriver flow in the Rappahannock River is second

only to that of the James River and is greater, on average, than in the Potomac River

(Wang 2003, personal communication). Given this rapid upriver flow beneath the

pycnocline, the below-pycnocline waters of the Rappahannock trench are not

depleted of dissolved oxygen until they reach the head of the trench. Based on a

decadal-scale analysis of dissolved oxygen within the trench, it appears that low

dissolved oxygen in the upriver portion is a chronic condition. 

Because of the unique hydrodynamics of the lower Rappahannock River, the deepwater and deep-channel designated uses are not uniform across this segment. From

the upriver shore of the Corrotoman River to the mouth of the Rappahannock River,

the deep-water designated use extends from the upper pycnocline to the bottom sediment-water interface. Upriver of this section to Belle Isle, the pycnocline volume has

a deep-water designated use and the below-pycnocline volume a deep-channel designated use (see Figure IV-23). 

York River 

The York trench, located principally in segment YRKMH, extends from where the

York River empties into Mobjack Bay up-river to Kings Creek. A 10-15 meter

channel runs from the down-river terminus of the trench, through Mobjack Bay to a

point in the mainstem Bay adjacent to the Chesapeake Bay mouth (see Figure IV19). This channel effectively connects the lower York River to ocean water flowing

▼104

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-28. Diagram of the hydrodynamics of flow over a sill. As lower layer waters

flow over the sill, downwelling surface waters occur.

Source: Chao and Paluszkiewicz 1991.

Lower Layer Up River Flow

Upper Layer Up River Flow Downwelling

Sill
into the Chesapeake Bay. This connection apparently is a benefit to bottom water

dissolved oxygen as concentrations below the pycnocline in this region do not get as

low as they do in other below-pycnocline trench areas of the Bay. For this reason, the

waters below the upper pycnocline down to the bottom sediment-water interface

from the York River mouth to Timberneck Creek have a deep-water designated use

(see Figure IV-23). 

SHALLOW-WATER BAY GRASS DESIGNATED USE BOUNDARIES

Restoration of underwater bay grasses to acreages supporting “the propagation and

growth of balanced, indigenous populations of ecologically, recreationally and

commercially important fish and shellfish inhabiting vegetated shallow-water habitats” is ultimately the best measure of attainment of shallow-water bay grass

designated use. Therefore, delineation of the shallow-water designated use boundaries must reflect the desired acreage of underwater bay grass restoration. In

shallow-water habitats out to the 2-meter depth contour, the exact shallow-water

designated use boundaries can:

• Follow a Chesapeake Bay Program segment-specific depth contour;

• Reflect an established segment-specific acreage of underwater bay grasses to

be restored; or 

• Match an established segment-specific acreage of shallow-water habitat meeting the water clarity criteria necessary to support achievement of the

underwater bay grasses restoration goal acreage.

The Chesapeake Bay Program segment-specific maximum depth of persistent, abundant underwater bay grasses growth sets the initial boundary for the habitat

necessary for supporting the shallow-water designated use. That same segmentspecific maximum depth was used in combination with the single best year of

underwater bay grass distribution mapped across the available 1930-2000 data

record to set the new restoration goals on a segment-by-segment basis. Finally, the

ratio of the above shallow-water habitat out to the maximum depth of persistent,

abundant plant growth and the corresponding segment-specific underwater bay

grasses restoration acreage are used to calculate an acreage of shallow-water habitat

meeting the water clarity criteria necessary to support achievement of the restoration

goal acreage. 

The following sections describe and quantify these three approaches to setting the

shallow-water designated use boundaries, which are consistent with options the EPA

put forth for measuring attainment of the Chesapeake Bay shallow-water underwater

bay grass designated use (U.S. EPA 2003). EPA recommends the states adopt one (or

more) of the three approaches to defining the shallow-water designated use boundaries in addition to adoption of numerical water clarity criteria into their water

quality standards. States can adopt shallow-water designated use boundaries

covering higher acreages or greater depths than those provided here during their

▼105

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼106

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

upcoming water quality standards adoption processes once the expanded riverspecific information has become available to be incorporated. During future state

triennial reviews of their water quality standards, states also may expand their

shallow-water designated use boundaries to reflect resulting levels of restoration of

underwater bay grasses in prior years.

MAXIMUM DEPTH OF PERSISTENT OR ABUNDANT 

PLANT GROWTH-BASED BOUNDARIES

The 2-meter depth contour was selected as the maximum depth for the lower vertical

boundary of the shallow-water designated use. This is the maximum depth to which

underwater bay grasses could be restored in many of the tidal tributaries and mainstem Chesapeake Bay shallow-water habitats. Although historical underwater bay

grass beds in the Chesapeake Bay probably grew to 3 meters or more, the 2-meter

depth was chosen following an extensive evaluation of grass bed distribution over the

past 70 years (1930s-2000) and of light levels anticipated to be required to restore

viable shallow-water habitats out to the 2-meter depth (Batiuk et al. 1992; Dennison

et al. 1993; Moore et al. 1999; Batiuk et al. 2000; Moore et al. 2001; Naylor 2002).

The intertidal zone was selected as the inner boundary for the shallow-water bay

grass designated use because some species can grow in the upper end of the intertidal zone (Batiuk et al. 2000; Koch 2001). Numerous field studies of underwater bay

grass distributions in the Chesapeake Bay and its tidal tributaries have indicated that

what is controlling the minimum depth of their distribution is not wave action or

other factors, but length of exposure to air at low tide (Moore, unpublished data;

Naylor, unpublished data).

Shallow-water habitats also may be offshore flats such as those observed in Tangier

Sound and Poquoson Flats in the lower mainstem Chesapeake Bay. These areas may

have an inner boundary not in the intertidal zone but rather a relatively deep and wide

channel between them and the shore. These areas are included in the delineation of

shallow-water bay grass designated use habitats if they have or have had underwater

bay grasses and met the decision rules described below. 

BENEFITS OF DEEPER UNDERWATER BAY GRASS DISTRIBUTION

There are obvious benefits to restoring underwater bay grasses to greater depths 

than where they currently exist in the Chesapeake Bay and its tidal tributaries 

(Table IV-10). Increasing the depth and, therefore, the areal distribution of the

grasses can greatly increase the habitat and food available to the Chesapeake Bay’s

fish, crabs and waterfowl.

It is important to note that underwater bay grass distribution is directly related to the

tidal bathymetry of the basins in which the beds occur. In a shallow bay with a gradual

slope to deeper waters, such as the Chesapeake Bay, even a moderate increase in water

clarity can result in tremendous increases in the areal extent of bay grasses.
HISTORICAL UNDERWATER BAY GRASS DISTRIBUTION 

The distribution and, therefore, the depth of historical underwater bay grass beds

were mapped from photographs dating from the late 1930s through the mid-1960s

by scientists at the Maryland Department of Natural Resources and the Virginia

Institute of Marine Science. Historical underwater bay grass distribution data from

Maryland and Virginia were aggregated into a single data set using ArcInfo GIS software. The two states’ approaches reflect differences in the quality and quantity of

historical aerial photographs available for interpretation. Full documentation of the

methods employed and the detailed results are reported in Moore et al. (1999, 2001)

and Naylor et al. (2002).

To determine historic underwater bay grass acreage, aerial photos of Maryland’s

portion of the Bay taken in 1938, 1952, 1957 and 1964 were evaluated to determine

the year in which the most underwater bay grass was visible for each area (Naylor

2002). The photos for the year of greatest abundance in each area were then scanned,

geo-referenced and photo-interpreted to determine the extent of underwater bay

grass beds during these years.

In the Virginia portion of the Chesapeake Bay and its tidal tributaries, historical

underwater bay grass acreage in the James River was mapped using photographs

taken in 1937, 1947, 1948, 1953, 1954, 1958, 1959, 1963, 1968, 1969, 1970 and

▼107

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

• Ensures growth of underwater bay grasses where previously there may have been none

because wave energy at shallower depths prevented plants from rooting in the bottom

sediments (e.g., the beds that formerly grew on the western side of Kent Island,

Maryland, at depths greater than where the critical wave energy threshold exists);

• Adds habitat below the grazing depth of non-native mute swans and non-migratory

Canada geese (approximately 1 and 0.5 meters, respectively) to increase food 

availability for native waterfowl;

• Reduces the likelihood of ice damage to the beds;

• Reduces the negative effects of unusually low tides;

• Minimizes thermal stress (as deeper beds are inherently cooler);

• Stabilizes sediments at greater depths (through the reduction of water velocity 

within the underwater bay grass beds);

• Increases overall nutrient uptake and supports increased denitrification;

• Increases summertime oxygen production (which is particularly important in the 

headwaters of tidal creeks); and

• Increases habitat for fish, crabs and macroinvertebrates.

Table IV-10. Ecological and water quality benefits of deeper underwater bay

grasses distribution in the Chesapeake Bay and its tidal tributaries. 
1973, with the historical coverage defined by the composite of the individual years

(Moore et al. 1999). Historical and recent ground survey results were superimposed

on the maps of historical underwater bay grass distributions to help determine

whether the patterns exhibited in the photographs were actually those of underwater

bay grass beds (Moore et al. 1999).

For the Rappahannock and York rivers and the adjacent smaller western shore rivers,

creeks and embayments, a series of photographs from 1952 to 1956 was chosen to

delineate the maximum coverage of bay grasses in these areas (Moore et al. 2001).

The 1936 and 1937 photographs of these rivers showed less underwater bay grass

coverage compared to the 1950s photographs. The difference appeared to be related

to poorer overall atmospheric and water clarity conditions (Moore et al. 2001).

The interpretation of these historic aerial photographs closely followed current

methods to delineate underwater bay grass beds throughout the Chesapeake Bay and

its tidal tributaries through annual aerial underwater bay grass surveys (e.g., Orth et

al. 2000). In neither state did a single year of photography provide comprehensive

coverage of each state’s tidal shorelines. 

These state-specific analyses provide a conservative estimate of past underwater bay

grass distributions prior to the 1970s. The conservative nature of the estimate is due,

in part, because the older photographs were not collected specifically to map underwater bay grasses, but were gathered to assist in analyzing land use or farming

practices. While atmospheric criteria were usually met, the factors that are important

for delineating and mapping underwater bay grasses (such as tidal stage, water transparency and plant growth stage) often were not met. Underwater bay grasses likely

grew at greater depths between the 1930s and 1960s, according to published and

anecdotal information, than was observed in a number of segments in the historical

photographs. Grasses that grow beyond the 1-meter depth contour become increasingly difficult to map, given the conditions under which the historical photographs

were collected. There were limited numbers of years—often only three to five—for

which historical photographs of a particular shallow-water habitat region were available for interpretation and mapping between the 1930s and early 1970s. Evidence

suggests that underwater bay grass distributions already had declined by the time

photographs of suitable quality were available for interpretation (Moore et al. 1999).

All of these factors led to conservative estimates of past underwater bay grasses

distributions and depths of bed growth.

UNDERWATER BAY GRASS NO-GROW ZONES

A series of underwater bay grass ‘no-grow zones’ were originally delineated in 1992

in the Chesapeake Bay Submerged Aquatic Vegetation Habitat Requirements and

Restoration Targets: A Technical Synthesis (Batiuk et al. 1992). Habitats exposed to

high wave energy or that have undergone physical modifications such that they could

not support underwater bay grasses growth were excluded based on an extensive

review of data available at the time. With the mapping of historical underwater bay

▼108

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
grass distributions, a composite of available distribution data from the 1930s through

2001 was superimposed on the 1992 bay grass no-grow zones. A number of shoreline habitats previously considered no-grow zones showed clear evidence of

historical underwater bay grass growth and, therefore, their no-grow zone designation was dropped. These revised underwater bay grass no-grow zones also include

areas where the no-grow zone applies to a 1- to 2-meter depth contour as well as a

0- to 2-meter depth contour.

The revised underwater bay grass no-grow zones illustrated in Figure IV-29 show

shoreline habitats of 2 meters or less where underwater bay grasses are never

expected to grow due to:

• Extreme physical wave energy, which prevents the plants from rooting in the

bottom sediments (e.g., Calvert Cliffs on Maryland’s lower western shore and

Willoughby Split to Cape Henry near the Chesapeake Bay mouth in Virginia);

• Permanent physical alterations to nearshore habitats, including dredging close

to shore accompanied by hardening of the shoreline and installation of permanent structures (i.e., shipping terminals) as observed in the inner Baltimore

Harbor and the Elizabeth River;

• Natural, extreme discoloration of the water from tidal-fresh wetlands (e.g.,

tidal-fresh ‘blackwater’ rivers on the Eastern Shore); or

• No functional shallow-water habitat due to natural river channeling (e.g., tidal

headwaters of several lower Eastern Shore rivers).

These underwater bay grass no-grow zones reflect the full set of findings on underwater bay grasses distributions from the historical (select years from the 1930s–early

1970s) and 1978–2001 data records, as well as altered nearshore/shoreline habitats

as described above. The no-grow zones illustrated in Figure IV-29 are based on the

best available information and are subject to future revision based on new research

and information.

If no physical reasons prevent underwater bay grasses from growing in a specific

shallow-water habitat, it should be expected that grasses can grow there, given

appropriate water quality conditions and local sources of propagules (i.e., reproductive vegetative materials such as seeds and rhizomes). For example, evidence exists

of underwater bay grasses growing within estuarine turbidity maximum zones in the

upper Chesapeake Bay mainstem and selected tidal tributaries (e.g., the Potomac

River), but not in other tidal tributaries. The Regional Criteria provides specific

guidance to the states on how to address estuarine turbidity maximum zones in

applying the Chesapeake Bay water clarity criteria (see Chapter 7 in U.S. EPA

2003). The lack of historical data on the presence of underwater bay grasses in a

particular habitat is not a valid reason to delineate that shallow-water area as an

underwater bay grass no-grow zone.

▼109

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Six Chesapeake Bay Program segments were not assigned a shallow-water bay grass

designated use depth boundary (see Table IV-13). The established bay grass no-grow

zones covered the 2-meter and less habitats along the entire tidal shoreline in each

of these segments–upper Choptank River, upper Pocomoke River, Western Branch

Elizabeth River, Southern Branch Elizabeth River, Eastern Branch Elizabeth River

and Lafayette River (see Appendix C). 

▼110

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-29. Map illustrating the revised underwater bay grass no-grow zones of the

Chesapeake Bay and its tidal tributaries.
DETERMINING THE MAXIMUM DEPTH OF 

PERSISTENT/ABUNDANT PLANT GROWTH 

The first step in the process to define the maximum depth of persistent and abundant

underwater bay grass beds by Chesapeake Bay Program segment (Table IV-11,

Figure IV-30) was to establish decision rules. The rules developed take full advantage of the entire record of underwater bay grass distribution and abundance survey

data and reflect the findings published in scientific literature (Table IV-12). Also, the

decision rules help ensure full consistency between the establishment of the shallowwater bay grass designated use depths (the depth at which the Chesapeake Bay water

clarity criteria will be applied) and the new quantitative underwater bay grasses

acreage restoration goal for Chesapeake Bay and its tidal tributaries.

The available data record included interpreted aerial photography from the 1930s to

the early 1970s as well as the annual baywide aerial survey data from 1978-2000.

From these photos and surveys, the acreage of underwater bay grasses within three

depth intervals was calculated for every Chesapeake Bay Program segment: 0-0.5

meters, > 0.5-1 meter and > 1-2 meters (Appendix B, Table B-1). Thus, each Chesapeake Bay Program segment has three ‘segment-depth intervals’ (e.g., CB4MH 1-2

meter is a segment-depth interval).

The total surface area within each segment-depth interval minus any delineated

underwater bay grass no-grow zones is an estimate of the area of potential underwater bay grass habitat in that segment-depth interval. Thus, there is an acreage of

potential underwater bay grass habitat for each of the three segment-depth intervals

in every Chesapeake Bay Program segment except for those segments that are

entirely no-grow zones (Appendix C, Table C-1).

The decision rules described in Table IV-12 are based on the observed single best

year of underwater bay grass coverage for each Chesapeake Bay Program segment

(i.e., not the single best year by segment-depth) (Appendix B, Table B-2). Using

each segment’s single best year, the percentage of available habitat at each segmentdepth interval that was occupied by underwater bay grasses in that single best year

was calculated (Appendix B, Table B-3). That percentage is a measure of the relative importance of each segment-depth interval as bay grass habitat. Upon

application of the decision rules (Table IV-12), a set of Chesapeake Bay Program

segment-specific shallow-water designated use depths was generated (Table IV-13). 

Rationale for the 20 Percent and 10 Percent Rules

In setting application depths, it was important to select a percentage of cover high

enough to assure that underwater plants definitely occupied that habitat, but low

enough that the resulting depths realistically represented true light availability

attained during the available historical data record. Underwater bay grass beds in

tidal waters of the Chesapeake Bay display a spatial heterogeneity that is characteristic of underwater grass beds elsewhere in the world (Lehmann et al.1997; Kuenen

and Debrot 1995; Carpenter and Titus 1984). This heterogeneity exists both in micro

▼111

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼112

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-11. Chesapeake Bay Program segmentation scheme segments.

Northern Chesapeake Bay . . . . . . . . . CB1TF

Upper Chesapeake Bay . . . . . . . . . . . CB2OH

Upper Central Chesapeake Bay . . . . CB3MH

Middle Central Chesapeake Bay . . . CB4MH

Lower Central Chesapeake Bay . . . . CB5MH

Western Lower Chesapeake Bay . . . . CB6PH

Eastern Lower Chesapeake Bay . . . . CB7PH

Mouth of the Chesapeake Bay . . . . . CB8PH

Bush River . . . . . . . . . . . . . . . . . . . . BSHOH

Gunpowder River . . . . . . . . . . . . . . GUNOH 

Middle River . . . . . . . . . . . . . . . . . . . MIDOH

Back River . . . . . . . . . . . . . . . . . . . . BACOH

Patapsco River . . . . . . . . . . . . . . . . . PATMH 

Magothy River . . . . . . . . . . . . . . . . MAGMH

Severn River . . . . . . . . . . . . . . . . . . . SEVMH

South River . . . . . . . . . . . . . . . . . . . SOUMH

Rhode River . . . . . . . . . . . . . . . . . . RHDMH

West River . . . . . . . . . . . . . . . . . . . . WSTMH

Upper Patuxent River . . . . . . . . . . . . PAXTF

Western Branch Patuxent River . . . . WBRTF

Middle Patuxent River . . . . . . . . . . . PAXOH

Lower Patuxent River . . . . . . . . . . . PAXMH

Upper Potomac River . . . . . . . . . . . . POTTF

Anacostia River . . . . . . . . . . . . . . . . . ANATF

Piscataway Creek . . . . . . . . . . . . . . . . PISTF

Mattawoman Creek . . . . . . . . . . . . . . MATTF

Middle Potomac River . . . . . . . . . . . POTOH

Lower Potomac River . . . . . . . . . . . POTMH

Upper Rappahannock River . . . . . . . . RPPTF

Middle Rappahannock River . . . . . . RPPOH

Lower Rappahannock River . . . . . . . RPPMH

Corrotoman River . . . . . . . . . . . . . . CRRMH

Piankatank River . . . . . . . . . . . . . . . . PIAMH

Upper Mattaponi River . . . . . . . . . . . MPNTF

Lower Mattaponi River . . . . . . . . . . MPNOH

Upper Pamunkey River . . . . . . . . . . PMKTF

Lower Pamunkey River . . . . . . . . . . PMKOH

Middle York River . . . . . . . . . . . . . . YRKMH

Lower York River . . . . . . . . . . . . . . . YRKPH

Mobjack Bay . . . . . . . . . . . . . . . . . . MOBPH

Upper James River . . . . . . . . . . . . . . . JMSTF

Appomattox River . . . . . . . . . . . . . . . APPTF

Middle James River . . . . . . . . . . . . . JMSOH

Chickahominy River . . . . . . . . . . . . CHKOH

Lower James River . . . . . . . . . . . . . . JMSMH

Mouth of the James River . . . . . . . . . JMSPH

Western Branch Elizabeth River . . . WBEMH

Southern Branch Elizabeth River . . . SBEMH

Eastern Branch Elizabeth River . . . . EBEMH

Lafayette River . . . . . . . . . . . . . . . . . LAFMH

Mouth to mid-Elizabeth River . . . . . . ELIPH

Lynnhaven River . . . . . . . . . . . . . . . . LYNPH

Northeast River . . . . . . . . . . . . . . . . . NORTF

C&D Canal . . . . . . . . . . . . . . . . . . . C&DOH

Bohemia River . . . . . . . . . . . . . . . . . BOHOH

Elk River . . . . . . . . . . . . . . . . . . . . . . ELKOH

Sassafras River . . . . . . . . . . . . . . . . . SASOH

Upper Chester River . . . . . . . . . . . . . CHSTF

Middle Chester River . . . . . . . . . . . . CHSOH

Lower Chester River . . . . . . . . . . . . CHSMH

Eastern Bay . . . . . . . . . . . . . . . . . . . EASMH

Upper Choptank River . . . . . . . . . . . CHOTF

Middle Choptank River . . . . . . . . . . CHOOH

Lower Choptank River . . . . . . . . . CHOMH1

Mouth of the Choptank River . . . . CHOMH2

Little Choptank River . . . . . . . . . . . LCHMH

Honga River . . . . . . . . . . . . . . . . . . HNGMH

Fishing Bay . . . . . . . . . . . . . . . . . . . FSBMH

Upper Nanticoke River . . . . . . . . . . . NANTF

Middle Nanticoke River . . . . . . . . . NANOH

Lower Nanticoke River . . . . . . . . . . NANMH

Wicomico River . . . . . . . . . . . . . . . . WICMH

Manokin River . . . . . . . . . . . . . . . . MANMH

Big Annemessex River . . . . . . . . . . . BIGMH

Upper Pocomoke River . . . . . . . . . . . POCTF

Middle Pocomoke River . . . . . . . . . . POCOH

Lower Pocomoke River . . . . . . . . . . POCMH

Tangier Sound . . . . . . . . . . . . . . . . . TANMH

Source: Chesapeake Bay Program 1999.
▼113

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-30. The geographical location of the 78 Chesapeake Bay Program segments.

Source: Chesapeake Bay Program 1999.
and macro scales, and as viewed by aerial photography results in a spatial distribution that is virtually never 100 percent coverage of available shallow-water habitat at

any depth. This growth pattern was true historically as well. Manning (1957) estimated that lower Patuxent River underwater bay grass beds covered only about

one-third of shoal waters. Photography from Maryland from 1938 and 1952 revealed

an average percent cover of 35 percent (Naylor 2002) at depths of less than 1 meter.

Virginia photographic analysis revealed up to 48 percent coverage in the York and

Rappahannock rivers at the less than 1-meter depth (Moore et al. 2001). These findings were supported by similar findings from analysis of the more recent 1978–2000

Chesapeake Bay underwater bay grass aerial survey distribution data. 

▼114

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-12. Methodology used in determining the shallow-water bay grass

designated use depths by Chesapeake Bay Program segment, which led to the

establishment of the 185,000 Chesapeake Bay baywide underwater grasses

restoration goal.

The baywide underwater bay grass goal acreage was established based on the single best

year acreage out to a shallow-water bay grass designated use depth determined as follows:

1. Bathymetry data and aerial photographs were used to divide the mapped single best year

underwater bay grasses acreage in each Chesapeake Bay Program segment into three

depth zones: 0-0.5 meters, > 0.5-1 meters and >1-2 meters. The delineated underwater

bay grass no-grow zones were then removed from consideration as shallow-water bay

grass designated use habitat.

2. The aerial photographs were used to determine the depth to which the mapped underwater bay grass beds grew in each Chesapeake Bay Program segment with either a

minimum abundance or minimum persistence. The underwater bay grass goal for a

Chesapeake Bay Program segment is the portion of the single best year acreage mapped

out to the higher depth in the determined depth range. The decision rules for this process

were as follows:

In all segments, the 0-0.5 meter depth interval was designated for shallow-water

bay grass use. In addition, the shallow-water bay grass use was designated for

deeper depths within a Chesapeake Bay Program segment if either:

A) The single best year of underwater bay grasses distribution covered at least 

20 percent of the potential habitat in a deeper depth interval; or,

B) The single best year of underwater bay grass distribution covered at least 

10 percent of the potential habitat in the segment-depth interval, and at least 

3 of the 4 five-year periods of the more recent record (1978–2000) showed 

at least 10 percent underwater bay grasses coverage of potential habitat 

in the segment-depth interval.

3. The single best year underwater bay grasses distribution acreage of all Chesapeake Bay

Program segments were clipped at the deeper depth of the segment-depth interval determined above. The resulting underwater bay grass acreage for each segment were added,

resulting in the total baywide underwater bay grass acreage goal of 185,000 acres. 
▼115

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-13.The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths.

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Northern Chesapeake Bay CB1TF Historical ▲ 2

Upper Chesapeake Bay CB2OH Historical ✪ 0.5 

Upper Central Chesapeake Bay CB3MH 1978 ▲ 0.5 

Middle Central Chesapeake Bay CB4MH Historical ▲ 2 

Lower Central Chesapeake Bay CB5MH Historical ▲ 2 

Western Lower Chesapeake Bay CB6PH Historical ▲ 1 

Eastern Lower Chesapeake Bay CB7PH Historical ▲ 2 

Mouth of the Chesapeake Bay CB8PH 1996 ✪ 0.5 

Bush River BSHOH Historical ✪ 0.5 

Gunpowder River GUNOH 2000 ▲ 2 

Middle River MIDOH Historical ▲ 2 

Back River BACOH * ✪ 0.5 

Patapsco River PATMH Historical ▲ 1 

Magothy River MAGMH Historical ▲ 1 

Severn River SEVMH 1999 ▲ 1 

South River SOUMH Historical ▲ 1 

Rhode River RHDMH Historical ✪ 0.5 

West River WSTMH Historical ▲ 0.5 

Upper Patuxent River PAXTF 1996 ▲ 0.5 

Western Branch (Patuxent River) WBRTF * ✪ 0.5 

Middle Patuxent River PAXOH 2000 ✪ 0.5 

Lower Patuxent River PAXMH Historical ▲ 1 

Upper Potomac River POTTF 1991 ✜ 2 

Anacostia River ANATF 1991 ✪ 0.5 

Piscataway Creek PISTF 1987 ▲ 2 

Mattawoman Creek MATTF 2000 ▲ 1 

Middle Potomac River POTOH 1998 ✜ 2 

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)

continued
▼116

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Lower Potomac River POTMH Historical ▲ 1 

Upper Rappahannock River RPPTF 2000 ✪ 0.5 

Middle Rappahannock River RPPOH * ✪ 0.5

Lower Rappahannock River RPPMH Historical ▲ 1 

Corrotoman River CRRMH Historical ▲ 1 

Piankatank River PIAMH Historical ▲ 2 

Upper Mattaponi River MPNTF 1998 ✪ 0.5 

Lower Mattaponi River MPNOH * ✪ 0.5 

Upper Pamunkey River PMKTF 1998 ✪ 0.5 

Lower Pamunkey River PMKOH * ✪ 0.5 

Middle York River YRKMH Historical ✪ 0.5 

Lower York River YRKPH Historical ▲ 1 

Mobjack Bay MOBPH Historical ▲ 2

Upper James River JMSTF Historical ✪ 0.5 

Appomattox River APPTF Historical ▲ 0.5

Middle James River JMSOH 1998 ✪ 0.5 

Chickahominy River CHKOH 2000 ✪ 0.5 

Lower James River JMSMH Historical ✪ 0.5 

Mouth of the James River JMSPH Historical ▲ 1 

Western Branch Elizabeth River WBEMH * ❖❖❖ * 

Southern Branch Elizabeth River SBEMH * ❖❖❖ * 

Eastern Branch Elizabeth River EBEMH * ❖❖❖ * 

Lafayette River LAFMH * ❖❖❖ * 

Mouth to mid-Elizabeth River ELIPH * ✪ 0.5 

Lynnhaven River LYNPH 1986 ✪ 0.5 

Northeast River NORTF Historical ✪ 0.5 

C&D Canal C&DOH 1978 ✪ 0.5 

Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths (cont.).

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)

continued
▼117

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Bohemia River BOHOH 2000 ✪ 0.5 

Elk River ELKOH 2000 ▲ 2 

Sassafras River SASOH 2000 ▲ 1 

Upper Chester River CHSTF * ✪ 0.5 

Middle Chester River CHSOH Historical ✪ 0.5 

Lower Chester River CHSMH Historical ▲ 1 

Eastern Bay EASMH Historical ▲ 2 

Upper Choptank River CHOTF * ❖❖❖ *

Middle Choptank River CHOOH Historical ✪ 0.5 

Lower Choptank River CHOMH2 Historical ▲ 1 

Mouth of the Choptank River CHOMH1 Historical ▲ 2 

Little Choptank River LCHMH Historical ▲ 2 

Honga River HNGMH Historical ▲ 2 

Fishing Bay FSBMH Historical ✪ 0.5 

Upper Nanticoke River NANTF * ✪ 0.5 

Middle Nanticoke River NANOH Historical ✪ 0.5 

Lower Nanticoke River NANMH Historical ✪ 0.5 

Wicomico River WICMH Historical ✪ 0.5

Manokin River MANMH Historical ▲ 2

Big Annemessex River BIGMH Historical ▲ 2 

Upper Pocomoke River POCTF * ❖❖❖ * 

Middle Pocomoke River POCOH * ✪ 0.5 

Lower Pocomoke River POCMH Historical ▲ 1

Tangier Sound TANMH Historical ▲ 2

✪ Decision rules not met – default depth interval of 0-0.5 meters applies. 

▲ Single best year percent of total potential habitat is 20 percent. 

✜ Percent of total potential habitat is 10-19.9% and underwater bay grasses are persistent (1978–2000). 

❖ Chesapeake Bay Program segment completely within the underwater bay grass no-grow zone. 

*Denotes no data available or no underwater bay grasses mapped (1930s-2000). 

Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths (cont.).

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)
▼118

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Several possible reasons account for less-than-complete habitat occupation. These

include small-scale sediment type differences, small-scale sediment movement

patterns, sediment slope, fetch, uneven seed distribution and localized disturbance. In

addition to these reasons for real variations in plant presence, only the most dense

areas of underwater bay grasses are visible using high-altitude photography. Very

sparse beds reveal no signature in the water and are never delineated through photo

interpretation. Each year, Chesapeake Bay researchers and resource managers find

dozens of underwater bay grass beds in places not identified in the annual aerial

survey due to these limitations. Thus, reporting of percent coverage is generally lower

than the total amount of habitat actually occupied by sparse plant beds, which further

lowers the total percent coverage. Given the starting point of 1 percent, and the typical

maximum of 35-48 percent from the historical photography, 20 percent was seen as a

defensible midpoint figure reflective of sufficient coverage to define maximum depth

of the underwater bay grasses growth (Moore 1999, 2001; Naylor 2002).

In order to provide an additional measure of the importance of a segment-depth

interval as underwater bay grass habitat, the record of underwater bay grass aerial

survey data from 1978–2000 (there is not a survey for every year between 1979-1983

and in 1988) was segmented into four five-year intervals (Appendix B, Table B-4).

The persistence of underwater bay grasses in each segment-depth interval was then

assessed by counting the number of five-year intervals in which at least 10 percent

of potential habitat was occupied by underwater bay grasses (see Table IV-12).

UNDERWATER BAY GRASS RESTORATION 

GOAL-BASED BOUNDARIES

The Chesapeake 2000 agreement committed to revising the existing underwater bay

grass restoration goals and strategies:

. . . to reflect historic abundance, measured as acreage and density from the

1930s to present. The revised goals will include specific levels of water clarity

which are to be met in 2010. Strategies to achieve these goals will address

water clarity, water quality and bottom disturbance.

The eligible segments and depths included in calculating the new underwater bay

grass restoration goal were limited to segment-depth intervals designated for

shallow-water bay grass use. The new restoration goal was derived from the total

single best year acreage summed over all the segment depths that were designated

for shallow-water bay grass use after considering a wide array of data and information (Figure IV-31).

Data Used to Establish the Restoration Goal

It was essential to use historical underwater bay grass data in determining the underwater bay grass acreage goal for the Chesapeake Bay. But using these data presented

obvious limitations. They were originally collected for agricultural landuse mapping

purposes and thus did not include all areas of tidal shallow-water habitats, which
▼119

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries 37,356 76,525 85,415 99,039 113,719 139,087 184,877 194,676 242,975

495,882

640,926

0

700,000600,000500,000400,000300,000200,000100,000

Acres

1984

Underwater

Bay Grasses

Single Best

Year for

Those Years

Designated

for the 

1992 CBP

Underwater

Bay Grasses

Restoration 

Goal

(1971-1990)

2001 

Underwater

Bay Grasses

1978-2000

Single Best 

Year

Underwater 

Bay Grasses

at All Depths

1992 CBP

Underwater

Bay Grasses

Restoration

Goal (1971-

1990

Composite

Underwater 

Bay Grasses)

1978-2000

Composite

Underwater

Bay Grasses

at All Depths

1930s-2000

Single Best

Year

Underwater

Bay Grasses

Out to

Maximum 

Depth of

Persistent/

Abundant

Plant Growth

1930s-2000

Composite

Underwater

Bay Grasses

Out to 

2-Meter

Depth Contour

Total 

ShallowWater

Habitat Out

to Maximum

Depth of

Persistent/

Abundant

Plant Growth

1930s-2000

Single Best

Year

Underwater

Bay Grasses

at All Depths

Total

ShallowWater

Habitat Out

to 2-Meter

Depth 

Contour

(minus 

underwater

bay grasses

no grow

zones)

Figure IV-31. Array of different underwater bay grass and shallow-water habitat acreages considered during the process for setting the shallow-water

designated use depth and establishing the new Chesapeake Bay underwater bay grass restoration goals.

Sources: Moore et al. 1999; Naylor 2002; Virginia Institute of Marine Science Chesapeake Bay SAV website http://www.vims.edu/bio/sav; Chesapeake Bay Program websitehttp://www.chesapeakebay.net.
resulted in an underestimate of the mapped acreage. Historic data also were limited

by the fact that pre-Hurricane Agnes (June 1972) underwater bay grass data exist

only for a limited number of years in each Chesapeake Bay Program segment. Thus,

using only historical data to determine a new goal would likely underestimate the

potential for underwater bay grass recovery.

Rationale for Use of the Single Best Year 

The single best year of underwater bay grass growth observed in each Chesapeake

Bay Program segment from the entire available record of aerial photographs

(1930s–2000) is the best available data on underwater bay grass occurrence over the

long-term. Of the 62 Chesapeake Bay Program segments with mapped underwater

bay grasses, 68 percent of the segment single best year acreages occurred in the 1930s

to early 1970s time period; 3 percent occurred in 1978; 5 percent occurred between

1986 and 1991; and 24 percent occurred between 1996 and 2000 (see Table IV-13).

There were several obvious benefits in using the single best year approach to setting

the new restoration goal. The single best year acreage is the most solid available data

on underwater bay grass acreage over the multi-decade data record. Even in suitable

water quality conditions, underwater bay grass beds often move around within a

segment. By combining acreage over a number of years into a composite acreage it

would be possible to overestimate the likely future abundance of underwater bay

grasses in any single year. 

Using the single best year as the basis for the new restoration goal ensures consistency

with the method for determining the segment-specific shallow-water designated use

depths and the resulting water clarity criteria application depths. The consistency

between methods links the segment-specific water clarity application depths, shallowwater designated use boundaries and underwater bay grass restoration goals. This

method is scientifically valid because when the acreage goals for segments in the

same salinity range are totaled (see “Shallow-Water Habitat Area to Support Restoration,” below), the percentage of available habitat covered by the restoration goal

acreage is consistent with the average rate of habitat occupancy described in the

scientific literature as reflecting healthy underwater bay grass growth.

The new underwater bay grass goal focuses the restoration effort on areas that demonstrated a minimal level of abundance or persistence in the past and which are likely to

respond to water clarity improvements in the future. Focusing on the single best year

versus a composite underwater bay grass coverage ensures that vegetated portions of

potential underwater bay grass habitats are not over-accounted-for based on underwater

bay grass beds that may have ‘migrated’ year-to-year over the past seven decades.

New Underwater Bay Grass Restoration Goal

Table IV-14 lists the Chesapeake Bay Program segment-specific single best year

acreage within the shallow-water bay grasses designated use depths that, added

together, make up the baywide 185,000 acre restoration goal.

▼120

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼121

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-14. Chesapeake Bay underwater bay grass restoration goals by

Chesapeake Bay Program segment.

Segment Name Segment Single Best Year Acres 

Northern Chesapeake Bay CB1TF Historical 12,908

Upper Chesapeake Bay CB2OH Historical 302

Upper Central Chesapeake Bay CB3MH 1978 943

Middle Central Chesapeake Bay CB4MH Historical 2,511

Lower Central Chesapeake Bay CB5MH Historical 14,961

Western Lower Chesapeake Bay CB6PH Historical 980

Eastern Lower Chesapeake Bay CB7PH Historical 14,620

Mouth of the Chesapeake Bay CB8PH 1996 6

Bush River BSHOH Historical 158

Gunpowder River GUNOH 2000 2,254

Middle River MIDOH Historical 838

Back River BACOH * 0

Patapsco River PATMH Historical 298

Magothy River MAGMH Historical 545

Severn River SEVMH 1999 329

South River SOUMH Historical 459

Rhode River RHDMH Historical 48

West River WSTMH Historical 214

Upper Patuxent River PAXTF 1996 5

Western Branch (Patuxent River) WBRTF * 0

Middle Patuxent River PAXOH 2000 68

Lower Patuxent River PAXMH Historical 1,325

Upper Potomac River POTTF 1991 4,368

Anacostia River ANATF 1991 6

Piscataway Creek PISTF 1987 783

Mattawoman Creek MATTF 2000 276

Middle Potomac River POTOH 1998 3,721

Lower Potomac River POTMH Historical 10,173

Upper Rappahannock River RPPTF 2000 20

Middle Rappahannock River RPPOH * 0

Lower Rappahannock River RPPMH Historical 5,380

Corrotoman River CRRMH Historical 516

Piankatank River PIAMH Historical 3,256

Upper Mattaponi River MPNTF 1998 75

Lower Mattaponi River MPNOH * 0

Upper Pamunkey River PMKTF 1998 155

Lower Pamunkey River PMKOH * 0

Middle York River YRKMH Historical 176

Lower York River YRKPH Historical 2,272

Mobjack Bay MOBPH Historical 15,096

continued
▼122

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Segment Name Segment Single Best Year Acres 

Upper James River JMSTF Historical 1,600

Appomattox River APPTF Historical 319

Middle James River JMSOH 1998 7

Chickahominy River CHKOH 2000 348

Lower James River JMSMH Historical 531

Mouth of the James River JMSPH Historical 604

Western Branch Elizabeth River WBEMH * 0

Southern Branch Elizabeth River SBEMH * 0

Eastern Branch Elizabeth River EBEMH * 0

Lafayette River LAFMH * 0

Mouth to mid-Elizabeth River ELIPH * 0

Lynnhaven River LYNPH 1986 69

Northeast River NORTF Historical 88

C&D Canal C&DOH 1978 0

Bohemia River BOHOH 2000 97

Elk River ELKOH 2000 1,648

Sassafras River SASOH 2000 764

Upper Chester River CHSTF * 0

Middle Chester River CHSOH Historical 63

Lower Chester River CHSMH Historical 2,724

Eastern Bay EASMH Historical 6,108

Upper Choptank River CHOTF * 0

Middle Choptank River CHOOH Historical 63

Lower Choptank River CHOMH2 Historical 1,499

Mouth of the Choptank River CHOMH1 Historical 8,044

Little Choptank River LCHMH Historical 3,950

Honga River HNGMH Historical 7,686

Fishing Bay FSBMH Historical 193

Upper Nanticoke River NANTF * 0

Middle Nanticoke River NANOH Historical 3

Lower Nanticoke River NANMH Historical 3

Wicomico River WICMH Historical 3

Manokin River MANMH Historical 4,359

Big Annemessex River BIGMH Historical 2,014

Upper Pocomoke River POCTF * 0

Middle Pocomoke River POCOH * 0

Lower Pocomoke River POCMH Historical 4,092

Tangier Sound TANMH Historical 37,965

Total acres 184,889

*No underwater grasses recorded for any year within the available 1930s–2000 data record.

Table IV-14. Chesapeake Bay underwater bay grass restoration goals by

Chesapeake Bay Program segment (cont.).
SHALLOW-WATER HABITAT AREA TO SUPPORT RESTORATION

GOAL-BASED BOUNDARIES

As described previously, the restoration of underwater bay grasses within a segment

requires that shallow-water habitat meet the Chesapeake Bay water clarity criteria

over a greater acreage than the underwater bay grasses will actually cover. The ratio

of underwater bay grass acreage to the required shallow-water habitat acreage varies

based on the different species of underwater bay grasses that inhabit the Bay’s four

salinity regimes. Shallow-water habitat acreage ratios have been derived scientifically through evaluation of extensive underwater bay grasses distribution data within

tidal fresh, low, medium and high salinity regimes (reflecting different levels of

coverage by different underwater bay grass communities).

The Chesapeake Bay Program segment-specific restoration goal acreage and

corresponding shallow-water designated use acreage (to the previously determined

maximum depth of abundant and persistent underwater plant growth) listed in 

Table IV-15 were summed by major salinity regime–tidal fresh (0-0.5 ppt), oligohaline (> 0.5-5 ppt), mesohaline (> 5ppt-18 ppt) and polyhaline (>18 ppt).13 The

underwater bay grasses acreage to shallow-water habitat acreage ratios were then

expressed as a percentage of the total shallow-water designated use habitat.

Compared with a baywide value of 38 percent, the tidal-fresh (37 percent), mesohaline (39 percent) and polyhaline (41 percent) values were all very close to the

baywide value as well as the other salinity regime-specific values (Table IV-16).

These values are consistent with findings published in the scientific literature and the

35 to 48 percent range derived from evaluation of the 1930s through early 1970s

historical data record by Naylor (2002) and Moore (1999, 2001). Influenced by the

natural presence of the estuarine turbidity maximum, the value was 21 percent in

oligohaline habitats.

CONFIRMING THAT THE REFINED DESIGNATED USES

MEET EXISTING USES

The EPA Water Quality Standards regulations at 40 CFR 131.10(g) and (j) specify

that states may remove a designated use that is not an existing use, or establish

subcategories of a use, if they can demonstrate that attaining the designated use is

not feasible. The current regulation at 40 CFR Part 131 identifies the factors that

must be considered in making such a demonstration. As the regulation explains,

existing uses, by definition, are attainable and must be protected by designated uses

in water quality standards (40 CFR 131.10[g], 131.10[h][1] and 131.10[i]). Any

▼123

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

13Note that all Chesapeake Bay Program segments have been assigned to one of the four salinity regimes

based on an evaluation of almost two decades of salinity data. The segment-naming convention documents each individual segment’s long-term averaged respective salinty regime: TF = tidal fresh, OH =

oligohaline, MH = mesohaline, and PH = polyhaline.
▼124

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals. Shallow- Percent Shallow- Existing Use Water Acreage Water Designated 2001 Acreage to Maximum Use Habitat Shallow- Underwater (1978–2000 Restoration Depth of Covered by Water Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth Northern Chesapeake Bay CB1TF 7979 7773 12,908 20,907 61.7 2 Upper Chesapeake Bay CB2OH 203 640 302 2405 12.5 0.5 Upper Central Chesapeake Bay CB3MH 1 1,296 943 2,011 46.9 0.5 Middle Central Chesapeake Bay CB4MH 112 176 2,511 10,630 23.6 2 Lower Central Chesapeake Bay CB5MH 4,487 4,240 14,961 29,959 49.9 2 Western Lower Chesapeake Bay CB6PH 715 1,208 980 3,939 24.9 1 Eastern Lower Chesapeake Bay CB7PH 9,168 10,729 14,620 33,304 43.9 2 Mouth of the Chesapeake Bay CB8PH 8 11 6 381 1.5 0.5 Bush River BSHOH 3 187 158 1,136 13.9 0.5 Gunpowder River GUNOH * 2,281 2,254 7,358 30.6 2 Middle River MIDOH * 698 838 2,479 33.8 2 Back River BACOH * 0 0 850 0.0 0.5 Patapsco River PATMH * 114 298 1,802 16.6 1 Magothy River MAGMH * 427 545 1,378 39.6 1 Severn River SEVMH 120 433 329 1347 24.4 1 South River SOUMH 27 50 459 1,432 32.1 1 Rhode River RHDMH * 14 48 267 18.0 0.5 West River WSTMH * 106 214 542 39.5 0.5 Upper Patuxent River PAXTF 205 44 5 24 22.2 0.5 Western Branch (Patuxent River) WBRTF * 0 0 0 0.0 0.5

Middle Patuxent River PAXOH 104 80 68 1,072 6.3 0.5Lower Patuxent River PAXMH 22 108 1,325 5121 25.9 1Upper Potomac River POTTF 1,964 4,465 4,368 17,501 25.0 2Anacostia River ANATF 4 11 6 85 6.6 0.5

continued
▼125

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use DepthPiscataway Creek PISTF * 783 783 914 85.7 2Mattawoman Creek MATTF * 311 276 695 39.7 1Middle Potomac River POTOH 3,070 3,766 3,721 15,193 24.5 2Lower Potomac River POTMH 1739 2130 10173 26075 39.0 1Upper Rappahannock River RPPTF 66 30 20 2175 0.9 0.5Middle Rappahannock River RPPOH * 0 0 1226 0 0.5Lower Rappahannock River RPPMH 478 841 5,380 19,793 27.2 1Corrotoman River CRRMH 389 419 516 1,819 28.4 1Piankatank River PIAMH 539 1,003 3,256 8,014 40.6 2Upper Mattaponi River MPNTF * 84 75 800 9.4 0.5Lower Mattaponi River MPNOH * 0 0 358 0.0 0.5Upper Pamunkey River PMKTF 140 184 155 1,860 8.4 0.5Lower Pamunkey River PMKOH * 0 0 420 0.0 0.5Middle York River YRKMH * 0 176 4,728 3.7 0.5Lower York River YRKPH 801 815 2272 4,949 45.9 1Mobjack Bay MOBPH 9,508 10,653 15096 33990 44.4 2Upper James River JMSTF 95 76 1,600 8,249 19.4 0.5Appomattox River APPTF * 0 319 1,085 29.4 0.5Middle James River JMSOH 15 8 7 3179 0.2 0.5Chickahominy River CHKOH 268 422 348 3283 10.6 0.5Lower James River JMSMH 2 3 531 9,618 5.5 0.5Mouth of the James River JMSPH 232 231 604 1,616 37.4 1Western Branch Elizabeth River WBEMH * 0 0 0 0.0 *Southern Branch Elizabeth River SBEMH * 0 0 0 0.0 *

continued
▼126

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Eastern Branch Elizabeth River EBEMH * 0 0 0 0.0 * Lafayette River LAFMH * 0 0 0 0.0 * Mouthof the Elizabeth River ELIPH * 0 0 0 0.0 * Lynnhaven River LYNPH 43 105 69 2476 2.8 0.5 Northeast River NORTF * 19 88 456 19.3 0.5 C&D Canal C&DOH 7 5 0 99 0.2 0.5 Bohemia River BOHOH 354 330 97 735 13.2 0.5 Elk River ELKOH 2034 2006 1,648 5,024 32.8 2 Sassafras River SASOH 1,169 1,116 764 2614 29.2 1 Upper Chester River CHSTF * 0 0 574 0 0.5 Middle Chester River CHSOH * 0 63 926 6.8 0.5 Lower Chester River CHSMH 205 2,369 2,724 6,980 39 1 Eastern Bay EASMH 2,886 4,610 6,108 20,805 29.4 2 Upper Choptank River CHOTF * 0 0 0 0.0 * Middle Choptank River CHOOH * 0 63 591 10.7 0.5 Lower Choptank River CHOMH2 148 193 1,499 3,770 39.8 1 Mouth of the Choptank River CHOMH1 5,257 6,445 8,044 20,857 38.6 2 Little Choptank River LCHMH 2,377 1,454 3,950 12,367 31.9 2 Honga River HNGMH 4,945 4,656 7,686 16,456 46.7 2

Fishing Bay FSBMH 6 59 193 2,467 7.8 0.5Upper Nanticoke River NANTF * 0 0 0 0.0 *Middle Nanticoke River NANOH * 0 3 1,141 0.3 0.5Lower Nanticoke River NANMH * 0 3 1583 0.2 0.5Wicomico River WICMH * 0 3 1,513 0.2 0.5Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth

continued
▼127

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Manokin River MANMH 404 420 4,359 10,700 40.7 2 Big Annemessex River BIGMH 721 546 2,014 5,065 39.8 2 Upper Pocomoke River POCTF * 0 0 0 0.0 * Middle Pocomoke River POCOH * 0 0 289 0.0 0.5 Lower Pocomoke River POCMH 1,528 1,831 4,092 9,936 41.2 1 Tangier Sound TANMH 13,310 17,688 37,965 68,578 55.4 2 Totals 77,854 100,701 184889 491,968

Table IV-15.

