United States

Environmental Protection

Agency

Office of Water

(4502F)

Washington, DC

EPA-843-B-96-001

October 1996

Protecting Natural

Wetlands

A Guide to Stormwater

Best Management Practices

Internet Address (URL) l http://www.epa.gov

Recycled/Recyclable l Printed with Vegetable Oil Based Inks on Recycled Paper (20% Postconsumer)
Protecting Natural Wetlands:

A Guide to Stormwater

Best Management Practices

Office of Water (4502F)

United States

Environmental Protection Agency

Washington, DC 20460
Contents

Contents

ACKNOWLEDGEMENTS .............................................................................................. vi

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l-l

2 . FACTORS TO CONSIDER WHEN SELECTING BMPS ........................................ 2-1

Introduction ............................................................................................................................. 2-l

Wetland Factors........................................................................................................................ .2-2

Wetland Type..................................................................................................................... .2-2

Hydrology ........................................................................................................................... 2-3

Biological Functions ........................................................................................................... 2-6

Microbes ............................................................................................................................. 2-6

Vegetation ........................................................................................................................... 2-6

Animals ............................................................................................................................... 2-7

Site-Specific Conditions ................................................................................................... .2-7

Soils..................................................................................................................................... 2-7

Climate ............................................................................................................................... 2-9

Landscape Position............................................................................................................ .2-9

Descriptions of SpecificWetland Types................................................................................2-10

PocosinWetlands........................................................................................................... .2-10

Cienegas.. .......................................................................................................................... 2-10

PlayaLakes...................................................................................................................... .2-11

Riverine or Riparian Wetland Areas of the Southwest.. ..............................................2-12

Prairie Potholes................................................................................................................ .2-12

Sand Hills Wetlands........................................................................................................ .2-13

Peatlands of the North-Central States ...........................................................................2-14

Bottomland Hardwoods ................................................................................................. .2-14

Swamps and Bogs of the Northeast .............................................................................. .2-15

Cypress Dome Wetlands.. ............................................................................................... .2-16

Permafrost/Tundra Wetlands.. ........................................................................................ .2-16

Stormwater Factors.. .............................................................................................................. .2-17

Stormwater Quantity.. ................................................................................................... .2-17

Runoff and Peak Flow..................................................................................................... .2-17

Rainfall .............................................................................................................................. 2-19

Stormwater Quality.. ...................................................................................................... .2-19

Overview o f BMPCapabilities ............................................................................................... 2-27

Assessing the Ability of a BMP to Protect a Wetland....................................................2-27

Nonstructural Controls .................................................................................................. .2-28

Watershed Planning ........................................................................................................ .2-29

Permitting Programs ....................................................................................................... .2-30

Preventive Construction Techniques............................................................................. .2-30

Operation and Maintenance .......................................................................................... .2-30

Outreach and Educational Programs............................................................................. .2-31

Structural Controls ................................................................................................................

.2-31

BMPsin Series.................................................................................................................

.2-32

BMP Maintenance Requirements.................................................................................. .2-32

Page iii
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Maintenance Factors .......................................................................................................2-33

Implementation .............................................................................................................. .2-34

Development of an Effective Maintenance Plan .......................................................... .2-35

Components of an Effective Maintenance Plan ........................................................... .2-36

Funding Sources ..................................................................................................................... .2-37

Taxes .................................................................................................................................2-37

Fees .................................................................................................................................... 2-38

Capacity Credits.. ............................................................................................................. 2-39

Fee-in-Lieu......................................................................................................................... 2-39

Bonds/Debt Financing ....................................................................................................2-39

State Revolving Funds ....................................................................................................2-40

Grants ............................................................................................................................... 2-40

Leases ...............................................................................................................................2-40

Matching Wetland/Stormwater Factors to BMP Design ....................................................2-41

Preliminary Treatment of Stormwater.. ........................................................................2-41

Matching Wetland Characteristics to BMP Design.. ....................................................2-41

Hydrology ........................................................................................................................ .2 -41

Climate ............................................................................................................................. 2-43

Water Quality .................................................................................................................. .2-44

Monitoring ...................................................................................................................... .2-44

Summary ................................................................................................................................. 2-46

References ................................................................................................................................ 2-47

3. CASE STUDIES ....................................................................................................... 3-1

Introduction ........................................................................................................................... .3-1

Regional Case Studies .............................................................................................................. .3-5

EPA Region 1 - Narrow River Special Area Management Plan, Rhode Island.. ........... .3-5

EPA Region 2 - Freshwater Wetlands Protection Act, State of New Jersey ................. .3-8

EPA Region 3 - Watershed Management Study, Prince William County Virginia.. .. .3-11

EPA Region 4 - Hidden River Wetland Stormwater Treatment Site, Tampa,

Florida.. ............................................................................................................. .3-16

EPA Region 5 - Lake McCarrons Wetland Treatment System, Roseville,

Minnesota ........................................................................................................ .3-17

- The Phalen Chain of Lakes Watershed Project, Ramsey and Washington

Counties, Minnesota ...................................................................................... .3-20

- The Prairie Wolf Slough Project, Chicago, Illinois .............................................3-23

EPA Region 6 - Tensas Cooperative River Basin Study, Louisiana .............................. .3-24

EPA Region 7 - Multi-Species Riparian Buffer Strips, Bear Creek Watershed, Iowa.. .3-30

EPA Region 8 - Watershed Approach to Municipal Stormwater Management,

Fort Collins, Colorado.. ................................................................................... .3-36

- Lemna Nonpoint Source Treatment System, Chatfield Reservoir, Colorado .3-41

EPA Region 9 - Lincoln-Alvarado Project, Union City, California .............................. .3-46

EPA Region 10 - Riparian Area Wetland Restoration Project, Sawmill

Creek, Idaho.. ...................................................................................................3-46

- Sublett Creek Restoration Project, Idaho ........................................................... .3-47

- Bear Creek Restoration Project, Crook County, Oregon.. .................................. .3-48

- Camp Creek Restoration, Crook County, Oregon ............................................. .3-50

- The Chewaucan River Project, Lake County, Oregon ........................................ 3-51

4. BEST MANAGEMENT PRACTICES ...................................................................... 4-1

Introduction ........................................................................................................................... .4-1

Nonstructural BMPs - Pollution Prevention ...................................................................4-2

Page iv
Contents

Nonstructural BMPs - Watershed Management Plans...................................................4-8

Nonstructural BMPs - Preventive Construction Techniques .......................................4-12

Nonstructural BMPs - Outreach and Educational Programs......................................4-13

Nonstructural BMPs - Riparian Areas............................................................................4-18

Structural BMPs - Infiltration Basins ............................................................................. 4-20

Structural BMPs - Infiltration Trenches.. ......................................................................4-25

Structural BMPs - Sand Filters.. ...................................................................................... 4-29

Structural BMPs - Grassed Swales .................................................................................. 4-32

Structural BMPs - Vegetative Filter Strips ..................................................................... 4-35

Structural BMPs - Vegetative Natural Buffers ..............................................................4-38

Structural BMPs - Open Spaces ...................................................................................... 4-41

Structural BMPs - Extended Detention Dry Basins ......................................................4-43

Structural BMPs - Wet Ponds .......................................................................................... 4-47

Structural BMPs - Constructed Wetlands ..................................................................... 4-50

Structural BMPs - Porous Pavement and Concrete Grid Pavemem .............................. 4-54

Structural BMPs - Oil/Grit Separators or Water Quality Inlets ...................................4-58

Structural BMPs - Level Spreaders .................................................................................. 4-61

Structural BMPs - French Drains .................................................................................... 4-63

Structural BMPs - Dry Wells or Roof Downspout Systems ..........................................4-65

Structural BMPs - Exfiltration Trenches......................................................................... 4-68

BMPs in Series - ................................................................................................................ 4-70

Page v
Acknowledgement

AcknowIedgements

This document was prepared by Tetra Tech, Inc., for the Wetlands Division in EPA’s Office of

Wetlands, Oceans and Watersheds. Fran Eargle was the EPA project manager. She was assisted

by Michael Plehn.