*No underwater bay grasses mapped or aerial photography collected due to 9/11/01 flight path restrictions. 

Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth
change in designated uses must show that the existing uses are still being protected.

As the EPA 1983 Water Quality Standards Handbook describes, an existing use can

be defined as fishing, swimming or other uses that have actually occurred since

November 28, 1975; or the water quality that is suitable to allow the use to be

attained—unless there are physical factors, such as substrate or flow, that prevent the

use from being attained (U.S. EPA 1983). Section 131.12(a)(1) in turn requires state

anti-degradation policies to protect existing water quality. This paragraph applies a

minimum level of protection to all waters. In setting the five subcategories of current

tidal-water designated uses, explicit steps were taken in developing the refined uses

and their boundaries to ensure that existing aquatic life uses would continue to be

protected.

MIGRATORY SPAWNING AND NURSERY EXISTING USE

The migratory fish spawning and nursery designated use will be protected by a set

of Chesapeake Bay-specific dissolved oxygen criteria that are more protective—

6 mg/l 7-day mean and 5 mg/l instantaneous minimum–than current state water

quality standards that apply to these same habitats from February 1 through May 31

(U.S. EPA 2003). Existing uses within the migratory fish spawning and nursery

habitats will continue to be protected.

SHALLOW-WATER EXISTING USE

In delineating the shallow-water use, the single best year of underwater bay grass

distribution mapped since the 1930s was used to define a shallow-water designated

use depth, underwater bay grass restoration goal and a corresponding shallow-water

habitat acreage to support achievement of the restoration goal for each respective

Chesapeake Bay Program segment. Most of the segment-specific restoration goal

acreage is higher than the established existing use underwater bay grass acreage

derived from the single best year of the 1978-2001 data record out to the maximum

depth of abundant/persistent underwater plant growth (see Table IV-15). In those

cases where the existing use acreage is higher than the restoration goal, the existing

use acreage will drive the shallow-water designated use boundary. As most of the

▼128

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-16. Percent of shallow-water designated use habitat covered by single

best year underwater bay grass acreage by salinity regime.

Tidal-Fresh Oligohaline Mesohaline Polyhaline 

Median 37.2 20.5 39.2 41.3

Minimum 0 0 0.2 1.5

Maximum 85.7 33.8 54.3 45.9

No. of Segments 14 20 29 7 
single best years were based on historical underwater bay grass distributions (1930s

through the early 1970s), the shallow-water bay grass uses existing since 1975 will

continue to be protected.

OPEN-WATER EXISTING USE

The application of the open-water fish and shellfish designated use dissolved oxygen

criteria will provide an equal level of protection to the same tidal waters as current

state water quality standards. The combined set of 5 mg/l 30-day mean, 4 mg/l 7-day

mean, and 3 mg/l instantaneous minimum have been documented to protect all life

stages of open-water habitat species in the Chesapeake Bay and its tidal waters (U.S.

EPA 2003). Existing uses within the open-water habitats will continue to be protected.

DEEP-WATER AND DEEP-CHANNEL EXISTING USES

The application of the deep-water seasonal fish and shellfish designated use and the

deep-channel seasonal refuge designated use and their respective oxygen criteria will

result in improvements to existing water quality conditions that currently do not

attain the applicable criteria (see Chapter V). Given that trends in dissolved oxygen

conditions have been generally degrading since the early 1970s (see Chapter III;

Hagy 2002), improvements to these conditions will ensure that existing uses within

the deep-water and deep-channel habitats will continue to be protected. 

LITERATURE CITED

Alldredge, A. L., T. J. Cowles, S. MacIntyre, J. E.B. Rines, P. L. Donaghay, C. F. Greenlaw,

D. V. Holliday, M. M. Dekshenieks, J. M. Sullivan, J. Ronald, V. Zaneveld. 2002. “Occurrence and mechanisms of formation of a dramatic thin layer of marine snow in a shallow

Pacific fjord.” Mar. Ecol. Prog. Ser. In Press.

Austin, H.M., A.D. Estes and D.M. Seaver. 2000. Estimation of juvenile striped bass: relative abundance in the Virginia portion of Chesapeake Bay. Annual Report 1999. Virginia

Institute of Marine Science, Gloucester Point, Virginia.

Batiuk, R.A., P. Bergstrom, M. Kemp, E. Koch, L. Murray, J.C. Stevenson, R. Bartleson, V.

Carter, N.B. Rybicki, J.M. Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K.A.

Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay submerged aquatic vegetation

water quality and habitat-based requirements and restoration targets: a second technical

synthesis. CBP/TRS 245/00 EPA 903-R-00-014. USEPA Chesapeake Bay Program,

Annapolis, Maryland.

Batiuk, R.A., R. Orth, K. Moore, J.C. Stevenson, W. Dennison, L. Staver, V. Carter, N.

Rybicki, R. Hickman, S. Kollar and S. Bieber. 1992. Submerged aquatic vegetation habitat

requirements and restoration targets: a technical synthesis. CBP/TRS 83/92. U.S. EPA

Chesapeake Bay Program, Annapolis, Maryland.

Boreman, J. and R. Klauda. 1988. Distribution of early life stages of striped bass in the

Hudson River Estuary, 1974-1979. American Fisheries Society Monographs 4:53-58.

▼129

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Carpenter, S.R. and Titus, J.E. 1984. Composition and spatial heterogeneity of submersed

vegetation in a softwater lake in Wisconsin. Vegetatio 57:153-165.

Chao, Shenn-Yu and T. Paluszkiewicz. 1991. The hydraulics of density currents over estuarine sills. Journal of Geophysical Research, 96 no. C4, 7065-7076.

Chesapeake Bay Living Resources Task Force. 1987. Habitat requirements for Chesapeake

Bay living resources: a report from the Chesapeake Bay Living Resources Task Force. Chesapeake Bay Program, Annapolis, Maryland.

Chesapeake Bay Program. 1999. Analytical Segmentation for the 1997 Reevaluation and

Beyond. Report from the Chesapeake Bay Program Monitoring Subcommittee’s Data

Analysis Workgroup. Annapolis, Maryland.

Chesapeake Bay Watershed Partners. 2001. Memorandum of understanding among the state

of Delaware, the District of Columbia, the State of Maryland, the State of New York, the

Commonwealth of Virginia, the State of West Virginia and the U.S. Environmental Protection Agency regarding cooperative efforts for the protection of the Chesapeake Bay and its

rivers. Chesapeake Bay Program, Annapolis, Maryland.

Chesapeake Executive Council. 1987. 1987 Chesapeake Bay Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

Chesapeake Executive Council. 2000. Chesapeake 2000 Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

Cooper, S.R. and G.S. Brush. 1991. Long-term history of Chesapeake Bay anoxia. Science

254:992-996.

Craig, J.K., L.B. Crowder, C.D. Gray, C.J. McDaniel, T.A. Henwood and J.G. Hanifen. 2001.

Ecological effects of hypoxia on fish, sea turtles and marine mammals in the Northwestern

Gulf of Mexico. Pp. 269-292. In: Coastal Hypoxia: Consequences for Living Resources and

Ecosystems, N.N. Rabalais and R.E. Turner, eds. Coastal and Estuarine Studies.

Dennison, W.C., R.J. Orth, K.A. Moore, J.C. Stevenson, V. Carter, S. Kollar, P.W. Bergstrom

and R.A. Batiuk. 1993. Assessing water quality with submersed aquatic vegetation. Habitat

requirements as barometers of Chesapeake Bay health. Bioscience 43:86-94.

Dey, W.P. 1981. Mortality and growth of young-of-the-year striped bass in the Hudson River

Estuary. Transactions of the American Fisheries Society. 110:151-157.

Eby, L.A. 2001. Response of a fish community to frequent and infrequent disturbances in an

estuarine ecosystem. Ph.D. dissertation. Duke University.

Fisher, T.R., A.B. Gustafson, H.L. Berndt, L. Walstad, L.W. Haas, and S. MacIntyre, “The

upper mixed layer of Chesapeake Bay, USA.” Submitted to Estuaries, 2003.

Funderburk, S.L., J.A. Mihursky, S.J. Jordan and D. Riley (eds.). 1991. Habitat requirements

for Chesapeake Bay living resources: second edition. Chesapeake Research Consortium,

Solomons, Maryland.

Hagy, J.D. 2002. Eutrophication, hypoxia and trophic transfer efficiency in Chesapeake Bay.

Ph.D. dissertation, University of Maryland, College Park, Maryland.

Howell, P. and D. Simpson. 1994. Abundance of marine resources in relation to dissolved

oxygen in Long Island Sound. Estuaries 17:394-408.

▼130

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Jordan, S.J., C. Stenger, M. Olson, R. Batiuk and K. Mountford. 1992. Chesapeake Bay

dissolved oxygen goal for restoration of living resource habitats: A Synthesis of Living

Resource Requirements with Guidelines for Their Use in Evaluating Model Results and

Monitoring Information. CPB/TRS 88/93. Chesapeake Bay Program Office, Annapolis,

Maryland. 

Keister, J.E., E.D. Houde and D.L. Breitburg. 2000. Effects of bottom-layer hypoxia on abundances and depth distributions of organisms in Patuxent River, Chesapeake Bay. Marine

Ecology Progress Series 205:43-59.

Kuenen, M.M. and A.O. Debrot. 1995. A quantitative study of the seagrass and algal

meadows of the Spaanse Water, Curacao, the Netherlands, Antilles. Aquatic Botany 51 291-

310.

Koch, E.W. 2001. Beyond light: physical, geological, and geochemical parameters as

possible submersed aquatic vegetation habitat requirements. Estuaries 24:1-17.

Lehmann, A.E., E. Castella and J.B. Lacharanne. 1997. Morphological traits and spatial

heterogeneity of aquatic plants along sediment and depth gradients, Lake Geneva, Switzerland. Aquatic Botany (55) 281-299.

MacGregor, J. and E.D. Houde. 1996. Onshore-offshore pattern and variability in distribution

and abundance of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay. Marine

Ecology Progress Series 138:15-25.

Malone, T.C., W.M. Kemp, H.W. Ducklow, W.R. Boynton, J.H. Tuttle and R.B. Jonas. 1986.

Lateral variation in the production and fate of phytoplankton in a partially stratified estuary.

Marine Ecology Progress Series 32:149-160.

Manning, J. H. 1957. The Maryland Soft Shell Clam Industry and its Effects on Tidewater

Resources: an Interim Report to the Maryland General Assembly. Maryland Department of

Research and Education Resource Study Report No. 11. Chesapeake Biological Laboratory,

Solomons, MD. 25 pages.

Mansueti, R.J. and E.H. Hollis, 1963. Striped bass in Maryland tidewater. Natural Resources

Institute, University of Maryland Education Series Number 61. 28 pages.

Miller, T.J., J. Stone and E.A. Sadler. 1997. Chapter 2, Gill Net Surveys, pp. 34-63. In:

Assessment of fish community structure near Site 104, T.J. Miller. (ed.) UMCES CBL 97-

123. Report to the Maryland Environmental Service, Annapolis, Maryland

Moore, K., D. Wilcox, R. Orth and E. Bailey. 1999. Analysis of historical distribution of

submerged aquatic vegetation (SAV) in the James River. Special Report No. 355 in Applied

Marine Science and Ocean Engineering. Virginia Institute of Marine Science, School of

Marine Science, College of William and Mary, Gloucester Point, Virginia.

Moore, K., D. Wilcox and B. Anderson. 2001. Analysis of historical distribution of

submerged aquatic vegetation (SAV) in the York and Rappahannock rivers as evidence of

historical water quality conditions. Special Report No. 375 in Applied Marine Science and

Ocean Engineering. Virginia Institute of Marine Science, School of Marine Science, College

of William and Mary, Gloucester Point, Virginia.

Naylor, M.D. 2002. Historic distribution of submerged aquatic vegetation (SAV) in Chesapeake Bay, Maryland. Maryland Department of Natural Resources, Annapolis, Maryland.

▼131

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Olney, John E. Personal Communication. December 17, 2002, Department of Fisheries

Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester

Point, Virginia.

Orth, R.J., D.J. Wilcox, L.S. Nagey, J.R. Whiting and J.R. Fishman. 2000. Distribution and

abundance of submerged aquatic vegetation in the Chesapeake Bay and coastal bays–1999.

VIMS Special Scientific Report Number 141. Final Report to the U.S. Environmental Protection Agency, Chesapeake Bay Program, Annapolis, Maryland.

Pothoven, S.A., S.B. Brandt, J.M. Jech and J.L. Horne. 1997. Chapter 3, Fish Abundance,

Size and Species Composition: Kent Island Site 104, pp. 78-125. In: Assessment of Fish

Community Structure Near Site 104. T J. Miller (ed.). UMCES CBL 97-123. Report to the

Maryland Environmental Service, Annapolis, Maryland.

Rickhus, W. and F. Stroup. 1987. Source document: characterization of the biology of and

fishery of Maryland stocks of yellow perch. Maryland Department of Natural Resources

Tidewater Administration, Annapolis, Maryland. Contract No. F40-85-008.

Rilling, G.C. and E.D. Houde. 1999. Regional and temporal variability in distribution and

abundance of bay anchovy (Anchova mitchilli) eggs and larvae in the Chesapeake Bay. Estuaries 22(4):1096-1109.

Rulifson, R.A. 1994. Status of anadromous Alosa along the east coast of North America.

Anadromous Alosa Symposium, Tidewater Chapter, American Fisheries Society.

Secor, D.H., E. Niklitschek, J.T. Stevenson, T.E. Gunderson, S. Minkkinen, B. Florence, M.

Mangold, J. Skjeveland and A. Henderson-Arzapalo. 2000. Dispersal and growth of yearling

Atlantic sturgeon Acipenser oxyinchus released into the Chesapeake Bay. Fisheries Bulletin

98(4):800-810.

Setlzer-Hamilton, E.M., W.R. Boynton, J.A. Mihursky, T.T. Polgar and K.V. Wood. 1981.

Spatial and temporal distribution of striped bass eggs, larvae and juveniles in the Potomac

Estuary. Transactions of the American Fisheries Society 110:121-136.

Setlzer-Hamilton, E.M. and L. Hall, Jr. 1991. Striped bass. In: Habitat requirements for

Chesapeake Bay living resources: second edition. Funderburk, S.L., J.A. Mihursky, S.J.

Jordan and D. Riley (eds.). Chesapeake Research Consortium, Solomons, Maryland.

Smith, D.E., M. Leffler and G. MacKiernan. 1992. Oxygen dynamics in the Chesapeake Bay:

a synthesis of recent research. Maryland and Virginia Sea Grant Programs. College Park,

Maryland.

Tresselt, E.F. 1952. Spawning grounds of the striped bass, Roccus saxatilis, in Virginia.

Bulletin of the Bingham Oceanographic Collection. 14(1): 98-110.

Tsai, C. and G. Gibson. 1971. Fecundity of the yellow perch Perca flavescens (Mitchil), in

the Patuxent River, Maryland. Chesapeake Science 12:270-284.

Tuttle, J.H., R.B. Jonas and T.C. Malone. 1987. Origin, development, and significance of

Chesapeake Bay anoxia. In: Contaminant Problems and Management of Living Chesapeake

Bay Resources S.K. Majumdar, L.W. Hall, Jr. and K.M. Austin (eds.). Pennsylvania Academy

of Science, Philadelphia, Pennsylvania, pp. 442-472.

U.S. Environmental Protection Agency. 2003. Ambient Water Quality Criteria for Dissolved

Oxygen, Water Clarity, and Chlorophyll a for Chesapeake Bay and its Tidal Tributaries. 

EPA 903-R-03-002. U.S. EPA, Region 3.

▼132

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
U.S. Environmental Protection Agency. 1983. Water Quality Standards Handbook. U.S. EPA,

Office of Water, Office of Science and Technology, Washington, D.C. 

Welsh, S.A., J.E. Skjeveland, M..F. Mangold and S.M. Eylver. 2000. Distribution of wild and

hatchery-reared Atlantic sturgeon in the Chesapeake Bay, Maryland. Biology, Management,

and Protection of Sturgeon Symposium, Electric Power Research Institute, Palo Alto,

California.

Zimmerman, A.R. and E.A. Canuel. 2000. A geochemical record of eutrophication and

anoxia in Chesapeake Bay sediments: Anthropogenic influence on organic matter composition. Marine Chemistry 69:117-137.

▼133

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼53

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

chapteriv

Refined Designated Uses 

for the Chesapeake Bay and

Tidal Tributaries

BACKGROUND

RENEWED COMMITMENT TO RESTORE 

CHESAPEAKE BAY WATER QUALITY

The Chesapeake 2000 agreement and the subsequent six-state, District of Columbia

and EPA memoranda of understanding challenged the Bay watershed jurisdictions

to, “by 2010, correct the nutrient- and sediment-related problems in the Chesapeake

Bay and its tidal tributaries sufficiently to remove the Bay and the tidal portions of

its tributaries from the list of impaired waters under the Clean Water Act.” (Chesapeake Executive Council 2000; Chesapeake Bay Watershed Partners 2001.)

These agreements included commitments to “define the water quality conditions

necessary to protect aquatic living resources” and to have the jurisdictions with tidal

waters “use their best efforts to adopt new or revised water quality standards consistent with the defined water quality conditions.” Against this backdrop of a renewed

commitment to restore Bay water quality (in part through the adoption of a consistent set of Chesapeake Bay water quality criteria as state standards), the Chesapeake

Bay watershed partners recognized that the underlying tidal-water designated uses

must be refined to better reflect desired Bay water quality conditions.

CURRENT STATE TIDAL-WATER DESIGNATED USES

Virginia, Maryland, Delaware and the District of Columbia have identified parts of

the Chesapeake Bay and its tidal tributaries as ‘state waters.’ The current designated

uses for these state waters are for the protection of aquatic life (Table IV-1; figures

IV-1 through IV-4). The accompanying current criteria addressing nutrient and sediment enrichment impairments are limited to different dissolved oxygen

concentrations, which apply separately to each jurisdiction’s tidal waters. 
▼54

chapter i • Introduction

Current Designated Use for Chesapeake Bay and 

State Tidal Tributary Waters 

Maryland • Use II (shellfish harvesting waters)—Chesapeake Bay proper

• Use I (water contact recreation, protection of aquatic life)—

All surface waters 

Virginia • Class II (estuarine waters) for tidal water—Coastal zone to fall

line—Primary and secondary contact recreation, fish and shellfish

consumption, aquatic life and wildlife

“All state waters, including wetlands, are designated for the

following uses: recreational uses, e.g., swimming and

boating; the propagation and growth of a balanced,

indigenous population of aquatic life, including game fish

which might reasonably be expected to inhabit them; wildlife;

and the production of edible and marketable natural resources,

e.g., fish and shellfish.”

Delaware • Broad Creek, Nanticoke River—Industrial water supply, primary

contact recreation, secondary contact recreation, fish and aquatic

life and wildlife, agriculture water supply with additional

classification as “waters of exceptional recreational and

ecological significance” (ERES waters).

District of Columbia • Potomac River Class A (primary contact recreation), B (primary

contact recreation and aesthetics), C (protection and propagation

of fish, shellfish, and wildlife), D (consumption of fish and

shellfish) and E (navigation). 

Table IV-1. Summary of current designated uses for states’ Chesapeake Bay 

and tidal tributary waters. 
▼55

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-1. Current designated uses for Chesapeake Bay and tidal tributary waters

located in Maryland.

Source: Code of Maryland Regulations 26.08.02 for water quality dated November 1, 1993.
▼56

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-2. Current designated uses for Chesapeake Bay and tidal tributary waters

located in Virginia.

Source: Virginia State Water Control Board Regulation 9 VAC 25-260-5-et. seq. Water Quality

Standards dated December 10, 1997.

All state waters are designed for the following uses:

recreational uses, e.g. swimming and boating; the propagation and growth of a balanced, indigenous population 

or aquatic life, including game fish, which might reasonably

be expected to inhabit them; and the production of edible

and marketable natural resources, e.g. fish and shellfish.

Boundaries for Class II Waters are established for determining application of the appropriate aquatic life criteria.

Freshwater criteria apply in the tidal freshwaters. The 

more stringent of either the freshwater or saltwater criteria

apply in transition zone waters. Saltwater criteria apply in

estuarine waters.

The Class II waters are Tidal Water—coastal zone to fall line.

Designated Uses

Class II Tidal Freshwater

Class II Transition Zone

Class II Estuarine
▼57

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-3. Current designated uses for Chesapeake Bay tidal tributary waters located 

in Delaware.

Source: State of Delaware Water Quality Regulations.

Designated Uses

1. Industrial Water Supply

2. Agricultural Water Supply

3. Primary Contact Recreation

4. Secondary Contact Recreation

5. Fish, Aquatic Life, and Wildlife

6. Waters of Exception Recreational

or Ecological Significance
▼58

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-4. Current designated uses for Chesapeake Bay tidal tributary waters located 

in the District of Columbia.

Source: District of Columbia Department of Consumer and Regulatory Affairs Notice of Final

Rulemaking.

Designated Uses

A. Primary contact recreation.

B. Secondary contact recreation and aesthetic enjoyment.

C. Protection and propagation of fish, shellfish, and wildlife.

D. Protection of human health related to consumption of fish

and shellfish.

E. Navigation.

Rivers and streams either outside of DC or

non-tidal sections are a lighter gray.
REFINING TIDAL-WATER DESIGNATED USES

The Chesapeake Bay Program watershed partners determined that the underlying

tidal-water designated uses must be refined to better reflect the desired and attainable Chesapeake Bay water quality conditions called for in the Chesapeake 2000

agreement. In refining the current tidal-water designated uses, the six Chesapeake

Bay watershed states and the District of Columbia took into account five principal

considerations:

• Habitats used in common by sets of species and during particular life stages

should be delineated as separate designated uses;

• Natural variations in water quality should be accounted for by the designated

uses;

• Seasonal uses of different habitats should be factored into the designated uses;

• The Chesapeake Bay criteria for dissolved oxygen, water clarity and chlorophyll a should be tailored to support each designated use; and

• The refined designated uses applied to the Chesapeake Bay and its tidal tributary waters will support the federal Clean Water Act goals and state goals for

uses existing in these water since 1975.

The Chesapeake Bay watershed partners are proposing five refined subcategories of

the current broad aquatic life designated uses contained in the existing state water

quality standards of the four jurisdictions bordering directly on Chesapeake Bay and

its tidal tributaries. Figure IV-5 illustrates the conceptual framework of the refined

tidal-water designated uses; Table IV-2 provides general descriptions of the five

designated uses and the aquatic communities they were established to protect.9 Four

of the refined designated uses were derived largely to address seasonally distinct

habitats and living resource communities with widely varying dissolved oxygen

requirements:

• Migratory fish spawning and nursery;

• Open-water fish and shellfish;

• Deep-water seasonal fish and shellfish; and

• Deep-channel seasonal refuge.

The fifth refined designated use, the shallow-water bay grass designated use, occurs

seasonally in conjunction with that part of the year-round open-water use which

borders the land along the tidal portions of the Chesapeake Bay and its tributaries

(Figure IV-5).

▼59

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

9Note that for brevity, these refined designated uses may be referred to as migratory spawning and

nursery, shallow-water, open-water, deep-water and deep-channel.
LIVING RESOURCE-BASED REFINED DESIGNATED USES AND

PROTECTIVE CRITERIA

The five refined designated uses were derived to reflect the habitats of an array of

recreationally, commercially and ecologically important species. The supporting

prey communities were given full consideration along with the ‘target species’ in

defining the designated uses. 

Two extensive syntheses of habitat requirements for important target species and

communities in the Chesapeake Bay and its tidal tributaries formed the basis from

which these refined designated uses were conceived and developed (Chesapeake Bay

▼60

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep-Channel

Seasonal Refuge Use

Deep-Channel

Seasonal Refuge Use

A. Cross-Section of Chesapeake Bay or Tidal Tributary

B. Oblique View of the Chesapeake Bay and its Tidal Tributaries

Shallow-Water

Bay Grass Use Open-Water

Deep-Water Fish and Shellfish Use

Seasonal Fish and

Shellfish Use

Deep-Water

Seasonal Fish and

Shellfish Use

Migratory Fish

Spawning and

Nursery Use

Shallow-Water

Bay Grass Use Open-Water

Fish and Shellfish Use

Figure IV-5. Conceptual illustration of the five Chesapeake Bay tidal-water designated

use zones.
Living Resource Task Force 1987; Funderburk et al. 1991). Only when coupled with

analyses of the extensive Chesapeake Bay Monitoring Program’s water quality,

biological and living resource databases, now spanning 19 years, could the refined

tidal-water designated uses described below be documented and delineated across all

tidal-water habitats without constraints by jurisdictional borders. 

The five tidal-water designated uses, in turn, provided the context for deriving

dissolved oxygen, water clarity and chlorophyll a water quality criteria for the

Chesapeake Bay and its tidal tributaries. These criteria, derived to protect each of the

five refined designated uses, were based on effects data from a wide array of biological communities to capture the range of sensitivity of the thousands of aquatic

species inhabiting the Chesapeake Bay and tidal tributary estuarine habitats (U.S.

EPA 2003). Table IV-3 shows the proposed refined designated uses by Chesapeake

Bay Program segment.

▼61

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-2. General descriptions of the five proposed Chesapeake Bay tidal-water

designated uses. 

Migratory Fish Spawning and Nursery Designated Use: Aims to protect migratory

finfish during the late winter/spring spawning and nursery season in tidal freshwater to 

low-salinity habitats. This habitat zone is primarily found in the upper reaches of many 

Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay and will benefit 

several species, including striped bass, perch, shad, herring and sturgeon.

Shallow-Water Designated Use: Designed to protect underwater bay grasses and the 

many fish and crab species that depend on the shallow-water habitat provided by 

underwater bay grass beds.

Open-Water Fish and Shellfish Designated Use: Aims to improve water quality in the

surface water habitats within tidal creeks, rivers, embayments and the mainstem Chesapeake

Bay year-round. This use protects diverse populations of sport fish including striped bass,

bluefish, mackerel and sea trout, bait fish such as menhaden and silversides, as well as the

listed shortnose sturgeon.

Deep-Water Seasonal Fish and Shellfish Designated Use: Aims to protect living

resources inhabiting the deeper transitional water column and bottom habitats between 

the well-mixed surface waters and the very deep channels during the summer months. 

This use protects many bottom-feeding fish, crabs and oysters, as well as other important

species, including the bay anchovy.

Deep-Channel Seasonal Refuge Designated Use: Designed to protect bottom sedimentdwelling worms and small clams that act as food for bottom-feeding fish and crabs in 

the very deep channel in summer. The deep-channel designated use recognizes that low

dissolved oxygen conditions prevail in the deepest portions of this habitat zone and will

naturally have very low to no oxygen during the summer. 
▼62

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment. 

Migratory

Spawning

and Nursery Deep-Water Deep-Channel Shallow-Water

Chesapeake Bay Program (CBP) CBP (Feb. 1– Open-Water (June 1– (June 1– (April 1–

Segment Name Segment May 31) (Year-Round) Sept. 30) Sept. 30) Oct. 30)

Northern Chesapeake Bay CB1TF x x x 

Upper Chesapeake Bay CB2OH x x x 

Upper Central Chesapeake Bay CB3MH x x x x x 

Middle Central Chesapeake Bay CB4MH x x x x 

Lower Central Chesapeake Bay CB5MH x x x x 

Western Lower Chesapeake Bay CB6PH x x x 

Eastern Lower Chesapeake Bay CB7PH x x x 

Mouth of the Chesapeake Bay CB8PH x x 

Bush River BSHOH x x x 

Gunpowder River GUNOH x x x 

Middle River MIDOH x x x 

Back River BACOH x x x 

Patapsco River PATMH x x x x 

Magothy River MAGMH x x x 

Severn River SEVMH x x x 

South River SOUMH x x x 

Rhode River RHDMH x x x 

West River WSTMH x x x 

Upper Patuxent River PAXTF x x x 

Western Branch (Patuxent River) WBRTF x x x 

Middle Patuxent River PAXOH x x x 

Lower Patuxent River PAXMH x x x x 

Upper Potomac River POTTF x x x 

Anacostia River ANATF x x x 

Piscataway Creek PISTF x x x 

Mattawoman Creek MATTF x x x 

Middle Potomac River POTOH x x x 

Lower Potomac River POTMH x x x x x 

Upper Rappahannock River RPPTF x x x 

Middle Rappahannock River RPPOH x x x 

Lower Rappahannock River RPPMH x x x x x 

Corrotoman River CRRMH x x x 

Piankatank River PIAMH x x x 

Upper Mattaponi River MPNTF x x x 

Lower Mattaponi River MPNOH x x x 

Upper Pamunkey River PMKTF x x x 

Lower Pamunkey River PMKOH x x x 

Middle York River YRKMH x x x 

Lower York River YRKPH x x x 

continued
▼63

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment (cont.). 

Migratory

Spawning

and Nursery Deep-Water Deep-Channel Shallow-Water

Chesapeake Bay Program (CBP) CBP (Feb. 1– Open-Water (June 1– (June 1– (April 1–

Segment Name Segment May 31) (Year-Round) Sept. 30) Sept. 30) Oct. 30)

Mobjack Bay MOBPH x x x 

Upper James River JMSTF x x x 

Appomattox River APPTF x x x 

Middle James River JMSOH x x x 

Chickahominy River CHKOH x x x 

Lower James River JMSMH x x x 

Mouth of the James River JMSPH x x 

Western Branch Elizabeth River WBEMH x 

Southern Branch Elizabeth River SBEMH x 

Eastern Branch Elizabeth River EBEMH x 

Mouth to mid-Elizabeth River ELIMH x 

Lafayette River LAFMH x 

Mouth of the Elizabeth River ELIPH x x x 

Lynnhaven River LYNPH x x 

Northeast River NORTF x x x 

C&D Canal C&DOH x x x 

Bohemia River BOHOH x x x 

Elk River ELKOH x x x 

Sassafras River SASOH x x x 

Upper Chester River CHSTF x x x 

Middle Chester River CHSOH x x x 

Lower Chester River CHSMH x x x x x 

Eastern Bay EASMH x x x x 

Upper Choptank River CHOTF x x 

Middle Choptank River CHOOH x x x 

Lower Choptank River CHOMH2 x x x 

Mouth of the Choptank River CHOMH1 x x x 

Little Choptank River LCHMH x x 

Honga River HNGMH x x 

Fishing Bay FSBMH x x x 

Upper Nanticoke River NANTF x x x 

Middle Nanticoke River NANOH x x x 

Lower Nanticoke River NANMH x x x 

Wicomico River WICMH x x x 

Manokin River MANMH x x x 

Big Annemessex River BIGMH x x x 

Upper Pocomoke River POCTF x x 

Middle Pocomoke River POCOH x x x 

Lower Pocomoke River POCMH x x x 

Tangier Sound TANMH x x 
▼64

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

CHESAPEAKE BAY TIDAL-WATER DESIGNATED USES

The migratory fish spawning and nursery designated use is described first, given its

unique seasonal role in protecting the spawning and nursery grounds of Chesapeake

Bay and East Coast anadromous fish species. The shallow-water bay grass designated use is then described, as it protects the vegetated shallow-water habitats that

are so critical to many individual estuarine species and living resource communities.

Next, the open-water, deep-water and deep-channel designated uses are described as

a series of year-round and seasonal subcategory designated uses formed around

unique habitats defined largely by natural conditions (e.g., stratification of the water

column, water circulation patterns) and physical barriers (Bay and tidal-water

bottom bathymetry) in the tidal waters.

The watershed states with tidally influenced Chesapeake Bay waters (Maryland,

Virginia and Delaware) and the District of Columbia ultimately are responsible for

defining and adopting the designated uses into their state water quality standards.

These uses will be adopted as subcategories of current state tidal-water designated

uses, which are designed to protect aquatic life. The formal process for refining

designated uses will meet the requirements of the Clean Water Act and any applicable jurisdiction-specific environmental laws or regulations.

The adopted designated uses will protect existing aquatic and human uses of the tidal

waters that have been present since 1975. These designations go beyond minimum

requirements (131.10[d] and [h][2]) and satisfy all requirements for meeting Clean

Water Act goals (131.10 [a]), downstream waters maintenance and protection

(131.10[b]) and for subcategorization as allowed by 131.10(g). The specific use definitions and the spatial application of the final designated uses will undergo public

review through the four jurisdictions’ respective regulatory adoption processes prior

to EPA approval of the states’ water quality standards.

MIGRATORY FISH SPAWNING AND NURSERY DESIGNATED USE

Waters with this designated use shall support the survival, growth and propagation

of balanced indigenous populations of ecologically, recreationally and commercially

important anadromous, semi-anadromous and tidal freshwater resident fish 

species inhabiting spawning and nursery grounds from February 1 through May 31

(Table IV-4). 

Designated Use Rationale

Based on a commitment within the 1987 Chesapeake Bay Agreement (Chesapeake

Executive Council 1987), a list of target anadromous and semi-anadromous species

was identified, including striped bass, American shad, hickory shad, alewife, blueback herring, white perch and yellow perch, based on their commercial, recreational

and ecological value and “the threat to sustained production due to population
▼65

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-4. Migratory fish spawning and nursery designated use summary. 

Applicable Criteria: Dissolved Oxygen:

6.0 mg/l 7-day mean (only tidal habitats with 0–0.5 ppt salinity) 

5.0 mg/l instantaneous minimum 

Application: February 1 through May 31 

Designated Use: This designated use supports the survival, growth and

propagation of balanced, indigenous populations of

ecologically, recreationally and commercially important

anadromous, semi-anadromous and tidal freshwater resident

fish species inhabiting spawning and nursery grounds. 

Designated Use Boundary: The boundaries of this use extend from the upriver extent 

of tidally influenced waters to the downriver and upper

Chesapeake Bay end of spawning and nursery habitats that

have been determined through a composite of all targeted

anadromous and semi-anadromous fish species’ spawning

and nursery habitats. The use extends horizontally from the

shoreline of the body of water to the adjacent shoreline, and

extends down through the water column to the bottom

sediment-water interface. 

Source for the Applicable Criteria: U.S. EPA 2003.

decline or serious habitat degradation” (Chesapeake Bay Living Resources Task

Force 1987). These species form a representative subset of species comprising a

“balanced, indigenous population.” Other ecologically important anadromous and

semi-anadromous fish species also will be protected under this designated use.

Chesapeake Bay tidal waters support spawning and nursery areas that are important

not only to Bay fishery populations, but also to populations that inhabit the entire East

Coast, such as striped bass. The eggs, larvae and early juveniles of anadromous and

semi-anadromous species often have more sensitive habitat quality requirements than

other species and life stages (Funderburk et al. 1991; Jordan et al. 1992). These same

habitats are critical spawning and nursery grounds for tidal freshwater resident fish

species from February 1 to May 31 (U.S. EPA 2003). Thus, the combined migratory

and tidal freshwater resident fish spawning and nursery habitats were delineated as a

refined tidal-water designated use for the Chesapeake Bay and its tidal tributaries.

Designated Use Boundary Delineation

The boundaries of the migratory fish spawning and nursery designated use were

delineated from the upriver extent of tidally influenced waters to the downriver and

upper Chesapeake Bay end of spawning and nursery habitats that have been

determined through a composite of all targeted anadromous and semi-anadromous

fish species’ spawning and nursery habitats (Figure IV-6).
Critical Support Communities—Food and Shelter

In this designated use, spawning adults and the resulting larvae and early juvenile

fish depend on phytoplankton, zooplankton, bottom-dwelling worms and clams and

forage fish as prey (Funderburk et al. 1991). The presence of underwater bay grasses

in the shallows of the designated use habitat provides essential shelter for young

juveniles as well as many prey species.

Seasonal Use Application

The migratory fish spawning and nursery designated use applies from February 1

through May 31. The defined season for applying this use is based on a composite

of the full range of spawning and nursery periods of all the target anadromous and

semi-anadromous species.

Striped bass and juveniles of other migratory spawners are passively dispersed as

eggs and larvae and move farther downstream as they grow. Most juveniles do not

leave the boundaries of their respective spawning and nursery areas. Adult yellow

perch migrate from downstream to their spawning areas in the lower-salinity upper

reaches of the tidal tributaries from mid-February through March (Richkus and

Stroup 1987; Tsai and Gibson 1971). By early June, young-of-the-year juvenile

striped bass begin to move shoreward, spending the summer and early fall in shoal

waters less than six feet deep (Setzler-Hamilton et al. 1981). As juveniles grow, they

▼66

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Migratory Fish

Spawning and Nursery

Designated Use

Figure IV-6. Illustration of the boundaries of the migratory fish spawning and nursery

designated use.
move progressively downriver (Boreman and Klauda 1988; Dey 1981; SetzlerHamilton et al. 1981). The February 1 beginning date reflects the initiation of the

yellow perch spawning season; the May 31 end date reflects when the eggs and

larvae have finished their transition to the juvenile life stage for all the target anadromous and semi-anadromous species.

Applicable Chesapeake Bay Water Quality Criteria10

The migratory fish spawning and nursery designated use is seasonally defined and

occurs in conjunction with the year-round open-water designated uses and the

seasonal shallow-water designated uses (see Figure IV-5). The migratory fish

spawning and nursery designated use provides for the protection of the early life

stages of anadromous, semi-anadromous and resident tidal-fresh species through the

application of dissolved oxygen criteria derived for that purpose (U.S. EPA 2003).

From February 1 through May 31, the migratory fish spawning and nursery

dissolved oxygen criteria ensure protection of the egg, larval and early juvenile life

stages (Table IV-4). Free-flowing streams and rivers, where several of the target

species (e.g., shad, river herring) migrate for spawning, are protected through other

existing state water quality standards.

The open-water fish and shellfish designated use dissolved oxygen criteria were

derived to be protective of juvenile and adult life stages of anadromous and semianadromous species after May 31 (see Table IV-6; U.S. EPA 2003). The overlapping

nature of these discrete designated uses will thus ensure that water quality conditions

protective of different species’ life stages are present in those designated use habitats. See chapters 3 and 6, respectively, in U.S. EPA 2003 for more details on the

individual dissolved oxygen criteria and criteria implementation procedures.

SHALLOW-WATER BAY GRASS DESIGNATED USE

Waters with this designated use support the survival, growth and propagation of

rooted, underwater bay grasses necessary for the propagation and growth of

balanced, indigenous populations of ecologically, recreationally and commercially

important fish and shellfish inhabiting vegetated shallow-water habitats (Table IV-5).

Designated Use Rationale

The shallow-water bay grass designated use protects a wide variety of species, such

as largemouth bass and pickerel, which inhabit vegetated tidal-fresh and low-salinity

habitats; juvenile speckled sea trout in vegetated higher salinity areas; and blue crabs

that inhabit vegetated shallow-water habitats covering the full range of salinities

encountered in the Chesapeake Bay and its tidal tributaries. Underwater bay grasses,

▼67

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

10Maryland, Virginia, Delaware and the District of Columbia currently have water quality standards in

place that address pH conditions within the migratory fish spawning and nursery habitats.
the critical community that the designated use protects, provide the shelter and food

that make shallow-water habitats so unique and integral to the productivity of the

Chesapeake Bay ecosystem. Many Chesapeake Bay species depend on vegetated

shallow-water habitats at some point during their life cycle (Funderburk et al. 1991).

Given the unique nature of this habitat and its critical importance to the Chesapeake

Bay ecosystem, shallow waters were delineated as a refined tidal-water designated

use for the Chesapeake Bay and its tidal tributaries.

The shallow-water bay grass designated use is intended specifically to delineate the

habitats where the water clarity criteria would apply. The open-water fish and

shellfish designated use and the accompanying dissolved oxygen criteria will fully

protect the biological communities inhabiting shallow-water habitats. The 

open-water designated use extends into the intertidal zone and protects shallowwater organisms beyond underwater bay grasses. The seasonal shallow-water bay

grass designated use, similar to the migratory fish spawning and nursery use,

actually occurs in conjunction with the year-round open-water designated use (see

Figure IV-5) and provides specific protection for underwater bay grasses through the

application of water clarity criteria.

Designated Use Boundary Delineation

The shallow-water bay grass designated use covers tidally influenced waters, from

the intertidal zone out to a Chesapeake Bay Program segment-specific depth contour

▼68

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-5. Shallow-water bay grass designated use summary. 

Applicable Criteria: Water Clarity:

13 percent ambient light through water (tidal habitats with

0–5 ppt salinity)

22 percent ambient light through water (tidal habitats with

greater than 5 ppt salinity)

Application: April 1 through October 31 for tidal-fresh, oligohaline and

mesohaline habitats (0–18 ppt salinity); March 1 through 

May 31 and September 1 through November 30 for

polyhaline habitats (>18 ppt salinity)

Designated Use: Waters with this designated use support the survival, growth

and propagation of rooted underwater bay grasses necessary

for the propagation and growth of balanced, indigenous

populations of ecologically, recreationally and commercially

important fish and shellfish inhabiting vegetated shallowwater habitats.

Designated Use Boundary: Tidally influenced waters from the intertidal zone out to a

Chesapeake Bay Program segment-specific depth contour

that varies from 0.5 to 2 meters. 

Source for the Applicable Criteria: U.S. EPA 2003.
that varies from 0.5 to 2 meters (Figure IV-7). The segment-specific depths were

based on rules described in detail in “Shallow-Water Bay Grass Designated Use

Boundaries” (see page 105) along with two other approaches to defining shallowwater use boundaries.

Critical Support Communities—Food and Shelter

Phytoplankton, zooplankton, forage fish and bottom-dwelling worms and clams feed

many fish, crab and mollusk species that inhabit shallow-water habitats for part or

all of their life stages (Funderburk et al. 1991). Water quality criteria necessary to

fully support the shallow-water designated use must provide for the survival, growth

and successful propagation of prey communities in sufficient quantities.

Applicable Bay Water Quality Criteria

The shallow-water bay grass designated use is a seasonal use designation that occurs

in conjunction with the year-round open-water use and the seasonal migratory

spawning and nursery designated uses (see Figure IV-5). The shallow-water bay

grass designated use boundary delineates where specific levels of water clarity must

be restored to support restoration of underwater bay grasses. The applicable salinity

regime-based water clarity criteria apply during the appropriate underwater bay

grass growing season: April 1 through October 31 for tidal-fresh, oligohaline and

mesohaline habitats and March 1 through May 31 and September 1 through

November 30 for polyhaline habitats (see Table IV-5; U.S. EPA 2003).

▼69

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Shallow-Water

Designated Use

Figure IV-7. Illustration of the boundaries of the shallow-water bay grass designated use. 
Underlying the seasonal shallow-water bay grass designated use is the year-round

open-water fish and shellfish designated use to support grass living resource communities inhabiting these shallow-water areas (see Table IV-6; U.S. EPA 2003). The

open-water fish and shellfish dissolved oxygen criteria apply into the shallows to the

intertidal zone. Therefore, nonvegetated shallow-water habitats and the living

resource communities that depend on those habitats will receive protection under the

open-water designated use. See chapters 3, 4 and 6, respectively, in U.S. EPA 2003

for more details on the individual dissolved oxygen criteria, water clarity criteria and

criteria implementation guidelines.

OPEN-WATER FISH AND SHELLFISH DESIGNATED USE

Waters with this designated use support the survival, growth and propagation of

balanced, indigenous populations of ecologically, recreationally and commercially

important fish and shellfish species inhabiting open-water habitats (Table IV-6).

Designated Use Rationale

The natural temperature and salinity stratification of open waters influences

dissolved oxygen concentrations and, thus, the distribution of Chesapeake Bay

species. Surface mixed-layer waters with higher oxygen levels located above the

pycnocline support a different community of species than deeper waters from late

spring to early fall. Several well-known species that inhabit these open waters are

menhaden, striped bass and bluefish. Their habitat requirements and prey needs

differ from those of species and communities inhabiting deeper water habitats during

the summer months. See the deep-water “Designated Use Rationale” on page 74 for

more detailed documentation.

Clear evidence from the Chesapeake Bay as well as other estuarine and coastal

systems, including Long Island Sound (Howell and Simpson 1994), AlbemarlePamlico Sound (Eby 2001) and the Gulf of Mexico (Craig et al. 2001), indicates that

the fish and other organisms inhabiting open-water habitats will use deeper withinpycnocline and below-pycnocline habitats, given suitable dissolved oxygen

conditions. It is the lack of sufficient oxygen, not the presence of stratification, that

limits the use of these deeper habitats. Therefore, the open-water designated use

applies to transitional pycnocline and bottom mixed-layer below-pycnocline habitats

where these below-pycnocline and pycnocline waters are sufficiently reoxygenated

by oceanic or riverine waters.

During their first winter of life, members of five important Chesapeake Bay species—

white perch, striped bass, Atlantic croaker, shortnose sturgeon and Atlantic

sturgeon—are constrained to oligohaline and mesohaline regions (< 20 ppt) in the

upper Chesapeake Bay mainstem, and seek out warmer temperatures that occur in

deeper channel waters below the thermocline. From October through May, the deepchannel habitats in the upper Bay adjacent to shallower summer and fall habitats

should be considered important nursery habitats for young-of-the-year juvenile white

▼70

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼71

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-6. Open-water fish and shellfish designated use summary. 