Tetra Tech project staff included Shannon Cauley, Jim Collins, Mary Beth Corrigan, Emily

Faalasli, Kelly Gathers, John Hochheimer, Robert Johnson, Marti Martin, Paula Proctor, Dave

Skibiak, Victoria Tanga, and Sharon Thorns. Subcontractual support was provided for several of

the case studies by Gary Bentrup of Aquatic and Wetland Consultants, Inc.

Page vi
Overview

Introduction

Section 1

Introduction

lthough wetlands have long been recognized for their flood control and water quality

improvement functions, there is an increasing concern that unrestricted use of natural

wetlands as receptacles for point and nonpoint sources of pollution, such as urban

ormwater and other diffuse sources of runoff, will have an adverse effect on wetlands and

wetland biota. As a result of this concern, the U.S. Environmental Protection Agency (EPA), in

cooperation with the State of Florida, the Association of State Floodplain Managers, Inc., and

the Association of State Wetland Managers, sponsored a workshop in January 1992 on wetlands and stormwater. The purpose of the workshop was to investigate various issues related to

the management of stormwater and wetlands, explore potential options, and learn from the

experiences of the participants (wetland scientists, engineers, and environmental managers)

about protection of natural wetlands that receive stormwater runoff.

One of the major findings of the workshop was that wetlands in urban areas can be

dramatically altered by uncontrolled runoff resulting from natural drainage or direct discharge

to wetland systems. Consequently, workshop participants included in their final recommendations a need for guidelines to provide a framework for baseline protection of wetlands that

receive stormwater runoff. This document is a first step toward providing such guidelines. The

purpose of this document is to describe the potential benefits, limitations, and

appropriate application of best management practices (BMPs)1 that can be

. . . wetlands implemented to protect the functions of natural wetlands from the impacts of

in urban areas urban stormwater discharges and other diffuse sources of runoff. This document is not designed to recommend specific management practices that

can be would be applicable under all circumstances. Instead, it presents information

dramatically to assist managers in making informed decisions concerning the appropriate

altered by use of BMPs to protect existing wetland resources.

uncontrolled Land use changes within a watershed that accompany urbanization can

result in a variety of impacts to wetlands and other receiving waters. As the

percentage of impervious surface increases with the building of roads, parking

lots, and buildings, resulting runoff volume, velocity, and pollutant loads can increase dramatically. Increases in impervious surfaces also reduce the opportunity for the rainfall or snowmelt

1BMPs can include planning, schedules of activities, prohibitions of practices, maintenance procedures, and other management

approaches necessary to prevent or reduce the pollution of waters of the United States.

Page l-l
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

to infiltrate, thereby lowering groundwater levels. The impacts of these changes on wetlands

can be severe, but they will vary depending on a number of factors including the natural

hydrology of the system, the degree of change in the landscape, and the size and type of

wetland being affected.

Where natural wetlands are the ultimate receivers of stormwater, either inadvertently or

by design, the potential for impacts to the wetlands (through changes in hydrology or water

quality) exists, and BMPs may be necessary to minimize these impacts. Existing wetland

characteristics need to be matched with site characteristics as well as stormwater characteristics

when selecting BMPs. Management practices can be designed to preserve existing wetlands in a

watershed in their current state so they can continue to provide water quality improvement

and other functions and/or to restore degraded wetlands. BMPs designed to control stormwater

can result in potential impacts on downstream wetlands as well as the wetlands directly

receiving stormwater discharge. Therefore, the impacts to both onsite and offsite wetlands

should be considered when determining the suitability of wetlands for receiving stormwater

and when selecting and designing stormwater BMPs to protect the functions of natural wetlands.

The ecological attributes of natural wetlands can be adversely affected as watersheds

develop and stormwater flows increase. Wetlands tend to exist in dynamic equilibrium with

surrounding conditions when activities in a watershed remain constant. Changes in the

volume or quality of stormwater runoff resulting from changing activities in a watershed can

affect the functions and values of a natural wetland by altering the hydrologic, water quality,

and sediment or soil characteristics of a wetland. Alteration of the physical and chemical

characteristics of a wetland can adversely affect the biological community and result in

negative impacts to the ecological functions of a wetland.