Applicable Criteria: Dissolved Oxygen

5.5 mg/l 30-day mean (tidal habitats with 0–0.5 ppt salinity)

5.0 mg/l 30-day mean (tidal habitats with greater 

than 0.5 ppt salinity)

4.0 mg/l 7-day mean

3.2 mg/l instantaneous minimum

Chlorophyll a:

Concentrations of chlorophyll a in free-floating microscopic

aquatic plants (algae) shall not exceed levels that result in

ecologically undesirable consequences–such as reduced water

clarity, low dissolved oxygen, food supply imbalances, proliferation of species deemed potentially harmful to aquatic life or

humans or aesthetically objectionable conditions–or otherwise

render tidal waters unsuitable for designated uses.

Application: Year-round: open-water designated use and dissolved 

oxygen criteria. 

March 1 through May 31 and July 1 through September 30:

chlorophyll a criteria.

Designated Use: Waters with this designated use support the survival, growth

and propagation of balanced, indigenous populations of

ecologically, recreationally and commercially important fish

and shellfish species inhabiting open-water habitats.

Designated Use Boundary: From June 1 through September 30 the open-water

designated use includes tidally influenced waters extending

horizontally from the shoreline to the adjacent shoreline. 

If a pycnocline is present and, in combination with bottom

bathymetry and water-column circulation patterns, presents a

barrier to oxygen replenishment of deeper waters, the openwater fish and shellfish designated use extends down into the

water column only as far as the measured upper boundary of

the pycnocline. If a pycnocline is present but other physical

circulation patterns (such as influx of oxygen rich oceanic

bottom waters) provide for oxygen replenishment of deeper

waters, the open-water fish and shellfish designated use

extends down into the water column to the bottom watersediment interface. 

From October 1 through May 31, the open-water designated

use includes all tidally influenced waters extending

horizontally from the shoreline to the adjacent shoreline,

extending down through the water column to the bottom

water-sediment interface. 

Source for the Applicable Criteria: U.S. EPA 2003.
▼72

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

perch, striped bass, and Atlantic croaker (Pothoven et al. 1997) as well as Atlantic and

shortnose sturgeon (Miller et al. 1997; Secor et al. 2000; Welsh et al. 2000).

During the coldest months, the interaction between temperatures and salinity tolerances may result in a ‘habitat squeeze’ or bottleneck, forcing juveniles into

deep-channel habitats seeking preferred temperatures. Unpublished data from the

Maryland Environmental Service indicate that a thermocline, separating the warmer

deep waters from colder overlaying waters, typically occurs at a 10-to 20-meter

depth in the deep channel from October through February. Therefore, from fall

through late spring when the open-water designated use applies to these natural

channel habitats, it also protects indigenous populations of important fish species

that depend on deep-channel habitats for overwintering.

Based on these natural conditions and their influence on oxygen levels and the

seasonal distributions of Chesapeake Bay species, open waters were delineated as a

refined tidal-water designated use in the Chesapeake Bay.

Designated Use Boundary Delineation

From June 1 through September 30 the open-water designated use includes tidally

influenced waters extending horizontally from the shoreline to the adjacent shoreline

(Figure IV-8). If a pycnocline is present and, in combination with bottom bathymetry

and water-column circulation patterns, presents a barrier to oxygen replenishment of

deeper waters, the open-water fish and shellfish designated use extends down into

the water column only as far as the measured upper boundary of the pycnocline

Open-Water

Designated Use

Figure IV-8. Illustration of the boundaries of the open-water fish and shellfish

designated use.
(Figure IV-9). If a pycnocline is present but other physical circulation patterns (such

as influx of oxygen rich oceanic bottom waters) provide for oxygen replenishment

of deeper waters, the open-water fish and shellfish designated use extends down

through the water column to the bottom water-sediment interface.

From October 1 through May 31, the boundaries of the open-water designated use

includes all tidally influenced waters extending horizontally from the shoreline to the

adjacent shoreline, extending down through the water column to the bottom watersediment interface. 

Critical Support Communities—Food and Shelter

Water column-dwelling phytoplankton, zooplankton and forage fish constitute the

major prey for other species in the Chesapeake Bay’s open waters (Funderburk et al.

1991). Water quality criteria to support the open-water designated use fully must

provide for the survival, growth and successful propagation of quality prey communities in sufficient quantities.

Applicable Bay Water Quality Criteria

The open-water dissolved oxygen criteria apply year-round (see Table IV-6). The

applicable salinity regime-based chlorophyll a criteria apply only in spring (March

1 through May 31) and summer (July 1 through September 30) to the open-water

designated use habitats. See chapters 3 and 5, respectively, in U.S. EPA (2003) for

more details on the individual dissolved oxygen and chlorophyll a criteria and

chapter 6 for detailed criteria implementation procedures.

DEEP-WATER SEASONAL FISH AND SHELLFISH DESIGNATED USE

Waters with this designated use protect the survival, growth and propagation of

balanced, indigenous populations of important fish and shellfish species inhabiting

deep-water habitats (Table IV-7).

▼73

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Open-Water Shallow

Water

Shallow

Water

Upper Pycnocline

Boundary

Figure IV-9. Illustration of the vertical boundaries for the refined open-water fish

and shellfish designated use.
Designated Use Rationale

In an eutrophic system such as the Chesapeake Bay, excess organic matter settles to

the bottom, where it fuels microbial activity (e.g., Malone et al. 1986; Tuttle et al.

1987). With more fuel, more oxygen is consumed and, where replenishment with

oxygen-saturated waters is restricted, the water becomes more severely oxygendepleted. There is evidence that hypoxic and anoxic conditions existed in the deeper

waters of the Chesapeake Bay prior to European settlement (Cooper and Brush

1991). These same data indicate that anthropogenic activity has increased the extent,

frequency and severity of oxygen depletion in the Chesapeake Bay (Zimmerman and

Canuel 2000; Hagy 2002).

Many parts of the Chesapeake Bay become, on a seasonal basis, vertically stratified

because of depth-related density differences in the water column, caused primarily

by variations in salinity and, to a lesser degree, temperature. Warmer, freshwater

from the rivers floats on top of the cooler, denser saltwater at the bottom that enters

the Bay from the ocean. The gravitational force of the downriver flow of freshwater

causes a wedge of deeper, saltier water to move up the Bay and upriver. Vertically,

at some point in the water column, a zone of maximum density difference is reached,

which inhibits or prevents the exchange between water above and below it. This

region is called the pycnocline. In the summer months, respiration by organisms

living below the pycnocline can deplete concentrations of dissolved oxygen.

▼74

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-7. Deep-water seasonal fish and shellfish designated use summary. 

Applicable Criteria: Dissolved Oxygen:

3 mg liter-1 30-day mean

2.3 mg liter-1 1-day mean

1.7 mg liter-1 instantaneous minimum

Application: June 1 through September 30

Designated Use: Waters with this designated use protect the survival, growth 

and propagation of balanced, indigenous populations of 

ecologically, recreationally, and commercially important 

fish and shellfish species inhabiting deep-water habitats.

Designated Use Boundary: Tidally influenced waters located between the measured depths

of the upper and lower boundaries of the pycnocline in areas

where the measured pycnocline, in combination with bottom

bathymetry and water circulation patterns, presents a barrier to

oxygen replenishment of deeper waters. In some areas where a

lower boundary of the pycnocline is not calculated, the deepwater designated use extends from the measured depth of the

upper boundary of the pycnocline down through the water

column to the bottom sediment-water interface. 

Source for the Applicable Criteria: U.S. EPA 2003.
Because waters in and below the pycnocline are isolated from well-mixed surface

waters, dissolved oxygen concentrations can decrease until they are stressful or

lethal to higher organisms.

The formation of the pycnocline is a natural process. In areas where stratification is

common, the pycnocline generally forms at about the same depth range, but is

subject to seasonal and annual variations in depth due to river flow, temperature and

salinity patterns. It is generally shallower at the mouths of rivers and the Chesapeake

Bay and deeper at the heads of rivers. The effect of the pycnocline also is not the

same everywhere in the Chesapeake Bay and is influenced by local characteristics

such as bathymetry, vertical and horizontal water circulation patterns, and proximity

to the ocean and major river fall-lines. In some parts of the Bay and its tidal rivers,

these factors create a more complex stratification pattern: a second pycnocline is

formed lower in the water column, dividing it into three layers. If a region is

contained by the pycnocline above and by bottom bathymetry laterally, it is even

more isolated from oxygen-replenishing waters.

Bay anchovy is a target species whose egg and larval life stages are spent in pycnocline waters (Keister et al. 2000; Rilling and Houde 1999; MacGregor and Houde

1996). Blue crabs, oysters, softshell clams, hard clams, spot, croaker, flounder and

catfish inhabit the near-bottom waters in the deep-water habitats (Funderburk et al.

1991). The oxygen requirements of these species differ from those of species inhabiting shallow-water, open-water and deep-channel habitats. Their feeding patterns

and distribution of eggs and larvae are greatly influenced by natural features of the

water column such as the pycnocline.

Deep waters were delineated as a refined tidal-water designated use for the Chesapeake Bay and its tidal tributaries based on the unique nature of the pycnocline

region as an important living resource habitat and the transitional nature of its water

quality conditions.

Designated Use Boundary Delineation

The deep-water designated use includes the tidally influenced waters between the

measured upper and lower boundaries of the pycnocline where, in combination with

bottom bathymetry and water circulation patterns, the pycnocline limits oxygen

replenishment of deeper waters (Figure IV-10). In some areas where a lower

boundary of the pycnocline is not calculated, the deep-water designated use extends

from the measured depth of the upper boundary of the pycnocline down through the

water column to the bottom sediment-water interface.

Critical Support Communities—Food and Shelter

Bottom-dwelling worms and clams and reef-dwelling forage fish are important food

sources for the fish and crabs in deep-water habitats (Funderburk et al. 1991). Water

quality criteria to support the deep-water designated use must provide for the

survival, growth and successful propagation of quality prey communities in sufficient quantities.

▼75

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Seasonal Use Application

The deep-water seasonal fish and shellfish designated use applies from June 1

through September 30. By June, a combination of natural water-column stratification

and increased biological oxygen consumption driven by higher water temperatures

prevents the Chesapeake Bay’s deep waters from retaining high concentrations of

dissolved oxygen. These natural conditions generally persist into September. From

October 1 through May 31 the open-water fish and shellfish designated use applies

to these same waters.

Applicable Bay Water Quality Criteria

The deep-water dissolved oxygen criteria apply from June 1 through September 30

(see Table IV-7). See chapters 3 and 6, respectively, in U.S. EPA 2003 for more

details on the deep-water dissolved oxygen criteria and criteria implementation

procedures.

DEEP-CHANNEL SEASONAL REFUGE DESIGNATED USE

Waters with this designated use must protect the survival of balanced, indigenous

populations of ecologically important benthic infaunal and epifaunal worms and

clams, which provide food for bottom-feeding fish and crabs (Table IV-8).

Designated Use Rationale

In the Chesapeake Bay, researchers have determined the oxygen minimum to be in

the below-pycnocline waters throughout the deep trough in the mainstem Chesapeake Bay in the late spring to early fall (Smith et al. 1992). Isolated from aerated

surface waters, low dissolved oxygen concentrations in this region are due to excess

oxygen consumption from bacterial breakdown of organic material over oxygen

additions from ocean waters flowing in from far down-Bay. North of this region, the

▼76

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep-Water

Upper Pycnocline

Boundary

Lower Pycnocline

Boundary

Figure IV-10. Illustration of the vertical boundaries for the refined deep-water

designated use. 
trough quickly becomes shallow and bottom waters are oxygenated as they mix with

aerated waters in the shoals. Below-pycnocline waters to the south are reoxygenated

through mixing with oxygenated oceanic waters entering the Chesapeake Bay mouth.

These deep channels are sinks for excess organic material which, in the process of

decaying, increase oxygen consumption. They are isolated from surface and oceanic

sources of oxygen replenishment. Vertical stratification and gravitational and horizontal circulation often cause severe, sudden oxygen depletion beginning just below

the lower boundary of the pycnocline and extending to the bottom (Smith et al.

1992). Given the physical nature of the deep trough leading to naturally severe

oxygen depletion during the summer, the deep-channel was delineated as a refined

tidal-water designated use for Chesapeake Bay.

Designated Use Boundary Delineation

Deep-channel designated use waters are defined as tidally influenced waters at

depths greater than the measured lower boundary of the pycnocline in areas where

the pycnocline, in combination with bottom bathymetry and water circulation

patterns, presents a barrier to oxygen replenishment of deeper waters (Figure IV-11).

The deep-channel designated use is defined laterally by bathymetry of the trough and

vertically by the lower boundary of the pycnocline above, and below, at the bottom

sediment-water interface.

▼77

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-8. Deep-channel seasonal refuge designated use summary. 

Applicable Criteria: Dissolved Oxygen:

1.0 mg/l instantaneous minimum

Application: June 1 through September 30

Designated Use: Waters with this designated use must protect the survival of

balanced, indigenous populations of ecologically important

benthic infaunal and epifaunal worms and clams, which

provide food for bottom-feeding fish and crabs.

Designated Use Boundary: Deep-channel designated use waters are defined as tidally

influenced waters at depths greater than the measured lower

boundary of the pycnocline in areas where, in combination

with bottom bathymetry and water circulation patterns, the

pycnocline presents a barrier to oxygen replenishment of

deeper waters. The deep-channel designated use is defined

laterally by bathymetry of the trough and vertically by the

lower boundary of the pycnocline above, and below, at the

bottom sediment-water interface.

Source for the Applicable Criteria: U.S. EPA 2003.
Critical Support Communities—Food and Shelter

Bottom-dwelling worms and clams are the principal food source of bottom-feeding

fish and crabs in the deep-channel (Funderburk et al. 1991). Water quality criteria 

for the deep-channel designated use must provide for the survival of these prey

communities.

Seasonal Use Application

The deep-channel designated use applies from June 1 through September 30. By

June, a combination of natural water-column stratification and increased water

temperature prevents the Chesapeake Bay’s deep-channel waters from retaining high

concentrations of dissolved oxygen. These natural conditions generally persist

through September. From October 1 through May 31 the open-water designated use

applies to these same habitats.

Applicable Bay Water Quality Criteria

The deep-channel dissolved oxygen criteria apply from June 1 through September

30 (see Table IV-8). See chapters 3 and 6, respectively, in U.S. EPA 2003 for more

details on the deep-channel dissolved oxygen criteria and criteria implementation

procedures.

CHESAPEAKE BAY TIDAL-WATER 

DESIGNATED USE BOUNDARIES

Correct application of the Chesapeake Bay water quality criteria depends on the

accurate delineation of the five tidal-water designated uses. Each of the designated

uses has different dissolved oxygen criteria derived to match the respective level of

protection required by different living resource communities. In case of the shallow-

▼78

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Deep Channel Lower Pycnocline

Boundary

Figure IV-11. Illustration of the vertical boundaries of the refined deep-channel

seasonal refuge designated use. 
water bay grass designated use, the location of the boundaries is critical to providing

sufficient suitable habitat for the restoration of the desired number of acres of underwater bay grasses.

The vertical depth and horizontal breadth of the designated use boundaries are based

on a combination of factors: natural water-column stratification, bottom bathymetric

features and circulation patterns, among other considerations. It is important to note

that these boundaries have been developed without consideration of attainability

from the perspective of potentially widespread social and economic impacts. The

states may find they need to adjust these boundaries according to such impacts

(131.19[g][6]), which may prevent attainment of the designated use, and must justify

these adjustments during their water quality standards adoption processes. The technology-based attainability of these refined tidal-water designated uses and their

boundaries is documented in Chapter V.

Four of the six factors defined in 40 CFR 101.10(g) justify deriving the boundaries

described in this chapter for the refined tidal-water designated uses:

• Natural, ephemeral, intermittent or low-flow conditions or water levels (e.g.,

application of a 10-year water quality data record (1985-1994) reflecting a

wide range of watershed hydrologic and tidal bay hydrodynamic conditions);

• Dams, diversion or other types of hydrologic modifications (e.g., dredged

shipping channels);

• Physical conditions related to the natural features of the water body, such as the

lack of a proper substrate, cover, flow, depth, pools, riffles and the like (e.g.,

water-column stratification, bottom bathymetry); and

• Naturally occurring pollutant concentrations (see Chapter III).

MIGRATORY FISH SPAWNING AND NURSERY 

DESIGNATED USE BOUNDARIES

The boundaries of the migratory fish spawning and nursery designated use were

delineated from the upriver extent of tidally influenced waters to the downriver and

upper Chesapeake Bay end of spawning and nursery habitats that have been determined through a composite of all targeted anadromous and semi-anadromous fish

species’ spawning and nursery habitats (Figure IV-12). Free-flowing streams and

rivers, where several of the target species (e.g., shad and river herring) migrate for

spawning, are protected through other existing state water quality standards.

To generate these boundaries, habitat distribution maps, drawn from the Habitat

Requirements for Chesapeake Bay Living Resources–Second Edition (Funderburk et

al. 1991), were used. The distribution maps used during delineation of the migratory

spawning and nursery designated use included:

• Alewife spawning and nursery;

• Alewife nursery;

▼79

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼80

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-12. Map showing the migratory spawning and nursery designated use for the

Chesapeake Bay and its tidal tributaries (black areas).
• American shad spawning and nursery;

• American shad nursery;

• Hickory shad spawning and nursery;

• Herring spawning and nursery;

• Herring nursery;

• Striped bass spawning reaches;

• Striped bass spawning rivers;

• White perch nursery;

• White perch spawning; and

• Yellow perch spawning and nursery.

For those species that had multiple habitat distribution maps for related life stages,

the maps were merged into a single coverage. Then individual species maps were

superimposed on a composite spawning and nursery habitat map.

The striped bass habitat distribution maps used in this process were originally titled

“Striped Bass Chesapeake Bay Spawning Reaches and Spawning Rivers” by

Funderburk et al. (1991). The sources of the spawning reach distributions were

research and monitoring findings synthesized by Setzler-Hamilton and Hall (1991).

However, the mapped extent of the nursery areas, referred to as spawning rivers in

the original map, was based on Maryland and Virginia legislative definitions,11 not

on fisheries survey findings.

Those regulations, which define “spawning rivers and areas,” did not attempt to

define “early juvenile nursery habitat” but rather those rivers in which striped bass

spawn. The spawning reach designation in the regulation was used to describe areas

where striped bass eggs and larvae had been found. This justification was based on

icthyoplankton collections done in the 1950s in Maryland (Mansueti and Hollis

1963). Tresselt (1952) defined spawning reaches in Virginia.

To further enhance understanding of nursery areas, discussions were held with

fishery scientists Herb Austin and Deane Este of the College of William and Mary’s

Virginia Institute of Marine Science, and Eric Durell, Maryland Department of

Natural Resources, who are responsible for their respective states’ juvenile striped

bass seine surveys. The primary nursery areas for young-of-the-year striped bass

were delineated based on a comparison of long-term Maryland and Virginia seine

survey data with the legislatively-defined extent of early juvenile nursery habitat. In

any given year, juvenile striped bass can be found throughout a broader range of

Chesapeake Bay tidal waters. The primary nursery areas where the highest concentrations of early juvenile life-stage striped bass are almost always found in the spring

▼81

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

11Code of Maryland Regulations 08.02.05.02 and Virginia Marine Resources Commission Regulation

450-01-0034 as cited inChesapeake Bay Living Resources Task Force (1987).
were identified and incorporated into the composite map described above (e.g.,

Austin et al. 2000). The striped bass nursery areas were supplemented to ensure that

shad and river herring spawning and nursery areas were fully represented within the

migratory fish spawning and nursery designated use boundaries (Rulifson 1994;

Olney 2002).

From February 1 through May 31, the migratory fish spawning and nursery designated use occurs in conjunction with, and, therefore, encompasses specific portions

of the seasonal shallow-water bay grass and year-round open-water fish and shellfish

designated use habitats (see shaded sections in Figure IV-5). The designated use

extends horizontally from the shoreline across the body of water to the adjacent

shoreline, and extends down through the water column to the bottom sediment-water

interface.

The exact spatial and temporal extent of migratory fish spawning and nursery

designated use would vary annually due to regional climatic patterns if actual

observed salinity and temperature were used to define year-by-year boundaries.

Because use of year-by-year delineation of the exact boundaries of the migratory fish

spawning and nursery designated adds complexity, a fixed set of boundaries was

established. The migratory fish spawning and nursery designated use habitat shown

in Figure IV-12 reflects both long-term, decadal average salinity conditions and

decades’ worth of fisheries-independent beach seine and trawl monitoring data.

States can adopt an approach (to be defined) for defining migratory spawning and

nursery designated use boundaries on a year-to-year basis by directly factoring in the

influence of interannual climatic patterns on the use boundaries.

OPEN-WATER, DEEP-WATER AND DEEP-CHANNEL 

DESIGNATED USE BOUNDARIES 

Background

The open-water, deep-water and deep-channel designated uses, the habitats they

represent and the dissolved oxygen criteria for ensuring their protection are inextricably related to physical structure (water-column stratification, bottom bathymetry)

and to physical, chemical, meteorological and fluvial forces and processes. Understanding these factors will enhance understanding of the designated use delineation

process as well as the issues underlying application of the dissolved oxygen criteria.

The following section provides background on these three principal factors: bathymetry, flow and circulation, and vertical density gradients and pycnoclines.

Bathymetry

Although the Chesapeake Bay is a relatively shallow estuary, bathymetric features

play a large role both in defining the Bay’s habitats as well as the eutrophicationrelated water quality problems observed throughout most of the tidal waters. 

▼82

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
The most prominent bathymetric feature in the Bay is the deep trench that runs from

the Chesapeake Bay Bridge between Annapolis and Kent Island, Maryland, to an

area midway between the southern shore of the mouth of the Potomac River and the

northern shore of the mouth of the Rappahannock River (figures IV-13 and IV-14).

The trench ranges from 24 to 48 meters in depth and extends generally midchannel

between the western and eastern shores of the mainstem Chesapeake Bay. It is

thought to be a remnant of the ancient Susquehanna River. A shallower trench

extends down along the Virginia Eastern Shore (Figure IV-15). Similar, smaller

trenches and holes exist elsewhere in Bay tidal waters, generally in the larger tidal

tributary rivers near their mouths. These are described later in the more detailed

regional descriptions that follow. 

▼83

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-13. Major bathymetric trenches within the Chesapeake Bay and its tidal tributaries.
▼84

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-14. Three-dimensional view of the Chesapeake Bay mainstem trench as

viewed from the south looking north. The depth versus width relationship has been

enhanced to improve viewing.

Figure IV-15. Three-dimensional view of the ‘Virginian Sea’ as viewed from the south

looking north. The depth versus width relationship has been enhanced to improve 

viewing.
These deep regions contrast with the Chesapeake Bay as a whole, which has an

average depth of only 6 meters. They also figure prominently in the Chesapeake

Bay’s dissolved oxygen problems. When it is overlain by a stratified water column,

the bottom water in the trenches and holes is isolated from the oxygenated surface

water and can become oxygen-depleted. This situation generally occurs in the late

spring and summer when oxygen-consuming activity is high and discontinuity in

water density through the water column can act as a barrier, i.e., act as a ‘lid,’

capping off the exchange of oxygenated water with the oxygen-depleted waters in

the trenches and holes. However, some of the deep areas of the Chesapeake Bay,

although capped as described, do not suffer from chronically low dissolved oxygen.

These areas generally have their downstream or seaward end open so that deep-water

exchange with the oxygenated deep water from the ocean can occur. 

FLOW AND CIRCULATION

Processes within the Chesapeake Bay and its tidal tributaries are strongly influenced

by flow and circulation patterns. These factors affect the mixing of the Bay’s waters

and the distribution of salinity, dissolved compounds and planktonic organisms. Like

most estuaries, the Chesapeake Bay has a two-layer flow pattern. Net flow in the

upper layer moves down the Bay or downriver, while net flow in the bottom layer

moves up the Bay or upriver. 

This two-layer flow is caused primarily by the difference in density between the less

dense, low-salinity water that flows off the land and the more dense, high-salinity

water that flows in from the ocean. The less dense, more buoyant, low salinity water

floats on the surface of higher salinity water. The tendency of ocean water in summer

to be cooler than freshwater also contributes to its higher density. Interannual and

seasonal differences in freshwater inflow to the rivers and the Chesapeake Bay, due

largely to meteorological factors, affect the interaction of the two layers. 

Tidal forces move water into and out of the Chesapeake Bay and its rivers. Tidal

currents interact with the bathymetric surfaces of the bottom, with the seaward flow

of freshwater and with the air-water interface affecting internal turbulence and

mixing. Tied to lunar cycles, the daily, monthly and seasonal tidal rhythms are relatively predictable components of flow and circulation. 

The Coriolis force is another important physical circulation process in the Chesapeake Bay. The Coriolis force is related to the earth’s rotation and causes moving

objects such as fluids to veer to the right (clockwise) in the Northern Hemisphere

and to the left (counter-clockwise) in the Southern Hemisphere. This force increases

with proximity to the poles. Currents in the Northern Hemisphere tend to move

clockwise over their course unless they encounter a barrier such as a land mass. Thus

ocean water flowing into the Chesapeake Bay at the mouth is deflected north due to

the Coriolis force. The current continues around to the right until it encounters the

Eastern Shore, which directs the flow up the Bay. Water flowing down and out of the

Chesapeake Bay on the surface, flows primarily down the Western Shore as the

▼85

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼86

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Coriolis force tends to push it to the right. This same phenomenon of inflow on the

bottom on the right and outflow on the surface on the left occurs in the Bay’s tidal

tributaries as well. 

VERTICAL DENSITY GRADIENTS AND PYCNOCLINES

In many parts of the Chesapeake Bay, the water column becomes stratified because

of differences in water density. These differences are caused primarily by differences

in salinity and, to lesser degree, in temperature. The water column becomes vertically stratified when, at some depth, a difference in water density from one depth to

the next is large enough to inhibit or prevent exchange between water above and

below it. Fisher et al. (2003) found the density gradient for defining inhibition or

prevention of water exchange in the Chesapeake Bay to be 0.1 kg/m4. The depth

nearest the surface where this first occurs is referred to as the pycnocline. The

discontinuity may be gradual, as shown in Figure IV-16a, exhibiting a generally

uniform gradient of increasing density from one depth to the next through the water

column. In such cases, one refers to the region of the pycnocline. 

a. b.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

151050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

151050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

Figure IV-16. The figures illustrate a variety of water density and dissolved oxygen

profiles found in the Chesapeake Bay and its tidal tributaries. The black line represents

water density (kg/m 4), the blue line represents dissolved oxygen concentration (mg/l). 

The vertical axis indicates depth (meters) below the surface. The horizontal line crossing

the density line, when present, indicates upper and lower pycnocline depth using the

Fisher et al. 2003 method. Figure ‘a’ is an example of a sharp, upper pycnocline with

density gradually increasing with distance from the surface. Figure ‘b’ is an example 

of a more distinct three-layer structure.

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
In areas where stratification is common, the pycnocline typically forms at about the

same depth, but is subject to seasonal and annual variations in depth due to river

flow, temperature and salinity patterns. The pycnocline is generally shallower at the

mouths of tidal rivers and the Chesapeake Bay and deeper with distance upriver and

up-Bay. In the central, deepest part of the mainstem Chesapeake Bay, the pycnocline

tends to deepen and ‘tilt’ slightly on the east-west axis, depending on the strength

and direction of prevailing winds as well as the relative balance of the several forces

controlling Chesapeake Bay circulation. North of this area, where the Bay narrows

and grows shallow, and north-moving bottom water shoals up from the deep trench,

the pycnocline is generally found closer to the surface. In upriver areas of tidal tributaries, pycnoclines may occur occasionally depending on episodic intrusions of

saline waters. In other areas, such as the mouth of Tangier Sound in the lower Chesapeake Bay, pycnoclines are occasional or intermittent because fresh and saline

waters are typically well-mixed by tidal currents and bathymetric features. 

In some areas, the many factors acting on circulation create a more complex stratification structure. Below the surface mixed layer, there is a layer where density

continues to change with depth. Then a second, sharp density discontinuity is

encountered, creating a discrete bottom mixed layer (Figure IV-16b). A density

gradient of 0.2 kg/m4 was found to inhibit upward vertical exchange and form a

boundary for this lower mixed zone. (See Appendix D for a more thorough explanation of the methods for determining the pycnocline.)

For these reasons, the shape of a density profile can be highly variable within and

between locations. The profile in Figure IV-16b is common in medium-to-deep areas

of the mainstem Chesapeake Bay and lower tributaries during the summer months.

There is an upper mixed layer several meters thick, followed by a distinct change in

the density gradient. This change marks the upper depth of the pycnocline and the

lower depth of the upper mixed layer. The thickness of the inter-pycnocline region

in this example is 9 meters, about a third of the water column. The bottom mixed

layer is fairly thick in this case, extending approximately 13 meters to the bottom.

The figure illustrates the effect of the pycnocline and density gradient on oxygen

concentration in this part of the Chesapeake Bay. Oxygen in the surface mixed layer

is close to saturation. Below the upper pycnocline depth, oxygen levels fall with

increasing distance from the oxygenated upper layer. The bottom mixed layer is

consistent at about 1 mg/l through the entire thickness to the bottom. 

Figure IV-17a shows a pycnocline type that is common to shallow to medium-depth

areas of the mainstem Chesapeake Bay and mid-to-lower areas of the tidal tributaries. There is a well-defined surface mixed layer, marked by a sharp density

discontinuity, but no lower mixed layer. The pycnocline extends through the water

column to the bottom sediment-water interface, with dissolved oxygen concentrations decreasing with distance from the upper pycnocline boundary. Figure IV-17b

shows a different density structure at the same location on a different date. There is

no density discontinuity, the upper mixed layer extends through the entire water

column and dissolved oxygen levels greater than 5 mg/l are sustained through to the

bottom sediment-water interface. The vertical profiles in figures IV-17a and IV-17b

▼87

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
are typical of tidal-fresh and shallow areas of the mainstem Chesapeake Bay and

tidal tributaries and can frequently be observed in medium-depth regions of the

mainstem Bay and mid- to lower sections of the tidal tributaries.

The relationship of dissolved oxygen to the presence or absence of a pycnocline and

density gradient is different in the lower Chesapeake Bay mainstem (Figure IV-17c).

A sharp pycnocline exists, but the gradient in dissolved oxygen concentrations is not

as pronounced. Vertical mixing is still retarded by the pycnocline as in other areas of

the Chesapeake Bay, but bottom waters are not as low in oxygen due to the replenishment of oxygenated waters from the ocean. 

Figure IV-18 is a snapshot of water density and dissolved oxygen profiles at various

sites in the Chesapeake Bay during the summer of 1997. The lines depicting water

density demonstrate the layering and mingling of water masses of different sources

and histories within the confines of the trenches and on the shoals. The plots also

▼88

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

a.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

0 5 10

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

b.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

0 5 10

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

c.

WaterDensity (kg/m4)/

Dissolved Oxygen

Concentration (mg/l)

15 25201050

0

-5

-10

-15

-20

-25

-30

Water Column Depth (meters)

Figure IV-17. The figures illustrate a variety of water density and dissolved oxygen profiles found in the

Chesapeake Bay and its tidal tributaries. The black represents water density (kg/m 4), the blue line represents

dissolved oxygen concentration (mg/l). The vertical axis is depth (meters) below the surface. The horizontal line

crossing the density line, when present, indicates upper and lower pycnocline depth using the Fisher et al. 2003

method. Figure ‘a’ represents vertical profiles of density and dissolved oxygen concentration at a relatively shallow site. A layer of homogenous, oxygenated low salinity water lies over water with a gradually increasing salinity/density gradient. Figure ‘b’ represents vertical profiles of density and dissolved oxygen at the same relatively

shallow site when the water column is fully mixed. Figure ‘c’ represents vertical profiles of density and dissolved

oxygen at a site in the lower mainstem Chesapeake Bay where dissolved oxygen levels are sustained throughout

the water column in the presence of a density gradient and pycnocline.

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼89

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-18. ‘Snapshot’ of water density and dissolved oxygen vertical depth profiles at various water quality

monitoring program stations in the Chesapeake Bay and its tidal tributaries in the summer of 1997. 

Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
▼90

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

illustrate the difference small and large variations in density can have on dissolved

oxygen concentrations as described above. For example, at monitoring station EE3.2

in Tangier Sound, the decrease in dissolved oxygen concentration (about 2 mg/l) at 14

meters has a density difference just large enough to be considered a pycnocline.

Downstream, at station CB7.2, the change in density is much larger but induces about

the same magnitude of decrease in the dissolved oxygen concentration gradient.

DELINEATING THE DESIGNATED USE BOUNDARIES

Vertical stratification has direct implications for delineating the designated use

boundaries. Much of the water in the Chesapeake Bay and its tidal tributaries is

shallow and well-mixed or easily aerated. These areas plus the surface mixed layers

overlying stratified water in channels and holes constitute the open-water fish and

shellfish designated use. The upper layer mixes on time scales of minutes to hours

(Alldredge et al. 2002), which means that all of the water in this layer comes in close

contact with the atmosphere and should be able to attain the most protective surface

water dissolved oxygen criterion. The open-water designated use boundary is, therefore, defined as the upper mixed layer, extending from the water surface to the

bottom water-sediment interface, where no stratification occurs or to the measured

depth of the upper pycnocline where, in combination with bottom bathymetry and

water-column circulation, it presents a barrier to oxygen replenishment of deeper

waters. From June through September, the open-water designated use accounts for

approximately 70 percent of the total volume of the Chesapeake Bay and its tidal

tributaries, and many Chesapeake Bay Program segments have only this one designated use (Table IV-9).

Water in the bottom mixed layer is essentially trapped. The bottom mixed layer is

separated from the upper mixed layer by the pycnocline and receives very limited

oxygen from either mixing or diffusion. Biological respiration and decomposition

processes deplete the ambient dissolved oxygen, and bottom sediments exert additional oxygen demand. The shape of the bottom mixed layer or deep-channel

designated use is essentially a thin layer along the bottom in most areas, with thicker

sections in some deeper areas of the Chesapeake Bay. Water within the pycnocline

between the upper and lower mixed layers is defined as the deep-water designated use.

However, as noted and illustrated above, a pycnocline and density gradient do not

affect dissolved oxygen concentration conditions to the same degree in all areas of

the Chesapeake Bay and its tidal tributaries. There are regional peculiarities in

bathymetry and flow that strongly influence the effect of a pycnocline on dissolved

oxygen concentrations, and these must be taken into account. 

THE BOUNDARY DELINEATION PROCESS

The process of identifying and delineating the open-water, deep-water and deepchannel designated use boundaries employed observed and model-simulated

characterizations of dissolved oxygen concentrations and the theoretical effects of

the physical and chemical processes discussed above. The process first identified the
▼91

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay

Program segment. Calculations are based on the 1998-2000 summer (June

through September) mean depths of the upper and lower pycnoclines.

Volume (cubic kilometers) 

Chesapeake Bay 

Program Segment Migratory Open-Water Deep-Water Deep Channel 

CB1TF .35/4% .35/1% 

CB2OH 1.22/14% 1.23/2% 

CB3MH 2.27/27% 1.05/2% .87/6% .47/5%

CB4MH 4.26/9% 2.73/9% 2.25/26%

CB5MH 7.57/15% 3.17/15% 4.62/52%

CB6PH 5.03/10% 5.03/10%

CB7PH 10.29/21% 10.29/21%

CB8PH 3.16/6%

BSHOH .05/<1% .02/<1%

GUNOH .06/<1% .06/<1%

MIDOH .03/<1% .03/<1%

BACOH .02/<1% .02/<1%

PATMH .37/4% .06/<1% .02/<1%

MAGMH .06/1% .08/<1%

SEVMH .08/1% .11/<1%

SOUMH .05/<1% .07/<1%

RHDMH .01/<1% .02/<1%

WSTMH .01/<1% .02/<1%

PAXTF .01/<1% .01/<1%

PAXOH .03/<1% .03/<1%

PAXMH .39/5% .38/1% .38/1%

POTTF .48/6% .48/1%

PISTF .003/<1% .003/<1%

MATTF .01/<1% .01/<1%

POTOH .84/10% .84/2%

POTMH 1.16/14% 3.17/6% 1.25/9% 1.20/14%

RPPTF .10/1% .10/<1%

RPPOH .05/<1% .05/<1%

RPPMH .17/2% 1.00/2% .33/2% .13/1%

CRRMH .07/1% .07/<1%

PIAMH .20/2% .20/<1%

MPNTF .01/<1% .01/<1%

MPNOH .04/<1% .04/<1%

PMKTF .03/<1% .03/<1%

PMKOH .06/<1% .06/<1%

YRKMH .08/1% .28/1%

YRKPH .24/<1% .15/<1%

MOBPH 1.33/3%

continued
▼92

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Volume (cubic kilometers) 

Chesapeake Bay 

Program Segment Migratory Open-Water Deep-Water Deep Channel 

JMSTF .26/3% .27/<1%

APPTF .002/<1 .002/<1%

JMSOH .43/5% .43/1%

CHKOH .05/<1% .05/<1%

JMSMH .36/4% .97/2%

JMSPH .43/1%

WBEMH .01/<1%

SBEMH .03/<1%

EBEMH .01/<1%

LAFMH .003/<1%

ELIPH .04/<1% .02/<1% .002/<1%

LYNPH .02/<1%

NORTF .03<1% .03<1%

C&DOH .02/<1% .02/<1%

BOHOH .02/<1% .02/<1%

ELKOH .10/1% .10/<1%

SASOH .08/1 .08/<1%

CHSTF .003/<1% .003/<1%

CHSOH .03/<1% .03/<1%

CHSMH .41/5% .41/1% .01/<1% <1%

EASMH .78/2% .09/1% .12/1%

CHOTF .02/<1% .02/<1%

CHOOH .04/<1% .04/<1%

CHOMH2 .12/1% .26/1%

CHOMH1 .02/<1% .95/2%

LCHMH .21/1%

HNGMH .19/<1%

FSBMH .14/2% .14/<1%

NANTF .01/<1% .01/<1%

NANOH .05/<1% .05/<1%

NANMH .03/<1% .10/<1%

WICMH .02/<1% .06/<1%

MANMH .01/<1% .09/<1%

BIGMH .002/<1% .04/<1%

POCTF .004/<1% .004/<1%

POCOH .02/<1% .02/<1%

POCMH .01/<1% .35/1%

TANMH 3.98/8%

Total 8.54/100% 49.65/100% 13.41/100% 8.79/100%

Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay

Program segment. Calculations are based on the 1998-2000 summer (June

through September) mean depths of the upper and lower pycnoclines (cont.).
▼93

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

deep-channel designated use habitats: the areas of the Chesapeake Bay and its tidal

tributaries that suffer chronic low dissolved oxygen concentrations due to the natural

interplay of water-column stratification, bottom bathymetry and water circulation

patterns. These areas are so strongly isolated by these factors that they become

immune from remediation. The next step was to identify the deep-water designated

use habitats—areas with chronically low dissolved oxygen concentrations driven

largely by water-column stratification, bottom bathymetry and water circulation

patterns, but with hypoxic conditions (extent and severity) that are responsive to

change, including changes in anthropogenic inputs. The rest of the tidal Bay habitats

were identified as open-water designated use habitats.

First it was necessary to identify potential areas for delineation as deep-channel and

deep-water designated use habitats by examining empirical dissolved oxygen

concentration and distribution data under the ‘best’ observed conditions. The 17-year

dissolved oxygen record from the Chesapeake Bay Program’s Water Quality Monitoring Program, 1984-2000, was reviewed to find the best summer dissolved oxygen

conditions in this time period.12 Using hypoxic volume-days as the metric, 1997 was

chosen. The dissolved oxygen conditions of that year largely reflect the effect of low

freshwater inflow and lower nutrient and sediment inputs from reduced rain and

subsequent runoff. 

Maps of bottom-water dissolved oxygen concentrations in the summer of 1997

revealed the areas with the most recalcitrant low dissolved oxygen concentrations.

These maps also revealed areas with adequate dissolved oxygen concentrations, but

with episodic low dissolved oxygen concentrations under other flow and runoff loading

conditions. Maps of the spatial extent of waters

with concentrations of 1 mg/l and 3 mg/l over the

17-year period helped identify areas where physical processes strongly influence dissolved

oxygen concentrations and where low dissolved

oxygen persists over a wide range of flows and

associated nutrient loads. The regions identified

as having chronic low dissolved oxygen concentrations attributable to the combined affects of

pycnocline, bathymetry and flow were as follows:

• Upper, middle and lower central Chesapeake

Bay segments (CB3MH, CB4MH and

CB5MH);

• Northern reaches of the western and eastern

lower Chesapeake Bay (CB6PH and

CB7PH);

12Historical dissolved oxygen data were available from as early as the 1950s; however, the temporal and

spatial coverage prior to 1984 was uneven and too coarse for this analysis.

Dissolved Oxygen 

and Temperature

As the temperature of a liquid

increases, the ability of gases

to dissolve into it decreases. 

In other words, as water gets

warmer, the concentration 

of gases, such as oxygen,

within it decreases. This

change has implications for

the Chesapeake Bay in the

summer time because, as the

water’s temperature increases,

it can hold less and less

oxygen.The inability to hold

oxygen happens at a time

when overall metabolism in

the Bay is increasing with

temperature. Higher metabolism is coupled with increased

dissolved oxygen consumption.
• Patapsco River (PATMH);

• Mesohaline segments of the Chester, Eastern Bay, Patuxent, Potomac and Rappahannock rivers (CHSMH, EASMH, PXTMH, POTMH and RPPMH); and 

• Polyhaline segment of the York River (YRKPH) (Figure IV-19).

How water-column stratification, bottom bathymetry and water circulation patterns

affect dissolved oxygen conditions and, therefore, the designated use boundaries in

each of these regions are discussed and illustrated below.

Upper Central Chesapeake Bay 

The upper central Chesapeake Bay, or segment CB3MH, includes the ‘head’ of the

mainstem Chesapeake Bay trench at its northern border near the Chesapeake Bay

Bridge (Figure IV-19). In this segment the flow shifts from a single to a two-layer

flow. The exact point where this occurs shifts south and north as the flow from the

Susquehanna River increases and decreases with seasonal and interannual variation.

Its location in the center of this estuarine transition zone puts segment CB3MH at

the extreme end of oxygen dynamics in the Chesapeake Bay. As ocean water moves

up the Bay beneath the pycnocline, metabolic processes are consuming its reserve of

dissolved oxygen. By the time this water reaches segment CB3MH, it has traveled

approximately 220 kilometers and, depending on the time of year, it can be partly or

completely deprived of dissolved oxygen. Because of this, the very southern portion

of segment CB3MH is the first part of the Chesapeake Bay mainstem to show

oxygen depletion in the spring and the last to become reoxygenated in the fall. As

the northward-flowing bottom water encounters the head of the mainstem trench, it

spills into the shallower waters of the middle portion of segment CB3MH before

meeting and mixing with the south-flowing waters of the Susquehanna River (Figure

IV-20). Therefore, even though this middle portion of segment CB3MH is not

‘trench-like’ in depth, this area has deep-channel and deep-water designated uses. 

Middle Central Chesapeake Bay 

The middle central Chesapeake Bay, or segment CB4MH, encompasses the entire

northern half of the Chesapeake Bay mainstem trench with the exception of the head,

which lies in segment CB3MH (Figure IV-19). The trench runs 20 to 35 meters deep

along the eastern side of the segment. Once a pycnocline develops in this segment,

it acts as a lid over the trench and effectively isolates below-pycnocline waters from

the overlying waters. The source of the below-pycnocline water in segment CB4MH

is the already depleted below-pycnocline water of segment CB5MH (Figure IV-21).

Therefore, the only source of dissolved oxygen for below-pycnocline segment

CB4MH water is the occasional storm-induced downwelling event. Given the size of

this segment, these events are relatively localized and short-lived. Because the pycnocline so effectively isolates the deeper waters in this segment, along with bottom

bathymetry and water circulation patterns, these within-pycnocline waters are designated as deep-water and the below-pycnocline waters are designated as deep-channel

designated use habitats.

▼94

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼95

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Lower Central Chesapeake Bay

The lower central Chesapeake Bay, or segment CB5MH, encompasses the entire

southern half of the Bay’s mainstem trench (see Figure IV-19). As in segment

CB4MH, the pycnocline in this segment can ‘cap’ waters in the trench so that the

only significant source of exchange is water flowing into the southern end of the

trench, beneath the pycnocline. During most of the year, as this source water enters

Figure IV-19. Chesapeake Bay Program segments identified as having chronic low dissolved oxygen

attributable to the combined effects of pycnocline, bathymetry and flow.

Lower

Chester River

(CHSMH)
▼96

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Up-bay movement of oxygendepleted sub-pycnocline water 

from the mainstem trench mixes 

with down-bay flow from the 

Susquehanna and becomes 

re-oxygenated.

Oxygen depleted water flows 

up-bay under the pycnocline in 

the mainstem trench. Upon 

reaching the northern terminus 

of the trench, it flows up and 

into the shallower waters of 

northern CB3MH and into the 

Patapsco River via the 

shipping channel.

Pycnocline

Northern terminus of 

the mainstem trench.

Shipping channel to 

Baltimore Harbor in 

the Patapsco River.

Figure IV-20. Three-dimensional schematic of the northern terminus of the mainstem Chesapeake Bay

trench. Flow is depicted by thick arrows. Above and below pycnocline waters are shaded differently.

Region depicted is boxed on inset map. 

Pycnocline

Rappahannock

Potomac

Patuxent Patapsco

As ocean water moves up the 

bay, under the pycnocline, it 

becomes gradually depleted 

in dissolved oxygen until it is 

hypoxic/anoxic when it 

reaches the head of the 

Chesapeake Bay mainstem 

trench.

Figure IV-21. Three-dimensional schematic of the hydrodynamics of the Chesapeake Bay mainstem

trench. View is from the southeast looking northwest.
the trench, its dissolved oxygen concentration is still relatively undepleted, because

it is not far from its ocean source. However, during July and August, temperatures in

the southern mainstem Chesapeake Bay can be warm enough and benthic metabolism high enough for this source water to have depleted oxygen supplies (see

“Dissolved Oxygen and Temperature” sidebar, above). As this water moves up the

trench during the late spring and summer months, metabolic processes under the

pycnocline gradually consume the available dissolved oxygen until it is severely

depleted by the time it reaches the northern part of segment CB5MH (Figure IV-21).

The southern half of segment CB5MH is generally the last part of the Chesapeake

Bay mainstem to become oxygen-depleted and the first to become replenished.

Because the pycnocline so effectively isolates the bottom waters in this segment,

along with bottom bathymetry and water circulation patterns, the within-pycnocline

waters are designated as deep-water designated use habitat and the below-pycnocline

waters are designated as deep-channel designated use habitat.

Western and Eastern Lower Chesapeake Bay

The western and eastern lower Chesapeake Bay, segments CB6PH and CB7PH,

respectively, together make up the broadest region of the Chesapeake Bay mainstem.