As discussed in Section 2 of this document, the hydrologic conditions in a wetland affect

abiotic factors such as salinity, soil oxygen availability, and nutrient availability These factors

in turn greatly influence the flora and fauna present in a wetland. Water depth and the natural

hydroperiod in a wetland also directly influence vegetative composition and density, primary

productivity, organic accumulation, nutrient cycling and availability, and the types and density

of aquatic and terrestrial fauna in a wetland. Stormwater inflows to wetlands can directly

affect the natural hydrology of wetlands by changing water depths and altering the

hydroperiod of the systems.

The impacts of stormwater runoff on the water quality in a wetland are dependent on

the volume and composition of the stormwater. Pollutants found in runoff from urban areas

tend to include sediments, oxygen-demanding substances, nutrients, heavy metals, pesticides,

hydrocarbons, increased temperature, and trash and debris (see Section 2). Changes in turbidity,

oxygen levels, and water temperature in a wetland can have direct impacts on the flora and

fauna in the wetland. In addition, the assimilation of heavy metals, pesticides, and hydrocarbons associated with stormwater runoff by the flora and fauna in a wetland can result in

negative impacts to the ecological characteristics of the wetland.

The morphological characteristics of the soils in a wetland can also be changed as a result

of introducing stormwater runoff into a wetland system. Changes in the texture of a wetland

soil can result from changes in the amount or particle size of sediments that enter the wetland

system. Changes in the texture of a wetland soil can affect the hydrology of the system by

changing wetland drainage characteristics. Adsorption of pollutants in stormwater runoff by

suspended sediments can result in the incorporation of heavy metals, hydrocarbons, nutrients,

Page l-2
Introduction

and bacteria into the soil when the sediments settle out of suspension. The pollutants can later

reappear throughout the wetland ecosystem via chemical transformations, vegetative uptake, or

resuspension.

The Code of Federal Regulations (CFR) provides definitions of “waters of the United

States” and “wetlands” at 40 CFR 122.2 (a) through (g). Because wetlands are included under

this definition of waters of the United States, their water quality must be protected to meet

the mandate of the CWA articulated in sectionl0l(a) "to restore and maintain the chemical,

physical, and biological integrity of the nation’s waters.” The protection of water quality must

address not only the water chemistry, but also the multiple elements, including aquatic life,

wildlife, habitat, vegetation, and hydrology, that together make up aquatic systems. Therefore,

relevant issues to address with respect to wetlands protection include the toxicity and

bioaccumulation of pollutants, diversity and composition of aquatic species, entrapment of

pollutants in sediment, habitat loss, and hydrologic changes.

Controlling stormwater runoff into natural wetlands can benefit the ecosystem by

helping to maintain natural conditions in the system. As mentioned, changes in the hydrology,

water quality, and/or soil characteristics of a wetland resulting from stormwater inflows can

result in shifts in the character of the wetland habitat, which in turn changes the overall

ecological characteristics of the system. Maintaining natural conditions in a wetland by

controlling upstream stormwater runoff can mitigate the impacts of a developing watershed

on the ecological attributes of a wetland by helping to maintain predevelopment hydrologic,

water quality, and soil conditions.

Implementation of BMPs to protect wetlands from runoff can include watershed planning

techniques and also site-specific structural approaches. The planning approaches are generally

preferable to the structural practices. However, where planning has failed or is no longer an

option, implementation of structural controls, including retrofitting stormwater management

facilities into BMPs, may be appropriate.

Some general guiding principles to use in protecting wetlands from stormwater and

nonpoint source runoff include the following:

l Wetlands serve valuable water quality functions; however, wetlands have a limited

capacity for handling increased flows or additional pollutants.

l The use of BMPs specifically designed to mitigate impacts to wetlands might offset

some of the impacts of stormwater runoff by controlling increased volumes and

velocities of runoff. However, BMP discharges to wetland can adversely affect wetland

functions and values.

l BMPs have the potential to reduce impacts to downstream wetlands or wetlands

directly receiving stormwater discharges. To reduce the impacts to a receiving wetland,

BMPs should be selected based on site-specific conditions, as well as regional variability

in stormwater characteristics, climate conditions, urban development patterns, soil

types, and wetland types.