The entire region is heavily influenced by the ocean. A 17- to 22-meter trench runs

along the axis of segment CB7PH, extending from the northern end of the segment

almost to its southern boundary (see Figure IV-19). The trench is approximately 

2.5 kilometers wide and deepens to an approximately 50-meter hole near its southern

terminus. Although the trench becomes capped by a pycnocline, below-pycnocline

dissolved oxygen concentrations within the trench are usually not affected. As ocean

water flows into the Chesapeake Bay mouth along the bottom, the Coriolis force

swings this flow northward along the lower eastern shore of the Chesapeake Bay. This

waterflow pattern carries ocean water directly into the trench in segment CB7PH and

provides a steady supply of oxygenated water to the below-pycnocline habitats.

Ocean water similarly replenishes the below-pycnocline waters of segment CB6PH. 

Only the very northern portions of segments CB6PH and CB7PH appear to have a

chronic dissolved oxygen depletion problem related to the pycnocline and local

bottom bathymetry. The northern boundary of these two segments forms a line,

inclining northeastward from the mouth of the Rappahannock River to a point at the

southern tip of the islands forming Tangier Sound (see Figure IV-19). The line

approximates the location of a broad shoal or sill on the Chesapeake Bay bottom.

The sill defines the southern terminus of the mainstem Chesapeake Bay deep trench

and functions as a ‘hydrologic control point’ for waters passing over it. 

A shipping channel cuts through the sill, connecting the trench in segment CB7PH

to the trench in the middle Chesapeake Bay (Figure IV-22). The channel enables an

exchange of oxygen-depleted bottom waters from the mainstem trench with water in

the northern portions of segments CB6PH and CB7PH. 

▼97

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Although the overall direction of flow in the bottom layer is northward in this region,

the smaller-scale actions of the outgoing tide can pulse bottom waters down-estuary

(Figure IV-22). Oxygen-deficient water intrudes on the bottom and as lenses into

mid-water depths. This effect can be intensified during a strong north-westerly wind

event (see sidebar, “Tides Affected by Moon and Sun” on page 100). 

The deep-water designated use, therefore, extends below the sill in these two segments.

Its lower boundary runs along a line more or less parallel to, but south of, the northern

segment line (Figure IV-23). The delineation of the boundary was determined by

examining maps of contemporary dissolved oxygen concentration distributions and the

anecdotal historical dissolved oxygen concentration data record. 

▼98

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Pycnocline

As ocean water encounters the sill 

that forms the southern terminus of 

the mainstem trench, it moves up 

and over the sill and into the trench. 

Ocean water also moves through 

the shipping channel in the sill and 

into Tangier Sound.

Subpycnocline water from the 

mainstem trench can move down 

bay through the shipping channel. 

This movement usually occurs 

due to the effects of wind and tide.

Shipping

Channel

Sill

To Tangler

Sound

Figure IV-22. Three-dimensional schematic of the hydrodynamics of the northern portion of segments

CB6PH and CB7PH. View is from the south. Area portrayed is boxed on the inset map.
▼99

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-23. Map showing the dissolved oxygen designated uses of the Chesapeake Bay and its

tidal tributaries.
Patapsco River

The Patapsco River, segment PATMH, is a highly urbanized tidal waterway, home to a large industrial center and

one of the largest shipping ports on the eastern seaboard.

It is heavily and routinely dredged, and a significant

portion of its shoreline has been hardened. Its shipping

channel is directly connected to the Chesapeake Bay

mainstem trench, allowing for the advection of oxygendepleted water to its below-pycnocline layer (figures

IV-20 and IV-24). The river has a complex three-layer

flow structure. The middle, pycnocline waters of the

Patapsco River are designated as a deep-water use, and

the below-pycnocline waters are designated as a deepchannel use.

Chester River

The downriver, mesohaline portion of the Chester River,

segment CHSMH, contains a trench that ranges in depth

from 20 to 25 meters (see Figure IV-19). The trench is

separated from the mainstem Chesapeake Bay by a sill.

This sill can potentially affect dissolved oxygen levels in

the deep waters of the trench that are chronically low in

the summer months. The pycnocline can form a ‘lid’ over

the trench, cutting off the exchange with surface waters.

Because of the sill at the mouth of the river, tidal flushing

by bottom waters can be restricted, reducing the replenishment of the bottom waters of the trench as well as the

▼100

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Tides Affected By Moon and Sun

Tides are controlled by the gravitational pull

of the sun as well as the moon. When the

moon and the sun are aligned, such as during

a full moon or a new moon, tides achieve

their highest highs and lowest lows. This

phenomenon is called a ‘spring’ tide. When

the pull of the sun and moon are at right

angles, they act to cancel each other out, and

tidal amplitude is at its lowest. This is called a

‘neap’ tide.

The higher amplitude tide that occurs during

‘spring’ tide results in increased tidal flow.

This can be beneficial as when this increased

flow advects oxygen rich water into an

estuary. Conversely, it can be detrimental if

the advected water is coming from deeper

waters with low dissolved oxygen.

Sun 

Earth 

Moon 

Gravitational 

Pull 

Diagram depicts

‘spring’ tide

alignment of

sun and moon.

Figure IV-24. The image on the left shows the bathymetry of the shipping channel

approach to Baltimore Harbor and how it is connected to the ‘head’ of the Chesapeake

Bay mainstem trench at the bottom of the picture (middle to right side). The image on

the right is of the bathymetry of Baltimore Harbor. To improve visualization, the depth

versus width relationship has been enhanced. 
potential mixing force that the inflow might have. It may also be the case that during

extreme (spring) tidal events (see sidebar, “Tides Affected by Moon and Sun,” on

previous page) low dissolved oxygen bottom water from the mainstem trench is

advected into the Chester River trench, where it is sequestered under the pycnocline

(Figure IV-25).

When a measurable pycnocline is observed (often due to these ‘spill-over events’),

the within-pycnocline waters of the lower Chester River (river mouth up to the sill

at Ringgold Point on Eastern Neck) have a deep-water designated use, and the

below-pycnocline waters have a deep-channel designated use. In the absence of

▼101

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Pycnocline

Water is pushed 

to the western shore

Easterly Wind

Mainstem Trench

Western Shore

Eastern Shore

A

B

C

{

Easterly Wind

Downward displacement of 

western pycnocline forces 

subpycnocline water out of 

trench and into the shallow 

waters of the eastern shore 

and into the eastern shore 

tributaries.

Pressure from water that 

‘piles up’ on western shore 

exerts a downward pressure 

on the pycnocline.

Figure IV-25. Panel A shows the 

‘normal’ state of the pycnocline over 

the Chesapeake Bay mainstem trench. 

In Panel B, a strong easterly wind pushes

water from the eastern shore to the

western shore. As water ‘piles up’ on 

the western shore in Panel C, it exerts a

downward pressure on the pycnocline

there. As the pycnocline is pushed down

on the western shore, a pressure differential is created between the west and east

shores causing water to be displaced up

and out of the Chesapeake Bay mainstem

trench and into the shallow waters of the

eastern shore and into the eastern shore

tributaries. Strong westerly winds result 

in the opposite phenomena, where the

pycnocline tilts in the opposite direction

and subpycnocline water is advected to

the western shore. 
water-column stratification, the open-water designated use will apply throughout the

water column to the bottom sediment-water interface in the lower Chester River. 

Eastern Bay 

In the Eastern Bay, segment EASMH, a trench extends from the river mouth, where

it connects with the mainstem trench to a point halfway up the Bay (see Figure IV19). This connection with the mainstem Chesapeake Bay trench has implications for

dissolved oxygen in the bottom waters of lower Eastern Bay, since the belowpycnocline waters of this portion of Eastern Bay and the mainstem Chesapeake Bay

trench exchange freely. This region of the mainstem trench has some of the worst

dissolved oxygen conditions in the entire Chesapeake Bay. Because of this, belowpycnocline waters in lower Eastern Bay are chronically low in dissolved oxygen in

summer. When a measurable pycnocline is observed, the within-pycnocline waters

of Eastern Bay have a deep-water designated use and the below-pycnocline waters

have a deep-channel designated use (see Figure IV-23). In the absence of watercolumn stratification, the open-water designated use will apply throughout the water

column to the bottom sediment-water interface in Eastern Bay. 

Patuxent River 

The trench in the lower Patuxent River, segment PXTMH, contains one of the

deepest points in the Chesapeake Bay just off of Point Patience. The Patuxent River

trench terminates at a sill at the mouth of the river (Figure IV-26). Dissolved oxygen

concentrations become depressed beneath the pycnocline in the summer, but not to

the degree they do in the mainstem Chesapeake Bay trench. These depressed

dissolved oxygen concentrations may be due to pycnocline-disrupting turbulence as

the river flows through the constriction at Point Patience. Below-pycnocline

dissolved oxygen does not become completely replenished, but these waters do naturally reoxygenate enough to maintain levels high enough for a deep-water designated

use (see Figure IV-23). Given the depth of this trench, it is likely that hypoxia is a

natural condition below the pycnocline in the summer. 

Potomac River

The lower Potomac River trench, located in segment POTMH, extends from the

mouth of the river up to Ragged Point and averages 15 to 25 meters deep (see Figure

IV-19). A 10- to 15-meter shelf extends from the sides of the trench and connects

with a similar region in the mainstem Chesapeake Bay (Figure IV-27). Although the

Potomac trench is not connected to the mainstem Bay trench there is not a sill across

the mouth of the Potomac. The pycnocline effectively isolates the water volume in

the trench from the surface waters. In addition, given the size of the Potomac River

watershed, a relatively large amount of organic matter could be delivered to the

below-pycnocline waters of the Potomac trench. It is very likely that, due to the size

and depth of this deep-water area coupled with strong water-column stratification,

low dissolved oxygen conditions are a natural feature of the Potomac trench. The

▼102

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
pycnocline waters of the lower Potomac River (POTMH) have a deep-water

designated use and the below-pycnocline waters have a deep-channel designated use

(see Figure IV-23). 

Rappahannock River

The Rappahannock trench, located in segment RPPMH, extends from the mouth of

the Rappahannock River to Belle Isle (see Figure IV-19). The downriver end of the

trench terminates in a sill that extends across the mouth of the river. Dissolved

oxygen concentrations in the bottom waters of the trench are affected by the formation of the pycnocline. However, bottom water in the upriver half of the trench is

more affected than the downriver half. This phenomenon may be related to strong

currents flowing in the Rappahannock River along the bottom and over the sill. Chao

and Paluskiewicz (1991) found that lower-layer density currents flowing over a sill

cause downward mixing upriver of the sill (Figure IV-28). If this downward mixing

is occurring in the downriver half of the Rappahannock trench, it would explain why

▼103

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-26. Bathymetry at 

the mouth of the Patuxent River. 

To improve visualization, the 

depth relative to the width 

has been enhanced.

Figure IV-27. Bathymetry at 

the mouth of the Potomac River. 

To improve visualization, the 

depth relative to width has 

been enhanced. 
bottom water dissolved oxygen is less affected by the pycnocline in this region. In

the Virginia rivers, bottom layer, upriver flow in the Rappahannock River is second

only to that of the James River and is greater, on average, than in the Potomac River

(Wang 2003, personal communication). Given this rapid upriver flow beneath the

pycnocline, the below-pycnocline waters of the Rappahannock trench are not

depleted of dissolved oxygen until they reach the head of the trench. Based on a

decadal-scale analysis of dissolved oxygen within the trench, it appears that low

dissolved oxygen in the upriver portion is a chronic condition. 

Because of the unique hydrodynamics of the lower Rappahannock River, the deepwater and deep-channel designated uses are not uniform across this segment. From

the upriver shore of the Corrotoman River to the mouth of the Rappahannock River,

the deep-water designated use extends from the upper pycnocline to the bottom sediment-water interface. Upriver of this section to Belle Isle, the pycnocline volume has

a deep-water designated use and the below-pycnocline volume a deep-channel designated use (see Figure IV-23). 

York River 

The York trench, located principally in segment YRKMH, extends from where the

York River empties into Mobjack Bay up-river to Kings Creek. A 10-15 meter

channel runs from the down-river terminus of the trench, through Mobjack Bay to a

point in the mainstem Bay adjacent to the Chesapeake Bay mouth (see Figure IV19). This channel effectively connects the lower York River to ocean water flowing

▼104

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-28. Diagram of the hydrodynamics of flow over a sill. As lower layer waters

flow over the sill, downwelling surface waters occur.

Source: Chao and Paluszkiewicz 1991.

Lower Layer Up River Flow

Upper Layer Up River Flow Downwelling

Sill
into the Chesapeake Bay. This connection apparently is a benefit to bottom water

dissolved oxygen as concentrations below the pycnocline in this region do not get as

low as they do in other below-pycnocline trench areas of the Bay. For this reason, the

waters below the upper pycnocline down to the bottom sediment-water interface

from the York River mouth to Timberneck Creek have a deep-water designated use

(see Figure IV-23). 

SHALLOW-WATER BAY GRASS DESIGNATED USE BOUNDARIES

Restoration of underwater bay grasses to acreages supporting “the propagation and

growth of balanced, indigenous populations of ecologically, recreationally and

commercially important fish and shellfish inhabiting vegetated shallow-water habitats” is ultimately the best measure of attainment of shallow-water bay grass

designated use. Therefore, delineation of the shallow-water designated use boundaries must reflect the desired acreage of underwater bay grass restoration. In

shallow-water habitats out to the 2-meter depth contour, the exact shallow-water

designated use boundaries can:

• Follow a Chesapeake Bay Program segment-specific depth contour;

• Reflect an established segment-specific acreage of underwater bay grasses to

be restored; or 

• Match an established segment-specific acreage of shallow-water habitat meeting the water clarity criteria necessary to support achievement of the

underwater bay grasses restoration goal acreage.

The Chesapeake Bay Program segment-specific maximum depth of persistent, abundant underwater bay grasses growth sets the initial boundary for the habitat

necessary for supporting the shallow-water designated use. That same segmentspecific maximum depth was used in combination with the single best year of

underwater bay grass distribution mapped across the available 1930-2000 data

record to set the new restoration goals on a segment-by-segment basis. Finally, the

ratio of the above shallow-water habitat out to the maximum depth of persistent,

abundant plant growth and the corresponding segment-specific underwater bay

grasses restoration acreage are used to calculate an acreage of shallow-water habitat

meeting the water clarity criteria necessary to support achievement of the restoration

goal acreage. 

The following sections describe and quantify these three approaches to setting the

shallow-water designated use boundaries, which are consistent with options the EPA

put forth for measuring attainment of the Chesapeake Bay shallow-water underwater

bay grass designated use (U.S. EPA 2003). EPA recommends the states adopt one (or

more) of the three approaches to defining the shallow-water designated use boundaries in addition to adoption of numerical water clarity criteria into their water

quality standards. States can adopt shallow-water designated use boundaries

covering higher acreages or greater depths than those provided here during their

▼105

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼106

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

upcoming water quality standards adoption processes once the expanded riverspecific information has become available to be incorporated. During future state

triennial reviews of their water quality standards, states also may expand their

shallow-water designated use boundaries to reflect resulting levels of restoration of

underwater bay grasses in prior years.

MAXIMUM DEPTH OF PERSISTENT OR ABUNDANT 

PLANT GROWTH-BASED BOUNDARIES

The 2-meter depth contour was selected as the maximum depth for the lower vertical

boundary of the shallow-water designated use. This is the maximum depth to which

underwater bay grasses could be restored in many of the tidal tributaries and mainstem Chesapeake Bay shallow-water habitats. Although historical underwater bay

grass beds in the Chesapeake Bay probably grew to 3 meters or more, the 2-meter

depth was chosen following an extensive evaluation of grass bed distribution over the

past 70 years (1930s-2000) and of light levels anticipated to be required to restore

viable shallow-water habitats out to the 2-meter depth (Batiuk et al. 1992; Dennison

et al. 1993; Moore et al. 1999; Batiuk et al. 2000; Moore et al. 2001; Naylor 2002).

The intertidal zone was selected as the inner boundary for the shallow-water bay

grass designated use because some species can grow in the upper end of the intertidal zone (Batiuk et al. 2000; Koch 2001). Numerous field studies of underwater bay

grass distributions in the Chesapeake Bay and its tidal tributaries have indicated that

what is controlling the minimum depth of their distribution is not wave action or

other factors, but length of exposure to air at low tide (Moore, unpublished data;

Naylor, unpublished data).

Shallow-water habitats also may be offshore flats such as those observed in Tangier

Sound and Poquoson Flats in the lower mainstem Chesapeake Bay. These areas may

have an inner boundary not in the intertidal zone but rather a relatively deep and wide

channel between them and the shore. These areas are included in the delineation of

shallow-water bay grass designated use habitats if they have or have had underwater

bay grasses and met the decision rules described below. 

BENEFITS OF DEEPER UNDERWATER BAY GRASS DISTRIBUTION

There are obvious benefits to restoring underwater bay grasses to greater depths 

than where they currently exist in the Chesapeake Bay and its tidal tributaries 

(Table IV-10). Increasing the depth and, therefore, the areal distribution of the

grasses can greatly increase the habitat and food available to the Chesapeake Bay’s

fish, crabs and waterfowl.

It is important to note that underwater bay grass distribution is directly related to the

tidal bathymetry of the basins in which the beds occur. In a shallow bay with a gradual

slope to deeper waters, such as the Chesapeake Bay, even a moderate increase in water

clarity can result in tremendous increases in the areal extent of bay grasses.
HISTORICAL UNDERWATER BAY GRASS DISTRIBUTION 

The distribution and, therefore, the depth of historical underwater bay grass beds

were mapped from photographs dating from the late 1930s through the mid-1960s

by scientists at the Maryland Department of Natural Resources and the Virginia

Institute of Marine Science. Historical underwater bay grass distribution data from

Maryland and Virginia were aggregated into a single data set using ArcInfo GIS software. The two states’ approaches reflect differences in the quality and quantity of

historical aerial photographs available for interpretation. Full documentation of the

methods employed and the detailed results are reported in Moore et al. (1999, 2001)

and Naylor et al. (2002).

To determine historic underwater bay grass acreage, aerial photos of Maryland’s

portion of the Bay taken in 1938, 1952, 1957 and 1964 were evaluated to determine

the year in which the most underwater bay grass was visible for each area (Naylor

2002). The photos for the year of greatest abundance in each area were then scanned,

geo-referenced and photo-interpreted to determine the extent of underwater bay

grass beds during these years.

In the Virginia portion of the Chesapeake Bay and its tidal tributaries, historical

underwater bay grass acreage in the James River was mapped using photographs

taken in 1937, 1947, 1948, 1953, 1954, 1958, 1959, 1963, 1968, 1969, 1970 and

▼107

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

• Ensures growth of underwater bay grasses where previously there may have been none

because wave energy at shallower depths prevented plants from rooting in the bottom

sediments (e.g., the beds that formerly grew on the western side of Kent Island,

Maryland, at depths greater than where the critical wave energy threshold exists);

• Adds habitat below the grazing depth of non-native mute swans and non-migratory

Canada geese (approximately 1 and 0.5 meters, respectively) to increase food 

availability for native waterfowl;

• Reduces the likelihood of ice damage to the beds;

• Reduces the negative effects of unusually low tides;

• Minimizes thermal stress (as deeper beds are inherently cooler);

• Stabilizes sediments at greater depths (through the reduction of water velocity 

within the underwater bay grass beds);

• Increases overall nutrient uptake and supports increased denitrification;

• Increases summertime oxygen production (which is particularly important in the 

headwaters of tidal creeks); and

• Increases habitat for fish, crabs and macroinvertebrates.

Table IV-10. Ecological and water quality benefits of deeper underwater bay

grasses distribution in the Chesapeake Bay and its tidal tributaries. 
1973, with the historical coverage defined by the composite of the individual years

(Moore et al. 1999). Historical and recent ground survey results were superimposed

on the maps of historical underwater bay grass distributions to help determine

whether the patterns exhibited in the photographs were actually those of underwater

bay grass beds (Moore et al. 1999).

For the Rappahannock and York rivers and the adjacent smaller western shore rivers,

creeks and embayments, a series of photographs from 1952 to 1956 was chosen to

delineate the maximum coverage of bay grasses in these areas (Moore et al. 2001).

The 1936 and 1937 photographs of these rivers showed less underwater bay grass

coverage compared to the 1950s photographs. The difference appeared to be related

to poorer overall atmospheric and water clarity conditions (Moore et al. 2001).

The interpretation of these historic aerial photographs closely followed current

methods to delineate underwater bay grass beds throughout the Chesapeake Bay and

its tidal tributaries through annual aerial underwater bay grass surveys (e.g., Orth et

al. 2000). In neither state did a single year of photography provide comprehensive

coverage of each state’s tidal shorelines. 

These state-specific analyses provide a conservative estimate of past underwater bay

grass distributions prior to the 1970s. The conservative nature of the estimate is due,

in part, because the older photographs were not collected specifically to map underwater bay grasses, but were gathered to assist in analyzing land use or farming

practices. While atmospheric criteria were usually met, the factors that are important

for delineating and mapping underwater bay grasses (such as tidal stage, water transparency and plant growth stage) often were not met. Underwater bay grasses likely

grew at greater depths between the 1930s and 1960s, according to published and

anecdotal information, than was observed in a number of segments in the historical

photographs. Grasses that grow beyond the 1-meter depth contour become increasingly difficult to map, given the conditions under which the historical photographs

were collected. There were limited numbers of years—often only three to five—for

which historical photographs of a particular shallow-water habitat region were available for interpretation and mapping between the 1930s and early 1970s. Evidence

suggests that underwater bay grass distributions already had declined by the time

photographs of suitable quality were available for interpretation (Moore et al. 1999).

All of these factors led to conservative estimates of past underwater bay grasses

distributions and depths of bed growth.

UNDERWATER BAY GRASS NO-GROW ZONES

A series of underwater bay grass ‘no-grow zones’ were originally delineated in 1992

in the Chesapeake Bay Submerged Aquatic Vegetation Habitat Requirements and

Restoration Targets: A Technical Synthesis (Batiuk et al. 1992). Habitats exposed to

high wave energy or that have undergone physical modifications such that they could

not support underwater bay grasses growth were excluded based on an extensive

review of data available at the time. With the mapping of historical underwater bay

▼108

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
grass distributions, a composite of available distribution data from the 1930s through

2001 was superimposed on the 1992 bay grass no-grow zones. A number of shoreline habitats previously considered no-grow zones showed clear evidence of

historical underwater bay grass growth and, therefore, their no-grow zone designation was dropped. These revised underwater bay grass no-grow zones also include

areas where the no-grow zone applies to a 1- to 2-meter depth contour as well as a

0- to 2-meter depth contour.

The revised underwater bay grass no-grow zones illustrated in Figure IV-29 show

shoreline habitats of 2 meters or less where underwater bay grasses are never

expected to grow due to:

• Extreme physical wave energy, which prevents the plants from rooting in the

bottom sediments (e.g., Calvert Cliffs on Maryland’s lower western shore and

Willoughby Split to Cape Henry near the Chesapeake Bay mouth in Virginia);

• Permanent physical alterations to nearshore habitats, including dredging close

to shore accompanied by hardening of the shoreline and installation of permanent structures (i.e., shipping terminals) as observed in the inner Baltimore

Harbor and the Elizabeth River;

• Natural, extreme discoloration of the water from tidal-fresh wetlands (e.g.,

tidal-fresh ‘blackwater’ rivers on the Eastern Shore); or

• No functional shallow-water habitat due to natural river channeling (e.g., tidal

headwaters of several lower Eastern Shore rivers).

These underwater bay grass no-grow zones reflect the full set of findings on underwater bay grasses distributions from the historical (select years from the 1930s–early

1970s) and 1978–2001 data records, as well as altered nearshore/shoreline habitats

as described above. The no-grow zones illustrated in Figure IV-29 are based on the

best available information and are subject to future revision based on new research

and information.

If no physical reasons prevent underwater bay grasses from growing in a specific

shallow-water habitat, it should be expected that grasses can grow there, given

appropriate water quality conditions and local sources of propagules (i.e., reproductive vegetative materials such as seeds and rhizomes). For example, evidence exists

of underwater bay grasses growing within estuarine turbidity maximum zones in the

upper Chesapeake Bay mainstem and selected tidal tributaries (e.g., the Potomac

River), but not in other tidal tributaries. The Regional Criteria provides specific

guidance to the states on how to address estuarine turbidity maximum zones in

applying the Chesapeake Bay water clarity criteria (see Chapter 7 in U.S. EPA

2003). The lack of historical data on the presence of underwater bay grasses in a

particular habitat is not a valid reason to delineate that shallow-water area as an

underwater bay grass no-grow zone.

▼109

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Six Chesapeake Bay Program segments were not assigned a shallow-water bay grass

designated use depth boundary (see Table IV-13). The established bay grass no-grow

zones covered the 2-meter and less habitats along the entire tidal shoreline in each

of these segments–upper Choptank River, upper Pocomoke River, Western Branch

Elizabeth River, Southern Branch Elizabeth River, Eastern Branch Elizabeth River

and Lafayette River (see Appendix C). 

▼110

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-29. Map illustrating the revised underwater bay grass no-grow zones of the

Chesapeake Bay and its tidal tributaries.
DETERMINING THE MAXIMUM DEPTH OF 

PERSISTENT/ABUNDANT PLANT GROWTH 

The first step in the process to define the maximum depth of persistent and abundant

underwater bay grass beds by Chesapeake Bay Program segment (Table IV-11,

Figure IV-30) was to establish decision rules. The rules developed take full advantage of the entire record of underwater bay grass distribution and abundance survey

data and reflect the findings published in scientific literature (Table IV-12). Also, the

decision rules help ensure full consistency between the establishment of the shallowwater bay grass designated use depths (the depth at which the Chesapeake Bay water

clarity criteria will be applied) and the new quantitative underwater bay grasses

acreage restoration goal for Chesapeake Bay and its tidal tributaries.

The available data record included interpreted aerial photography from the 1930s to

the early 1970s as well as the annual baywide aerial survey data from 1978-2000.

From these photos and surveys, the acreage of underwater bay grasses within three

depth intervals was calculated for every Chesapeake Bay Program segment: 0-0.5

meters, > 0.5-1 meter and > 1-2 meters (Appendix B, Table B-1). Thus, each Chesapeake Bay Program segment has three ‘segment-depth intervals’ (e.g., CB4MH 1-2

meter is a segment-depth interval).

The total surface area within each segment-depth interval minus any delineated

underwater bay grass no-grow zones is an estimate of the area of potential underwater bay grass habitat in that segment-depth interval. Thus, there is an acreage of

potential underwater bay grass habitat for each of the three segment-depth intervals

in every Chesapeake Bay Program segment except for those segments that are

entirely no-grow zones (Appendix C, Table C-1).

The decision rules described in Table IV-12 are based on the observed single best

year of underwater bay grass coverage for each Chesapeake Bay Program segment

(i.e., not the single best year by segment-depth) (Appendix B, Table B-2). Using

each segment’s single best year, the percentage of available habitat at each segmentdepth interval that was occupied by underwater bay grasses in that single best year

was calculated (Appendix B, Table B-3). That percentage is a measure of the relative importance of each segment-depth interval as bay grass habitat. Upon

application of the decision rules (Table IV-12), a set of Chesapeake Bay Program

segment-specific shallow-water designated use depths was generated (Table IV-13). 

Rationale for the 20 Percent and 10 Percent Rules

In setting application depths, it was important to select a percentage of cover high

enough to assure that underwater plants definitely occupied that habitat, but low

enough that the resulting depths realistically represented true light availability

attained during the available historical data record. Underwater bay grass beds in

tidal waters of the Chesapeake Bay display a spatial heterogeneity that is characteristic of underwater grass beds elsewhere in the world (Lehmann et al.1997; Kuenen

and Debrot 1995; Carpenter and Titus 1984). This heterogeneity exists both in micro

▼111

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼112

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-11. Chesapeake Bay Program segmentation scheme segments.

Northern Chesapeake Bay . . . . . . . . . CB1TF

Upper Chesapeake Bay . . . . . . . . . . . CB2OH

Upper Central Chesapeake Bay . . . . CB3MH

Middle Central Chesapeake Bay . . . CB4MH

Lower Central Chesapeake Bay . . . . CB5MH

Western Lower Chesapeake Bay . . . . CB6PH

Eastern Lower Chesapeake Bay . . . . CB7PH

Mouth of the Chesapeake Bay . . . . . CB8PH

Bush River . . . . . . . . . . . . . . . . . . . . BSHOH

Gunpowder River . . . . . . . . . . . . . . GUNOH 

Middle River . . . . . . . . . . . . . . . . . . . MIDOH

Back River . . . . . . . . . . . . . . . . . . . . BACOH

Patapsco River . . . . . . . . . . . . . . . . . PATMH 

Magothy River . . . . . . . . . . . . . . . . MAGMH

Severn River . . . . . . . . . . . . . . . . . . . SEVMH

South River . . . . . . . . . . . . . . . . . . . SOUMH

Rhode River . . . . . . . . . . . . . . . . . . RHDMH

West River . . . . . . . . . . . . . . . . . . . . WSTMH

Upper Patuxent River . . . . . . . . . . . . PAXTF

Western Branch Patuxent River . . . . WBRTF

Middle Patuxent River . . . . . . . . . . . PAXOH

Lower Patuxent River . . . . . . . . . . . PAXMH

Upper Potomac River . . . . . . . . . . . . POTTF

Anacostia River . . . . . . . . . . . . . . . . . ANATF

Piscataway Creek . . . . . . . . . . . . . . . . PISTF

Mattawoman Creek . . . . . . . . . . . . . . MATTF

Middle Potomac River . . . . . . . . . . . POTOH

Lower Potomac River . . . . . . . . . . . POTMH

Upper Rappahannock River . . . . . . . . RPPTF

Middle Rappahannock River . . . . . . RPPOH

Lower Rappahannock River . . . . . . . RPPMH

Corrotoman River . . . . . . . . . . . . . . CRRMH

Piankatank River . . . . . . . . . . . . . . . . PIAMH

Upper Mattaponi River . . . . . . . . . . . MPNTF

Lower Mattaponi River . . . . . . . . . . MPNOH

Upper Pamunkey River . . . . . . . . . . PMKTF

Lower Pamunkey River . . . . . . . . . . PMKOH

Middle York River . . . . . . . . . . . . . . YRKMH

Lower York River . . . . . . . . . . . . . . . YRKPH

Mobjack Bay . . . . . . . . . . . . . . . . . . MOBPH

Upper James River . . . . . . . . . . . . . . . JMSTF

Appomattox River . . . . . . . . . . . . . . . APPTF

Middle James River . . . . . . . . . . . . . JMSOH

Chickahominy River . . . . . . . . . . . . CHKOH

Lower James River . . . . . . . . . . . . . . JMSMH

Mouth of the James River . . . . . . . . . JMSPH

Western Branch Elizabeth River . . . WBEMH

Southern Branch Elizabeth River . . . SBEMH

Eastern Branch Elizabeth River . . . . EBEMH

Lafayette River . . . . . . . . . . . . . . . . . LAFMH

Mouth to mid-Elizabeth River . . . . . . ELIPH

Lynnhaven River . . . . . . . . . . . . . . . . LYNPH

Northeast River . . . . . . . . . . . . . . . . . NORTF

C&D Canal . . . . . . . . . . . . . . . . . . . C&DOH

Bohemia River . . . . . . . . . . . . . . . . . BOHOH

Elk River . . . . . . . . . . . . . . . . . . . . . . ELKOH

Sassafras River . . . . . . . . . . . . . . . . . SASOH

Upper Chester River . . . . . . . . . . . . . CHSTF

Middle Chester River . . . . . . . . . . . . CHSOH

Lower Chester River . . . . . . . . . . . . CHSMH

Eastern Bay . . . . . . . . . . . . . . . . . . . EASMH

Upper Choptank River . . . . . . . . . . . CHOTF

Middle Choptank River . . . . . . . . . . CHOOH

Lower Choptank River . . . . . . . . . CHOMH1

Mouth of the Choptank River . . . . CHOMH2

Little Choptank River . . . . . . . . . . . LCHMH

Honga River . . . . . . . . . . . . . . . . . . HNGMH

Fishing Bay . . . . . . . . . . . . . . . . . . . FSBMH

Upper Nanticoke River . . . . . . . . . . . NANTF

Middle Nanticoke River . . . . . . . . . NANOH

Lower Nanticoke River . . . . . . . . . . NANMH

Wicomico River . . . . . . . . . . . . . . . . WICMH

Manokin River . . . . . . . . . . . . . . . . MANMH

Big Annemessex River . . . . . . . . . . . BIGMH

Upper Pocomoke River . . . . . . . . . . . POCTF

Middle Pocomoke River . . . . . . . . . . POCOH

Lower Pocomoke River . . . . . . . . . . POCMH

Tangier Sound . . . . . . . . . . . . . . . . . TANMH

Source: Chesapeake Bay Program 1999.
▼113

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Figure IV-30. The geographical location of the 78 Chesapeake Bay Program segments.

Source: Chesapeake Bay Program 1999.
and macro scales, and as viewed by aerial photography results in a spatial distribution that is virtually never 100 percent coverage of available shallow-water habitat at

any depth. This growth pattern was true historically as well. Manning (1957) estimated that lower Patuxent River underwater bay grass beds covered only about

one-third of shoal waters. Photography from Maryland from 1938 and 1952 revealed

an average percent cover of 35 percent (Naylor 2002) at depths of less than 1 meter.

Virginia photographic analysis revealed up to 48 percent coverage in the York and

Rappahannock rivers at the less than 1-meter depth (Moore et al. 2001). These findings were supported by similar findings from analysis of the more recent 1978–2000

Chesapeake Bay underwater bay grass aerial survey distribution data. 

▼114

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-12. Methodology used in determining the shallow-water bay grass

designated use depths by Chesapeake Bay Program segment, which led to the

establishment of the 185,000 Chesapeake Bay baywide underwater grasses

restoration goal.

The baywide underwater bay grass goal acreage was established based on the single best

year acreage out to a shallow-water bay grass designated use depth determined as follows:

1. Bathymetry data and aerial photographs were used to divide the mapped single best year

underwater bay grasses acreage in each Chesapeake Bay Program segment into three

depth zones: 0-0.5 meters, > 0.5-1 meters and >1-2 meters. The delineated underwater

bay grass no-grow zones were then removed from consideration as shallow-water bay

grass designated use habitat.

2. The aerial photographs were used to determine the depth to which the mapped underwater bay grass beds grew in each Chesapeake Bay Program segment with either a

minimum abundance or minimum persistence. The underwater bay grass goal for a

Chesapeake Bay Program segment is the portion of the single best year acreage mapped

out to the higher depth in the determined depth range. The decision rules for this process

were as follows:

In all segments, the 0-0.5 meter depth interval was designated for shallow-water

bay grass use. In addition, the shallow-water bay grass use was designated for

deeper depths within a Chesapeake Bay Program segment if either:

A) The single best year of underwater bay grasses distribution covered at least 

20 percent of the potential habitat in a deeper depth interval; or,

B) The single best year of underwater bay grass distribution covered at least 

10 percent of the potential habitat in the segment-depth interval, and at least 

3 of the 4 five-year periods of the more recent record (1978–2000) showed 

at least 10 percent underwater bay grasses coverage of potential habitat 

in the segment-depth interval.

3. The single best year underwater bay grasses distribution acreage of all Chesapeake Bay

Program segments were clipped at the deeper depth of the segment-depth interval determined above. The resulting underwater bay grass acreage for each segment were added,

resulting in the total baywide underwater bay grass acreage goal of 185,000 acres. 
▼115

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-13.The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths.

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Northern Chesapeake Bay CB1TF Historical ▲ 2

Upper Chesapeake Bay CB2OH Historical ✪ 0.5 

Upper Central Chesapeake Bay CB3MH 1978 ▲ 0.5 

Middle Central Chesapeake Bay CB4MH Historical ▲ 2 

Lower Central Chesapeake Bay CB5MH Historical ▲ 2 

Western Lower Chesapeake Bay CB6PH Historical ▲ 1 

Eastern Lower Chesapeake Bay CB7PH Historical ▲ 2 

Mouth of the Chesapeake Bay CB8PH 1996 ✪ 0.5 

Bush River BSHOH Historical ✪ 0.5 

Gunpowder River GUNOH 2000 ▲ 2 

Middle River MIDOH Historical ▲ 2 

Back River BACOH * ✪ 0.5 

Patapsco River PATMH Historical ▲ 1 

Magothy River MAGMH Historical ▲ 1 

Severn River SEVMH 1999 ▲ 1 

South River SOUMH Historical ▲ 1 

Rhode River RHDMH Historical ✪ 0.5 

West River WSTMH Historical ▲ 0.5 

Upper Patuxent River PAXTF 1996 ▲ 0.5 

Western Branch (Patuxent River) WBRTF * ✪ 0.5 

Middle Patuxent River PAXOH 2000 ✪ 0.5 

Lower Patuxent River PAXMH Historical ▲ 1 

Upper Potomac River POTTF 1991 ✜ 2 

Anacostia River ANATF 1991 ✪ 0.5 

Piscataway Creek PISTF 1987 ▲ 2 

Mattawoman Creek MATTF 2000 ▲ 1 

Middle Potomac River POTOH 1998 ✜ 2 

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)

continued
▼116

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Lower Potomac River POTMH Historical ▲ 1 

Upper Rappahannock River RPPTF 2000 ✪ 0.5 

Middle Rappahannock River RPPOH * ✪ 0.5

Lower Rappahannock River RPPMH Historical ▲ 1 

Corrotoman River CRRMH Historical ▲ 1 

Piankatank River PIAMH Historical ▲ 2 

Upper Mattaponi River MPNTF 1998 ✪ 0.5 

Lower Mattaponi River MPNOH * ✪ 0.5 

Upper Pamunkey River PMKTF 1998 ✪ 0.5 

Lower Pamunkey River PMKOH * ✪ 0.5 

Middle York River YRKMH Historical ✪ 0.5 

Lower York River YRKPH Historical ▲ 1 

Mobjack Bay MOBPH Historical ▲ 2

Upper James River JMSTF Historical ✪ 0.5 

Appomattox River APPTF Historical ▲ 0.5

Middle James River JMSOH 1998 ✪ 0.5 

Chickahominy River CHKOH 2000 ✪ 0.5 

Lower James River JMSMH Historical ✪ 0.5 

Mouth of the James River JMSPH Historical ▲ 1 

Western Branch Elizabeth River WBEMH * ❖❖❖ * 

Southern Branch Elizabeth River SBEMH * ❖❖❖ * 

Eastern Branch Elizabeth River EBEMH * ❖❖❖ * 

Lafayette River LAFMH * ❖❖❖ * 

Mouth to mid-Elizabeth River ELIPH * ✪ 0.5 

Lynnhaven River LYNPH 1986 ✪ 0.5 

Northeast River NORTF Historical ✪ 0.5 

C&D Canal C&DOH 1978 ✪ 0.5 

Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths (cont.).

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)

continued
▼117

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Bohemia River BOHOH 2000 ✪ 0.5 

Elk River ELKOH 2000 ▲ 2 

Sassafras River SASOH 2000 ▲ 1 

Upper Chester River CHSTF * ✪ 0.5 

Middle Chester River CHSOH Historical ✪ 0.5 

Lower Chester River CHSMH Historical ▲ 1 

Eastern Bay EASMH Historical ▲ 2 

Upper Choptank River CHOTF * ❖❖❖ *

Middle Choptank River CHOOH Historical ✪ 0.5 

Lower Choptank River CHOMH2 Historical ▲ 1 

Mouth of the Choptank River CHOMH1 Historical ▲ 2 

Little Choptank River LCHMH Historical ▲ 2 

Honga River HNGMH Historical ▲ 2 

Fishing Bay FSBMH Historical ✪ 0.5 

Upper Nanticoke River NANTF * ✪ 0.5 

Middle Nanticoke River NANOH Historical ✪ 0.5 

Lower Nanticoke River NANMH Historical ✪ 0.5 

Wicomico River WICMH Historical ✪ 0.5

Manokin River MANMH Historical ▲ 2

Big Annemessex River BIGMH Historical ▲ 2 

Upper Pocomoke River POCTF * ❖❖❖ * 

Middle Pocomoke River POCOH * ✪ 0.5 

Lower Pocomoke River POCMH Historical ▲ 1

Tangier Sound TANMH Historical ▲ 2

✪ Decision rules not met – default depth interval of 0-0.5 meters applies. 

▲ Single best year percent of total potential habitat is 20 percent. 

✜ Percent of total potential habitat is 10-19.9% and underwater bay grasses are persistent (1978–2000). 

❖ Chesapeake Bay Program segment completely within the underwater bay grass no-grow zone. 

*Denotes no data available or no underwater bay grasses mapped (1930s-2000). 

Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria

used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay

grass designated use boundary depths (cont.).

Recommended

Shallow-Water

Designated

Chesapeake Bay Program CBP Single Use Depth

(CBP) Segment Name Segment Best Year 0–0.5 0.5–1 1–2 (meters)

Maximum Depth Interval

Application of the

Water Clarity Criteria (meters)
▼118

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Several possible reasons account for less-than-complete habitat occupation. These

include small-scale sediment type differences, small-scale sediment movement

patterns, sediment slope, fetch, uneven seed distribution and localized disturbance. In

addition to these reasons for real variations in plant presence, only the most dense

areas of underwater bay grasses are visible using high-altitude photography. Very

sparse beds reveal no signature in the water and are never delineated through photo

interpretation. Each year, Chesapeake Bay researchers and resource managers find

dozens of underwater bay grass beds in places not identified in the annual aerial

survey due to these limitations. Thus, reporting of percent coverage is generally lower

than the total amount of habitat actually occupied by sparse plant beds, which further

lowers the total percent coverage. Given the starting point of 1 percent, and the typical

maximum of 35-48 percent from the historical photography, 20 percent was seen as a

defensible midpoint figure reflective of sufficient coverage to define maximum depth

of the underwater bay grasses growth (Moore 1999, 2001; Naylor 2002).

In order to provide an additional measure of the importance of a segment-depth

interval as underwater bay grass habitat, the record of underwater bay grass aerial

survey data from 1978–2000 (there is not a survey for every year between 1979-1983

and in 1988) was segmented into four five-year intervals (Appendix B, Table B-4).

The persistence of underwater bay grasses in each segment-depth interval was then

assessed by counting the number of five-year intervals in which at least 10 percent

of potential habitat was occupied by underwater bay grasses (see Table IV-12).

UNDERWATER BAY GRASS RESTORATION 

GOAL-BASED BOUNDARIES

The Chesapeake 2000 agreement committed to revising the existing underwater bay

grass restoration goals and strategies:

. . . to reflect historic abundance, measured as acreage and density from the

1930s to present. The revised goals will include specific levels of water clarity

which are to be met in 2010. Strategies to achieve these goals will address

water clarity, water quality and bottom disturbance.

The eligible segments and depths included in calculating the new underwater bay

grass restoration goal were limited to segment-depth intervals designated for

shallow-water bay grass use. The new restoration goal was derived from the total

single best year acreage summed over all the segment depths that were designated

for shallow-water bay grass use after considering a wide array of data and information (Figure IV-31).

Data Used to Establish the Restoration Goal

It was essential to use historical underwater bay grass data in determining the underwater bay grass acreage goal for the Chesapeake Bay. But using these data presented

obvious limitations. They were originally collected for agricultural landuse mapping

purposes and thus did not include all areas of tidal shallow-water habitats, which
▼119

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries 37,356 76,525 85,415 99,039 113,719 139,087 184,877 194,676 242,975

495,882

640,926

0

700,000600,000500,000400,000300,000200,000100,000

Acres

1984

Underwater

Bay Grasses

Single Best

Year for

Those Years

Designated

for the 

1992 CBP

Underwater

Bay Grasses

Restoration 

Goal

(1971-1990)

2001 

Underwater

Bay Grasses

1978-2000

Single Best 

Year

Underwater 

Bay Grasses

at All Depths

1992 CBP

Underwater

Bay Grasses

Restoration

Goal (1971-

1990

Composite

Underwater 

Bay Grasses)

1978-2000

Composite

Underwater

Bay Grasses

at All Depths

1930s-2000

Single Best

Year

Underwater

Bay Grasses

Out to

Maximum 

Depth of

Persistent/

Abundant

Plant Growth

1930s-2000

Composite

Underwater

Bay Grasses

Out to 

2-Meter

Depth Contour

Total 

ShallowWater

Habitat Out

to Maximum

Depth of

Persistent/

Abundant

Plant Growth

1930s-2000

Single Best

Year

Underwater

Bay Grasses

at All Depths

Total

ShallowWater

Habitat Out

to 2-Meter

Depth 

Contour

(minus 

underwater

bay grasses

no grow

zones)

Figure IV-31. Array of different underwater bay grass and shallow-water habitat acreages considered during the process for setting the shallow-water

designated use depth and establishing the new Chesapeake Bay underwater bay grass restoration goals.

Sources: Moore et al. 1999; Naylor 2002; Virginia Institute of Marine Science Chesapeake Bay SAV website http://www.vims.edu/bio/sav; Chesapeake Bay Program websitehttp://www.chesapeakebay.net.
resulted in an underestimate of the mapped acreage. Historic data also were limited

by the fact that pre-Hurricane Agnes (June 1972) underwater bay grass data exist

only for a limited number of years in each Chesapeake Bay Program segment. Thus,

using only historical data to determine a new goal would likely underestimate the

potential for underwater bay grass recovery.

Rationale for Use of the Single Best Year 

The single best year of underwater bay grass growth observed in each Chesapeake

Bay Program segment from the entire available record of aerial photographs

(1930s–2000) is the best available data on underwater bay grass occurrence over the

long-term. Of the 62 Chesapeake Bay Program segments with mapped underwater

bay grasses, 68 percent of the segment single best year acreages occurred in the 1930s

to early 1970s time period; 3 percent occurred in 1978; 5 percent occurred between

1986 and 1991; and 24 percent occurred between 1996 and 2000 (see Table IV-13).

There were several obvious benefits in using the single best year approach to setting

the new restoration goal. The single best year acreage is the most solid available data

on underwater bay grass acreage over the multi-decade data record. Even in suitable

water quality conditions, underwater bay grass beds often move around within a

segment. By combining acreage over a number of years into a composite acreage it

would be possible to overestimate the likely future abundance of underwater bay

grasses in any single year. 

Using the single best year as the basis for the new restoration goal ensures consistency

with the method for determining the segment-specific shallow-water designated use

depths and the resulting water clarity criteria application depths. The consistency

between methods links the segment-specific water clarity application depths, shallowwater designated use boundaries and underwater bay grass restoration goals. This

method is scientifically valid because when the acreage goals for segments in the

same salinity range are totaled (see “Shallow-Water Habitat Area to Support Restoration,” below), the percentage of available habitat covered by the restoration goal

acreage is consistent with the average rate of habitat occupancy described in the

scientific literature as reflecting healthy underwater bay grass growth.