l There might be opportunities to use degraded urban wetlands or wetlands in arid

areas to provide final polishing treatment or to restore some wetland functions (e.g.,

hydrology), provided there is adequate treatment of the stormwater before it is

discharged to a wetland.

l Stormwater management should be integrated within other programs at the federal,

state, and local levels. Basinwide planning is needed to address stormwater managePage l-3
Using his Manual

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

ment objectives and wetland protection goals (i.e., advance planning, watershed

management plans, state wetlands conservation plans, or other planning tools).

l Because wetlands have a limited capacity to mitigate increased flows of stormwater and

increased pollutants, any proposal to use natural wetlands for final polishing of treated

stormwater discharges should include monitoring and maintenance as components of the

plan.

l In urbanizing areas, former wetlands whose vegetation has been removed and hydrology

altered to the extent that they no longer function as wetlands (e.g., prior converted

croplands), can offer valuable opportunities to restore wetland functions.

l While additional research is needed, existing studies suggest that constructed wetlands

can provide better pollutant removal and more consistent, predictable filtering of

stormwater than natural wetlands. Constructed wetlands should therefore be located

upstream of natural wetland locations, so their treated discharges can be directed to

natural wetlands or other waters.

l Multiple BMPs in series, or the ‘treatment train” approach, whereby a series of BMPs

provide alternative nonstructural approaches (e.g., watershed planning) or various

structural control techniques (i.e., grassed swales or longer flow paths to settle solids,

regulate flow, and reduce pollutants), may provide greater protection for natural

wetlands than individual BMPs.

Although a number of manuals describe best management practices to be used to address

stormwater runoff, this manual is a first attempt at addressing the specific water quality

concerns related to wetlands. It is intended for use by anyone addressing potential impacts to

wetlands from stormwater runoff, and it presents a wide range of planning approaches as well

as specific BMPs that can be employed in a variety of situations. Regardless of what type of

approach is taken, and at what level, this manual should be used as a starting point in a process

to identify and evaluate appropriate BMPs to protect wetland resources (see Figure l-l).

The information in this document is presented in four sections. Section 2 describes the

factors (wetland and stormwater characteristics) that should be considered when developing

BMPs to protect wetlands and their natural functions from the potential impacts of stormwater

discharges and other diffuse sources of runoff. Wetland factors to consider include wetland type,

hydrology, climate, and site-specific conditions. Stormwater factors to

...this manual is a

consider include the quantity and quality of runoff and the frequency of

runoff events.

starting point

to identify Although they are described separately, the wetland factors and

appropriate BMPs to

stormwater factors are closely related. For example, climate influences the

frequency and intensity of storm events; the wetland type affects the

protect wetland capacity of the wetland to handle a given quantity or quality of stormwater

resources. runoff; and the functional attributes of a particular wetland can be severely

affected by the introduction of even small amounts of certain contaminants.

When deciding what BMPs may be appropriate for a particular situation,

both sets of variables-wetland factors and stormwater factors-should be considered individually

and in combination. Helpful tables that detail these factors (for example, wetland types or typical

Page l-4
Introduction

I

Identify/Evaluate desired

natural wetland functions

I

Identify potential threats

to wetland functions

ldentlfy watershed management

measures to prevent uncontrolled

runoff to wetlands.

Select BMPs to address potential

threats to wetland functions

No Are BMPs effective?

Are wetland functions

See discussion of wetland factors

and types (consider wetland

functions, soils, climate,

hydrology, etc.), pp. 2-2 to 2-17.

See discussion of stormwater

factors (land use, climate, etc.)

pp. 2-17 to 2-26.

See benefits to wetland functions

(Table 2-7) p. 2-42.

See description of BMPs and

BMPs in series in Section 4.

Consider potential impacts to

wetland functions, and capital

and maintenance costs.

See Case Studies (Section 3) and

BMP Fact Sheets (Section 4) for

information on implementation

of BMPs.

See page 244 for overview of

monitoring.

Figure l-l. How to use this manual.

Page l-5
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

pollutants found in stormwater runoff) are provided in Section 2 to assist managers in considering

the factors in depth. A third set of factors-the characteristics of potential BMPs-should also

be considered in combination with the wetland and stormwater factors. An overview of BMPs

for controlling the effects of stormwater on the functions of natural wetlands is provided in

Section 2; details are provided in the BMP fact sheets in Section 4.

Section 3 of this document presents several case studies that describe examples of situations where BMPs were used to protect natural wetland functions from the impacts of runoff

and to restore the functional quality of degraded wetlands. Case studies were selected from

both arid and nonarid climates, as well as from temperate and colder climates. Some of the case

studies include an in-depth overview of a particular experience using BMPs to protect wetlands,

whereas others present only anecdotal information. Since states have only recently had

stormwater management programs in place, or will begin implementation of such programs

within the next decade, only a limited number of well-documented case studies show the

effectiveness of stormwater management BMPs and natural wetlands.

Section 4 presents fact sheets describing specific BMPs and their potential relationship to

natural wetlands. For each BMP, a fact sheet is provided with the following information:

definition and purpose of the BMP, its scope and applicability, design criteria considerations,

potential effects on wetlands (i.e., benefits and limitation for use), cost-effectiveness (where

applicable), maintenance, and sources of additional information. BMPs included in this document represent examples of some of the more commonly used practices. Numerous BMP

manuals from state and local governments throughout the country were used to gather the

information presented in the fact sheets.

Page 1-6
Factors to Consider When Selecting BMPs

Section 2

Factors to Consider

When Selecting BMPs

Introduction

est management practices (BMPs)-both structural and nonstructural1- are used to

protect natural wetlands from the impacts of stormwater and other diffuse or nonpoint

sources of runoff,2 including changes in wetland hydrology or water quality When natural

wetlands are the final discharge point, BMPs may be used to provide preliminary treatment

of runoff that might impact the receiving natural wetland. Natural wetlands, usually by

virtue of their position in the landscape, directly receive stormwater runoff. In this case, BMPs

should be used to control the runoff-outside the wetland-to maintain the wetland’s existing

hydrology and functions. BMPs should be selected after carefully considering the combination of

variables that influence a potentially impacted wetland and the characteristics of the runoff

entering that particular wetland, as well as the capabilities and applicability of the potential

BMPs.

Wetland factors to consider include wetland type, hydrology, biological functions, and sitespecific conditions. A consideration of stormwater factors should consist of an evaluation of the

geographical area producing runoff, including existing and future impervious surfaces and

stormwater infrastructure, quantity and quality of runoff, and the frequency of runoff events.

Factors like zoning and changes in planned land use should also be considered to evaluate the

potential impacts from future development on the quantity and quality of stormwater and the

ability of existing treatment systems to control the runoff adequately. BMP capabilities include

factors such as flood storage; infiltration; and sediment, nutrient, and pollutant removal.

By evaluating the wetland characteristics in concert with the stormwater characteristics,

and applying the appropriate BMPs described in Section 4, the effects on the wetland system can

be minimized. For example, if it is anticipated that a certain type of development will cause

higher sediment loading to receiving waters and the wetland on the site is sensitive to increased

sedimentation, BMPs that control sedimentation should be employed to minimize the effects on

the wetland.

Wetland factors, stormwater factors, and BMP capabilities are described in this section. This

information can be used when evaluating the BMPs presented in Section 4.

1

Structural best management practices are those practices which entail construction of human-made structures (USEPA,

1992b). Examples of structural BMPs include infiltration basins, sand filters, vegetated filter strips, and constructed wetlands.

Nonstructural best management practices are regularly scheduled activities or programmatic actions (USEPA, 1992b). Examples

of nonstructural BMPs include pollution prevention, watershed planning, vegetated buffer areas, street sweeping, inspections, and

improved materials-handling practices.

2

For the purpose of this document, the term runoff should be interpreted to include stormwater discharges and nonpoint

sources of pollution, including urban sources. These other sources of nonpoint pollution can include agriculture, forestry, marinas,

and hydromodification activities. The reader should refer to Guidance Specifying Management Measures for Sources of Nonpoint

Pollution in Coastal Waters (USEPA, 1993) for additional information on all sources of nonpoint pollution.