The new underwater bay grass goal focuses the restoration effort on areas that demonstrated a minimal level of abundance or persistence in the past and which are likely to

respond to water clarity improvements in the future. Focusing on the single best year

versus a composite underwater bay grass coverage ensures that vegetated portions of

potential underwater bay grass habitats are not over-accounted-for based on underwater

bay grass beds that may have ‘migrated’ year-to-year over the past seven decades.

New Underwater Bay Grass Restoration Goal

Table IV-14 lists the Chesapeake Bay Program segment-specific single best year

acreage within the shallow-water bay grasses designated use depths that, added

together, make up the baywide 185,000 acre restoration goal.

▼120

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
▼121

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-14. Chesapeake Bay underwater bay grass restoration goals by

Chesapeake Bay Program segment.

Segment Name Segment Single Best Year Acres 

Northern Chesapeake Bay CB1TF Historical 12,908

Upper Chesapeake Bay CB2OH Historical 302

Upper Central Chesapeake Bay CB3MH 1978 943

Middle Central Chesapeake Bay CB4MH Historical 2,511

Lower Central Chesapeake Bay CB5MH Historical 14,961

Western Lower Chesapeake Bay CB6PH Historical 980

Eastern Lower Chesapeake Bay CB7PH Historical 14,620

Mouth of the Chesapeake Bay CB8PH 1996 6

Bush River BSHOH Historical 158

Gunpowder River GUNOH 2000 2,254

Middle River MIDOH Historical 838

Back River BACOH * 0

Patapsco River PATMH Historical 298

Magothy River MAGMH Historical 545

Severn River SEVMH 1999 329

South River SOUMH Historical 459

Rhode River RHDMH Historical 48

West River WSTMH Historical 214

Upper Patuxent River PAXTF 1996 5

Western Branch (Patuxent River) WBRTF * 0

Middle Patuxent River PAXOH 2000 68

Lower Patuxent River PAXMH Historical 1,325

Upper Potomac River POTTF 1991 4,368

Anacostia River ANATF 1991 6

Piscataway Creek PISTF 1987 783

Mattawoman Creek MATTF 2000 276

Middle Potomac River POTOH 1998 3,721

Lower Potomac River POTMH Historical 10,173

Upper Rappahannock River RPPTF 2000 20

Middle Rappahannock River RPPOH * 0

Lower Rappahannock River RPPMH Historical 5,380

Corrotoman River CRRMH Historical 516

Piankatank River PIAMH Historical 3,256

Upper Mattaponi River MPNTF 1998 75

Lower Mattaponi River MPNOH * 0

Upper Pamunkey River PMKTF 1998 155

Lower Pamunkey River PMKOH * 0

Middle York River YRKMH Historical 176

Lower York River YRKPH Historical 2,272

Mobjack Bay MOBPH Historical 15,096

continued
▼122

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Segment Name Segment Single Best Year Acres 

Upper James River JMSTF Historical 1,600

Appomattox River APPTF Historical 319

Middle James River JMSOH 1998 7

Chickahominy River CHKOH 2000 348

Lower James River JMSMH Historical 531

Mouth of the James River JMSPH Historical 604

Western Branch Elizabeth River WBEMH * 0

Southern Branch Elizabeth River SBEMH * 0

Eastern Branch Elizabeth River EBEMH * 0

Lafayette River LAFMH * 0

Mouth to mid-Elizabeth River ELIPH * 0

Lynnhaven River LYNPH 1986 69

Northeast River NORTF Historical 88

C&D Canal C&DOH 1978 0

Bohemia River BOHOH 2000 97

Elk River ELKOH 2000 1,648

Sassafras River SASOH 2000 764

Upper Chester River CHSTF * 0

Middle Chester River CHSOH Historical 63

Lower Chester River CHSMH Historical 2,724

Eastern Bay EASMH Historical 6,108

Upper Choptank River CHOTF * 0

Middle Choptank River CHOOH Historical 63

Lower Choptank River CHOMH2 Historical 1,499

Mouth of the Choptank River CHOMH1 Historical 8,044

Little Choptank River LCHMH Historical 3,950

Honga River HNGMH Historical 7,686

Fishing Bay FSBMH Historical 193

Upper Nanticoke River NANTF * 0

Middle Nanticoke River NANOH Historical 3

Lower Nanticoke River NANMH Historical 3

Wicomico River WICMH Historical 3

Manokin River MANMH Historical 4,359

Big Annemessex River BIGMH Historical 2,014

Upper Pocomoke River POCTF * 0

Middle Pocomoke River POCOH * 0

Lower Pocomoke River POCMH Historical 4,092

Tangier Sound TANMH Historical 37,965

Total acres 184,889

*No underwater grasses recorded for any year within the available 1930s–2000 data record.

Table IV-14. Chesapeake Bay underwater bay grass restoration goals by

Chesapeake Bay Program segment (cont.).
SHALLOW-WATER HABITAT AREA TO SUPPORT RESTORATION

GOAL-BASED BOUNDARIES

As described previously, the restoration of underwater bay grasses within a segment

requires that shallow-water habitat meet the Chesapeake Bay water clarity criteria

over a greater acreage than the underwater bay grasses will actually cover. The ratio

of underwater bay grass acreage to the required shallow-water habitat acreage varies

based on the different species of underwater bay grasses that inhabit the Bay’s four

salinity regimes. Shallow-water habitat acreage ratios have been derived scientifically through evaluation of extensive underwater bay grasses distribution data within

tidal fresh, low, medium and high salinity regimes (reflecting different levels of

coverage by different underwater bay grass communities).

The Chesapeake Bay Program segment-specific restoration goal acreage and

corresponding shallow-water designated use acreage (to the previously determined

maximum depth of abundant and persistent underwater plant growth) listed in 

Table IV-15 were summed by major salinity regime–tidal fresh (0-0.5 ppt), oligohaline (> 0.5-5 ppt), mesohaline (> 5ppt-18 ppt) and polyhaline (>18 ppt).13 The

underwater bay grasses acreage to shallow-water habitat acreage ratios were then

expressed as a percentage of the total shallow-water designated use habitat.

Compared with a baywide value of 38 percent, the tidal-fresh (37 percent), mesohaline (39 percent) and polyhaline (41 percent) values were all very close to the

baywide value as well as the other salinity regime-specific values (Table IV-16).

These values are consistent with findings published in the scientific literature and the

35 to 48 percent range derived from evaluation of the 1930s through early 1970s

historical data record by Naylor (2002) and Moore (1999, 2001). Influenced by the

natural presence of the estuarine turbidity maximum, the value was 21 percent in

oligohaline habitats.

CONFIRMING THAT THE REFINED DESIGNATED USES

MEET EXISTING USES

The EPA Water Quality Standards regulations at 40 CFR 131.10(g) and (j) specify

that states may remove a designated use that is not an existing use, or establish

subcategories of a use, if they can demonstrate that attaining the designated use is

not feasible. The current regulation at 40 CFR Part 131 identifies the factors that

must be considered in making such a demonstration. As the regulation explains,

existing uses, by definition, are attainable and must be protected by designated uses

in water quality standards (40 CFR 131.10[g], 131.10[h][1] and 131.10[i]). Any

▼123

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

13Note that all Chesapeake Bay Program segments have been assigned to one of the four salinity regimes

based on an evaluation of almost two decades of salinity data. The segment-naming convention documents each individual segment’s long-term averaged respective salinty regime: TF = tidal fresh, OH =

oligohaline, MH = mesohaline, and PH = polyhaline.
▼124

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals. Shallow- Percent Shallow- Existing Use Water Acreage Water Designated 2001 Acreage to Maximum Use Habitat Shallow- Underwater (1978–2000 Restoration Depth of Covered by Water Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth Northern Chesapeake Bay CB1TF 7979 7773 12,908 20,907 61.7 2 Upper Chesapeake Bay CB2OH 203 640 302 2405 12.5 0.5 Upper Central Chesapeake Bay CB3MH 1 1,296 943 2,011 46.9 0.5 Middle Central Chesapeake Bay CB4MH 112 176 2,511 10,630 23.6 2 Lower Central Chesapeake Bay CB5MH 4,487 4,240 14,961 29,959 49.9 2 Western Lower Chesapeake Bay CB6PH 715 1,208 980 3,939 24.9 1 Eastern Lower Chesapeake Bay CB7PH 9,168 10,729 14,620 33,304 43.9 2 Mouth of the Chesapeake Bay CB8PH 8 11 6 381 1.5 0.5 Bush River BSHOH 3 187 158 1,136 13.9 0.5 Gunpowder River GUNOH * 2,281 2,254 7,358 30.6 2 Middle River MIDOH * 698 838 2,479 33.8 2 Back River BACOH * 0 0 850 0.0 0.5 Patapsco River PATMH * 114 298 1,802 16.6 1 Magothy River MAGMH * 427 545 1,378 39.6 1 Severn River SEVMH 120 433 329 1347 24.4 1 South River SOUMH 27 50 459 1,432 32.1 1 Rhode River RHDMH * 14 48 267 18.0 0.5 West River WSTMH * 106 214 542 39.5 0.5 Upper Patuxent River PAXTF 205 44 5 24 22.2 0.5 Western Branch (Patuxent River) WBRTF * 0 0 0 0.0 0.5

Middle Patuxent River PAXOH 104 80 68 1,072 6.3 0.5Lower Patuxent River PAXMH 22 108 1,325 5121 25.9 1Upper Potomac River POTTF 1,964 4,465 4,368 17,501 25.0 2Anacostia River ANATF 4 11 6 85 6.6 0.5

continued
▼125

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use DepthPiscataway Creek PISTF * 783 783 914 85.7 2Mattawoman Creek MATTF * 311 276 695 39.7 1Middle Potomac River POTOH 3,070 3,766 3,721 15,193 24.5 2Lower Potomac River POTMH 1739 2130 10173 26075 39.0 1Upper Rappahannock River RPPTF 66 30 20 2175 0.9 0.5Middle Rappahannock River RPPOH * 0 0 1226 0 0.5Lower Rappahannock River RPPMH 478 841 5,380 19,793 27.2 1Corrotoman River CRRMH 389 419 516 1,819 28.4 1Piankatank River PIAMH 539 1,003 3,256 8,014 40.6 2Upper Mattaponi River MPNTF * 84 75 800 9.4 0.5Lower Mattaponi River MPNOH * 0 0 358 0.0 0.5Upper Pamunkey River PMKTF 140 184 155 1,860 8.4 0.5Lower Pamunkey River PMKOH * 0 0 420 0.0 0.5Middle York River YRKMH * 0 176 4,728 3.7 0.5Lower York River YRKPH 801 815 2272 4,949 45.9 1Mobjack Bay MOBPH 9,508 10,653 15096 33990 44.4 2Upper James River JMSTF 95 76 1,600 8,249 19.4 0.5Appomattox River APPTF * 0 319 1,085 29.4 0.5Middle James River JMSOH 15 8 7 3179 0.2 0.5Chickahominy River CHKOH 268 422 348 3283 10.6 0.5Lower James River JMSMH 2 3 531 9,618 5.5 0.5Mouth of the James River JMSPH 232 231 604 1,616 37.4 1Western Branch Elizabeth River WBEMH * 0 0 0 0.0 *Southern Branch Elizabeth River SBEMH * 0 0 0 0.0 *

continued
▼126

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Eastern Branch Elizabeth River EBEMH * 0 0 0 0.0 * Lafayette River LAFMH * 0 0 0 0.0 * Mouthof the Elizabeth River ELIPH * 0 0 0 0.0 * Lynnhaven River LYNPH 43 105 69 2476 2.8 0.5 Northeast River NORTF * 19 88 456 19.3 0.5 C&D Canal C&DOH 7 5 0 99 0.2 0.5 Bohemia River BOHOH 354 330 97 735 13.2 0.5 Elk River ELKOH 2034 2006 1,648 5,024 32.8 2 Sassafras River SASOH 1,169 1,116 764 2614 29.2 1 Upper Chester River CHSTF * 0 0 574 0 0.5 Middle Chester River CHSOH * 0 63 926 6.8 0.5 Lower Chester River CHSMH 205 2,369 2,724 6,980 39 1 Eastern Bay EASMH 2,886 4,610 6,108 20,805 29.4 2 Upper Choptank River CHOTF * 0 0 0 0.0 * Middle Choptank River CHOOH * 0 63 591 10.7 0.5 Lower Choptank River CHOMH2 148 193 1,499 3,770 39.8 1 Mouth of the Choptank River CHOMH1 5,257 6,445 8,044 20,857 38.6 2 Little Choptank River LCHMH 2,377 1,454 3,950 12,367 31.9 2 Honga River HNGMH 4,945 4,656 7,686 16,456 46.7 2

Fishing Bay FSBMH 6 59 193 2,467 7.8 0.5Upper Nanticoke River NANTF * 0 0 0 0.0 *Middle Nanticoke River NANOH * 0 3 1,141 0.3 0.5Lower Nanticoke River NANMH * 0 3 1583 0.2 0.5Wicomico River WICMH * 0 3 1,513 0.2 0.5Table IV-15. Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth

continued
▼127

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries Manokin River MANMH 404 420 4,359 10,700 40.7 2 Big Annemessex River BIGMH 721 546 2,014 5,065 39.8 2 Upper Pocomoke River POCTF * 0 0 0 0.0 * Middle Pocomoke River POCOH * 0 0 289 0.0 0.5 Lower Pocomoke River POCMH 1,528 1,831 4,092 9,936 41.2 1 Tangier Sound TANMH 13,310 17,688 37,965 68,578 55.4 2 Totals 77,854 100,701 184889 491,968

Table IV-15.

*No underwater bay grasses mapped or aerial photography collected due to 9/11/01 flight path restrictions. 

Summary of Chesapeake Bay underwater bay grass and shallow-water designated use acreage and goals (cont.).

Shallow- Percent ShallowExisting Use Water Acreage Water Designated

2001 Acreage to Maximum Use Habitat ShallowUnderwater (1978–2000 Restoration Depth of Covered by Water

Chesapeake Bay Program CBP Bay Grass Single Best Goal Persistent/Abundant Restoration Goal Designate 

Segment Name Segment Acreage Year) Acreage Plant Growth Acreage Use Depth
change in designated uses must show that the existing uses are still being protected.

As the EPA 1983 Water Quality Standards Handbook describes, an existing use can

be defined as fishing, swimming or other uses that have actually occurred since

November 28, 1975; or the water quality that is suitable to allow the use to be

attained—unless there are physical factors, such as substrate or flow, that prevent the

use from being attained (U.S. EPA 1983). Section 131.12(a)(1) in turn requires state

anti-degradation policies to protect existing water quality. This paragraph applies a

minimum level of protection to all waters. In setting the five subcategories of current

tidal-water designated uses, explicit steps were taken in developing the refined uses

and their boundaries to ensure that existing aquatic life uses would continue to be

protected.

MIGRATORY SPAWNING AND NURSERY EXISTING USE

The migratory fish spawning and nursery designated use will be protected by a set

of Chesapeake Bay-specific dissolved oxygen criteria that are more protective—

6 mg/l 7-day mean and 5 mg/l instantaneous minimum–than current state water

quality standards that apply to these same habitats from February 1 through May 31

(U.S. EPA 2003). Existing uses within the migratory fish spawning and nursery

habitats will continue to be protected.

SHALLOW-WATER EXISTING USE

In delineating the shallow-water use, the single best year of underwater bay grass

distribution mapped since the 1930s was used to define a shallow-water designated

use depth, underwater bay grass restoration goal and a corresponding shallow-water

habitat acreage to support achievement of the restoration goal for each respective

Chesapeake Bay Program segment. Most of the segment-specific restoration goal

acreage is higher than the established existing use underwater bay grass acreage

derived from the single best year of the 1978-2001 data record out to the maximum

depth of abundant/persistent underwater plant growth (see Table IV-15). In those

cases where the existing use acreage is higher than the restoration goal, the existing

use acreage will drive the shallow-water designated use boundary. As most of the

▼128

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries

Table IV-16. Percent of shallow-water designated use habitat covered by single

best year underwater bay grass acreage by salinity regime.

Tidal-Fresh Oligohaline Mesohaline Polyhaline 

Median 37.2 20.5 39.2 41.3

Minimum 0 0 0.2 1.5

Maximum 85.7 33.8 54.3 45.9

No. of Segments 14 20 29 7 
single best years were based on historical underwater bay grass distributions (1930s

through the early 1970s), the shallow-water bay grass uses existing since 1975 will

continue to be protected.

OPEN-WATER EXISTING USE

The application of the open-water fish and shellfish designated use dissolved oxygen

criteria will provide an equal level of protection to the same tidal waters as current

state water quality standards. The combined set of 5 mg/l 30-day mean, 4 mg/l 7-day

mean, and 3 mg/l instantaneous minimum have been documented to protect all life

stages of open-water habitat species in the Chesapeake Bay and its tidal waters (U.S.

EPA 2003). Existing uses within the open-water habitats will continue to be protected.

DEEP-WATER AND DEEP-CHANNEL EXISTING USES

The application of the deep-water seasonal fish and shellfish designated use and the

deep-channel seasonal refuge designated use and their respective oxygen criteria will

result in improvements to existing water quality conditions that currently do not

attain the applicable criteria (see Chapter V). Given that trends in dissolved oxygen

conditions have been generally degrading since the early 1970s (see Chapter III;

Hagy 2002), improvements to these conditions will ensure that existing uses within

the deep-water and deep-channel habitats will continue to be protected. 

LITERATURE CITED

Alldredge, A. L., T. J. Cowles, S. MacIntyre, J. E.B. Rines, P. L. Donaghay, C. F. Greenlaw,

D. V. Holliday, M. M. Dekshenieks, J. M. Sullivan, J. Ronald, V. Zaneveld. 2002. “Occurrence and mechanisms of formation of a dramatic thin layer of marine snow in a shallow

Pacific fjord.” Mar. Ecol. Prog. Ser. In Press.

Austin, H.M., A.D. Estes and D.M. Seaver. 2000. Estimation of juvenile striped bass: relative abundance in the Virginia portion of Chesapeake Bay. Annual Report 1999. Virginia

Institute of Marine Science, Gloucester Point, Virginia.

Batiuk, R.A., P. Bergstrom, M. Kemp, E. Koch, L. Murray, J.C. Stevenson, R. Bartleson, V.

Carter, N.B. Rybicki, J.M. Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K.A.

Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay submerged aquatic vegetation

water quality and habitat-based requirements and restoration targets: a second technical

synthesis. CBP/TRS 245/00 EPA 903-R-00-014. USEPA Chesapeake Bay Program,

Annapolis, Maryland.

Batiuk, R.A., R. Orth, K. Moore, J.C. Stevenson, W. Dennison, L. Staver, V. Carter, N.

Rybicki, R. Hickman, S. Kollar and S. Bieber. 1992. Submerged aquatic vegetation habitat

requirements and restoration targets: a technical synthesis. CBP/TRS 83/92. U.S. EPA

Chesapeake Bay Program, Annapolis, Maryland.

Boreman, J. and R. Klauda. 1988. Distribution of early life stages of striped bass in the

Hudson River Estuary, 1974-1979. American Fisheries Society Monographs 4:53-58.

▼129

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Carpenter, S.R. and Titus, J.E. 1984. Composition and spatial heterogeneity of submersed

vegetation in a softwater lake in Wisconsin. Vegetatio 57:153-165.

Chao, Shenn-Yu and T. Paluszkiewicz. 1991. The hydraulics of density currents over estuarine sills. Journal of Geophysical Research, 96 no. C4, 7065-7076.

Chesapeake Bay Living Resources Task Force. 1987. Habitat requirements for Chesapeake

Bay living resources: a report from the Chesapeake Bay Living Resources Task Force. Chesapeake Bay Program, Annapolis, Maryland.

Chesapeake Bay Program. 1999. Analytical Segmentation for the 1997 Reevaluation and

Beyond. Report from the Chesapeake Bay Program Monitoring Subcommittee’s Data

Analysis Workgroup. Annapolis, Maryland.

Chesapeake Bay Watershed Partners. 2001. Memorandum of understanding among the state

of Delaware, the District of Columbia, the State of Maryland, the State of New York, the

Commonwealth of Virginia, the State of West Virginia and the U.S. Environmental Protection Agency regarding cooperative efforts for the protection of the Chesapeake Bay and its

rivers. Chesapeake Bay Program, Annapolis, Maryland.

Chesapeake Executive Council. 1987. 1987 Chesapeake Bay Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

Chesapeake Executive Council. 2000. Chesapeake 2000 Agreement. Chesapeake Bay

Program, Annapolis, Maryland.

Cooper, S.R. and G.S. Brush. 1991. Long-term history of Chesapeake Bay anoxia. Science

254:992-996.

Craig, J.K., L.B. Crowder, C.D. Gray, C.J. McDaniel, T.A. Henwood and J.G. Hanifen. 2001.

Ecological effects of hypoxia on fish, sea turtles and marine mammals in the Northwestern

Gulf of Mexico. Pp. 269-292. In: Coastal Hypoxia: Consequences for Living Resources and

Ecosystems, N.N. Rabalais and R.E. Turner, eds. Coastal and Estuarine Studies.

Dennison, W.C., R.J. Orth, K.A. Moore, J.C. Stevenson, V. Carter, S. Kollar, P.W. Bergstrom

and R.A. Batiuk. 1993. Assessing water quality with submersed aquatic vegetation. Habitat

requirements as barometers of Chesapeake Bay health. Bioscience 43:86-94.

Dey, W.P. 1981. Mortality and growth of young-of-the-year striped bass in the Hudson River

Estuary. Transactions of the American Fisheries Society. 110:151-157.

Eby, L.A. 2001. Response of a fish community to frequent and infrequent disturbances in an

estuarine ecosystem. Ph.D. dissertation. Duke University.

Fisher, T.R., A.B. Gustafson, H.L. Berndt, L. Walstad, L.W. Haas, and S. MacIntyre, “The

upper mixed layer of Chesapeake Bay, USA.” Submitted to Estuaries, 2003.

Funderburk, S.L., J.A. Mihursky, S.J. Jordan and D. Riley (eds.). 1991. Habitat requirements

for Chesapeake Bay living resources: second edition. Chesapeake Research Consortium,

Solomons, Maryland.

Hagy, J.D. 2002. Eutrophication, hypoxia and trophic transfer efficiency in Chesapeake Bay.

Ph.D. dissertation, University of Maryland, College Park, Maryland.

Howell, P. and D. Simpson. 1994. Abundance of marine resources in relation to dissolved

oxygen in Long Island Sound. Estuaries 17:394-408.

▼130

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Jordan, S.J., C. Stenger, M. Olson, R. Batiuk and K. Mountford. 1992. Chesapeake Bay

dissolved oxygen goal for restoration of living resource habitats: A Synthesis of Living

Resource Requirements with Guidelines for Their Use in Evaluating Model Results and

Monitoring Information. CPB/TRS 88/93. Chesapeake Bay Program Office, Annapolis,

Maryland. 

Keister, J.E., E.D. Houde and D.L. Breitburg. 2000. Effects of bottom-layer hypoxia on abundances and depth distributions of organisms in Patuxent River, Chesapeake Bay. Marine

Ecology Progress Series 205:43-59.

Kuenen, M.M. and A.O. Debrot. 1995. A quantitative study of the seagrass and algal

meadows of the Spaanse Water, Curacao, the Netherlands, Antilles. Aquatic Botany 51 291-

310.

Koch, E.W. 2001. Beyond light: physical, geological, and geochemical parameters as

possible submersed aquatic vegetation habitat requirements. Estuaries 24:1-17.

Lehmann, A.E., E. Castella and J.B. Lacharanne. 1997. Morphological traits and spatial

heterogeneity of aquatic plants along sediment and depth gradients, Lake Geneva, Switzerland. Aquatic Botany (55) 281-299.

MacGregor, J. and E.D. Houde. 1996. Onshore-offshore pattern and variability in distribution

and abundance of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay. Marine

Ecology Progress Series 138:15-25.

Malone, T.C., W.M. Kemp, H.W. Ducklow, W.R. Boynton, J.H. Tuttle and R.B. Jonas. 1986.

Lateral variation in the production and fate of phytoplankton in a partially stratified estuary.

Marine Ecology Progress Series 32:149-160.

Manning, J. H. 1957. The Maryland Soft Shell Clam Industry and its Effects on Tidewater

Resources: an Interim Report to the Maryland General Assembly. Maryland Department of

Research and Education Resource Study Report No. 11. Chesapeake Biological Laboratory,

Solomons, MD. 25 pages.

Mansueti, R.J. and E.H. Hollis, 1963. Striped bass in Maryland tidewater. Natural Resources

Institute, University of Maryland Education Series Number 61. 28 pages.

Miller, T.J., J. Stone and E.A. Sadler. 1997. Chapter 2, Gill Net Surveys, pp. 34-63. In:

Assessment of fish community structure near Site 104, T.J. Miller. (ed.) UMCES CBL 97-

123. Report to the Maryland Environmental Service, Annapolis, Maryland

Moore, K., D. Wilcox, R. Orth and E. Bailey. 1999. Analysis of historical distribution of

submerged aquatic vegetation (SAV) in the James River. Special Report No. 355 in Applied

Marine Science and Ocean Engineering. Virginia Institute of Marine Science, School of

Marine Science, College of William and Mary, Gloucester Point, Virginia.

Moore, K., D. Wilcox and B. Anderson. 2001. Analysis of historical distribution of

submerged aquatic vegetation (SAV) in the York and Rappahannock rivers as evidence of

historical water quality conditions. Special Report No. 375 in Applied Marine Science and

Ocean Engineering. Virginia Institute of Marine Science, School of Marine Science, College

of William and Mary, Gloucester Point, Virginia.

Naylor, M.D. 2002. Historic distribution of submerged aquatic vegetation (SAV) in Chesapeake Bay, Maryland. Maryland Department of Natural Resources, Annapolis, Maryland.

▼131

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
Olney, John E. Personal Communication. December 17, 2002, Department of Fisheries

Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester

Point, Virginia.

Orth, R.J., D.J. Wilcox, L.S. Nagey, J.R. Whiting and J.R. Fishman. 2000. Distribution and

abundance of submerged aquatic vegetation in the Chesapeake Bay and coastal bays–1999.

VIMS Special Scientific Report Number 141. Final Report to the U.S. Environmental Protection Agency, Chesapeake Bay Program, Annapolis, Maryland.

Pothoven, S.A., S.B. Brandt, J.M. Jech and J.L. Horne. 1997. Chapter 3, Fish Abundance,

Size and Species Composition: Kent Island Site 104, pp. 78-125. In: Assessment of Fish

Community Structure Near Site 104. T J. Miller (ed.). UMCES CBL 97-123. Report to the

Maryland Environmental Service, Annapolis, Maryland.

Rickhus, W. and F. Stroup. 1987. Source document: characterization of the biology of and

fishery of Maryland stocks of yellow perch. Maryland Department of Natural Resources

Tidewater Administration, Annapolis, Maryland. Contract No. F40-85-008.

Rilling, G.C. and E.D. Houde. 1999. Regional and temporal variability in distribution and

abundance of bay anchovy (Anchova mitchilli) eggs and larvae in the Chesapeake Bay. Estuaries 22(4):1096-1109.

Rulifson, R.A. 1994. Status of anadromous Alosa along the east coast of North America.

Anadromous Alosa Symposium, Tidewater Chapter, American Fisheries Society.

Secor, D.H., E. Niklitschek, J.T. Stevenson, T.E. Gunderson, S. Minkkinen, B. Florence, M.

Mangold, J. Skjeveland and A. Henderson-Arzapalo. 2000. Dispersal and growth of yearling

Atlantic sturgeon Acipenser oxyinchus released into the Chesapeake Bay. Fisheries Bulletin

98(4):800-810.

Setlzer-Hamilton, E.M., W.R. Boynton, J.A. Mihursky, T.T. Polgar and K.V. Wood. 1981.

Spatial and temporal distribution of striped bass eggs, larvae and juveniles in the Potomac

Estuary. Transactions of the American Fisheries Society 110:121-136.

Setlzer-Hamilton, E.M. and L. Hall, Jr. 1991. Striped bass. In: Habitat requirements for

Chesapeake Bay living resources: second edition. Funderburk, S.L., J.A. Mihursky, S.J.

Jordan and D. Riley (eds.). Chesapeake Research Consortium, Solomons, Maryland.

Smith, D.E., M. Leffler and G. MacKiernan. 1992. Oxygen dynamics in the Chesapeake Bay:

a synthesis of recent research. Maryland and Virginia Sea Grant Programs. College Park,

Maryland.

Tresselt, E.F. 1952. Spawning grounds of the striped bass, Roccus saxatilis, in Virginia.

Bulletin of the Bingham Oceanographic Collection. 14(1): 98-110.

Tsai, C. and G. Gibson. 1971. Fecundity of the yellow perch Perca flavescens (Mitchil), in

the Patuxent River, Maryland. Chesapeake Science 12:270-284.

Tuttle, J.H., R.B. Jonas and T.C. Malone. 1987. Origin, development, and significance of

Chesapeake Bay anoxia. In: Contaminant Problems and Management of Living Chesapeake

Bay Resources S.K. Majumdar, L.W. Hall, Jr. and K.M. Austin (eds.). Pennsylvania Academy

of Science, Philadelphia, Pennsylvania, pp. 442-472.

U.S. Environmental Protection Agency. 2003. Ambient Water Quality Criteria for Dissolved

Oxygen, Water Clarity, and Chlorophyll a for Chesapeake Bay and its Tidal Tributaries. 

EPA 903-R-03-002. U.S. EPA, Region 3.

▼132

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
U.S. Environmental Protection Agency. 1983. Water Quality Standards Handbook. U.S. EPA,

Office of Water, Office of Science and Technology, Washington, D.C. 

Welsh, S.A., J.E. Skjeveland, M..F. Mangold and S.M. Eylver. 2000. Distribution of wild and

hatchery-reared Atlantic sturgeon in the Chesapeake Bay, Maryland. Biology, Management,

and Protection of Sturgeon Symposium, Electric Power Research Institute, Palo Alto,

California.

Zimmerman, A.R. and E.A. Canuel. 2000. A geochemical record of eutrophication and

anoxia in Chesapeake Bay sediments: Anthropogenic influence on organic matter composition. Marine Chemistry 69:117-137.

▼133

chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
In developing revised water quality criteria, designated uses and boundaries for those

uses in the Chesapeake Bay and its tidal tributaries, the Chesapeake Bay Program

used tiered scenarios of pollution controls to model water quality responses to

varying levels of technology-based implementation. Although these scenarios do not

represent actual management strategies that will be employed by states in achieving

water quality standards (states are likely to find more cost-effective mixes of controls

for achieving target reductions), the Chesapeake Bay Program partners sought to

provide the public with information on the potential costs and effects associated with

these different levels of effort. 

This chapter summarizes three economic analyses that the Chesapeake Bay Program

has performed—estimated costs, screening-level and economic impacts and benefits—which are documented in Economic Analyses Associated with the Identification

of Chesapeake Bay Designated Uses and Attainability (U.S. EPA 2003). In particular,

Part I of the Economic Analyses provides estimates of the total annual cost of

achieving the three levels of controls (the Tier 1 through 3 scenarios presented in

Chapter V) based on the costs of best management practices (BMPs) to remove

nitrogen and phosphorus loads to the Chesapeake Bay. This cost information includes

total capital cost requirements, and to the extent that information could be compiled,

estimates of how these costs may be shared between the public and private sectors. 

It is important to note, however, that the Chesapeake Bay Program partners did not

use these economic analyses to show why the current designated uses to protect

aquatic life in the Chesapeake Bay tidal waters are not attainable (Chapter III); to

define the refined designated uses and boundaries presented in Chapter IV; or to

assess attainability of the refined designated uses (Chapter V). Rather, the analyses

are intended to provide information to assist the jurisdictions during their tributary

strategy and water quality standards development processes. 

▼163

chapter vi • Summary and Economic Analyses

chaptervi

Summary and

Economic Analyses
ESTIMATED COSTS

The Chesapeake Bay Program estimated the costs of implementing three levels of

controls captured in the Tier 1 through 3 scenarios. These are just three scenarios in

what could be an infinite number of combinations of reduction actions. The Chesapeake Bay Program developed them by layering available reduction technologies

and not by combining the most cost-effective mix of controls. Therefore, the costs

may represent a near-worst case estimate of what will actually be incurred to meet

the dissolved oxygen criteria. Not only are the types and combinations of nutrient

reduction measures artificial, but when nutrient reduction costs will be incurred or

how these reduction measures will be funded also is unknown. The Chesapeake Bay

Program did not estimate costs for the E3 scenario because the reduction measures

in this scenario are not physically plausible in all cases. 

Implementation of sediment-related BMPs likely to be necessary to meet the water

clarity criteria for underwater bay grass protection were not included in the tier

scenarios, and thus their costs are not estimated, beyond what is inherently removed

through nutrient reduction measures. Costs to meet the chlorophyll a criteria also are

not included beyond those actions included in the tiers because these were published

as narrative criteria, which provide no single value around which to determine reduction requirements or costs. In the process of setting the new nutrient and sediment

cap load allocations, the Chesapeake Bay Program partners determined that, for the

most part, reduction actions to meet the dissolved oxygen criteria defined by the tiers

will be sufficient to meet anticipated region-specific numerical chlorophyll a criteria,

except in certain local situations that will require individual state evaluations. 

The tier scenarios include controls on publicly-owned treatment works, industrial

facilities, forestry, agriculture, municipal storm water and onsite waste management

systems sources of nitrogen and phosphorus to the Chesapeake Bay. Costs for

publicly-owned treatment works and industrial sources (more than 330 combined

sources) were based on facility-provided estimates and engineering calculations

based on methods developed by the Chesapeake Bay Program’s Nutrient Removal

Technology Task Force and documented in Nutrient Reduction Technology Cost

Estimations for Point Sources in the Chesapeake Bay Watershed (Chesapeake Bay

Program 2003). The Nutrient Removal Technology Task Force generally accepted

estimates provided by facilities ‘as is’ during the development of point source costs.

Some documentation of the cost estimates, particularly for the largest facilities, is

provided in the appendix to the report. Further review and refinement of these costs

is left to states should they pursue additional economic analyses associated with

revised adoption of water quality standards for the Chesapeake Bay tidal waters. 

Costs for urban, agriculture, forestry and onsite system BMPs are based on the units

(e.g., acres) of BMP implementation in each tier scenario and BMP-specific estimates of capital and operation and maintenance costs. The Chesapeake Bay Program

performed an extensive literature search to estimate such costs. To estimate the costs

▼164

chapter vi • Summary and Economic Analyses
▼165

chapter vi • Summary and Economic Analyses

for the onsite system denitrification BMP, the Chesapeake Bay Program collected

data from manufacturers of such technology. The Chesapeake Bay Program gave

preference to well-documented sources and studies in or near the Chesapeake Bay

watershed and typically used a simple average of the estimated costs from

appropriate sources.

Aside from controls specified in Tier 1 for the District of Columbia, the tier

scenarios do not include controls on combined sewer overflows (CSOs) and sanitary

sewer overflows (SSOs) because these sources are regulated separately, and costs are

associated with the protection of human health parameters such as fecal coliform

reduction. However, the Chesapeake Bay Program partners recognize that Bay

watershed municipalities required to implement CSO and SSO measures will bear

the burden of the additional cost, and such information will be relevant to the jurisdictions in assessing the total costs that certain cities may incur. Furthermore, it is

recognized that there must be priority funding decisions to accommodate CSO/SSO

and nutrient removal technology improvements at the federal, state and local levels

of government. The appendices to the separately published Economic Analyses

document (U.S. EPA 2003) include additional information on potential CSO and

SSO costs.

Table VI-1 summarizes the total capital and annual operating and maintenance costs

associated with the tier scenarios. The estimates for each tier are cumulative costs

beyond what has already been expended up to the year 2000 (including already

funded publically-owned treatment works upgrades). The estimates include costs to

businesses and households as well as federal and state governments that provide

funding for nutrient controls through cost-share programs, with existing cost-share

programs alone possibly accounting for almost one-third of annual costs. Total

capital costs represent total initial expenditures to achieve the level of control or

degree of BMP implementation specified for each scenario. However, these costs

will not be incurred in any single year but will be spread across many years though

gradual implementation and financing. Similarly, total annual costs represent those

Table VI-1. Estimated cumulative costs and pollutant loading reductions.

Total Nitrogen/Total

Phosphorus Reduction

from Levels in 2000 Total Capital Costs Total Annual Costs

Scenario (millions of pounds per year)1 (in millions of 2001 dollars)2 (in millions of 2001 dollars)3

Tier 1 23.9 $1,442 $198 

Tier 2 63.5 $3,644 $555 

Tier 3 104.0 $7,975 $1,138 

1. Loadings based on Phase 4.3 of the Chesapeake Bay Program’s Watershed Model.

2. Costs include those paid by private-sector businesses and households in addition to those paid by public entities

that provide cost-share funding for nutrient reduction controls and BMPs.

3. Total annual costs include amortized capital costs plus operating and maintenance costs. 
at full implementation of the scenarios. Therefore, actual annual costs in the years

prior to meeting the full implementation goals are expected to be lower.

A number of limitations and uncertainties are associated with the estimated costs.

These considerations are described in detail in the separately published Economic

Analyses document (U.S. EPA 2003). In addition, as noted above, the tier scenarios

are not likely representative of any actual tributary strategy that states will adopt, nor

do they represent the most cost-effective mix of controls possible. 

SCREENING-LEVEL IMPACT ANALYSIS

One of the factors that states may consider in evaluating use attainability is whether

controls more stringent than those required by sections 30l(b)( l)(A) and (B) and 306

of the Clean Water Act would result in substantial and widespread economic and

social impacts. The EPA’s Interim Economic Guidelines for Water Quality Standards

Workbook (U.S. EPA 1995) provides detailed worksheets and guidance for evaluating whether meeting water quality standards would result in such impacts. Before

embarking on the analysis of widespread impacts, the Chesapeake Bay Program did

not implement this guidance for the tier scenarios because of the tremendous amount

of data and resources required to do so. However, the Chesapeake Bay Program’s

UAA Workgroup performed a screening analysis to rule out areas that would not

experience such negative effects. The screening analysis is based on the cost of each

tier, although the tier scenarios likely do not represent the actual control strategies

that will be employed by states, and the Chesapeake Bay Program’s estimated costs

of these scenarios are not precise values. 

The Chesapeake Bay Program partners decided not to draw conclusions regarding

affordability based on the screening analysis for several reasons. First, the analyses

are screening-level, and do not represent the type required to support a claim of

substantial and widespread economic and social impacts.14 Second, the tier scenarios

do not necessarily reflect a cost-effective mix of controls, which would be necessary

to support a claim of substantial and widespread economic and social impacts.

Finally, as discussed above, the estimated costs do not accurately reflect when costs

will be incurred, or how such reduction measures will be funded. On a regional, state

or large watershed scale, economic impacts can be mitigated by cost-share, loans and

new federal or state funding programs. Therefore, the screening analyses may not

indicate the actual potential for impacts. Analysis of the socioeconomic impacts

associated with meeting water quality standards is best performed during the process

of establishing tributary strategies, with more accurate information on actual reduction measures and costs within the respective jurisdictions. 

▼166

chapter vi • Summary and Economic Analyses

14The Economic Analyses Associated with the Identification of Chesapeake Bay Designated Uses and

Attainability (U.S. EPA 2003) provides information for jurisdictions on the types of information and

economic analyses they would need to conduct and submit as part of a UAA.
▼167

chapter vi • Summary and Economic Analyses

The screening analysis does provide some comparative information at the county

level throughout the Chesapeake Bay watershed. This analysis consists of 12 countylevel variables or ratios designed to indicate whether either substantial or widespread

economic and social impacts would be likely (Table VI-2). For some sectors, the

ratios indicate when the estimated control costs are small relative to household

incomes and, therefore, substantial impacts are unlikely. For other sectors, the ratios

indicate whether the sector is small relative to the local economy and, therefore,

widespread impacts are unlikely. Because these screening variables cannot indicate

when substantial and widespread impacts would occur, the report also directs states

regarding the types of information and economic analyses that they would need to

conduct and submit to support such a claim. 

The screening analysis provides information, in addition to the modeling results

described previously (see “Estimated Costs,” above), related to evaluating whether the

tier scenarios would result in substantial and widespread impacts. Although the

Table VI-2. Screening-level impact analysis variables. 

Impact Condition 

Sector Substantial (Financial) Widespread 

POTWs Current household sewer rate plus average None

new household cost/median household income 

Industrial None Percent of county earnings from 

industrial sectors containing affected

facilities/total county earnings 

Agriculture • Average BMP costs/net cash return; Percent of county earnings from 

• Crop plus portion of hay BMP costs/ agriculture, agriculture services,

crop plus hay sales; food and kindred products, and 

• Livestock plus portion of hay BMP costs/ tobacco sectors/total county

livestock sales; and earnings

• Average BMP costs/median household income. 

Forestry None Percent of county earning from 

forestry and logging/total county 

earnings 

Urban Average BMP costs/median household income None 

POTWs and urban Total sewer costs (current plus new) plus average None

urban BMP cost/median household income 

Onsite Treatment Average BMP costs/median household income Percent of households affected in 

Systems county 
Chesapeake Bay Program partners did not use this information to delineate boundaries

for the designated refined uses, this information may be useful for states as they

conduct their own UAAs. The information may also be valuable for determining where

additional funding, possibly in the form of government cost-shares or loans, would be

most useful, or in determining the most appropriate level of funding assistance.

ECONOMIC IMPACTS AND BENEFITS

As stated previously, when evaluating use attainability, states may consider whether

controls more stringent than those required by sections 30l(b)(l)(A) and (B) and 306

of the Clean Water Act would result in substantial and widespread economic and

social impacts. The EPA’s National Center for Environmental Economics (NCEE)

offers economic models that can estimate changes in the value of regional output or

goods produced, employment and wages and income, providing information on the

widespread socio-economic effects of pollution controls. Estimating potential

economic benefits also is integral to understanding the economic impacts of

improving water quality in the Chesapeake Bay and its tidal tributaries. 

Using economic models allows the evaluation of baseline conditions in the future as

well as the direct and indirect effects of expenditures on pollution controls. Although

the tier scenarios likely do not represent the actual control strategies that will be

employed by states, and the Chesapeake Bay Program’s estimated costs of these

scenarios are not precise values, the Chesapeake Bay Program wanted to provide

states with this type of information (such as baseline forecasts and direct and indirect impacts). To provide this information, the NCEE used a regional forecasting

model developed by Regional Economic Modeling, Inc. (REMI), and an economic

impact model (IMPLAN) from the Minnesota IMPLAN Group. The NCEE used

IMPLAN to estimate the socio-economic changes resulting from the estimated

expenditures; the REMI model provides a baseline forecast (for one state) over the

next decades without tier scenario implementation. 

The IMPLAN model indicates that the Tier 3 scenario would result in a net increase

in output, employment, and value-added in the six Chesapeake Bay watershed states

and the District of Columbia. In addition, the REMI model forecasts that gross

regional product in the State of Maryland will grow by 37 percent by 2010, corresponding to 19 percent growth in employment and 17 percent growth in real

disposable personal income. This estimated growth is not accounted for in the

IMPLAN results (which are based on current economic conditions). The economic

stimulus from Tier 3 results from increased spending in high-wage industries (e.g.,

wastewater treatment technologies) as well as an influx of funds for pollution

controls (e.g., federal cost shares for agricultural BMPs); additional market benefits

likely to result from improved water quality (e.g., commercial and recreational

fishing industries) are not included. Therefore, the regional economy should expand

as a result of the tier scenarios.

▼168

chapter vi • Summary and Economic Analyses
Some members of the Chesapeake Bay Program’s UAA Workgroup raised the issue

of other potential social impacts stemming from limits on wastewater treatment

plants, as a result of water quality standards eventually imposed by the jurisdictions.

Their concern is that nutrient allocation caps on wastewater treatment plants will

promote urban sprawl. Most Chesapeake Bay Program partners contend that urban

sprawl is occurring now regardless of the nutrient reduction measures that may ultimately be required, that it will not necessarily be affected by POTW caps and that not

all jurisdictions will be imposing such caps. They further contend that current policies

and growth trends, left unchecked (i.e., the baseline scenario), would result in greater

environmental impacts than the tier scenarios. However, deliberations on this issue

may be valuable on a watershed basis as sprawl is also an interstate issue. The Chesapeake Bay Program partners’ concerns and deliberations to date also are provided in

the separately published Economic Analyses document referenced above.

Numerous goods and services are associated with the Chesapeake Bay’s ecological

resources. Changes in water quality will lead to changes in ecological resources, and

corresponding values of related goods and services. Time and resource constraints

limited the ability of the Chesapeake Bay Program’s UAA Workgroup to conduct

original research and estimate comprehensive benefit values. However, the

Economic Analyses document (U.S. EPA 2003) provides a brief summary of the

benefits provided by estuaries such as the Chesapeake Bay and existing studies

related to the value of these services.

The Chesapeake Bay Program expects that changes in water quality will affect many

different aspects of the Bay’s ecology (e.g., underwater bay grasses, fish and shellfish populations, water clarity and aesthetics), all of which affect how the

Chesapeake Bay community, and society in general, will use and value the Chesapeake Bay. For example, ecological benefits will be derived from the increased size

of fish, shellfish and aquatic plant populations and the increased stability (i.e.,

reduced variability) of these populations, and how humans value these improvements. Commercial fishery yields should improve, generating greater potential for

economic returns, and secondary benefits accrue as support industries (e.g., sales and

repair of harvest equipment, fuel) and value-added industry sectors (e.g., processing

and retail facilities) expand in response to increased catch. Both market and

nonmarket benefits should accrue from enhanced recreational opportunities,

including hunting, fishing, boating, ecotourism and photography. For example, the

increased value of recreational angling and support industries (e.g., gear, bait, charter

boats) may be significant, and increased numbers of anglers will generate increased

sales of fuel, lodging, and dining as the quality and number of fishing trips and

opportunities increase. 

Although no comprehensive estimate of the benefits from nutrient and sediment

reduction actions in the Chesapeake Bay watershed is available, data suggest that the

Chesapeake Bay affects industries that generate approximately $20 billion and

340,000 jobs (including commercial fishing, boat building and repair and tourism).

Tourism, as a composite industry, represents the 14th largest source of output, and

▼169

chapter vi • Summary and Economic Analyses
the 8th largest source of employment, in the Chesapeake Bay watershed. It is not

clear the extent to which each of these sectors relies on Chesapeake Bay water

quality; however, participation rates and expenditures on recreational fishing suggest

that a significant percentage of tourism output is likely linked to the quality of water

bodies such as the Chesapeake Bay. For example, the U.S. Fish and Wildlife

Service’s 2001 National Survey of Fishing, Hunting and Wildlife-Associated Recreation reports annual expenditures by fishermen of $1,261 million, and 1,859,000

fishing participants, in the states of Maryland, Virginia and Delaware.

Available studies of benefits include Bockstael et al. (1989), which estimate the total

value of 20 percent improvement in nitrogen and phosphorous concentrations in the

Chesapeake Bay to be $17 million to $76 million in 1996 dollars. Similarly, Krupnick (1988) estimated the total value of a 40 percent improvement in nitrogen and

phosphorus concentrations at $43 million to $123 million (in 1996 dollars). 