Page 2-l
Wetland Factors

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Wetlands are integral parts of a watershed; their position in the landscape is influenced by

and influences the characteristics of a watershed. Wetlands can function as nutrient sinks,

temporary water storage areas, groundwater recharge areas, and critical wildlife habitat. Natural

and anthropogenic (human-induced) activities within a watershed influence the functions of

natural wetlands. When these activities remain relatively constant, the functions of natural

wetlands tend to exist in dynamic equilibrium with the surrounding conditions. However,

changes in the established combination of natural and anthropogenic activities within a

watershed can result in dramatic changes in the functions of natural wetlands.

The physical, chemical, and biological characteristics of natural wetlands combine to

determine unique wetland types. Differences in these characteristics range from subtle to obvious

among different wetland types depending on many factors associated with wetlands that include,

but are not limited to, hydrology, biological functions, site-specific factors, the climate and

geology of the region, landscape position, and soils. These factors are not independent, but form a

complex interrelationship to make each wetland type unique.

An assessment of the current status of these factors for a particular wetland is important to

understand the effects of certain factors, such as increased or decreased quantities of stormwater

runoff, on an individual wetland. Understanding the interactions of a particular wetland with the

other watershed features provides a broader and more comprehensive perspective of impacts of

various activities within the wetland and the watershed as a whole. For example, by changing the

hydrology of a wetland, the water retention and sediment attenuation functions can be lost,

resulting in downstream hydrological and water quality impacts; or vegetative species and

composition within and surrounding a wetland might change, resulting in habitat quality

changes.

Some of the factors affecting wetland type are influenced more by stormwater runoff than

others. For the purpose of this document, hydrology, biological functions, soils, and site-specific

conditions are considered to be factors that can be significantly affected by stormwater runoff.

Other factors, such as climate and landscape position (which might be linked to hydrology), are a

function of the location of a particular wetland. They are not affected by stormwater runoff, but

they contribute significantly to the determination of wetland type.

Selection and design of stormwater BMPs should consider the wetland type, hydrology,

biological functions, site-specific features, and other wetland factors, as well as the relationship

of the wetland to other watershed features, including climate. Additionally, the impacts of a

particular BMP need to be considered in the context of both the individual wetland and the

entire watershed to determine potential impacts on other resources.

Wetland Type

The effects of stormwater on a particular wetland depend, in part, on the type of wetland in

question. Wetland type can be defined as the combination of attributes (e.g., physical, chemical,

and biological) that make a particular wetland different from other wetlands. A wide range of

wetland types, which are the result of the cumulative effect of many environmental variables,

exist in the United States. In an effort to bring precision and standardization to the classification

of wetland types, Cowardin and others (1979) developed Classification of Wetlands and Deepwater

Habitats of the United States for use in the National Wetlands Inventory Their classification

Page 2-2
Factors to Consider When Selecting BMPs

system breaks wetlands into systems, subsystems, and classes analogous to plant or animal

taxonomic classifications.

The classification system developed by Cowardin and others (1979) is very comprehensive.

However, because it contains too much detail for this document, a simpler classification system,

proposed by Mitsch and Gosselink (1993), is used here. 3

 In their classification system, Mitsch

and Gosselink (1993) divided wetlands into two major groups--coastal and inland-as shown in

Table 2-1. Some wetlands in the United States are not adequately described by the Mitsch and

Gosselink (1993) classification system, but the system is intended as only a preliminary guide to

evaluate wetlands.

Hydrology

Hydrology is described by Mitsch and Gosselink (1986) as probably the most important factor in

the establishment and maintenance of specific types of wetlands and wetland processes. Precipitation,

surface water inflow and outflow, groundwater exchange, and evapotranspiration are the major

factors influencing the hydrology of most wetlands. Figure 2-l shows a simplified diagram of a

wetland hydrologic cycle.

Mitsch and Gosselink (1986) concluded that hydrologic conditions are extremely important for the

maintenance of a wetland’s structure and function, although simple cause-and-effect relationships are

difficult to establish. Hydrologic conditions affect many abiotic factors, including salinity, soil

oxygen levels (which can cause anoxia), and nutrient availability. These abiotic factors, in turn,

determine the flora and fauna that develop in a wetland. Finally, biotic components are active in

altering the wetland hydrology completing the cycle.