LITERATURE CITED

Bockstael, N., K. McConnell and I. Strand. 1989. Measuring the benefits of improvements in

water quality: The Chesapeake Bay. Marine Resource Economics 6:1-18.

Chesapeake Bay Program. 2003. Nutrient Reduction Technology Cost Estimations for Point

Sources in the Chesapeake Bay Watershed. Chesapeake Bay Program Office, Annapolis,

Maryland.

Krupnick, A. 1988. Reducing bay nutrients: An economic perspective. Maryland Law Review

47(2):453-480.

U.S. Environmental Protection Agency. 2003. Economic Analyses Associated with the Identification of Chesapeake Bay Designated Uses and Attainability. Chesapeake Bay Program

Office, Annapolis, Maryland. 

U.S. EPA. 1995. Interim Economic Guidance for Water Quality Standards, Workbook. Office

of Water, Washington, D.C. 

▼170

chapter vi • Summary and Economic Analyses
Airshed. A geographical region that, due to topography, meteorology and climate,

shares the same air.

Anadromous. Fish that spend most of their lives in salt water but migrate into freshwater tributaries to spawn (such as shad and sturgeon).

Anoxia. A condition in which no oxygen is present. Much of the ‘anoxic zone’ is

anaerobic and contains no oxygen. In this condition toxic hydrogen sulfide gas is

emitted in the decomposition process.

Anthropogenic. Of human origin.

Bathymetry. The physical characteristics—including the depth, contour and

shape—of the bottom of a body of water.

Benthos. A group of organisms, often invertebrates, that live in or on the bottom in

aquatic habitats (such as clams that live in the sediments) and that are typically

immotile or have limited mobility or range.

Biomass. The quantity of living matter, expressed as a concentration or weight per

unit area.

Cap loads. The maximum pollutant load of nutrients and sediments that can be

allowed and still meet water quality criteria.

Chlorophyll a. A pigment contained in plants that converts light energy into food.

Chlorophyll a also gives plants their green color and is used to indicate the amount

of microscopic algae growing in a water body.

Designated use. An element of a water quality standard, expressed as a narrative

statement, describing an appropriate intended human or aquatic life objective for a

body of water. Designated uses for a water body may refer to recreation, shellfishing,

water supply and aquatic life habitat.

▼171

Glossary

Glossary
Dissolved oxygen. Microscopic bubbles of oxygen that are mixed in the water and

occur between water molecules. Dissolved oxygen is necessary for healthy lakes,

rivers, and estuaries. Most aquatic plants and animals need oxygen to survive. Fish

will drown in water when the dissolved oxygen levels become too low. The absence

of dissolved oxygen in water is a sign of possible pollution.

Epifaunal. Plants, animals and bacteria that are attached to the hard bottom or

substrate (for example, to rocks or debris); are capable of movement; or that live on

the sediment surface.

Epiphyte. Algae that grow on the surfaces of plants or other objects. The epiphyte

does not “eat” the plant on which it grows, but merely uses it for structural support

or as a means to enter the canopy environment. By encrusting leaf surfaces, they

reduce the light available to the plant leaves and lead to loss of underwater bay

grasses.

Estuarine species. A permanent resident of an estuary. Also called a resident

species.

Estuary. A semi-enclosed body of water, such as the Chesapeake Bay, that has a free

connection with the open sea and within which seawater from the ocean is diluted

measurably with freshwater derived from land drainage. Brackish estuarine waters

are decreasingly salty in the upstream direction, and vice versa. The ocean tides are

projected upstream to the fall lines.

Eutrophic. A condition of an aquatic system containing high nutrient concentrations, which fuels algal growth. When the algae die off and decompose, the amount

of dissolved oxygen in the water is reduced. 

Filter feeders. Organisms that filter food from the environment using a straining

mechanism, such as gills (e.g., barnacles, oysters and menhaden).

Hypoxia. A condition in which only very low levels of oxygen are present.

Light attenuation. The absorption, scattering or reflection of light by water, chlorophyll a, dissolved substances or particulate matter. Light attenuation reduces the

amount of light available to underwater bay grasses.

Mean Low Water. The average of all the low water heights observed over the

National Tidal Datum Epoch. 

Mesohaline. Pertaining to moderately brackish water with low to middle range

salinities (from 5 to 18 parts per thousand)

Mesotrophic. A condition of an aquatic system containing medium nutrient concentrations and, therefore, is between eutrophic (nutrient enriched) and oligotrophic

(nutrient poor) conditions.

Mg liter-1. Concentration unit milligrams per liter.

▼172

Glossary
▼173

Glossary

Mixed open. Herbaceous land that is not agricultural. 

Nitrogen saturated. A state in which the forest vegetation and soils have reached

their capacity to retain additional nitrogen. This state leads to greater leakage of

nitrogen to sub-surface or ground waters.

Nutrients. Compounds of nitrogen and phosphorus dissolved in water that are

essential to plants and animals. Too much nitrogen and phosphorus act as pollutants

and can lead to unwanted consequences—primarily algae blooms that cloud the

water and rob it of oxygen critical to most forms of aquatic life. Sewage treatment

plants, industries, vehicle exhaust, acid rain and runoff from agricultural, residential

and urban areas are sources of nutrients that enter the Bay.

Oligohaline. Pertaining to moderately brackish water with low range salinities (from

0.5 to 5 parts per thousand).

Percent-light-through-water. The amount of light reaching just above the canopy

of underwater bay grasses, expressed as a fraction of the light at the water surface.

Phosphorus. A key nutrient in the Bay’s ecosystem, phosphorus occurs in dissolved

organic and inorganic forms, often attached to particles of sediment. This nutrient is

a vital component in the process of converting sunlight into usable energy forms for

the production of food and fiber. It is also essential to cellular growth and reproduction for organisms such as phytoplankton and bacteria. Phosphates, the inorganic

form, are preferred, but organisms will use other forms of phosphorus when phosphates are unavailable.

Phytoplankton. Microscopic plants, such as algae, that are capable of making food

via photosynthesis. They float and cannot move independent of water currents. 

Polyhaline. Pertaining to waters with a higher range of salinities (18 to 30 parts per

thousand).

Ppt. Parts per thousand (used as a measurement of salinity).

Pycnocline. The portion of the water column where density changes rapidly because

of salinity and temperature. In an estuary the pycnocline is the zone separating deep,

more saline waters from the less saline, well-mixed surface layer waters.

Salinity. A measure of the salt concentration of water. Higher salinity means more

dissolved salts. Usually measured in parts per thousand (ppt).

Salinity regimes. A portion of an estuary distinguished by the amount of tidal influence and salinity of the water. The major salinity regimes are, from least saline to

most saline:

• Tidal fresh—Describes waters with salinity between 0 and 0.5 parts per thousand (ppt). These areas are at the extreme reach of tidal influence. 
• Oligohaline—Describes waters with salinity between 0.5 and 5 ppt. These

areas are typically in the upper portion of an estuary. 

• Mesohaline—Describes waters with salinity between 5 and 18 ppt. These areas

are typically in the middle portion of an estuary.

• Polyhaline—Describes waters with salinity between 18 and 30 ppt. These areas

are typically in the lower portion of an estuary, where the ocean and estuary

meet.

Saturation. The state of a compound or solution that is fully saturated. For example,

a condition in which water at a specific temperature contains all the dissolved

oxygen it can hold. Dissolved oxygen percent saturation is an important measurement of water quality. Cold water can hold more dissolved oxygen than warm water.

Also, high levels of bacteria from sewage pollution or large amounts of decomposing

plants can cause the percent saturation to decrease. This can cause large fluctuations

in dissolved oxygen levels throughout the day, which can affect the ability of plants

and animals to thrive.

Secchi depth. A measure of cloudiness or turbidity of surface water determined by

the depth at which the ‘Secchi disk,’ a flat black and white disk, cannot be seen any

more. It is the greatest depth to which light can penetrate underwater.

Seiching. Formation of standing waves in a water body due to wave formation and

subsequent reflections from the ends. These waves may be incited by earthquake

motions (similar to the motions caused by shaking a glass of water), impulsive winds

over the surface, or due to wave motions entering the basin. In the Chesapeake Bay,

sustained winds force bottom water onto the shallows through this physical process.

Sill. A submerged ridge at relatively shallow depth separating the basins of two

bodies of water.

Stratification. The formation, accumulation or deposition of materials in layers,

such as layers of fresh water overlying higher salinity water (salt water) in estuaries.

Submerged Aquatic Vegetation (SAV). Rooted vegetation that grows under water

in shallow zones where light penetrates. Also known as ‘underwater bay grasses.’

Subpycnocline. Bottom mixed layer waters located below the pycnocline layer (see

definition for ‘pycnocline’).

Surficial. Of, relating to, or occurring on or near the surface of the sediment bottom.

Thermocline. A specific depth where the water temperature changes dramatically.

Warmer surface water is separated from the cooler deep water. This temperature

gradient results in the formation of a density barrier.

Total Suspended Solids (TSS). Solids in water that can be trapped by a filter

(usually with a pore size greater than 0.45 micrometer). TSS can include a wide

▼174

Glossary
▼175

Glossary

variety of material, such as silt, decaying plant and animal matter, industrial wastes

and sewage. High concentrations of suspended solids can cause many problems for

Chesapeake Bay health and aquatic life. For example, high TSS can block light from

reaching underwater bay grasses, increase surface water temperature, because the

suspended particles absorb heat from sunlight, and affect the ability of fish to see and

catch food.

Trophic level. Layer in the food chain in which one group of organisms serves as

the source of nutrition of another group of animals.

Turbidity. The decreased clarity in a body of water due to the suspension of silt or

sedimentary material.

Underwater bay grass. Submerged vascular plants often referenced in the scientific

literature as submerged aquatic vegetation or SAV, not to be confused with emergent

wetland plants.

Water clarity. Measurement of how far you can see through the water. The greater

the water clarity, the further you can see through the water.

Water column. The open-water environment, as distinct from the bed or shore,

which may be inhabited by swimming marine, estuarine or freshwater organisms. 

Water-column light requirement. The amount of light just above the leaf surface

(estimated as the fraction of the light at the water surface) that is necessary for the

survival and growth of underwater bay grasses.

Water quality criteria. Numeric or narrative description of a water quality parameter that represent a quality of water that supports a particular designated use.

Adopted by states, along with designated uses, into water quality standards.

Water quality standards. A provision of State or Federal law consisting of a designated use or uses for a water body and a narrative or quantifiable criterion protective

of the use(s) describing the desired conditions of the subject waters or water body to

which they apply.

Watershed. A region bounded at the periphery by physical barriers that cause water

to part and ultimately drain to a particular body of water.

Young-of-the-year. All of the fish of a species younger than one year of age. Usually

scientists assign an arbitrary ‘birth date’ to all fish of a species hatched over a two or

three month period in one year. The fish are then assigned to Age 1 status on that

birth date. By convention, this is usually January 1.

Zooplankton. A community of floating, often microscopic animals that inhabit

aquatic environments. Unlike phytoplankton, zooplankton cannot produce their own

food, and so are consumers. 
BMP best management practice

CAA Clean Air Act

CFD cumulative frequency

distribution

CSO combined sewer overflow

CWA Clean Water Act

E3 everything, everywhere 

by everybody

EPA U.S. Environmental

Protection Agency

ESD environmental site design

km2 kilometers squared

lbs pounds

LID low impact development

m meter

MGD million gallons per day

mg/l milligrams per liter

mmBtu million British thermal unit

Nox nitrogen oxides

NRT nutrient reduction technology

POTW publically-owned treatment

works

SAV submerged aquatic vegetation

SED sediment

SIP state implementation plan

SO2 sulfur dioxide

TN total nitrogen

TP total phosphorus

TSS total suspended solid

μg/l micrograms per liter

▼177

Acronyms

Acronyms

Listed in this appendix are the assumptions and methods employed in determining

four best management BMP (including point source technologies) implementation

levels for the three tiers and ‘everything, everywhere, by everybody’ (E3) scenarios.

The scenarios were developed by the Chesapeake Bay Program’s Nutrient Subcommittee Workgroups to provide reference points for load reductions of nutrients and

sediment that could be associated with increasing levels of BMP implementation for

both point and nonpoint sources in the Chesapeake Bay watershed. The Use Attainability Analysis (UAA) workgroup was provided with examples of the types of

BMPs and implementation levels to develop a defensible costing tool. These four

scenarios range from Tier 1, which represents the current level of implementation

throughout the watershed plus regulatory requirements implemented through the

year 2010, up to a limit of technology scenario referred to as the E3 scenario. Tier 2

and Tier 3 represent intermediate levels of implementation between Tier 1 and the

E3 scenario. Each tier has associated with it a given nitrogen, phosphorus and sediment load reduction effected by the different technologies assigned to the tier. The

nutrient and sediment sources were divided into the following categories for tier

development:

• point sources;

• nonpoint source agriculture;

• nonpoint source urban;

• nonpoint source forests;

• onsite treatment systems; and

• atmospheric deposition.

The Chesapeake Bay Program partners have acknowledged that the E3 scenario goes

beyond what is physically possible in some cases, and that the feasibility of implementing certain reduction measures at Tier 3 are also questionable. These tiers are a

broad brush estimate of technological reduction measures that could be implemented

▼A1

appendix A • Development of the Level-of-Effort Scenarios

appendixA

Development of the 

Level-of-Effort Scenarios
at the bay watershed level without regard to physical limitations. Certainly, there will

be local circumstances and conditions that make implementation of these tiers as

defined unreasonable. It will be up to the individual jurisdictions to tailor reduction

programs that fit their specific capabilities and needs. The series of ranging scenarios

were simulated using the Chesapeake Bay Program’s Phase 4.3 Watershed Model,

and the resultant loads for nitrogen, phosphorus, and sediment were used as inputs

to the Chesapeake Bay Water Quality Model. Evaluation of dissolved oxygen, water

clarity and chlorophyll a concentrations from the Water Quality Model, in turn,

provided a sense of the response of key water quality parameters to the various

loading levels. For the tiered and the E3 scenario scenarios, the BMP implementation levels, the resultant modeled loads, and the measured responses in tidal water

quality are all informational. They are not intended to prescribe control measures the

jurisdictions must implement to meet Chesapeake 2000 nutrient and sediment cap

load allocations. 

All above and below fall line nitrogen, phosphorus, and sediment loads are included

in the loadings for each tier. Shoreline erosion control sediment reductions at 2000

progress levels are assumed for all tiers.

The costs for specific management practices developed by the UAA Workgroup

could be used by Chesapeake Bay basin jurisdictions for their individual UAAs. The

Water Quality Steering Committee of the Chesapeake Bay Program believed it

would be useful to provide data to the jurisdictions to promote coordination and

consistency across all jurisdictions. It is a jurisdiction’s prerogative to use the basinwide cost analyses in developing its individual UAA.

Implementation levels in all of the tiers and the E3 scenario are not the most cost

effective. More cost-effective combinations of BMPs will be evaluated by jurisdictions and their tributary strategy watershed teams as their strategies are developed.

In addition, levels of BMP implementation for the E3 scenario are theoretical since,

generally, the scenario does not account for physical limitations or participation

levels in its design.

The tier and the E3 scenario BMP implementation levels were mostly deliberated

and set by the ‘source’ workgroups of the Chesapeake Bay Program’s Nutrient

Subcommittee. These workgroups are made up of representatives of Chesapeake

Bay watershed jurisdictions and Chesapeake Bay Program Office personnel. The

specific workgroups that decided BMP implementation levels include the Agricultural Nutrient Reduction Workgroup, the Forestry Workgroup, the Point Source

Workgroup, and the Urban Storm Water Workgroup. The Tributary Strategy Workgroup and Nutrient Subcommittee finalized the E3 scenario definitions after review

and further deliberation.

To conform to Chesapeake 2000 goals, all of the scenarios were based on 2010

projections of landuses, animals, point source flows, and septic systems as well as

2007/2010 or 2020 air emission controls. Landuses and animal populations in the

▼A2

appendix A • Development of the Level-of-Effort Scenarios
▼A3

appendix A • Development of the Level-of-Effort Scenarios

Chesapeake Bay Program Watershed Model are developed from an array of national,

regional, and state databases as described in Chesapeake Bay Watershed Model Land

Use and Model Linkages to the Airshed and Estuarine Models (Chesapeake Bay

Program, 2000). The modeled landuses include the following categories:

• forest;

• conventional-tilled (high-till);

• conservation-tilled (low-till);

• hay;

• pasture;

• manure acres (model accounting of runoff from animal feeding operations);

• pervious urban;

• impervious urban; and

• mixed open.

The 2010 agricultural landuses were projected from 1982, 1987, 1992, and 1997

Agricultural Census information by county according to methods chosen by individual states. Projected animal populations, to estimate manure applications, were

based on county Agricultural Census trends and information from state environmental and agricultural agencies.

Implementation of Low Impact Development (LID) or Environmental Site Design

(ESD) in the tiered scenarios was used to reflect urban pollutant load reductions that

go above and beyond conventional storm water management practices. The tiered

scenarios reflect an ongoing shift from conventional storm water management to the

more innovative LID/ESD practices that address both storm water quantity (replicating pre-development hydrology) and quality (reducing pollutant loads). The

LID/ESD approach encourages practices that promote groundwater recharge, stream

channel protection, flood protection, and improved water quality. The pollutant

removal efficiencies for LID/ESD were developed by the Urban Storm Water Workgroup, based on national and watershed studies and expert professional judgement.

The workgroup evaluated pollutant removal efficiencies for over 50 best management practices from sources such as the American Society of Civil Engineers Best

Management Practices national database, the Center for Watershed Protection’s

National Pollutant Removal Performance Database for Stormwater Treatment Practices, the 2000 Maryland Stormwater Design Manual, the Virginia Stormwater

Handbook, and Prince George’s County’s Low Impact Development Design Strategies manual. Maintenance costs of ESD/LID approaches were based on data

primarily from Maryland (which promotes ESD) and Prince George’s County

(which promotes LID). There are several jurisdictions that are actively promoting

ESD (Maryland state storm water regulations) and LID (Prince George’s County,

District of Columbia, various municipalities in Virginia).
The 2010 urban landuses were mostly projected from methods involving human

population changes as determined by the U.S. Census Bureau for 1990 and 2000,

and by individual state agencies for 2010. The population changes were related to

1990 high-resolution satellite imagery of the Chesapeake Bay watershed, which is

the primary source of urban and forest acreages. In the case of Maryland, urban

growth from 2000 to 2010 was determined by Maryland Department of Natural

Resources and the Maryland Department of Planning.

For all jurisdictions except Maryland and Virginia, 2010 forest and mixed open

landuses were determined by proportioning the net change between 2010 and 1990

agricultural and urban land to 1990 mixed open and 1990 forest. Maryland and

Virginia forest acreage changes followed methodologies or data submitted by these

states.

Each agricultural BMP in the tier scenarios is associated with research that identifies

the expected level of nutrient reduction. In many cases this could be viewed as the

best reduction one can expect from a BMP given optimal growing conditions and

expected annual maintenance. However, the yield reserve BMP is slightly different.

This BMP is not based solely on hydrologic conditions, but includes the known

response of a particular crop to nutrient availability. There is an additional amount or

cushion within universally recommended nutrient application rates to insure optimal

yield under ideal growing conditions. Real world observations have shown that

optimal growing conditions occur infrequently, and ‘average’ hydrologic conditions

may result in substantially less than optimal yield. By combining this management

practice with an insurance plan to protect against yield loss in suboptimal growth

years, potential nitrogen leaching and phosphorus runoff are reduced while providing

plant nutrient requirements seven or eight years out of every ten. The insurance

program protects producers in those two to three years of yield loss. Since this is the

reduction of a direct input based on plant response curves and not an estimate of

nutrient reduction efficiency, the potential benefits from a yield reserve program can

be fully modeled. Since yield is a function of rainfall and nutrient availability, the

benefits of this type of program can be seen best in years with less than average rainfall when yields drop, yet spring application rates were high.

Estimates of the number of septic systems in the watershed in 2010 were derived

from human population projections and people per septic system ratios from the

1990 U.S. Census Bureau survey.

Point sources were divided into categories which include 1) significant municipal

wastewater treatment facilities—generally discharging flows greater than or equal to

0.5 million gallon per day, 2) significant industrial facilities—discharging nutrient

loads of greater than or equivalent to municipal facilities with flows greater than or

equal to 0.5 million gallon per day, and 3) non-significant municipal wastewater

treatment facilities—discharging flows less than 0.5 million gallon per day, and

limited to facilities in Maryland and Virginia due to availability of data.

▼A4

appendix A • Development of the Level-of-Effort Scenarios
▼A5

appendix A • Development of the Level-of-Effort Scenarios

Point source nitrogen and phosphorus loads from significant and non-significant

municipal wastewater treatment facilities were determined using flows projected for

the year 2010 for POTWs located in all jurisdictions of the Chesapeake Bay Watershed. These future flows were developed either from population projections or

information obtained directly from the municipal facility operators. The tier and E3

scenario flows for industrial dischargers remained at 2000 levels because industrial

flows are not necessarily subject to growth due to population.

Technologies in municipal facilities varied among the tiers depending on the nutrient

concentrations to be achieved under each tier description. The technologies include

extended aeration processes and denitrification zones, chemical additions, additional

clarification tanks, deep bed denitrification filters, and micro-filtration. For industrial

dischargers, site-specific information on reductions by facility was obtained via

phone contacts or site visits.

Estimation of atmospheric deposition to the Chesapeake Bay watershed for all tier

and E3 scenarios employed deposition data from the Regional Acid Deposition

Model (RADM) which also provides deposition estimates representing current

conditions used for 2000 Progress model runs. All of the air scenarios involve

nitrogen oxide emissions reductions made by roughly 37 states (the deposition

modeling domain). Air scenarios in Tiers 1 and 2 describe existing Clean Air Act

regulations that have passed; the Tier 3 and E3 air scenarios describe additional

voluntary control measures.

Table A-1 provides a brief overview of the reduction measures in the tiers organized

by nutrient source. Table A-2 shows the implementation levels of the BMPs in the

tier scenarios in terms of landuse acres, or their appropriate unit of measurement

(Figures A-1 through A-3). The text that follows provides a more detailed overview

of the reduction measures per source, organized by tier scenario.

In the listing of BMP levels in Table A-2, there are cases where implementation

levels may be lower in a higher tier, or may be lower for the 2010 scenarios, when

compared to 2000 Progress. It is important to note that landuses change from 2000

to 2010 and that these changes were based on trends specified by individual jurisdictions with concurrence from the Chesapeake Bay Program Nutrient Subcommittee’s

Tributary Strategy Workgroup. Also, landuses change through the 2010 tiers and the

E3 scenario depending on degrees of BMP implementation (i.e., riparian buffers,

wetland restoration, land retirement, carbon sequestration for agricultural land). In

other words, as landuses change, less land may be available to apply BMPs in a

higher level-of-effort scenario. Overall however, nutrient and sediment reductions

will increase through the tiers to the E3 scenario as the combined impact of nonpoint

source BMPs increases. Note that riparian buffer information is presented both in

terms of acres and 1-side stream miles. 
▼A6

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario.

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Buffers—

pasture to forest

Continue current

level of

implementation

using average rate

of 1997–2000.

Note: Includes

fencing

Increase level of

implementation up

to a total of 20% of

the remaining

stream reaches in

pasture. Note:

Includes fencing

Increase level of

implementation up

to a total of 30% of

the remaining

stream reaches in

pasture. Note:

Includes fencing

Both sides of all

stream reaches

within pasture

receive 100 foot

forest buffers and

fencing.

CROPLAND CONVERSIONS TO FOREST HAYLAND

Buffers—

cropland to forest

Continue current

level of

implementation

using average rate

of 1997-2000.

Increase level of

implementation up

to a total of 20% of

the remaining

stream reaches in

cropland.

Increase level of

implementation up

to a total of 30% of

the remaining

stream reaches in

cropland.

Both sides of all

stream reaches

within cropland

receive forest

buffers.

Buffers—

cropland to grass

Continue current

level of

implementation

using average rate

of 1997-2000.

25% of remaining

stream reaches

within cropland.

50% of remaining

stream reaches

within cropland.

Buffers—

hayland to forest

Continue current

level of

implementation

using average rate

of 1997-2000.

25% of remaining

stream reaches

within hayland over

Tier 1.

50% of remaining

stream reaches

within hayland over

Tier 1.

Both sides of all

stream reaches

within hayland

receive forest

buffers.

Wetland Reserve

(cropland to forest)

Continue current

level of

implementation

using average rate

of 1997-2000.

Increase level of

implementation up

to a total of 33% of

the remaining goal.

Increase level of

implementation up

to a total of 66% of

the remaining goal.

Wetland Reserve

equals 25,000 acres

in signatory 

states (based on

Chesapeake 2000

goal).

CRP/CREP

(cropland to 

mixed open)

Continue current

level of

implementation

using average rate

of 1997-2000.

CRP-CREPWetland Reservebuffers (combined)

comprise 10% of

cropland within

each county. 

CRP-CREPWetland Reservebuffers (combined)

comprise 15% of

cropland within

each county. 

CRP-CREPWetland Reserve

buffers (combined)

comprise 25% of

cropland within

each county.

continued
▼A7

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Conservation

Tillage

Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 30% of

remaining cropland

beyond Tier 1.

Applied to 60% of

remaining cropland

beyond Tier 1.

Conservation

tillage on 100% of

cropland.

AGRICULTURE NPS

Farm Plans Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 30% of

remaining

agricultural land

(crop, hay, pasture)

beyond Tier 1.

Applied to 70% of

remaining

agricultural land

(crop, hay, pasture)

beyond Tier 1.

Applied to 100% of

agricultural land

(crop, hay, pasture).

Cover Crops Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 40% of

remaining cropland

beyond Tier 1.

Applied to 75% of

remaining cropland

beyond Tier 1.

Applied to 100% of

cropland

Nutrient

Management

Planning

MD & DE: 100%

cropland and

hayland under

nutrient

management. Other

basin states:

Continue current

level of

implementation

using average rate

of 1997-2000.

MD & DE: 100%

cropland and

hayland under

nutrient

management. Other

basin states:

Applied to 30% of

remaining cropland

and hayland

beyond Tier 1.

MD & DE: 100%

cropland and

hayland under

nutrient

management. Other

basin states:

Applied to 30% of

remaining cropland

and hayland

beyond Tier 2.

Applied to 100% of

cropland and

hayland.

Carbon

Sequestration &

Bioenergy

Applied to 15% of

remaining the E3

scenario cropland

after land

conversion

programs applied.

Applied to 25% of

remaining cropland

after land

conversion

programs applied.

Yield Reserve Applied to 30% of

the cropland and

hayland under

nutrient management. Replaces

nutrient application

component of

nutrient

management plan.

Applied to 100% of

cropland and

hayland. Replaces

nutrient application

component of

nutrient

management plan.

continued
▼A8

appendix A • Development of the Level-of-Effort Scenarios

Excess Nutrients Assume alternative

use for excess

manure.

Assume alternative

use for excess

manure.

Assume alternative

use for excess

manure.

Assume alternative

use for excess

manure.

Agriculture Waste

Systems

Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 25% of

remaining confined

animal units

beyond Tier 1

(combines storage

system and

barnyard runoff

controls). 

Applied to 60% of

remaining confined

animal units

beyond Tier 1

(combines storage

system and

barnyard runoff

controls).

Applied to 100% of

confined animal

units (combines

storage system and

barnyard runoff

controls).

Stream Protection

without fencing

Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 10% of

remaining stream

reaches within

pasture land

beyond Tier 1. 

Applied to 25% of

remaining stream

reaches within

pasture land

beyond Tier 1. 

N/A (see buffersforest-pasture)

Stream Protection

with fencing

Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 15% of

remaining stream

reaches within

pasture land

beyond Tier 1. 

Applied to 75% of

remaining stream

reaches within

pasture land

beyond Tier 1. 

N/A (see buffersforest-pasture)

Grazing Land

Protection

Continue current

level of

implementation

using average rate

of 1997-2000.

Applied to 25% of

remaining pasture

land beyond Tier 1.

Applied to 50% of

remaining pasture

land beyond Tier 1.

Applied to 100% of

pasture land.

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

AGRICULTURE NPS (cont.)

Urban Land

Conversion (PA,

MD, VA and DC

only)

Full 2000-2010

urban land

conversion based

on 2010

population.

2000-2010 urban

conversion -

reduced 10% (acres

'returned' as 65%

forest, 20% mixed

open, 15%

agriculture).

2000-2010 urban

conversion -

reduced 20% (acres

'returned' as 65%

forest, 20% mixed

open, 15%

agriculture).

2000-2010 urban

conversion -

reduced 30% (acres

'returned' as 100%

forest).

URBAN NPS

continued
▼A9

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Storm water

management &

LID—New

Development

(2001-2010)

66% of new

development has

storm water

management.

(TN=35, TP=45,

TSS=80)

75% of new

development has

storm water management. 25% of

new development

employs environmental site design

and low-impact

development techniques. Efficiencies

represent a

75%/25% weighted

average reduction.

(TN=40, TP=55,

TSS=85)

50% of new

development has

storm water management. 50% of

new development

employs environmental site design

and low-impact

development techniques. Efficiencies

represent a

50%/50% weighted

average reduction.

(TN=45, TP=57,

TSS=87)

100% of new

development

employs

environmental site

design and lowimpact development techniques

(TN=50, TP=60,

TSS=90).

Stormwater

management—

Recent

Development

(1986-2000)

60% of recent

development has

storm water

management.

(TN=27,

TP=40,TSS=65)

60% of recent

development has

storm water

management.

(TN=27,

TP=40,TSS=65)

60% of recent

development has

storm water

management.

(TN=27,

TP=40,TSS=65)

Retrofits—Recent

(1986-2000) & Old

(pre 1986)

Development

0.8% of recent and

old (pre-1986)

development is

retrofitted (TN=20,

TP=30,TSS=65)

5% of recent and

old (pre-1986)

development is

retrofitted (TN=20,

TP=30,TSS=65)

20% of recent and

old (pre-1986)

development is

retrofitted (TN=20,

TP=30,TSS=65)

100% of recent and

old (pre-1986)

development is

retrofitted (TN=40,

TP=40, TSS=80).

Urban Nutrient

Management

Continue to

implement BMP at

average annual rate

through 2010,

using average of

1997-2000.

(TN=17%,

TP=22%)

40% of urban

pervious and mixed

open lands are

under nutrient

management.

(TN=17%,

TP=22%)

75% of urban

pervious and mixed

open lands are

under nutrient

management.

(TN=17%,

TP=22%)

No fertilizer is

applied to urban

pervious or mixed

open land.

Buffers—

Grass (existing)

All urban stream

reaches are assumed

to have either grass

or tree buffers.

Where urban

disturbance has

altered a stream

reach beyond

repair/restoration, it

is not included as a

potential buffer area.

Reduce grass

buffers by 10%

below Tier 1 level.

(conversion to

forest buffers)

Reduce grass

buffers by 30%

below Tier 1 level.

(conversion to

forest buffers)

continued
▼A10

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Buffers—

Grass to Forest

Increase forest

buffer acreage by

the same amount of

'reduced' grass

buffer acreage.

Increase forest

buffer acreage by

the same amount of

'reduced' grass

buffer acreage.

50-foot forest

buffer on both sides

of stream reaches

in urban pervious

areas. No credit

given on upstream

effects, land

conservation only.

Buffers—

Mixed Open 

to Forest

Continue current

level of implementation using

average rate of

1997-2000.

Increase forest

buffer acreage by

the same amount as

forest buffers on

urban pervious.

Increase forest

buffer acreage by

the same amount as

forest buffers on

urban pervious.

100-foot forest

buffer on mixed

open. No credit

given on upstream

effects, land

conservation only.

Existing Systems

(pre-2001)

Maintain current

concentration/load

per system. 

Maintain current

concentration/load

per system. 

1% of existing (per

year) treatment

systems will meet

an edge of drainage

field concentration

for nitrogen of 

10 mg/L TN per

system. (1%

represents failed

systems and

opportunities for

upgrades.) Remaining systems

maintain existing

concentrations/

loads.

100% of existing

treatment systems

will meet an edge

of drainage field

concentration of

nitrogen of 

10 mg/L TN 

per system.

URBAN NPS (cont.)

New Systems 

(post-2000)

Maintain current

concentration/load

per system.

10% of new

treatment systems

will meet an edge

of drainage field

concentration for

nitrogen of 10

mg/L TN per

system. Remaining

systems meet

existing concentration/load levels.

100% of new

treatment systems

will meet an edge

of drainage field

concentration for

nitrogen of 

10 mg/L TN 

per system. 

100% of new

treatment systems

will meet an edge

of drainage field

concentration of

nitrogen of 

10 mg/L TN 

per system.

ONSITE TREATMENT SYSTEMS

continued
▼A11

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Industrial

Wastewater

Treatment

(Significant

Facilities as 

of 2000) 

Maintain current

levels.

Generally a 50%

reduction from

Tier 1 (2000

concentrations) 

or permit

conditions if less.

Generally an 80%

reduction from

Tier 1 (2000

concentrations) 

or permit

conditions if less.

TN = 3.0; 

TP = 0.1 or 

permit conditions 

if less.

Municipal

Wastewater

Treatment (Nonsignificant

Facilities as of

2000) 

Maintain current

TN/TP

concentrations with

2010 flows.

Maintain current

TN/TP

concentrations with

2010 flows. 

Maintain current

TN/TP

concentrations with

2010 flows. 

Maintain 8.0 mg/L

nitrogen and 2.0

mg/L phosphorus

concentrations or

2000 concentrations if less with

2010 flows.

CSO Control (DC) 43% reduction in

CSOs.

43% reduction in

CSOs.

43% reduction in

CSOs.

Zero discharge

from DC CSOs.

Municipal

Wastewater

Treatment

(Significant

Facilities as of

2000) 

Existing NRT and

those planned to go

to NRT by 2010:

2010 flow at 8.0

mg/l TN and 2000

concentrations for

TP. For all

remaining facilities

without NRT existing or planned:

2000 TN & TP. For

certain VA facilities

in lower VA tributaries TP=1.5 mg/l

Reach and maintain

8.0 mg/l TN and

1.0 mg/l TP

concentrations at

2010 flows at all

facilities.

(Phosphorus

concentration is 1.0

mg/l or permit

limit, whichever is

lower).

Reach and maintain

5.0 mg/l TN and

0.5 mg/l TP

concentrations at

2010 flows at all

facilities.

(Phosphorus

concentration is 0.5

mg/l or permit

limit, whichever is

lower.)

Reach and maintain

3.0 mg/l TN and

0.10 mg/l TP

concentrations at

2010 flows at all

facilities.

(Phosphorus

concentration is 0.1

mg/l or permit

limit, whichever is

lower).

POINT SOURCES

continued
▼A12

appendix A • Development of the Level-of-Effort Scenarios

Table A-1. Description of the source reduction measures by tier scenario (cont.).

Nutrient

Reduction

Activity Tier 1 Tier 2 Tier 3 E3

Forest Harvest

BMPs

Forestry BMPs are

properly installed

on 80% of all

harvested lands.

Forestry BMPs are

properly installed

on 90% of all

harvested lands.

Forestry BMPs are

properly installed

on 100% of all

harvested lands

with no measurable

increase in nutrient

and sediment

discharge.

Forestry BMPs are

properly installed

on 100% of all

harvested lands

with no measurable

increase in nutrient

and sediment

discharge.

FOREST NPS

Air Controls (NOx

only)

2007/2010 Base

with NOx SIP.

2020 CAA with

Tier 2 and heavy

duty diesel

regulations.

2020 CAA with

aggressive utility

controls.

2020 CAA

aggressive utility

controls and

industry-point and

mobile controls.

AIR EMISSIONS
▼A13

appendix A

• Development of the Level-of-Effort Scenarios

Table A-2. 2000 Progress, 2010 tiers, and 2010 E3 scenario BMP implementation levels.

Unit of Applicable 2000 2010 2010 2010 2010

BMP Measure Landuse Progress Tier 1 Tier 2 Tier 3 ES

Conservation Tillage Acres Low Till 1,994,745 1,962,824 2,340,908 2,300,093 2,312,209Riparian Forest Buffers Acres Row Crop, Hay 9,054 30,588 133,772 206,663 494,450

Riparian Forest Buffers 1 side stream miles, Row Crop, Hay 747 2,524 11,036 17,050 40,792

100 foot width

Wetland Restoration Acres Row Crop, Hay 1,277 2,862 10,260 17,659 25,282Land Retirement Acres Row Crop, Hay 87,488 128,510 500,452 742,695 1,090,540Grass Buffers Acres Row Crop 4,294 15,036 71,985 113,800 0Tree Planting Acres Row Crop, Pasture 8,568 4,142 0 0 0Riparian Forest Buffers Acres Pasture 0 0 46,732 63,851 184,081Riparian Forest Buffers 1 side stream miles, Pasture 0 0 3,855 5,268 15,187

100 foot width

Carbon Sequestration/ Acres Row Crop 0 0 0 509,431 770,736

Bio EnergyStandard Nutrient Management Acres Row Crop, Hay 2,283,426 3,023,742 3,850,244 2,967,870 0Plan ImplementationYield Reserve Implementation Acres Row Crop, Hay 0 0 0 1,271,944 4,830,817

Total Nutrient Management Acres Row Crop, Hay 2,283,426 3,023,742 3,850,244 4,239,814 4,830,817

Plan ImplementationFarm Plans Acres Agriculture 3,666,165 5,075,549 5,860,003 6,854,953 7,202,280Cover Crops Acres Row Crop 220,134 152,766 1,544,635 2,203,196 2,312,209Stream Protection With Fencing Acres Pasture 40,744 69,257 171,739 580,365 712,302Stream Protection Without Fencing Acres Pasture 26,166 27,979 83,584 63,583 0Grazing Land Protection Acres Pasture 134,327 304,868 853,863 1,394,909 2,371,463Animal Waste Management Acres Manure Acres 4,886 6,425 6,953 7,692 8,537Animal Waste Management Animal Units Manure Acres 708,498 931,677 1,008,208 1,115,351 1,237,801Manure Excess Wet Tons As Excreted N/A 1,270,139 1,927,899 2,145,277 1,870,085 8,856,825

AGRICULTURAL BMPs

continued
▼A14

appendix A • Development of the Level-of-Effort Scenarios Table A-2. 2000 Progress, 2010 tiers, and 2010 E3 scenario BMP implementation levels (cont.). Unit of Applicable 2000 2010 2010 2010 2010 BMP Measure Landuse Progress Tier 1 Tier 2 Tier 3 ES Abandoned Mine Reclamation Acres Urban/Exposed 6,062 0 0 0 0 Urban Growth Reduction Acres Urban 38,787 0 26,096 52,192 78,288 Riparian Forest Buffers Acres Pervious Urban 0 364 9,808 28,522 93,643 Riparian Forest Buffers 1 side stream miles, Pervious Urban 0 60 1,618 4,706 15,451 50 foot width Grass Buffers Acres Pervious Urban 0 95,022 84,997 65,702 0 Storm Water Management Acres Urban 0 153,157 207,705 183,440 159,560 on New Development

SWM on Recent Development Acres Urban 165,040 374,357 373,817 373,236 0SWM on Recent and Acres Urban 0 29,959 187,185 748,488 3,740,806Old DevelopmentTotal Storm Water Management Acres Urban 165,040 557,474 768,707 1,305,164 3,900,366Erosion and Sediment Control Acres Urban 25,911 0 0 0 0Urban Nutrient Management Acres Pervious Urban 6,608 28,630 1,055,077 1,964,784 2,601,733Tree Planting Acres Mixed Open 22,596 44,280 0 0 0Riparian Forest Buffers Acres Mixed Open 0 0 54,702 73,757 413,922

Riparian Forest Buffers 1 side stream miles, Mixed Open 0 0 4,513 6,085 34,149

100 ft. width

Mixed Open Nutrient Acres Mixed Open 0 60,791 1,997,497 3,870,252 4,950,621

Management

URBAN AND MIXED OPEN BMPs

continued
▼A15

appendix A

• Development of the Level-of-Effort Scenarios

Table A-2. 2000 Progress, 2010 tiers, and 2010 E3 scenario BMP implementation levels (cont.).

Unit of Applicable 2000 2010 2010 2010 2010

BMP Measure Landuse Progress Tier 1 Tier 2 Tier 3 ES

FORESTRY BMPs

Forest Harvesting Practices Acres Forest 67,448 0 0 0 0Septic BMPsSeptic Connections Systems Septic 31,514 31,514 31,514 31,514 31,514Septic Pumping Systems Septic 2,954 N/A N/A N/A N/ASeptic Denitrification Systems Septic 312 312 N/A N/A N/ADenitrification/Pumping on Systems Septic N/A N/A 8,305 93,014 1,357,026New & Existing Systems

SEPTIC BMPs
2010 TIER 1 SCENARIO

2010 Tier 1 BMP implementation levels were generally determined by continuing

current levels-of-effort and cost-share in the Chesapeake Bay watershed. In addition,

expected regulatory measures, jurisdictional programs, and construction schedules

between 2000 and 2010 were included.

2010 TIER 1 SCENARIO NONPOINT SOURCE BMPs

For most nonpoint source BMPs, implementation rates between 1997 and 2000 were

continued to the year 2010 with limits that levels could not exceed the available or

the E3 scenario land area to which BMPs levels could be applied. The scale of the

calculations was a county segment, or the intersection of a county political boundary

and a model hydrologic segment. This is the same scale on which most jurisdictions

report BMP implementation levels to the Chesapeake Bay Program Office.

Every effort was made to include BMPs submitted by the jurisdictions for progress

model runs into Tier 1. Since historic BMP data were not available from New York,

Delaware, and West Virginia, 2010 Tier 1 projections were determined from watershedwide implementation rates in the states which employ and track the practice.

2010 Tier 1 BMPs were extrapolated from recent implementation rates by the

landuse types submitted by the states for each BMP. For example, if a jurisdiction

submits data for nutrient management on crop, 2010 Tier 1 crop was projected and

then split among high-till, low-till, and hay according to relative percentages. If a

jurisdiction submits data as nutrient management on high-till, low-till, and hay individually, projections were done for each of these landuse categories.

The 2010 Tier 1 scenario does not include tree planting on tilled land, forest conservation, and forest harvesting practices as these BMPs are not part of the tier and E3

scenarios. For forest harvesting practices and erosion and sediment control, the

model simulation does not account for additional loads from disturbed forest and

construction areas, respectively. For forest conservation, planting above what is

removed during development is accounted for in the 2010 urban and forest projections. Tree planting on agricultural land was included in Tier 1 for pasture as forest

buffers since this BMP is also part of the tier and E3 scenarios and pasture tree

planting and pasture buffers are treated the same in the model.

2010 TIER 1 SCENARIO AGRICULTURAL BMPs

• Tier 1 Conservation tillage

–Continue 1997–2000 implementation rates of conservation-tillage.

–Low-till acres cannot be below 2000 levels or greater than 75 percent of the

available cropland by county-segment.

–Landuse conversion of high-till to low-till.

▼A16

appendix A • Development of the Level-of-Effort Scenarios
• Tier 1 Riparian forest buffers on agriculture

–Continue 1997–2000 implementation rates of riparian forest buffers on cropland

and hay to the year 2010.

–Continue 1997–2000 implementation rates of tree planting on pasture to the year

2010.

–Tier 1 implementation levels cannot exceed the available or E3 scenario land

area to which BMPs could be applied.

–The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles

(each side) associated with crop, hay, and pasture.

–Landuse conversion of crop, hay, and pasture to forest.

–For every acre of crop and hay converted, two upland acres of crop and hay

receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).

–There is no upland benefit associated with forest buffers on pasture.

• Tier 1 Wetland restoration

–Continue 1997–2000 implementation rates of wetland restoration on cropland

and hay to the year 2010.

–Landuse conversion of crop and hay to forest.

• Tier 1 Agricultural land retirement

–Continue 1997–2000 implementation rates of cropland and hay retirement to the

year 2010.

–The sum of the acreage in Tier 1 riparian forest buffers, wetland restoration, and

land retirement cannot exceed 25 percent of the total crop and hay in a countysegment.

–Landuse conversions of crop and hay to mixed open.

• Tier 1 Riparian grass buffers on cropland

–Continue 1997–2000 implementation rates of riparian grass buffers on cropland

to the year 2010 with limits that levels cannot exceed the available or the E3

scenario land area to apply the BMPs to.

–The E3 scenario levels are revised following the same methodologies but

account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each

side) associated with agricultural land.

–Landuse conversions of crop to mixed open.

–For every acre of cropland converted, two upland acres of crop receive a reduction of 43 percent (TN), 53 percent (TP), and 53 percent (SED).

▼A17

appendix A • Development of the Level-of-Effort Scenarios
• Tier 1 Nutrient Management Plan Implementation

–Continue 1997–2000 rates of nutrient management plan implementation on crop

and hay to the year 2010 in all jurisdictions except MD and DE where all crop

and hay acres are fully implementing nutrient management plans.

–Nutrient management plan implementation levels cannot exceed the available

land area to apply the BMPs to.

–Under nutrient management plans, crop and hay acres do not receive more than

130 percent of their TN and TP need.

• Tier 1 Manure excess

–Excess nutrients resulting from the differences between manure generated and

conforming to nutrient management rules and losses in agricultural land are

reported.

–It is assumed that all of the excess manure has alternative uses that do not affect

loads to the Chesapeake Bay tidal waters.

• Tier 1 Animal waste management/runoff control

–Continue 1997–2000 implementation rates of animal waste management on

‘manure acres’ to the year 2010 with limits that levels cannot exceed the available area to apply the BMPs to.

–Manure acres are the model’s accounting of runoff from animal feeding operations based on the number of animal units.

–The BMP combines storage systems and barnyard runoff controls and reduction

factors of 75 percent (TN and TP) are applied to protected manure acres.

• Tier 1 Farm Plans (non-nutrient management)

–Continue 1997–2000 rates of Farm Plan implementation on agricultural land

(crop, hay, and pasture) to the year 2010 with limits that levels cannot exceed the

available land area to apply the BMPs to.

–Nutrient and sediment reduction factors for Farm Plans on high-till are 10

percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors

are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for

Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).

• Tier 1 Cover crops

–Since cover crop acreage varies annually or is not cumulative, cover crop implementation is determined as the average of 1997–2000 implementation acreage

(or years in that period where data exists from the jurisdictions) with limits that

levels cannot exceed the available land area to apply the BMPs to.

–BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are

applied to cover crop acres.

▼A18

appendix A • Development of the Level-of-Effort Scenarios
• Tier 1 Streambank protection with fencing

–Continue 1997–2000 implementation rates of streambank protection with

fencing on pasture to the year 2010 with limits that levels cannot exceed the

available of the E3 scenario land area to apply the BMPs to.

–The E3 scenario levels are revised following the same methodologies but

account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes for every stream mile protected, 51 upland acres of

pasture receive a reduction benefit.

–BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture

acres protected.

• Tier 1 Streambank protection without fencing

–Continue 1997–2000 implementation rates of streambank protection without

fencing on pasture to the year 2010 with limits that levels cannot exceed the

available pasture land area to apply the BMPs to.

–BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture

acres protected.

• Tier 1 Grazing land protection

–Continue 1997–2000 implementation rates of rotational grazing on pasture to the

year 2010 with limits that levels cannot exceed the available land area to apply

the BMPs to.

–BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to

protected pasture acres.

2010 TIER 1 URBAN AND MIXED OPEN BMPs

• Tier 1 Storm Water Management on new development

–Storm water management applied to 66 percent of new development between

2000 and 2010.

–Storm water management practices are designed to reduce TN by 35 percent,

TP by 45 percent, and SED by 80 percent.

• Tier 1 Storm Water Management on recent development

–60 percent of recent development (1986–2000) is has storm water management

that are designed to reduce nutrients and sediment in storm water runoff by 

27 percent (TN), 40 percent (TP), and 65 percent (SED).

• Tier 1 Storm Water retrofits on old and recent development

–0.8 percent of pre-1986 urban land and 1986–2000 recent development is retrofitted with a suite of practices that reduce nutrients and sediment in runoff by 

20 percent (TN), 30 percent (TP), and 65 percent (SED).

▼A19

appendix A • Development of the Level-of-Effort Scenarios
• Tier 1 Riparian forest and grass buffers on urban

–It is assumed that all urban stream reaches have either forest or grass riparian

buffers except where urban disturbance has altered a stream reach beyond

repair/restoration (i.e., impervious surface).

–50-foot buffers on all un-buffered stream miles (each side) associated with

pervious urban.

–Landuse conversion of pervious urban to mixed open (grass buffers) or forest

(forest buffers).

–There is no upland benefit associated with forest and grass buffers on urban.

• Tier 1 Riparian forest buffers on mixed open

–Continue 1997–2000 implementation rates of tree planting on mixed open to the

year 2010 with limits that levels can not exceed the available or the E3 scenario

land area to which BMPs could be applied.

–100-foot forest buffers on all un-buffered stream miles (each side) associated

with mixed open.

–Landuse conversion of mixed open to forest.

–There is no upland benefit associated with forest buffers on mixed open.

• Tier 1 Nutrient management on urban and mixed open

–Continue 1997–2000 implementation rates of nutrient management on pervious

urban and mixed open to the year 2010 with limits that levels cannot exceed the

available land area to which BMPs could be applied.

–BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to

acres under nutrient management.

2010 TIER 1 FOREST HARVEST BMPs

• It is assumed that forestry BMPs designed to minimize the environmental impacts

from timber harvesting, such as road building and cutting/thinning operations, are

properly installed on all harvested lands with no measurable increase in nutrient

and sediment discharge.

• The assumption is based on maintaining the state of forest loads as measured

during the calibration of the Chesapeake Bay Watershed Model.

2010 TIER 1 SEPTIC BMPs

• Current edge-of-septic-field concentrations and flows per system are maintained.

• The number of systems varies according to population projections from 2000 to

2010.

• Septic BMPs incorporate submissions from the Chesapeake Bay-basin jurisdictions on the current number of systems employing denitrification technologies

▼A20

appendix A • Development of the Level-of-Effort Scenarios
(50 percent TN reduction) and those with regular maintenance through pumping

(5 percent TN reduction).

2010 TIER 1 POINT SOURCE BMPs

• Tier 1 Significant municipal wastewater treatment facilities

–Nitrogen – POTWs with existing nutrient-removal technologies (NRT) and

those planned to go to NRT by 2010 are at 2010 projected flows and 8 mg TN/L

effluent concentrations (annual average). All remaining significant facilities are

at 2010 projected flows and 2000 TN effluent concentrations.

–Phosphorus – 2010 projected flows and 2000 TP/L effluent concentrations

except those targeted in VA which are at 1.5 mg TP/L (annual average).

• Tier 1 Significant industrial dischargers

–2000 flows and maintain current (2000) levels of effluent concentrations for TN

and TP or the permit limit, whichever is less. 

• Tier 1 Non-significant municipal wastewater treatment facilities

–2000 TN and TP effluent concentrations applied to 2010 projected flows.

2010 TIER 1 COMBINED SEWER OVERFLOW BMPs

• There is a 43 percent reduction in the current discharge from DC combined sewer

overflows, the only CSO loads among all jurisdictions for which the Chesapeake

Bay Program has nutrient load data specifically quantified in the model simulation.

• The reduction from 2000 loads is what is expected by the District to be achieved

by 2010.

2010 TIER 1 ATMOSPHERIC DEPOSITION BMPs

Tier 1 atmospheric deposition assumes implementation of the 1990 Clean Air Act

projected for the year 2010 with nitrogen oxide emissions regulations for groundlevel ozone and acid rain that have passed. Estimated changes in deposition for the

Tier 1 scenario includes the following controls on nitrogen oxide emissions:

• 2007 non-utility (industrial) point source and area source emissions.

• 2007 mobile source emissions with ‘Tier II’ tail pipe standards on light duty

vehicles.

• 2010 utility emissions with Title IV (Acid Rain Program) fully implemented and

20-state NOx SIP call reductions at 0.15 lbs/MMbtu during the May to September

ozone season only.

The impacts of Tier 1 emissions and deposition to the Chesapeake Bay watershed’s

land area and non-tidal waters are part of the reported nutrient loads from the

▼A21

appendix A • Development of the Level-of-Effort Scenarios
individual landuse source categories (i.e., agriculture, urban, mixed open, forest, and

non-tidal surface waters). The reported Watershed Model loads, however, usually do

not include contributions from atmospheric deposition to tidal waters although the

water quality responses, as measured by the Water Quality Model, account for this

source at levels prescribed by Tier 1.

2010 TIER 1 SHORELINE EROSION BMPs

• Tier 1 shoreline erosion controls include structural and non-structural practices at

2000 levels.

The impacts of Tier 1 shoreline erosion controls are not included in the reported

Watershed Model loads although the water quality responses, as measured by the

Model, account for this source at BMP levels prescribed by Tier 1. 

2010 TIER 2 SCENARIO 

2010 Tier 2 BMP implementation levels for nonpoint sources were generally determined by increasing levels above Tier 1 by a percentage of the difference between

the Tier 1 and the E3 scenario levels for each BMP. These percentages were mostly

recommended by individual source workgroups under the Chesapeake Bay Program

Nutrient Subcommittee, and were applied watershed-wide by county segments, or

the intersections of county political boundaries and the Watershed Model’s hydrologic segmentation.

For Tier 2 point source municipal facilities, technologies to achieve 8 mg TN/L

include extended aeration processes and denitrification zones, along with chemical

addition to achieve a phosphorus discharge of 1.0 mg/l where facilities are not

already achieving these levels.

In the design of the Tier 2 scenario, considerations of the costs of BMP implementation, participation levels, and physical limitations are very limited. Tier 2 BMP

levels are considered technically possible, and are listed below for each of the major

source categories.

2010 TIER 2 SCENARIO AGRICULTURAL BMPs

• Tier 2 Conservation tillage

–Applied to ‘Tier 1’ levels plus 30 percent of the available crop acres between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of high-till to low-till.

▼A22

appendix A • Development of the Level-of-Effort Scenarios
• Tier 2 Riparian forest buffers on agriculture

–Applied to ‘Tier 1’ levels plus 20 percent of the available stream reaches in cropland and pasture and 25 percent of the remaining stream reaches in hay between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles

(each side) associated with crop, hay, and pasture.

–Tier 1 forest buffers on pasture are rooted in agricultural tree planting from jurisdictional BMP reporting.

–Landuse conversions of crop, hay, and pasture to forest.

–For every acre of crop and hay converted, two upland acres of crop and hay

receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).

–There is no upland benefit associated with forest buffers on pasture.

• Tier 2 Wetland restoration

–Applied to ‘Tier 1’ levels plus 33 percent of the available crop and hay acres in

PA, MD, and VA between ‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of crop and hay to forest.

• Tier 2 Agricultural land retirement

–The remainder of 10 percent of the total crop and hay acres and those acres

converted through forest buffers and wetland restoration is retired to a grass

condition.

–Landuse conversions of crop and hay to mixed open.

• Tier 2 Riparian grass buffers on cropland

–Applied to ‘Tier 1’ levels plus 25 percent of the available stream reaches in cropland between ‘Tier 1’ and the ‘E3’ scenario levels and after forest buffer planting.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each

side) associated with agricultural land.

–Landuse conversions of crop to mixed open.

–For every acre of cropland converted, two upland acres of crop receive a reduction of 43 percent (TN), 53 percent (TP), and 53 percent (SED).

• Tier 2 Nutrient Management Plan Implementation

–Applied to ‘Tier 1’ levels plus 30 percent of the available crop and hay acres

between ‘Tier 1’ and the ‘E3’ scenario levels in PA, VA, NY, and WV.

▼A23

appendix A • Development of the Level-of-Effort Scenarios
–All crop and hay acres in MD and DE are fully implementing nutrient management plans.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Under nutrient management plans, crop and hay acres do not receive more than

130 percent of their TN and TP need.

• Tier 2 Manure excess

–Excess nutrients resulting from the differences between manure generated and

conforming to nutrient management rules and losses in agricultural land are

reported.

–It is assumed that all of the excess manure has alternative uses that do not affect

loads to the Chesapeake Bay tidal waters.

• Tier 2 Animal waste management/runoff control

–Applied to ‘Tier 1’ levels plus 25 percent of the available manure acres between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 75 percent (TN and TP) are applied to protected

manure acres.

• Tier 2 Farm Plans (non-nutrient management)

–Applied to ‘Tier 1’ levels plus 30 percent of the available agricultural acres (crop,

hay, and pasture) between ‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Nutrient and sediment reduction factors for Farm Plans on high-till are 10

percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors

are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for

Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).

• Tier 2 Cover crops

–Applied to ‘Tier 1’ levels plus 40 percent of the available cropland between ‘Tier

1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are

applied to cover crop acres.

• Tier 2 Streambank protection with fencing

–Applied to ‘Tier 1’ levels plus 15 percent of the available pasture land that can

be protected between ‘Tier 1’ and the ‘E3’ scenario levels.

▼A24

appendix A • Development of the Level-of-Effort Scenarios
–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture

acres protected.

• Tier 2 Streambank protection without fencing 

–Applied to ‘Tier 1’ levels plus 10 percent of the available pasture land area to

apply the BMPs to accounting for the acres protected by fencing.

–Tier 1 levels are revised following the same methodologies but account for previously applied BMPs that involve landuse changes and streambank protection

with fencing.

–BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture

acres protected.

• Tier 2 Grazing land protection

–Applied to ‘Tier 1’ levels plus 25 percent of the available pasture land between

‘Tier 1’ and the ‘E3’ scenario’ levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to

protected pasture acres.

2010 TIER 2 URBAN AND MIXED OPEN BMPs

• Tier 2 Reduction in 2000–2010 urban growth

–10 percent of the projected pervious and impervious urban growth in PA, MD,

VA, and DC between 2000 and 2010 is not developed.

–It is assumed that 65 percent of the reduction in projected urban growth is

retained in forest, 20 percent in mixed open, and 15 percent in agriculture.

–Landuse conversions of pervious and impervious urban to forest, mixed open,

and agriculture (crop, hay, and pasture).

• Tier 2 Storm Water Management and environmental site design/low-impact development on new development

–Storm water management applied to 75% of new development between 2000 and

2010.

–Environmental site design/low-impact development practices applied to 25% of

new development between 2000 and 2010.

–Efficiencies of storm water management and environmental site design and lowimpact development practices represent a 75%/25% weighted average reduction

of 40% for TN, 55% for TP, and 85% for TSS. 

▼A25

appendix A • Development of the Level-of-Effort Scenarios
• Tier 2 Storm Water Management on recent development

–60 percent of recent development (1986–2000) has storm water management

practices that are designed to reduce nutrients and sediment in storm water

runoff by 27 percent (TN), 40 percent (TP), and 65 percent (SED).

• Tier 2 Storm Water retrofits on old and recent development

–5 percent of pre-1986 urban land and 1986–2000 recent development has storm

water management practices that reduce nutrients and sediment in runoff by 20

percent (TN), 30 percent (TP), and 65 percent (SED).

• Tier 2 Riparian grass buffers on urban lands

–Urban grass buffer acreage is reduced 10 percent below ‘Tier 1’ levels and is

converted to urban forest buffers.

–Tier 1 levels are revised following the same methodology but account for previously applied BMPs that involve landuse changes.

–The assumption is maintained that all urban stream reaches have 50-foot riparian

buffers in either forest or grass except where urban disturbance has altered a

stream reach beyond repair/restoration (i.e., impervious surface).

–There is no upland benefit associated with grass buffers on urban.

• Tier 2 Riparian forest buffers on urban lands

–Urban forest buffer acreage is increased by the same amount as the reduction in

urban grass buffers.

–The assumption is maintained that all urban stream reaches have 50-foot riparian

buffers in either forest or grass except where urban disturbance has altered a

stream reach beyond repair/restoration (i.e., impervious surface).

–There is no upland benefit associated with forest buffers on urban.

• Tier 2 Riparian forest buffers on mixed open lands 

–Mixed open forest buffer acreage is increased from ‘Tier 1’ levels by the same

amount as the increase in urban forest buffers between ‘Tier 1’ and Tier 2.

–Tier 1 levels are revised following the same methodology but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of mixed open to forest.

–There is no upland benefit associated with forest buffers on mixed open.

• Tier 2 Nutrient management on urban and mixed open lands

–It is assumed that 40 percent of pervious urban and 40 percent of mixed open

land are under nutrient management.

–BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to

acres under nutrient management.

▼A26

appendix A • Development of the Level-of-Effort Scenarios
2010 TIER 2 FOREST HARVEST BMPs

• It is assumed that forestry BMPs designed to minimize the environmental impacts

from timber harvesting, such as road building and cutting/thinning operations, are

properly installed on all harvested lands with no measurable increase in nutrient

and sediment discharge.

• The assumption is based on maintaining the state of forest loads as measured

during the calibration of the Chesapeake Bay Watershed Model.

2010 TIER 2 SEPTIC BMPs

• 10 percent of new treatment systems between 2000 and 2010 employ denitrification technologies and are maintained through regular pumping to meet an edge of

septic field TN concentration of 10 mg/l or 2.3 lbs TN per person-year.

• Remaining new and existing systems are at current edge of septic field concentrations and flows per system.

• Septic BMPs incorporate submissions from the Chesapeake Bay basin jurisdictions of the current number of systems employing denitrification

technologies (50 percent TN reduction) and those with regular maintenance

through pumping (5 percent TN reduction).

2010 TIER 2 POINT SOURCE BMPs

• Tier 2 Significant municipal wastewater treatment facilities

–Nitrogen – All significant POTWs are at 2010 projected flows and reach and

maintain effluent concentrations of 8 mg TN/L (annual average) including those

facilities that planned to go to NRT by 2010.

–Phosphorus – POTWs are at 2010 projected flows and reach and maintain

effluent concentrations of 1.0 mg TP/L (annual average) or the permit limit,

whichever is less.

• Tier 2 Significant industrial dischargers

–2000 flows and generally maintain effluent concentrations that are 50 percent

less that those in Tier 1 or the permit limit, whichever is less.

• Tier 2 Non-significant municipal wastewater treatment facilities

–2000 TN and TP effluent concentrations applied to 2010 projected flows.

2010 TIER 2 COMBINED SEWER OVERFLOW BMPs

• There is a 43 percent reduction in the current discharge from District of Columbia

combined sewer overflows, the only CSO loads among all jurisdictions for which

the Chesapeake Bay Program has nutrient load data specifically quantified in the

model simulation.

▼A27

appendix A • Development of the Level-of-Effort Scenarios
• The reduction from 2000 loads is what is expected by the District of Columbia to

be achieved by 2010.

2010 TIER 2 ATMOSPHERIC DEPOSITION BMPs

Atmospheric deposition under Tier 2 reflects implementation of the 1990 Clean Air

Act projected for the year 2020 with nitrogen oxide emissions regulations described

in Tier 1 plus heavy-duty diesel regulations that have passed. Estimated changes in

deposition for the Tier 2 scenario reflects the following controls on nitrogen oxide

emissions:

• 2020 non-utility (industrial) point source and area source emissions with no additional controls beyond Tier 1.

• 2020 mobile source emissions with the effect of the Tier II tail pipe standards on

light duty vehicles being felt, and the implementation of the heavy-duty diesel

standards to further reduce NOx emissions.

• 2020 utility emissions with Title IV (Acid Rain Program) fully implemented and

20-state NOx SIP call reductions at 0.15 lbs/MMbtu during the May to September

ozone season only—Same as Tier 1 controls.

The impacts of emissions and deposition to the Chesapeake Bay watershed’s land

area and non-tidal waters under Tier 2 are part of the reported nutrient loads from the

individual landuse source categories (i.e., agriculture, urban, mixed open, forest, and

non-tidal surface waters). The reported Watershed Model loads, however, usually do

not include contributions from atmospheric deposition to tidal waters although the

water quality responses, as measured by the Water Quality Model, account for this

source at levels prescribed by Tier 2.

2010 TIER 2 SHORELINE EROSION BMPs

• Tier 2 shoreline erosion controls include structural and non-structural practices at

2000 levels.

The impacts of Tier 2 shoreline erosion controls are not included in the reported

Watershed Model loads although the water quality responses, as measured by the

Water Quality Model, account for this source at BMP levels prescribed by Tier 2.

2010 TIER 3 SCENARIO 

The 2010 Tier 3 BMP implementation levels for nonpoint sources were generally

determined by increasing levels above the Tier 1 scenario by a percentage of the

difference between the Tier 1 and the E3 scenario levels, with the percentages being

higher than those used in the Tier 2 scenario. As with the Tier 2 scenario, the levels

of nonpoint source control were applied watershed-wide by county segments, or the

intersections of county political boundaries and the Watershed Model’s hydrologic

segmentation.

▼A28

appendix A • Development of the Level-of-Effort Scenarios
For Tier 3 municipal point source facilities, technologies to achieve 5 mg TN/L

include extended aeration processes beyond those in the Tier 2 scenario, a secondary

anoxic zone plus methanol addition, additional clarification tanks, and additional

chemicals to achieve a phosphorus discharge of 0.5 mg TP/L.

In the Tier 3 scenario, considerations of the costs of BMP implementation, participation levels, and physical limitations are very limited. Tier 3 BMP levels,

considered technically possible, are listed below for each of the major source

categories.

2010 TIER 3 AGRICULTURAL BMPs

• Tier 3 Conservation tillage

–Applied to ‘Tier 1’ levels plus 60 percent of the available crop acres between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of high-till to low-till.

• Tier 3 Riparian forest buffers on agriculture

–Applied to ‘Tier 1’ levels plus 30 percent of the available stream reaches in cropland and pasture and 50 percent of the remaining stream reaches in hay between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles

(each side) associated with crop, hay, and pasture.

–Tier 1 forest buffers on pasture are rooted in agricultural tree planting from jurisdictional BMP reporting.

–Landuse conversions of crop, hay, and pasture to forest.

–For every acre of crop and hay converted, two upland acres of crop and hay

receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).

–There is no upland benefit associated with forest buffers on pasture.

• Tier 3 Wetland restoration

–Applied to ‘Tier 1’ levels plus 66 percent of the available crop and hay acres in

PA, MD, and VA between ‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of crop and hay to forest.

▼A29

appendix A • Development of the Level-of-Effort Scenarios
• Tier 3 Agricultural land retirement

–The remainder of 15 percent of the total crop and hay acres and those acres

converted through forest buffers and wetland restoration is retired to a grass

condition.

–Landuse conversions of crop and hay to mixed open.

• Tier 3 Carbon sequestration/bio-energy

–15 percent of crop acres (after BMP landuse conversions) are replaced with longterm grasses that serve as a carbon bank and could be converted to energy

through combustion.

–Landuse conversion of low-till to hay.

• Tier 3 Riparian grass buffers on cropland

–Applied to ‘Tier 1’ levels plus 50 percent of the available stream reaches in cropland between ‘Tier 1’ and the ‘E3’ scenario levels and after forest buffer planting.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each

side) associated with agricultural land.

–Landuse conversions of crop to mixed open.

–For every acre of cropland converted, two upland acres of crop receive a reduction of 43 percent (TN), 53 percent (TP), and 53 percent (SED).

• Tier 3 Nutrient Management Plan Implementation (standard and yield reserve

program)

–Nutrient management is applied to ‘Tier 2’ levels plus 30 percent of the available

crop and hay acres between ‘Tier 2’ and the ‘E3’ scenario levels in PA, VA, NY,

and WV.

–Tier 2 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–All crop and hay acres in MD and DE are fully implementing nutrient management plans.

–Of the crop and hay acres available for nutrient management, 30 percent

conforms to a yield reserve program where the land receives 25 percent less TN

and TP than standard nutrient management applications - Do not receive more

than 98 percent of TN and TP need.

–Yield reserve program assumes farmer insurance for yield losses.

–The remaining 70 percent of land available for nutrient management follows

standard rules where crop and hay acres do not receive more than 130 percent of

their TN and TP need.

▼A30

appendix A • Development of the Level-of-Effort Scenarios
• Tier 3 Manure excess

–Excess nutrients resulting from the differences between manure generated and

conforming to nutrient management rules and losses in agricultural land are

reported.

–It is assumed that all of the excess manure has alternative uses that do not affect

loads to the Chesapeake Bay tidal waters.

• Tier 3 Animal waste management/runoff control

–Applied to ‘Tier 1’ levels plus 60 percent of the available manure acres between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 75 percent (TN and TP) are applied to protected

manure acres.

• Tier 3 Farm Plans (non-nutrient management)

–Applied to ‘Tier 1’ levels plus 70 percent of the available agricultural acres (crop,

hay, and pasture) between ‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–Nutrient and sediment reduction factors for Farm Plans on high-till are 10

percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors

are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for

Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).

• Tier 3 Cover crops

–Applied to ‘Tier 1’ levels plus 75 percent of the available cropland between ‘Tier

1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are

applied to cover crop acres.

• Tier 3 Streambank protection with fencing

–Applied to ‘Tier 1’ levels plus 75 percent of the available pasture land that can

be protected between ‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture

acres protected.

▼A31

appendix A • Development of the Level-of-Effort Scenarios
• Tier 3 Streambank protection without fencing

–Applied to ‘Tier 1’ levels plus 25 percent of the available pasture land area to

apply the BMPs to accounting for the acres protected by fencing.

–Tier 1 levels are revised following the same methodologies but account for previously applied BMPs that involve landuse changes and streambank protection

with fencing.

–BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture

acres protected.

• Tier 3 Grazing land protection

–Applied to ‘Tier 1’ levels plus 50 percent of the available pasture land between

‘Tier 1’ and the ‘E3’ scenario levels.

–Tier 1 and the E3 scenario levels are revised following the same methodologies

but account for previously applied BMPs that involve landuse changes.

–BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to

protected pasture acres.

2010 TIER 3 URBAN AND MIXED OPEN BMPs

• Tier 3 Reduction in 2000–2010 urban growth

–20 percent of the projected pervious and impervious urban growth in PA, MD,

VA, and DC between 2000 and 2010 is not developed.

–It is assumed that 65 percent of the reduction in projected urban growth is

retained in forest, 20 percent in mixed open, and 15 percent in agriculture.

–Landuse conversions of pervious and impervious urban to forest, mixed open,

and agriculture (crop, hay, and pasture).

• Tier 3 Storm Water Management and environmental site design/low-impact development on new development 

–Storm water management applied to 50 percent of new development between

2000 and 2010.

–Environmental site design/low-impact development practices applied to 50

percent of new development between 2000 and 2010. 

–Efficiencies of storm water management and environmental site design and lowimpact development practices represent a 50%/50% weighted average reduction

of 45% for TN, 57% for TP, and 87% for TSS. 

• Tier 3 Storm Water Management on recent development

–60 percent of recent development (1986–2000) has storm water management

practices that are designed to reduce nutrients and sediment in stormwater runoff

by 27 percent (TN), 40 percent (TP), and 65 percent (SED).

• Tier 3 Storm Water retrofits on old and recent development

–20 percent of pre-1986 urban land and 1986–2000 recent development has storm

water management practices that reduce nutrients and sediment in runoff by 

20 percent (TN), 30 percent (TP), and 65 percent (SED).

▼A32

appendix A • Development of the Level-of-Effort Scenarios
• Tier 3 Riparian grass buffers on urban lands

–Urban grass buffer acreage is reduced 30 percent below ‘Tier 1’ levels and is

converted to urban forest buffers.

–Tier 1 levels are revised following the same methodology but account for previously applied BMPs that involve landuse changes.

–The assumption is maintained that all urban stream reaches have 50-foot riparian

buffers in either forest or grass except where urban disturbance has altered a

stream reach beyond repair/restoration (i.e., impervious surface).

–There is no upland benefit associated with grass buffers on urban.

• Tier 3 Riparian forest buffers on urban lands

–Urban forest buffer acreage is increased by the same amount as the reduction in

urban grass buffers.

–The assumption is maintained that all urban stream reaches have 50-foot riparian

buffers in either forest or grass except where urban disturbance has altered a

stream reach beyond repair/restoration (i.e., impervious surface).

–There is no upland benefit associated with forest buffers on urban.

• Tier 3 Riparian forest buffers on mixed open lands

–Mixed open forest buffer acreage is increased from ‘Tier 1’ levels by the same

amount as the increase in urban forest buffers between ‘Tier 1’ and Tier 3.

–Tier 1 levels are revised following the same methodology but account for previously applied BMPs that involve landuse changes.

–Landuse conversion of mixed open to forest.

–There is no upland benefit associated with forest buffers on mixed open.

• Tier 3 Nutrient management on urban and mixed open lands

–It is assumed that 75 percent of pervious urban and 75 percent of mixed open

land are under nutrient management.

–BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to

acres under nutrient management.

2010 TIER 3 FOREST HARVEST BMPs

• It is assumed that forestry BMPs designed to minimize the environmental impacts

from timber harvesting, such as road building and cutting/thinning operations, are

properly installed on all harvested lands with no measurable increase in nutrient

and sediment discharge.

• The assumption is based on maintaining the state of forest loads as measured

during the calibration of the Chesapeake Bay Watershed Model.

▼A33

appendix A • Development of the Level-of-Effort Scenarios
2010 TIER 3 SEPTIC BMPs

• 100 percent of new treatment systems between 2000 and 2010 and 1 percent of

existing systems employ denitrification technologies and are maintained through

regular pumping to meet an edge-of-septic-field TN concentration of 10 mg/L or

2.3 lbs TN per person-year.

• The 1 percent of existing systems represents failed systems and opportunities for

upgrades.

• The remaining existing systems are at current edge of septic field concentrations

and flows per system.

• Septic BMPs incorporate submissions from the Chesapeake Bay basin jurisdictions of the current number of systems employing denitrification technologies

(50 percent TN reduction) and those with regular maintenance through pumping

(5 percent TN reduction).

2010 TIER 3 POINT SOURCE BMPs

• Tier 3 Significant municipal wastewater treatment facilities

–Nitrogen – All significant POTWs are at 2010 projected flows and reach and

maintain effluent concentrations of 5 mg TN/L (annual average) including those

facilities that planned to go to NRT by 2010.

–Phosphorus – POTWs are at 2010 projected flows and reach and maintain

effluent concentrations of 0.5 mg TP/L (annual average) or the permit limit,

whichever is less.

• Tier 3 Significant industrial dischargers

–2000 flows and generally maintain effluent concentrations that are 80 percent

less that those in Tier 1 or the permit limit, whichever is less.

• Tier 3 Non-significant municipal wastewater treatment facilities

–2000 TN and TP effluent concentrations applied to 2010 projected flows.

2010 TIER 3 COMBINED SEWER OVERFLOW BMPs

• There is a 43 percent reduction in the current discharge from District of Columbia

combined sewer overflows, the only CSO loads among all jurisdictions for which

the Chesapeake Bay Program has nutrient load data specifically quantified in the

model simulation.

• The reduction from 2000 loads is what is expected by the District of Columbia to

be achieved by 2010.

▼A34

appendix A • Development of the Level-of-Effort Scenarios
2010 TIER 3 ATMOSPHERIC DEPOSITION BMPs

Atmospheric deposition under the Tier 3 scenario reflects existing regulatory

nitrogen oxide emissions controls under the 1990 Clean Air Act, as well as more

aggressive but voluntary emissions controls on the utility sector, projected for the

year 2020. Estimated changes in deposition for the Tier 3 scenario reflect the

following controls on nitrogen oxide emissions:

• 2020 non-utility (industrial) point source and area source emissions with no additional controls than Tiers 1 and 2.

• 2020 mobile source emissions with the effect of the Tier II tail pipe standards on

light duty vehicles being felt, and the implementation of the heavy duty diesel

standards to further reduce NOx emissions. Same as Tier 2 controls.

• 2020 utility emissions with major (90 percent) reductions in SO2 and aggressive

20-state NOx SIP call reductions through utilities going to 0.10 lbs/MMbtu for the

entire year—no longer just seasonal.

The impacts of emissions and deposition to the Chesapeake Bay watershed’s land

area and non-tidal waters under the Tier 3 scenario are part of the reported nutrient

loads from the individual landuse source categories (i.e., agriculture, urban, mixed

open, forest, and non-tidal surface waters). The reported loads, however, usually do

not include contributions from atmospheric deposition to tidal waters although the

water quality responses, as measured by the Water Quality Model, account for this

source at levels prescribed by the Tier 3 scenario.

2010 TIER 3 SHORELINE EROSION BMPs

• Tier 3 shoreline erosion controls include structural and non-structural practices at

2000 levels.

The impacts of Tier 3 shoreline erosion controls are not included in the reported

Watershed Model loads although the water quality responses, as measured by the

Water Quality Model, account for this source at BMP levels prescribed by the Tier 3

scenario. 

2010 E3 SCENARIO

BMP implementation levels in the tier scenarios were bounded by the E3 scenario.

The E3 scenario was specifically designed to take out most of the subjectivity

surrounding what can or cannot be achieved in control measures. The E3 scenario

BMP implementation levels were, in part, based on earlier work of the Chesapeake

Bay Program partners when a ‘limit-of-technology’ condition was assessed by the

Tributary Strategy Workgroup. However, the E3 scenario is less subjective than the

limit-of-technology scenario in terms of maximum implementation levels. The BMP

▼A35

appendix A • Development of the Level-of-Effort Scenarios
levels in the E3 scenario are theoretical: there are no cost and few physical limitations to implementing BMPs for point and nonpoint sources. In addition, the E3

scenario includes new BMP technologies and programs that are not currently part of

jurisdictional pollutant control strategies.

For most nonpoint source BMPs, the workgroups assumed that the load from every

available acre of the relevant land area was being controlled by a full suite of existing

or innovative practices. In addition, management programs convert landuses from

those with high-yielding nutrient and sediment loads to those with lower. For point

sources in the E3 scenario, municipal wastewater treatment facilities reach and maintain effluent concentrations of 3 mg TN/L, and at least 0.1 mg TP/L, through

technologies such as deep-bed denitrification filters and micro-filtration.

The E3 scenario implementation levels and their associated reductions in nutrients

and sediment were developed without consideration of site specific physical

constraints, costs, or even plausible BMP program participation levels. The Chesapeake Bay Program partners acknowledge that if these factors are considered,

several aspects of the E3 scenario could not be achieved. On the other hand, there

are some control measures in the E3 scenario that physically could be more aggressive. The E3 scenario conditions for these BMPs were established because a

theoretical maximum implementation level would have been entirely subjective.

BMP implementation levels for the E3 scenario are described in detail below for the

major source categories—agriculture, urban and mixed open, point sources, septic,

and atmospheric deposition.

PHYSICAL LIMITATIONS TO THE E3 SCENARIO

In all appropriate circumstances, BMP implementation levels in the E3 scenario

were applied to all relevant landuse areas or current limits-of-technology. In many

cases and to remove the subjectivity in determining human-caused conditions that

cannot be remedied, there were no physical limitations to employing the practices or

programs. 

For many BMPs, the E3 scenario implementation levels could not be physically

achieved. For example, space may not be available for 50-foot riparian buffers in

urban areas, or certain developed lands may not allow for retrofitting with practices

that attain pollutant reduction efficiencies used in the E3 scenario. As other examples, certain crop types cannot be conservation-tilled, and it may be physically

impossible to completely eliminate runoff from animal feeding operations.

It is also unlikely that every homeowner and farmer would efficiently apply fertilizers so that only the needs of the vegetation are met and that water-front property

owners would plant 50-foot buffers even if it were physically possible. As a whole,

‘feasible’ participation levels are not built into the E3 scenario. All of the abovementioned instances are examples of where the E3 scenario may overestimate

reductions.

▼A36

appendix A • Development of the Level-of-Effort Scenarios
UNDERESTIMATIONS OF LOAD REDUCTIONS 

UNDER THE E3 SCENARIO

Contrarily, there are assumptions in the E3 scenario where BMP implementation

levels could physically be even higher than those currently defined in the E3

scenario. For example, it is physically possible that more than 25,000 acres of cropland and hay in Chesapeake Bay watershed could be restored to wetlands. This limit

on wetland acres restored in the E3 scenario in Pennsylvania, Maryland and Virginia

was used to reflect the Chesapeake 2000 goal since a theoretical maximum implementation level for wetlands restoration would be entirely subjective. 

As an other example, 25 percent of cropland was replaced with long-term grasses

that serve as a carbon bank and could be converted to energy through combustion.

Benefits of a carbon sequestration program, in terms of lower pollutant loads, would

increase as more agricultural land is converted. Conversion of more than 25 percent

of cropland is physically possible. In addition, the 30 percent reduction in urban

sprawl over a decade could be physically set at a higher level. This rate was

employed in the E3 scenario to adhere to a Chesapeake 2000 goal.

The E3 scenario only includes shoreline erosion controls at current levels for lack of

a ‘maximum’ limit that would not be entirely subjective. It has been demonstrated

through modeling efforts that additional controls of shoreline erosion can significantly improve tidal water quality. In general, much opportunity exists for reducing

sediment and nutrient loads from eroding shorelines that would not be reflected in

the E3 scenario water quality model results. 

If greater BMP implementation levels than those designated in the E3 scenario could

be physically achieved for any BMPs, pollutant loadings would decrease and the

there would be corresponding improved responses in water quality. For the most

part, however, the E3 scenario does not include real physical limitations to BMP

implementation or participation levels.

2010 E3 AGRICULTURAL BMPs

• The E3 scenario conservation tillage

–All cropland (high-till and low-till) is conservation-tilled.

–Landuse conversion of high-till to low-till.

• The E3 scenario riparian forest buffers on agriculture

–100-foot forest buffers on all un-buffered stream miles (each side) associated

with crop, hay, and pasture.

–Landuse conversion of low-till, hay, and pasture to forest.

–For every acre of low-till and hay converted, two upland acres of low-till and hay

receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).

–There is no upland benefit associated with forest buffers on pasture.

▼A37

appendix A • Development of the Level-of-Effort Scenarios
• The E3 scenario wetland restoration

–In accordance with the Chesapeake 2000 agreement, 25,000 acres of crop and

hay in PA, MD, and VA are converted to and simulated as forest.

–The 25,000 acre restoration goal is allocated among these states as follows to

conform to agreements subsequent to Chesapeake 2000: PA = 4,250 acres, MD

= 15,000 acres, and VA = 5,750 acres.

• The E3 scenario agricultural land retirement

–The remainder of 25 percent of the total crop and hay acres and those acres

converted through forest buffers and wetland restoration is retired to a grass

condition.

–Landuse conversions of low-till and hay to mixed open.

• The E3 scenario carbon sequestration/bio-energy

–25 percent of crop acres (after BMP landuse conversions) are replaced with longterm grasses that serve as a carbon bank and could be converted to energy

through combustion.

–Landuse conversion of low-till to hay.

• The E3 scenario yield reserve program

–All crop and hay acres (after BMP landuse conversions) receive 25 percent less

TN and TP than normal nutrient management applications; do not receive more

than 98 percent of TN and TP need.

–Yield reserve program assumes farmer insurance for yield losses.

• The E3 scenario manure excess

–Excess nutrients resulting from the differences between manure generated and

conforming to yield reserve (nutrient management) rules and losses in agricultural land are reported.

–It is assumed that all of the excess manure has alternative uses that do not affect

loads to the Chesapeake Bay tidal waters.

• The E3 scenario animal waste management/runoff control

–There is no runoff from manure in animal feeding operations.

–Modeled landuse acres that account for runoff from animal feeding operations

are converted to pasture.

–Landuse conversion of manure acres to pasture.

• The E3 scenario Farm Plans (non-nutrient management)

–Farm Plans are fully implemented on all agricultural land (crop, hay, and

pasture).

–Nutrient and sediment reduction factors for Farm Plans on low-till and hay are 4

percent (TN) and 8 percent (TP and SED). Pasture reduction factors are 20

percent (TN) and 14 percent (TP and SED).

▼A38

appendix A • Development of the Level-of-Effort Scenarios
• The E3 scenario cover crops

–All crop landuses have cover crops.

–BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are

applied to all low-till.

• The E3 scenario streambank protection with fencing

–Streambank protection with fencing on all unprotected stream miles (each side)

associated with pasture.

–For every stream mile protected, 51 upland acres of pasture receive a reduction

of 75 percent for TN, TP and SED.

• The E3 scenario grazing land protection

–All pasture land is protected through rotational grazing.

–BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied.

2010 E3 SCENARIO URBAN AND MIXED OPEN BMPs

• The E3 scenario reduction in 2000–2010 urban growth

–30 percent of the projected pervious and impervious urban growth in PA, MD,

VA, and DC between 2000 and 2010 remains in forest to conform to the Chesapeake 2000 agreement.

–It is assumed that the reduction in projected urban growth in PA, MD, VA, and

DC over the decade is retained or planted in forest.

–Landuse conversions of pervious and impervious urban to forest.

• The E3 scenario environmental site design/low-impact development on new

development

–Environmental site design/low-impact development practices applied to all

urban growth between 2000 and 2010.

–Environmental site design and low-impact development practices are designed to

reduce TN by 50 percent, TP by 60 percent, and SED by 90 percent.

• The E3 scenario storm water retrofits on existing urban

–All pre-2001 urban areas are retrofitted with a suite of practices to reduce nutrients and sediment in storm water runoff by 40 percent (TN), 40 percent (TP), and

80 percent (SED).

• The E3 scenario riparian forest buffers on urban

–50-foot forest buffers on all un-buffered stream miles (each side) associated with

pervious urban.

–Landuse conversion of pervious urban to forest.

–There is no upland benefit associated with forest buffers on urban.

▼A39

appendix A • Development of the Level-of-Effort Scenarios
• The E3 scenario riparian forest buffers on mixed open

–100-foot forest buffers on all un-buffered stream miles (each side) associated

with mixed open.

–Landuse conversion of mixed open to forest.

–There is no upland benefit associated with forest buffers on mixed open.

• The E3 scenario nutrient management on urban and mixed open

–All pervious urban and mixed open acres do not receive nutrient applications

from chemical fertilizers.

2010 E3 SCENARIO FOREST HARVEST BMPs

• It is assumed that forestry BMPs designed to minimize the environmental impacts

from timber harvesting, such as road building and cutting/thinning operations, are

properly installed on all harvested lands with no measurable increase in nutrient

and sediment discharge.

• The assumption is based on maintaining the state of forest loads as measured

during the calibration of the Chesapeake Bay Program Watershed Model.

2010 E3 SCENARIO SEPTIC BMPs

• All septic systems employ denitrification technologies and are maintained

through regular pumping to meet an edge-of-septic-field TN concentration of 10

mg/L or 2.3 lbs TN per person-year.

2010 E3 SCENARIO POINT SOURCE BMPs

• The E3 scenario significant municipal wastewater treatment facilities

–Nitrogen – POTWs are at 2010 projected flows and reach and maintain effluent

concentrations of 3 mg TN/L (annual average).

–Phosphorus – POTWs are at 2010 projected flows and reach and maintain

effluent concentrations of 0.1 mg TP/L (annual average).

• The E3 scenario significant industrial dischargers

–Nitrogen – 2000 flows and effluent concentrations of 3.0 mg TN/L (annual

average) or the permit limit, whichever is less.

–Phosphorus – 2000 flows and effluent concentrations of 0.1 mg TP/L (annual

average) or the permit limit, whichever is less.

• The E3 scenario non-significant municipal wastewater treatment facilities

–Nitrogen – POTWs are at 2010 projected flows and reach and maintain effluent

concentrations of 8 mg TN/L (annual average).

▼A40

appendix A • Development of the Level-of-Effort Scenarios
–Phosphorus – POTWs are at 2010 projected flows and reach and maintain

effluent concentrations of 2.0 mg TP/L (annual average) or 2000 concentrations,

whichever is less.

2010 E3 SCENARIO COMBINED SEWER OVERFLOW BMPs

• There is no discharge from DC combined sewer overflows, the only CSO loads

among all jurisdictions for which the Chesapeake Bay Program has nutrient load

data specifically quantified in the model simulation.

2010 E3 SCENARIO ATMOSPHERIC DEPOSITION BMPs

Levels of atmospheric deposition in the E3 scenario reflect existing regulatory

nitrogen oxide emissions controls under the 1990 Clean Air Act, as well as more

aggressive but voluntary emissions controls on the utility, industrial, and mobile

source sectors, projected for the year 2020. Estimated changes in deposition for the

E3 scenario reflects the following controls on nitrogen oxide emissions:

• 2020 non-utility (industrial) point source emissions cut almost in half for both

SO2 and NOx.

• 2020 area source emissions that are the same as the Tier 1-3 scenarios.

• 2020 mobile source emissions assuming super ultra-low emissions for light duty

vehicles and heavy duty diesel standards to further reduce NOx emission beyond

Tier 2 and Tier 3.

• 2020 utility emissions with major (90 percent) reductions in SO2 and aggressive

20-state NOx SIP call reductions through utilities going to 0.10 lbs/MMbtu for the

entire year—same as Tier 3 controls.

The impacts of emissions and deposition to the Chesapeake Bay watershed’s land

area and non-tidal waters under the E3 scenario are part of the reported nutrient loads

from the individual landuse source categories (i.e., agriculture, urban, mixed open,

forest, and non-tidal surface waters). The reported Watershed Model loads, however,

usually do not include contributions from atmospheric deposition to tidal waters

although the water quality responses, as measured by the Water Quality Model,

account for this source at levels prescribed by the E3 scenario.

2010 E3 SCENARIO SHORELINE EROSION BMPs

• The E3 scenario shoreline erosion controls include structural and non-structural

practices at 2000 levels.

The impacts of the E3 scenario shoreline erosion controls are not included in the

reported Watershed Model loads although the water quality responses, as measured

by the Water Quality Model, account for this source at BMP levels prescribed by the

E3 scenario.

▼A41

appendix A • Development of the Level-of-Effort Scenarios
BAY-WIDE LOADS FOR 2000, 

TIERS 1 TO 3, AND E3 SCENARIO

Figures A-1 through A-3 depict modeled Chesapeake Bay-wide nutrient and sediment loads delivered to the Chesapeake Bay and its tidal tributaries by major source

category for each of the tier scenarios as well as the E3 scenario. As references, the

estimated loads for the year 2000 are also portrayed.

The delivered loads are a yearly average of loads simulated over a 10-year period

(1985–1994). This convention removes considerations of the effects of variable

precipitation levels or flows on loads. Also, nutrient loads are reported in units of

million pounds per year while sediment fluxes are in million tons per year.

Load reductions through the tiers to the E3 scenario show the impact of most point

and nonpoint source BMPs in the scenarios as described previously in this Appendix.

Atmospheric deposition to the Chesapeake Bay watershed’s land area and non-tidal

waters are part of the reported loads, but the loads do not include contributions from

atmospheric deposition to tidal waters. In addition, the reported loads do not reflect

▼A42

appendix A • Development of the Level-of-Effort Scenarios

101.1

76.0

55.5

25.3

62.8

56.6

45.5

30.6

18.3

39.9

39.7

39.2

40.2

30.3

29.0

25.9

22.9

12.2

18.4

18.8

18.9

18.1

14.9

11.9

12.6

12.6

12.0

3.3

116.3

41.5

3.6

3.0

2.7

2.4

2.2

0

30

60

90

120

150

180

210

240

270

300

330

2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3

Nitrogen Loads

(million pounds/year)

Non-Tidal

Water

Deposition

Septic

Mixed Open

Urban Runoff

Forest

Point Source

Agriculture

Figure A-1. Nitrogen loads delivered to the Chesapeake Bay and its tidal tributaries by source.
▼A43

appendix A • Development of the Level-of-Effort Scenarios

8.99

7.69

6.71

5.54

3.74

4.26

5.10

3.72

2.21

0.69

0.41

0.36

0.35

0.34

0.37

3.12

3.13

2.89

2.59

2.07

2.18 2.51

2.57

2.52

3.03

0.16 0.16

0.17

0.18

0.19

0

2

4

6

8

10

12

14

16

18

20

22

2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3

Phosphorus Loads 

(million pounds/year)

Non-Tidal

Water

Deposition

Mixed Open

Urban

Runoff

Forest

Point

Source

Agriculture

Figure A-2. Phosphorus loads delivered to the Chesapeake Bay and its tidal tributaries by source.

3.188

2.714

2.179

1.669

1.274

0.995

1.000

1.010

1.020

1.067

0.475

0.479

0.461

0.414

0.105

0.386

0.451

0.494

0.522

0.507

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3

Sediment Loads

(million tons/year)

Mixed Open

Urban

Runoff

Forest

Agriculture

Figure A-3. Sediment loads delivered to the Chesapeake Bay and its tidal tributaries by source.
shoreline erosion controls employed in the scenarios. The water quality responses as

measured by the Watershed Model, however, account for both atmospheric deposition to tidal waters and shoreline erosion at levels prescribed by the tier and E3

scenarios.

It is important to note that landuses and animal populations change considerably

between 2000 Progress and the tier and E3 scenarios, which are based on projected

2010 landuses and populations. Therefore, nutrient applications to agricultural land

change considerably over the decade. Also, the number of septic systems and the

flows from municipal wastewater treatment facilities shift dramatically from 2000 to

2010 based on an increasing population. For example, point source phosphorous

loads increase from 2000 to 2010 Tier 1 because of increases in POTW flows which,

unlike nitrogen, are not offset by technologies to reduce this nutrient in effluents.

In addition to changes between 2000 and 2010 tier and E3 scenarios, it is imperative

to consider landuse changes among the tier and E3 scenarios due to increasing nonpoint source BMP implementation levels. For example, sediment loads from forested

land increase through the tier to E3 scenarios because the land area increases as, for

example, more and more riparian buffers are planted on agricultural and urban land.

In addition, increases in loads from mixed open land is attributable to greater acreage

in this category as, for example, agricultural land is retired.

INFLUENCE OF EMISSION CONTROLS AND 

ATMOSPHERIC DEPOSITION ON LOADS

The impacts of emission controls and the resultant lower atmospheric deposition to

the Chesapeake Bay watershed’s land area and non-tidal waters are part of the

reported nutrient loads from the individual landuse source categories in the tier and

E3 scenarios (i.e., agriculture, urban, mixed open, forest, and non-tidal surface

waters). As mentioned previously, the reported loads however, usually do not include

contributions from atmospheric deposition to tidal waters although the model simulated tidal Bay water quality responses account for this source.

To estimate the effects of only the tier and E3 scenarios air emission controls—

without the influences of other point and non-point source BMPs—the following

histogram (Figure A-4) show changes in atmospheric deposition of nitrogen to the

watershed’s land area and non-tidal waters, and the response in delivered loads. In

these model simulations, all land uses, fertilizer applications, point sources, septic

loads, and BMP implementation levels were held constant at 2000 conditions; only

atmospheric deposition varied.

What these scenarios say is that “If projected emission and deposition reductions

associated with the tiers and E3 scenarios were realized today (2000), loads to the

Chesapeake Bay and its tidal tributaries are estimated to be the following.” As

references, Tier 1 and Tier 2 scenario loads delivered from the watershed are shown

in the graphics.

▼A44

appendix A • Development of the Level-of-Effort Scenarios
As can be seen in Figure A-4, atmospheric deposition to the watershed progressively

declines from 2000 through the tier to E3 scenarios as more emission controls are

included in the model simulation. But note how the loads from the watershed’s land

area and non-tidal waters respond to these progressive emission and deposition

reductions, but to a much smaller degree. 

The most significant reason for the dampened response is that the Chesapeake Bay

watershed is about 57 percent forested—or 57 percent of atmospheric nitrogen

deposits on forests—and among landuses, forests have the greatest potential to

uptake nitrogen. Generally, forests in the Chesapeake Bay basin are not nitrogensaturated—whereby they leak nitrogen to sub-surface or ground water.

The largest single source of nitrogen loads to the Chesapeake Bay is agriculture

where nitrogen-based commercial fertilizers and animal manure applied to agricultural land are currently eight times the input of nitrogen to agricultural land from

atmospheric deposition.

It is the impacts of emission controls on loads that are important in evaluating water

quality responses, the development of a cost estimating tool, and the establishment

of tributary strategies—rather than the contribution to loads from atmospheric

▼A45

appendix A • Development of the Level-of-Effort Scenarios

442.2

369.3

328.2

295.7

270.9

284.8 276.5 270.7 265.0 261.1

0

50

100

150

200

250

300

350

400

450

500

2000 Progress

(Baseline)

2000 Base w/

Tier 1 Deposition

2000 Base w/

Tier 2 Deposition

2000 Base w/

Tier 3 Deposition

2000 Base w/ E3

Deposition

(million lbs/year)

Atmospheric Deposition Delivered Load Tier 1 Load Tier 2 Load

Figure A-4. Nitrogen deposits versus delivered loads.
deposition. Understanding the loading responses to changes in deposition better

addresses to what degree the loads can be controlled. The proportion of the loads

attributed to atmospheric deposition changes dramatically from 2000 through the

tiers and E3 scenarios because of both variable emission controls and changes in

landuses to which the atmospheric nitrogen is deposited.

In the most dramatic case, deposition of nitrogen to the watershed decreases 

171 million pounds/year from the 2000 Progress to 2010 E3 scenarios. If this reduction in deposition were realized today, (i.e., deposition was to 2000 landuses with all

other present conditions), nitrogen loads to the Chesapeake Bay would decrease 

21 million pounds/year or would be at levels associated with the Tier 1 scenario.

It is important to note that the E3 scenario levels of emission controls are considered

to be the current limits of technology with aggressive controls on all major sources

—utilities, mobile, and industrial—and follow the format of defining the E3 scenario

BMPs. It is not important that these emission controls would be voluntary, as

opposed to regulatory, as the E3 scenario implementation levels for almost all other

point and nonpoint source BMPs did not consider physical limitations, participation

rates, and costs. In other words, the tier scenarios are not intended to establish what

can and cannot be done through management actions—either regulatory or voluntary

—as this is the responsibility of Chesapeake Bay watershed jurisdictions. However,

the air scenarios involve actions taken by 37 states not just the Chesapeake Bay

watershed states.

▼A46

appendix A • Development of the Level-of-Effort Scenarios
Chesapeake Bay Program Segment 0–0.5 Meter Depth 0.5–1 Meter Depth 1–2 Meter Depth 

Northern Chesapeake Bay (CB1TF) 5,893 7,828 7,185 

Northern Chesapeake Bay (CB1TF) 5,893 7,828 7,185

Upper Chesapeake Bay (CB2OH) 2,406 2,496 3,885

Upper Central Chesapeake Bay (CB3MH) 2,011 1,702 957

Middle Central Chesapeake Bay (CB4MH) 3,252 2,688 4,689

Lower Central Chesapeake Bay (CB5MH) 9,223 6,184 14,693

Western Lower Chesapeake Bay (CB6PH) 2,324.4 1,614 1,630

Eastern Lower Chesapeake Bay (CB7PH) 17,308 11,154 5,623

Mouth of the Chesapeake Bay (CB8PH) 381 314 355

Bush River (BSHOH) 1,136 932 2,536

Gunpowder River (GUNOH) 1,393 1,402 4,564

Middle River (MIDOH) 938 491 1,050

Back River (BACOH) 850 451 1,558

Patapsco River (PATMH) 1,042 766 1,610

Magothy River (MAGMH) 838 540 677

Severn River (SEVMH) 775 572 761

South River (SOUMH) 840 592 804

Rhode River (RHDMH) 267 162 281

West River (WSTMH) 542 491 435

▼B1

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals

appendixB

Data Supporting Determination

of the Shallow-Water

Designated Use Depths and

Underwater Bay Grasses 

Restoration Goals

Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake

Bay Program segment.

continued
Chesapeake Bay Program Segment 0–0.5 Meter Depth 0.5–1 Meter Depth 1–2 Meter Depth 

Upper Patuxent River (PAXTF) 24 10 20

Western Branch Patuxent River (WBRTF) 0 0 0

Middle Patuxent River (PAXOH) 1,072 362 638

Lower Patuxent River (PAXMH) 3,376 1,745 3,672

Upper Potomac River (POTTF) 4,751 2,944 9,807

Anacostia River (ANATF) 85 99 137

Piscataway Creek (PISTF) 241 347 326

Mattawoman Creek (MATTF) 397 298 693

Middle Potomac River (POTOH) 3,148 4,038 8,008

Lower Potomac River (POTMH) 15,964 10,111 19,729

Upper Rappahannock River (RPPTF) 2,175 1,012 1,324

Middle Rappahannock River (RPPOH) 1,226 427 857

Lower Rappanhannock River (RPPMH) 12,282 7,511 10,315

Corrotoman River (CRRMH) 1,279 540 792

Piankatank River (PIAMH) 3,237 2,429 2,348

Upper Mattaponi River (MPNTF) 835 203 371

Lower Mattaponi River (MPNOH) 323 80 151

Upper Pamunkey River (PMKTF) 1,860 327 465

Lower Pamunkey River (PMKOH) 420 129 258

Middle York River (YRKMH) 4,728 3,703 4,285

Lower York River (YRKPH) 3,332 1,617 2,049

Mobjack Bay (MOBPH) 14,207 8,761 11,022

Upper James River (JMSTF) 8,249 2,149 2,438

Appomattox River (APPTF) 1,084 221 298

Middle James River (JMSOH) 3,179 3,289 4,476

Chickahominy River (CHKOH) 3,283 222 996

Lower James River (JMSMH) 9,618 5,455 11,525

Mouth of the James River (JMSPH) 1,037 578 786

Western Branch Elizabeth River (WBEMH) 0 0 0

Southern Branch Elizabeth River (SBEMH) 0 0 0

Eastern Branch Elizabeth River (EBEMH) 0 0 0

Lafayette River (LAFMH) 0 0 0

Mouth to Mid-Elizabeth River (ELIPH) 0 0 0

Lynnhaven River (LYNPH) 2,476 807 658

▼B2

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals

Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake

Bay Program segment (cont.).

continued
▼B3

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals

Chesapeake Bay Program Segment 0–0.5 Meter Depth 0.5–1 Meter Depth 1–2 Meter Depth

Northeast River (NORTF) 456 476 1,810

C & D Canal (C&DOH) 99 24 48

Bohemia River (BOHOH) 735 397 772

Elk River (ELKOH) 1,595 1,186 2,244

Sassafrass River (SASOH) 1,644 971 1,096

Upper Chester River (CHSTF) 574 192 104

Middle Chester River (CHSOH) 926 736 646

Lower Chester River (CHSMH) 4,183 2,798 4,520

Eastern Bay (EASMH) 7,423 5,659 7,723

Upper Choptank River (CHOTF) 0 0 0

Middle Choptank River (CHOOH) 592 260 432

Lower Choptank River (CHOMH2) 2,264 1,507 3,062

Mouth of the Choptank River (CHOMH1) 8,101 4,861 7,895

Little Choptank River (LCHMH) 5,012 3,011 4,344

Honga River (HNGMH) 6,117 4,513 5,826

Fishing Bay (FSBMH) 2,467 4,461 6,714

Upper Nanticoke River (NANTF) 0 0 0

Middle Nanticoke River (NANOH) 1,141 380 531

Lower Nanticoke River (NANMH) 1,583 1,605 4,524

Wicomico River (WICMH) 1,514 1,525 2,872

Manokin River (MANMH) 3,590 3,132 3,979

Big Annemessex River (BIGMH) 1,994 1,199 1,872

Upper Pocomoke River (POCTF) 0 0 0

Middle Pocomoke River (POCOH) 289 58 111

Lower Pocomoke River (POCMH) 3,915 6,090 4,412

Tangier Sound (TANMH) 20,101 18,720 31,052

Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake

Bay Program segment (cont.).
▼B4

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals Table B-2. Underwater bay grass acreage by Chesapeake Bay Program segment and year with the single best year of acreage highlighted. Segment Historical 1978 1979 1980 1981 1984 1985 1986 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 CB1TF 13,124 2,057 527 5,338 5,033 5,774 5,461 4,798 4,378 4,161 4,348 4,360 6,614 5,087 5,185 6,008 5,529 6,209 7,619 CB2OH 985 116 42 21 277 31 199 16 9 86 19 8 19 47 242 272 1 640 CB3MH 834 1,296 905 887 808 420 532 205 74 40 412 767 767 799 827 832 665 6 7 CB4MH 2,803 176 8 21 62 12 9 1 11 5 17 12 46 23 CB5MH 16,121 857 952 73 316 650 1,255 1,068 2,064 2,430 2,987 1,976 3,909 2,958 1,758 1,611 1,629 1,685 1,496 2,110 2,998 CB6PH 1,232 692 433 542 748 796 771 583 843 888 932 1,100 1,208 1,070 1,023 933 859 734 635 682 CB7PH 14,753 5,973 4,446 5,627 6,875 7,036 7,273 7,115 7,825 7,960 9,618 9,986 10,729 9,676 8,569 9,223 9,474 8,675 8,006 8,107 CB8PH 10 11 11 10 7 7 BSHOH 227 1 2 25 35 4 88 79 4 187 GUNOH 1,889 464 326 110 71 41 203 160 220 62 172 148 819 1,463 2,029 235 2,281 MIDOH 870 236 442 193 87 17 6 14 102 15 56 10 67 269 93 87 698 BACOH* PATMH 494 114 5 1 6 5 13 MAGMH 682 319 427 23 8 2 1 32 42 74 79 116 167 60 83 SEVMH 341 318 303 0 77 123 262 293 376 433 123 SOUMH 532 47 4 5 20 37 50 16 RHDMH 86 14 WSTMH 313 106 5 1 11 8 PAXTF* 10 34 23 44 31 38 16 WBRTF* PAXOH 44 2 31 55 58 67 72 80 PAXMH 1,630 56 24 108 34 101 1 2 2 3 9 POTTF 835 1,134 2,797 3,144 3,032 2,988 3,663 4,466 3,154 3,186 2,186 1,368 1,488 1,259 2,537 3,106 3,670 ANATF 9 8 5 9 10 10 11 11 13 13 15 13 8 5 8 10 PISTF 341 520 753 783 22 137 265 16 33 73 78 121 296 304 114 309 continued
▼B5

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals

Table B-2.

Segment Historical 1978 1979 1980 1981 1984 1985 1986 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Underwater bay grass acreage by Chesapeake Bay Program segment and year with the single best year of acreage highlighted (cont.).

MATTF 23 17 7 96 99 143 138 132 66 27 103 117 151 194 311POTOH 902 569 361 429 952 857 1,080 2,683 2,800 2,974 3,184 2,750 2,683 2,084 2,262 2,478 3,766 2,752 3,393POTMH 12,765 439 109 133 99 114 232 250 312 221 253 455 565 925 1,497 1,520 2,130 947RPPTF* 13 15 20RPPOH*RPPMH 7,694 65 1 33 20 19 244 841 261 119 160 301 69 48 54 27 16 78 173CRRMH 645 4 147 412 419 354 329 214 123 18 51 35 38 164 243PIAMH 3,426 107 5 10 25 26 25 97 323 556 615 738 1,003 569 333 326 403 305 273 390MPNTF 84MPNOH*PMKTF 184 167PMKOH*YRKMH 228YRKPH 2,740 260 253 274 435 428 421 458 566 662 649 663 672 706 722 731 815 719 629 736MOBPH 15,602 6,673 5,725 5,915 6,673 6,936 6,877 7,080 8,838 9,627 10,341 10,506 10,653 10,504 10,528 10,306 10,641 9,771 8,571 8,815JMSTF 1,724 72 52APPTF 353JMSOH 8 3CHKOH 0 113 29 388 79 422JMSMH 638 2 232JMSPH 682 22 7 9 7 7 9 10 15 38 46 184 129 77 93WBEMH*SBEMH*EBEMH*LAFMH*ELIPH*

continued
▼B6

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals Table B-2. Segment Historical 1978 1979 1980 1981 1984 1985 1986 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 Underwater bay grass acreage by Chesapeake Bay Program segment and year with the single best year of acreage highlighted (cont.). LYNPH 94 90 105 93 89 68 54 46 50 97 29 69 37 38 91 46 NORTF 163 10 1 0 16 15 11 10 18 11 19 C&DOH 2 BOHOH 45 16 1 17 17 1 4 0 3 27 29 32 105 77 172 ELKOH 269 2 33 92 11 18 465 871 656 586 227 434 300 100 157 484 768 1,670 SASOH 4 14 17 56 34 18 214 69 60 15 175 178 423 221 247 143 216 908 CHSTF* CHSOH 103 CHSMH 3,558 2,369 2,062 955 775 327 623 161 72 80 168 702 919 997 691 910 1,026 669 EASMH 6,296 3,158 939 194 884 588 2,130 1,966 903 157 1,306 1,736 2,311 3,184 3,475 4,201 2,480 4,610 CHOTF* CHOOH 79 CHOMH2 1,899 193 161 80 20 14 6 3 CHOMH1 8,581 4,328 1,942 130 3,171 646 674 1,988 275 197 2,232 4,110 3,425 3,513 5,512 6,444 5,228 3,646 1,622 LCHMH 4,008 301 8 56 797 341 164 65 160 70 315 368 121 41 809 1,220 1,375 1,454 1,046 HNGMH 7,873 319 367 32 743 623 1,546 2,344 2,769 3,122 3,520 4,245 3,192 2,081 1,434 2,096 725 1,816 2,674 FSBMH 726 0 5 19 13 1 32 36 59 27 5 6 NANTF* NANOH 4 NANMH 6 WICMH 8 MANMH 4,396 187 168 328 327 200 239 263 326 357 145 214 18 130 32 226 420 BIGMH 2,180 435 0 334 388 212 299 291 396 379 400 344 388 194 311 207 409 546 POCTF* POCOH* POCMH 4,851 209 22 278 608 1,050 938 1,344 1,158 1,442 1,430 1,738 1,711 1,831 1,575 1,558 1,545 1,251 1,076 1,090 1,126 TANMH 39,589 7,126 1,704 4,512 6,226 11,019 11,675 13,944 12,245 15,336 15,886 16,966 17,688 16,463 12,086 11,205 10,829 9,268 6,479 10,386 12,272

Numbers in blue = Year of maximum underwater bay grass acreage.

* = No recorded underwater bay grass for any year.
▼B7

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals Northern Chesapeake Bay CB1TF 51.0 26.3 14.9 61.1 29.8 17.3 66.0 30.0 9.5 80.1 36.8 9.4 Upper Chesapeake Bay CB2OH 4.6 1.2 0.2 7.9 8.5 1.8 2.3 1.9 0.2 13.2 8.1 6.2 Upper Central Chesapeake Bay CB3MH 52.7 21.3 7.5 41.3 4.5 0.9 39.4 4.6 1.0 41.9 6.1 0.8 Middle Central Chesapeake Bay CB4MH 5.5 0.6 0.0 2.5 0.0 0.0 0.7 0.0 0.0 2.1 0.0 0.0 Lower Central Chesapeake Bay CB5MH 15.8 8.4 1.2 23.1 15.9 3.5 24.4 21.3 5.1 18.8 18.6 4.0 Western Lower Chesapeake Bay CB6PH 22.2 25.7 4.8 23.3 25.3 3.6 30.7 31.4 4.9 25.5 25.3 4.0 Eastern Lower Chesapeake Bay CB7PH 33.1 26.1 10.8 38.2 27.6 11.0 43.7 31.0 13.6 42.1 29.0 13.9 Mouth of the Chesapeake Bay CB8PH 0.0 0.0 0.0 0.0 0.0 0.0 1.0 1.3 0.4 2.2 1.4 0.4 Bush River BSHOH 0.2 0.0 0.0 2.8 1.4 0.0 0.4 0.0 0.0 11.4 9.4 1.2 Gunpowder River GUNOH 15.9 8.9 4.2 8.6 6.9 3.4 12.7 7.4 3.4 54.1 40.1 30.0 Middle River MIDOH 43.4 18.1 3.8 11.9 11.3 9.1 10.3 4.8 0.7 41.0 41.1 19.0 Back River BACOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Patapsco River PATMH 6.0 5.3 0.7 0.0 0.0 0.0 0.1 0.0 0.0 1.0 0.4 0.0 Magothy River MAGMH 40.5 16.8 6.5 0.8 0.4 0.0 8.6 2.3 0.3 21.8 5.5 1.0 Severn River SEVMH 25.4 19.5 7.8 0.0 0.0 0.0 7.9 8.9 1.7 27.7 24.7 11.7 South River SOUMH 4.5 0.8 0.4 0.0 0.0 0.0 0.5 0.3 0.0 6.4 1.7 0.4 Rhode River RHDMH 4.6 0.7 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 West River WSTMH 17.8 1.8 0.2 0.9 0.0 0.0 2.1 0.0 0.0 1.4 0.0 0.0 Upper Patuxent River PAXTF 0.0 0.0 0.0 0.0 0.0 0.0 23.1 15.4 9.6 39.5 22.6 15.3 Western Branch (Patuxent River) WBRTF * * * * * * * * * * * 0 Middle Patuxent River PAXOH 0.2 0.0 0.0 0.0 0.0 0.0 5.5 0.1 0.0 8.4 2.9 0.5 Lower Patuxent River PAXMH 2.0 0.4 0.1 3.7 3.1 0.8 0.1 0.0 0.0 0.3 0.1 0.0 Upper Potomac River POTTF 5.3 17.4 3.3 32.7 65.6 24.4 39.5 60.2 16.4 36.1 51.5 11.2 Bay 1978–1984 1985–1990 1991–1995 1996–2000 CBP Segment Name Segment 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m

Table B-3. Percent of potential shallow-water habitat covered by underwater bay grass from 1978–2000 at five-year intervals by Chesapeake Bay Program Segment.

continued
▼B8

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals Bay 1978–1984 1985–1990 1991–1995 1996–2000 CBP Segment Name Segment 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m Table B-3. Percent of potential shallow-water habitat covered by underwater bay grass from 1978–2000 at five-year intervals by Chesapeake Bay Program Segment (cont.). Anacostia River ANATF 5.8 1.8 1.2 7.0 2.9 3.1 8.5 4.3 4.4 9.6 4.1 3.2 Piscataway Creek PISTF 40.3 50.0 21.6 76.7 96.0 90.6 29.4 48.1 18.0 67.2 49.7 17.6 Mattawoman Creek MATTF 0.0 0.0 0.0 14.6 7.3 7.6 18.5 11.3 8.7 55.8 32.0 5.5 Middle Potomac River POTOH 20.2 5.1 0.2 46.0 23.7 11.8 51.3 31.6 13.1 66.3 45.5 15.0 Lower Potomac River POTMH 2.9 0.6 0.0 2.5 0.7 0.2 4.4 1.2 0.1 15.7 5.2 0.6 Upper Rappahannock River RPPTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.3 0.4 0.1 Middle Rappahannock River RPPOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lower Rappahannock River RPPMH 0.5 0.2 0.1 6.5 2.3 0.2 2.2 0.8 0.2 1.2 0.3 0.2 Corrotoman River CRRMH 0.2 0.2 0.1 29.7 16.0 2.9 25.7 13.1 3.2 17.6 6.6 1.8 Piankatank River PIAMH 2.5 1.2 0.7 11.7 7.4 2.5 17.3 15.2 7.2 9.8 7.8 2.5 Upper Mattaponi River MPNTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.4 2.5 1.0 Lower Mattaponi River MPNOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Upper Pamunkey River PMKTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 13.1 8.9 2.0 Lower Pamunkey River PMKOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Middle York River YRKMH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lower York River YRKPH 12.1 6.7 1.0 13.9 13.7 2.5 15.8 15.3 2.7 18.3 16.2 3.2 Mobjack Bay MOBPH 36.3 37.4 5.8 41.2 44.0 8.9 44.5 49.7 8.3 45.1 48.6 8.2 Upper James River JMSTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.5 0.5 Appomattox River APPTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Middle James River JMSOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 Chickahominy River CHKOH 2.9 3.7 0.8 0.6 1.9 0.3 0.0 0.0 0.0 14.8 27.6 3.5 Lower James River JMSMH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Mouth of the James River JMSPH 1.6 1.0 0.0 1.1 0.0 0.0 3.4 0.7 0.0 17.2 10.1 0.8 continued
▼B9

appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals Western Branch Elizabeth River WBEMH * * * * * * * * * * * 0 Southern Branch Elizabeth River SBEMH * * * * * * * * * * * 0 Eastern Branch Elizabeth River EBEMH * * * * * * * * * * * 0 Lafayette River LAFMH * * * * * * * * * * * 0 Mouth of the Elizabeth River ELIPH * * * * * * * * * * * 0 Lynnhaven River LYNPH 2.3 3.0 1.7 4.1 4.9 2.7 3.6 2.6 1.6 3.5 3.3 1.1 Northeast River NORTF 2.1 0.1 0.0 0.3 0.0 0.0 5.8 0.3 0.0 6.8 0.0 0.0 C&D Canal C&DOH 0.2 0.9 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Bohemia River BOHOH 0.0 0.0 0.0 4.0 1.8 0.0 4.0 0.1 0.0 14.6 8.0 6.1 Elk River ELKOH 1.8 0.5 0.0 18.1 24.8 22.1 19.0 20.3 22.4 36.3 33.8 34.5 Sassafras River SASOH 1.4 0.7 0.0 6.8 6.5 7.9 18.0 15.9 0.9 28.0 40.5 12.7 Upper Chester River CHSTF 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Middle Chester River CHSOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lower Chester River CHSMH 52.5 25.2 5.0 22.9 5.5 1.0 22.4 7.7 1.4 24.9 10.0 2.1 Eastern Bay EASMH 33.1 13.8 2.5 37.5 11.7 1.6 38.4 11.9 1.5 54.8 28.3 3.9 Upper Choptank River CHOTF * * * * * * * * * * * 0 Middle Choptank River CHOOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lower Choptank River CHOMH2 9.4 4.4 0.8 3.3 0.9 0.1 0.8 0.2 0.0 0.1 0.0 0.0 Mouth of the Choptank River CHOMH1 43.4 20.4 6.2 44.4 14.8 2.1 46.8 25.4 5.2 64.8 38.9 8.4 Little Choptank River LCHMH 6.4 0.7 0.1 19.3 4.4 0.6 9.0 2.5 0.5 37.5 16.9 2.7 Honga River HNGMH 6.9 0.9 0.0 47.8 13.6 1.2 61.2 18.8 1.2 46.2 14.3 1.4 Fishing Bay FSBMH 0.0 0.0 0.0 1.1 0.1 0.0 2.5 0.7 0.1 0.2 0.0 0.0 Upper Nanticoke River NANTF * * * * * * * * * * * 0 Middle Nanticoke River NANOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lower Nanticoke River NANMH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Bay 1978–1984 1985–1990 1991–1995 1996–2000 CBP Segment Name Segment 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m

Table B-3. Percent of potential shallow-water habitat covered by underwater bay grass from 1978–2000 at five-year intervals by Chesapeake Bay Program Segment (cont.).

continued
▼B10

Wicomico River WICMH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Manokin River MANMH 3.9 1.4 0.0 11.8 3.9 0.1 10.6 5.1 0.2 11.1 2.9 0.1Big Annemessex River BIGMH 13.3 13.7 0.3 24.6 11.6 0.7 21.2 8.6 0.2 24.2 11.3 0.3Upper Pocomoke River POCTF * * * * * * * * * * * 0Middle Pocomoke River POCOH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Lower Pocomoke River POCMH 11.7 12.4 0.7 17.7 17.5 3.9 19.7 17.8 2.9 17.7 16.8 2.4Tangier Sound TANMH 33.2 23.2 5.3 47.3 32.8 8.7 50.0 34.0 8.9 40.0 26.1 6.6Percentages in blue bold = Underwater bay grasses cover ≥ 10 percent of potential habitat for all 4 of the time periods.Percentages in bold = Underwater bay grasses cover ≥ 10 percent of potential habitat for 3 of the time periods.

Note: While some periods span more than 5 years, each period represents only 5 years worth of data. There were some years when no underwater bay grass surveys occurred (i.e., 1982, 1983 and 1988).*Denotes no data available or no underwater bay grasses mapped.

Bay 1978–1984 1985–1990 1991–1995 1996–2000

CBP Segment Name Segment 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 m 0–0.5 m 0–1 m 1-2 mTable B-3. Percent of potential shallow-water habitat covered by underwater bay grass from 1978–2000 at five-year intervals by Chesapeake Bay Program Segment (cont.).
▼C1

appendix C • Underwater Bay Grasses No-Grow Zones Acreage

appendixC

Underwater Bay Grasses

No-Grow Zones Acreage

Table C-1. Underwater bay grasses no-grow zones acreage by Chesapeake Bay

Program segment.

Chesapeake Bay Program CBP Acres in 

Segment Segment No Grow Zones Reason

Northern Chesapeake Bay CB1TF 679 1

Upper Chesapeake Bay CB2OH 1,564 1

Upper Central Chesapeake Bay CB3MH 4,537 1

Middle Central Chesapeake Bay CB4MH 14,590 1

Lower Central Chesapeake Bay CB5MH 5,061 1

Western Lower Chesapeake Bay CB6PH 3,684 1

Eastern Lower Chesapeake Bay CB7PH 8,339 1

Mouth of the Chesapeake Bay CB8PH 1,186 1

Patapsco River PATMH 5,701 2

Magothy River MAGMH 199 1

South River SOUMH 102 1

Rhode River RHDMH 375 1

West River WSTMH 132 1

Lower Potomac River POTMH 19 1

Lower Rappahannock River RPPMH 395 1

Piankatank River PIAMH 105 1

Mobjack Bay MOBPH 635 1

Lower James River JMSMH 4,312 1

Mouth of the James River JMSPH 619 1

Western Branch Elizabeth River WBELI 1,484 2

Southern Branch Elizabeth River SBELI 2,073 2

Eastern Branch Elizabeth River EBELI 1,426 2

Lafayette River LAFMH 1,421 2

Mouth of the Elizabeth River ELIPH 20,626 2

continued
▼C2

appendix C • Underwater Bay Grasses No-Grow Zones Acreage

Northeast River NORTF <1 1

Sassafras River SASOH 2 1

Eastern Bay EASMH 134 1

Upper Choptank River CHOTF 2,200 4

Middle Choptank River CHOOH 984 4

Mouth of the Choptank River CHOMH1 37 1

Little Choptank River LCHMH 6 1

Upper Nanticoke River NANTF 1,138 3

Wicomico River WICMH 708 3

Big Annemessex River BIGMH 4 1

Upper Pocomoke River POCTF 988 3

Middle Pocomoke River POCOH 2,466 1

Lower Pocomoke River POCMH 13,293 1

Tangier Sound TANMH 6,198 1

Reason Codes:

1 - Extreme physical wave energy.

2 - Permanent physical alteration to near-shore habitat.

3 - Natural, extreme coloration of the water.

4 - Natural river channelization.

Chesapeake Bay Program CBP Acres in 

Segment Segment No Grow Zones Reason

Table C-1. Underwater bay grasses no-grow zones acreage by Chesapeake Bay

Program segment (cont.).
The pycnocline has a functional role in defining designated use boundaries. The definitions of the designated use boundaries take into account the types and needs of the

living resources that inhabit different parts of the Chesapeake Bay, as well as the

bathymetry, hydrology, physical features, and natural stratification of the Chesapeake Bay waters as described in Chapter IV.

STRATIFICATION

Vertical stratification is foremost among the physical factors affecting dissolved

oxygen concentrations in some parts of Chesapeake Bay and its tidal tributaries.

Stratification arises from differences in water density within the water column due

to vertical differences in the salinity and temperature of the source waters feeding

into Chesapeake Bay tidal waters. The water coming into Chesapeake Bay and its

tidal tributaries from the land via the tributaries is fresh while water from the ocean

is saline. In the summer period, the water coming from the land is also warmer than

ocean water. Colder water is more dense than warmer water, and saline water is more

dense than fresh. The simple model is that the less dense freshwater moves seaward

over the layer of more dense seawater moving from the mouth of Chesapeake Bay

northward. An idealized example is shown in Figure D-1. To the extent that the two

(or more) layers remain self-contained and poorly mixed, the waters are stratified. If

the density discontinuity is great enough to prevent mixing of the layers and constitutes a vertical barrier to diffusion of dissolved oxygen, then a pycnocline is said

to exist. 

When physical features like channels, holes and sills inhibit lateral exchange of

waters and a pycnocline inhibits vertical exchange, oxygen that is consumed in

biological respiration or other oxygen-consuming processes in the imprisoned

subpycnocline waters cannot be replenished. When there is no barrier to lateral

exchange, the effect of the pycnocline on lower layer oxygen levels may be ameliorated. For this reason, the extent of isolation caused by a pycnocline, as well as the

frequency of formation and the depth of the pycnocline when present are factors to

be considered in defining designated use boundaries. 

▼D1

appendix D • Vertical Stratification and the Pycnocline

appendixD

Vertical Stratification

and the Pycnocline
CALCULATING PYCNOCLINE DEPTH

DENSITY GRADIENT THRESHOLD

The threshold for the density gradient that defines the upper pycnocline depth 

(0.1 kg/m4) is taken from Fisher, et al. (2003). The density gradient sufficient to stop

turbulent mixing for any water body is somewhat determined by the local physical

processes in that body. Density gradient thresholds vary by water body. Fisher, et al

determined the Chesapeake Bay upper pycnocline threshold by examining existing

literature for other oceanic and estuarine systems and applying those methods to the

Chesapeake Bay. Determination of this number involved examining thousands of

vertical plots of density, dissolved oxygen concentration, and the vertical slopes of

these two parameters to find a reasonable threshold value. The value of 0.1 kg/m4

was judged to be the most reasonable value for the upper pycnocline depth in the

Chesapeake Bay and is in line with values for other estuarine systems. The actual

▼D2

appendix D • Vertical Stratification and the Pycnocline

Figure D-1. Illustration of stratification of the water column in the mainstem of the Chesapeake Bay.

Source: Chesapeake Bay Program website http://chesapeakebay.net/data.htm.

0

-5

-10

-15

-20

-25

Water Column Depth (meters)

Density/Dissolved Oxygen

0 5 10 15

density

DO

upper pyc

lower pyc
▼D3

appendix D • Vertical Stratification and the Pycnocline

pycnocline depths were not overly sensitive to the threshold value chosen, since

mixed layer gradients tend to be much less than 0.1 kg/m4 and inter-pycnocline

gradients tend to be much greater than 0.1 kg/m4.

Using similar methods, the value of 0.2 kg/m4 was chosen as the lower pycnocline

depth gradient by the monitoring data analysis team at the Chesapeake Bay Program.

Vertical density and dissolved oxygen concentration plots from around the Chesapeake Bay and its tidal tributaries were examined to determine the threshold value

that was most representative of the density gradient defining the upper boundary of

the lower mixed layer, when and where it existed. The upper layer density threshold

of 0.1 kg/m4 was judged to be too low as it sometimes placed the lower pycnocline

depth at levels that did not have a large effect on the dissolved oxygen concentration.

PYCNOCLINE CALCULATION METHODOLOGIES

The Chesapeake Bay Program Water Quality Monitoring Program collects vertical

profiles of temperature, salinity and conductivity measurements (among other

parameters) at 1 to 2 meter intervals at each of its sampling stations. From these

measurements, there are at least two approaches for determining a pycnocline.

Vertical Density Profile

The upper and lower pycnocline depths can be determined by constructing a vertical

density (sigma_t) profile and applying an absolute density change threshold. This is

the method used for all pycnocline calculations in this document and is recommended for application by the states in defining designated use boundaries. For a

detailed explanation of the derivation of this method see Fisher et al. (2003). 

1) Calculate density using the following equations:

temp c = water temperature in degrees Celsius

sigo = –0.069+((1.47808*((salinity-0.03)/1.805))

(0.00157*(((salinityB0.03)/1.805)**2))

+0.0000398*(((salinityB0.03)/1.805)**3)));

tsum = (–1*(((tempc-3.98)**2)/503.57))* 

((tempc+283)/(tempc+67.26));

sa = (10**–3)*tempc)*(4.7867- 

(0.098185*tempc)+(0.0010843*(tempc**2)));

sb = ((10**–6)*tempc)*(18.030–

(0.8164*tempc)+(0.01667*(tempc**2)));

Sigma_t = tsum+((sigo+0.1324)*(1–sa+sb*(sigo –0.1324))); 
2) Apply the following rules to the density profile:

i) From the water surface, the first density slope observation that is greater

than 0.1 kg/m4 is designated as the upper pycnocline depth provided that:

a) That observation is not the first observation in the water column; and 

b) The next density slope observation below is positive.

ii) From the bottom, the first density slope observation that is greater than

0.2 kg/m4 is designated as the lower pycnocline depth provided that:

a) An upper pycnocline depth exists;

b) There is a bottom mixed layer, defined by the first or second density

slope observation from the bottom being less than 0.2 kg/m4; and

c) The next density slope observation above is positive.

Vertical Differences in Conductivity

A ‘working’ pycnocline depth can be calculated using vertical differences in conductivity. The following is the Chesapeake Bay Water Quality Monitoring Program field

method applied during water quality monitoring sampling cruises for determining

the presence of a pycnocline and, if one or more exist, the depth of the upper and

lower boundary and, therefore, depths at which to collect water samples for chemical analysis in the laboratory.

1) Find the average rate of change from surface to bottom: i.e., subtract surface

conductivity from bottom conductivity and divide by the depth.

2) Multiply the average rate of change by 2. This product is called the threshold.

3) If the threshold is less than 500, then it is determined that no pycnocline exists

at the site.

4) It the threshold is 500 or greater, then each interval from surface to bottom is

checked to determine if the difference from one meter to the next is greater than

or equal to the threshold. The upper pycnocline is defined as the first encounter

of a difference that exceeds the threshold and the upper pycnocline depth is set

at one-half the depth interval distance. For example, if the threshold is first

exceeded between 4 and 5 meters, then the pycnocline is set at 4.5 meters.

5) Then the process is reversed and each interval from bottom to surface is checked.

If the threshold is exceeded at a depth more than 1.5 meters from the upper pycnocline, then a second pycnocline is said to exist and the lower pycnocline depth

is set at one-half the depth interval distance, as before.

Table D-1 provides some statistics on the frequency of occurrence, depth of pycnoclines, and the distance between upper and lower pycnoclines in spring and summer

at locations throughout the Chesapeake Bay and its tidal tributaries. The statistics are

for each Chesapeake Bay Water Quality Monitoring Program station over the period

analyzed for the allocations process 1985–1994. (See the Chesapeake Bay Program

website at http://www.chesapeakebay.net for a map of these stations.)

▼D4

appendix D • Vertical Stratification and the Pycnocline
▼D5

appendix D • Vertical Stratification and the Pycnocline

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994.

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

CB1.1 6.1 - - - 0% 0%

CB2.1 6.0 2.3 - - 17% 0%

CB2.2 12.1 4.0 2.8 6.9 68% 20%

CB3.1 12.8 2.9 5.0 7.9 99% 76%

CB3.2 11.7 2.9 4.2 7.1 93% 57%

CB3.3C 23.7 4.2 10.6 14.8 100% 88%

CB3.3E 8.2 2.6 1.6 4.2 80% 18%

CB3.3W 9.0 2.7 2.3 5.0 77% 13%

CB4.1C 31.8 5.6 11.7 17.3 100% 96%

CB4.1E 23.1 6.5 7.8 14.3 99% 84%

CB4.1W 9.1 3.4 2.6 5.9 56% 19%

CB4.2C 26.8 6.9 9.6 16.5 100% 98%

CB4.2E 9.3 4.1 2.1 6.2 65% 13%

CB4.2W 9.3 4.3 1.2 5.5 46% 11%

CB4.3C 25.9 6.5 8.6 15.2 100% 94%

CB4.3E 22.1 7.1 7.8 14.8 97% 86%

CB4.3W 9.7 4.4 1.2 5.6 51% 10%

CB4.4 29.4 6.6 10.3 16.9 100% 100%

CB5.1 33.3 6.4 8.6 15.0 100% 99%

CB5.1W 9.1 4.4 - - 24% 0%

CB5.2 29.5 7.5 9.0 16.6 100% 100%

CB5.3 26.2 6.1 7.2 13.2 100% 96%

CB5.4 32.6 5.3 12.8 18.1 100% 97%

CB5.4W 5.3 2.5 1.0 3.5 29% 3%

CB5.5 19.5 4.7 8.4 13.1 99% 79%

CB6.1 13.1 4.5 4.3 8.7 100% 80%

CB6.2 11.2 4.3 3.3 7.6 96% 76%

CB6.3 12.8 3.7 4.5 8.1 97% 87%

continued
▼D6

appendix D • Vertical Stratification and the Pycnocline

CB6.4 10.3 3.3 3.3 6.6 90% 54%

CB7.1 25.2 4.8 9.7 14.5 85% 65%

CB7.1N 31.7 5.9 12.5 18.4 69% 35%

CB7.1S 16.1 3.8 5.5 9.3 96% 87%

CB7.2 22.1 3.4 9.0 12.4 97% 95%

CB7.2E 13.4 3.2 3.7 6.9 88% 72%

CB7.3 13.8 3.3 5.8 9.1 96% 81%

CB7.3E 17.8 4.1 6.1 10.2 93% 73%

CB7.4 13.9 3.2 5.3 8.5 95% 79%

CB7.4N 12.9 3.3 3.9 7.3 74% 44%

CB8.1 9.8 3.5 3.7 7.2 95% 38%

CB8.1E 17.9 4.3 6.2 10.5 96% 82%

EBE1 8.4 3.2 1.8 5.0 61% 9%

EBE2 9.0 2.5 - - 100% 0%

EE1.1 12.3 6.6 2.6 9.2 74% 31%

EE2.1 7.8 3.3 1.4 4.7 53% 12%

EE2.2 13.1 5.0 3.6 8.6 72% 49%

EE3.0 7.1 2.8 - - 12% 0%

EE3.1 13.2 4.1 2.5 6.6 60% 16%

EE3.2 26.8 6.9 10.7 17.6 42% 9%

EE3.3 3.9 1.5 - - 19% 0%

EE3.4 4.7 2.0 0.5 2.5 26% 4%

EE3.5 27.3 7.0 8.7 15.7 41% 19%

ELI1 8.0 3.5 - - 100% 0%

ELI2 13.5 5.9 4.9 10.8 87% 30%

ELI3 12.0 3.5 6.0 9.5 100% 100%

ET1.1 2.9 - - - 0% 0%

ET10.1 5.2 - - - 0% 0%

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994 (cont.).

continued
▼D7

appendix D • Vertical Stratification and the Pycnocline

ET2.1 13.2 4.0 - - 3% 0%

ET2.2 2.9 - - - 0% 0%

ET2.3 12.3 4.5 - - 8% 0%

ET3.1 5.3 - - - 0% 0%

ET4.1 5.4 1.8 - - 5% 0%

ET4.2 13.9 5.4 4.4 9.8 70% 43%

ET5.1 5.7 2.0 - - 8% 0%

ET5.2 11.8 3.7 3.4 7.1 76% 20%

ET6.1 5.0 1.5 - - 3% 0%

ET6.2 3.8 1.5 - - 49% 0%

ET7.1 7.7 2.3 0.6 2.9 71% 14%

ET8.1 5.1 1.7 2.8 4.5 31% 3%

ET9.1 4.8 1.5 1.0 2.5 11% 6%

LAF1 5.2 2.5 - - 40% 0%

LE1.1 12.1 4.8 2.7 7.5 75% 25%

LE1.2 17.1 5.7 3.9 9.6 68% 16%

LE1.3 23.3 7.3 5.3 12.6 43% 9%

LE1.4 14.9 7.5 3.0 10.5 44% 4%

LE2.2 11.2 3.4 3.7 7.1 91% 64%

LE2.3 19.7 5.7 7.4 13.1 95% 77%

LE3.1 5.5 4.0 - - 34% 0%

LE3.2 12.2 6.2 2.2 8.4 73% 43%

LE3.3 4.1 4.0 - - 3% 0%

LE3.4 11.3 6.6 3.7 10.2 72% 23%

LE3.6 9.9 3.9 2.5 6.4 81% 30%

LE3.7 7.4 3.7 1.3 5.0 52% 8%

LE4.1 7.5 4.3 1.7 6.0 60% 6%

LE4.2 11.6 4.8 3.0 7.8 51% 17%

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994 (cont.).

continued
▼D8

appendix D • Vertical Stratification and the Pycnocline

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994 (cont.).

LE4.3 14.3 7.0 5.1 12.1 66% 39%

LE5.1 6.6 4.7 1.3 6.0 24% 1%

LE5.2 7.6 4.2 2.0 6.3 79% 10%

LE5.3 6.3 4.0 2.0 6.0 68% 3%

LE5.4 13.7 5.4 6.6 12.0 44% 13%

LE5.5 21.2 5.1 10.5 15.6 96% 73%

LE5.6 13.7 7.0 5.0 12.0 71% 16%

MAT0016 6.8 - - - 0% 0%

MAT0078 1.0 - - - 0% 0%

PIS0033 1.0 - - - 0% 0%

RET1.1 11.1 4.7 2.8 7.5 64% 9%

RET2.1 7.3 - - - 0% 0%

RET2.2 9.8 5.1 1.9 7.0 22% 2%

RET2.3 9.2 - - - 0% 0%

RET2.4 15.7 5.4 5.4 10.8 79% 33%

RET3.1 5.2 4.0 - - 12% 0%

RET3.2 4.0 - - - 0% 0%

RET4.1 4.5 4.0 - - 1% 0%

RET4.2 10.9 7.1 0.9 8.0 18% 1%

RET4.3 4.7 4.0 - - 4% 0%

RET5.1 1.1 - - - 0% 0%

RET5.1A 2.8 - - - 0% 0%

RET5.2 7.5 4.9 - - 15% 0%

SBE1 14.0 3.5 - - 100% 0%

SBE2 12.5 4.4 4.9 9.3 83% 43%

SBE3 11.0 2.5 5.0 7.5 100% 100%

SBE4 12.0 2.5 - - 100% 0%

SBE5 11.0 3.6 3.5 7.1 100% 70%

continued
▼D9

appendix D • Vertical Stratification and the Pycnocline

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994 (cont.).

TF1.2 1.0 - - - 0% 0%

TF1.3 1.0 - - - 0% 0%

TF1.4 1.2 - - - 0% 0%

TF1.5 10.5 - - - 0% 0%

TF1.6 6.0 - - - 0% 0%

TF1.7 2.9 1.8 - - 5% 0%

TF2.1 19.0 - - - 0% 0%

TF2.2 8.3 - - - 0% 0%

TF2.3 12.8 - - - 0% 0%

TF2.4 8.9 - - - 0% 0%

TF3.1A 2.9 - - - 0% 0%

TF3.1B 2.9 - - - 0% 0%

TF3.1C 4.0 - - - 0% 0%

TF3.1D 2.7 - - - 0% 0%

TF3.1E 2.8 - - - 0% 0%

TF3.2 6.1 - - - 0% 0%

TF3.2A 4.0 - - - 0% 0%

TF3.3 5.7 4.2 - - 14% 0%

TF4.1A 5.8 - - - 0% 0%

TF4.2 5.9 - - - 0% 0%

TF4.4 2.7 - - - 0% 0%

TF4.4A 6.3 - - - 0% 0%

TF5.2 1.0 - - - 0% 0%

TF5.2A 7.0 - - - 0% 0%

TF5.3 9.8 - - - 0% 0%

TF5.4 5.8 - - - 0% 0%

TF5.5 8.2 - - - 0% 0%

TF5.5A 7.4 - - - 0% 0%

continued
TF5.6 8.5 6.0 - - 1% 0%

TF5.6A 7.8 - - - 0% 0%

WBE1 4.7 2.8 - - 17% 0%

WE4.1 6.1 2.9 0.7 3.6 35% 9%

WE4.2 14.5 6.3 4.2 10.5 86% 35%

WE4.3 6.0 2.8 0.8 3.5 20% 1%

WE4.4 7.6 2.3 1.5 3.8 19% 4%

WT1.1 2.3 - - - 0% 0%

WT2.1 2.0 - - - 0% 0%

WT3.1 3.3 1.5 - - 5% 0%

WT4.1 1.8 - - - 0% 0%

WT5.1 14.5 3.6 7.7 11.3 100% 69%

WT6.1 5.4 2.5 1.0 3.5 57% 5%

WT7.1 8.6 3.1 2.4 5.4 87% 31%

WT8.1 8.6 2.2 1.7 3.8 91% 58%

WT8.2 2.9 1.5 - - 2% 0%

WT8.3 3.3 1.5 - - 15% 0%

WXT0001 1.1 - - - 0% 0%

XFB1986 1.5 - - - 0% 0%

XGG8251 5.5 2.5 - - 8% 0%

Literature Cited: Fisher, T.R., A.B. Gustafson, H.L. Berndt, L. Walstad, L.W. Haas, and S. MacIntyre, “The upper mixed layer of

Chesapeake Bay, USA.” Submitted to Estuaries, 2003. 

▼D10

appendix D • Vertical Stratification and the Pycnocline

Upper Interpyc Lower Upper Lower

Station Depth Depth Depth Depth Percent Percent

Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and

percent occurrence: 1985-1994 (cont.).