3

The reader should refer to Cowardin and others (1979) if a more detailed classification system is needed

Page 2-3
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Figure 2-1. Wetland Hydrological Cycle.

Some wetlands remain permanently inundated or saturated, some are wet for only a short

period during the year; and others may remain dry over periods of several years. The periods of

saturation or dryout in wetlands have strong implications for the characteristic structures that

develop in wetlands (Kadlec and Knight, 1996). Each wetland type exhibits a unique hydroperiod

that is fundamental in the stability of a wetland system. Hydroperiod is defined as the periodic or

regular occurrence of flooding and/or saturated soil conditions (Marble, 1992). Mitsch and

Gosselink (1986) suggested characterizing hydroperiod as the ratio of flood duration divided by

flood frequency over a given period of time. Cowardin and others (1979) provided general

descriptions of hydroperiod for both tidal and nontidal wetland systems (listed in Table 2-2). The

hydroperiod for a particular wetland is a function of the water budget (i.e., inflow and outflow

water balance) and storage capacity, which is affected by the surface contours of the landscape

and subsurface soil, geology, and groundwater conditions (Mitsch and Gosselink, 1986).

Since wetlands typically represent a transition between terrestrial and open-water

ecosystems, the effects of changed hydrology are extremely variable. Several principles outlining

the importance of hydrology to wetlands have been described by Mitsch and Gosselink (1986)

and include the following:

1. Hydrology leads to a unique vegetation composition, but can limit or enhance species

richness. For example, different species of vegetation respond differently to flooding

and large trees tolerate flooding better than seedlings.

2. Primary productivity in wetlands is enhanced by flowing conditions and a pulsing

hydroperiod. Primary productivity is often depressed by stagnant conditions.

Page 2-4
Table 2-2. Definitions of Wetland Hydroperiods

Hydroperiod Definition

Factors to Consider When Selecting BMPs

Tidal wetlands

Subtidal

Irregularly Exposed

Regularly Flooded

Irregularly Flooded

Nontidal Wetlands

Permanently Flooded

lntermittently Exposed

Semipermanently Flooded

Seasonally Flooded

Saturated

Temporarily Flooded

Intermittently Flooded

Artificially Flooded

The substrate is permanently flooded with tidal water.

The land surface is exposed by tides less often than dally.

Tidal water alternately floods and exposes the land surface at

least once dally.

Tidal water floods the land surface less often than dally.

Water covers the land surface throughout the year in all years.

Vegetation is composed of obligate hydrophytes.

Surface water is present throughout the year except in years

of extreme drought.

Surface water persists throughout the growing season in most

years. When surface water is absent, the water table is usually

at or very near the land surface.

Surface water is present for extended periods, especially early

in the growing season, but is absent by the end of the season

in most years. When surface water is absent, the water table is

often near the land surface.

The substrate is saturated to the surface for extended periods

during the growing season, but surface water is seldom

present.

Surface water Is present for brief periods during the growing

season, but the water table usually lies well below the soil

surface for most of the season. Plants that grow both in

uplands and wetlands are characteristic of the temporarlly

flooded regime.

The substrate is usually exposed, but surface water is present

for variable periods without detectable seasonal periodicity.

Weeks, months, or even years may intervene between periods

of inundation. The dominant plant communities under this

regime may change as soil moisture conditions change.

The amount and duration of flooding are controlled by means

of pumps or siphons in combination with dikes or dams.

Vegetation present cannot be considered a reliable indicator

of water regime.

Source: Adapted from Mitsch and Gosselink, 4993; Cowardin et al., 1979.

3. Organic accumulation in wetlands is controlled by hydrology through its influence on

primary productivity, decomposition, and export of particulate organic matter.

4. Nutrient cycling and nutrient availability are both significantly influenced by

hydrologic conditions.

Page 2-5
biological Functions

Microbes

Vegetation

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Changes in the natural hydrology of a wetland can therefore affect many of the functions of

a wetland. When volumes of stormwater runoff to a wetland increase, or when a wetland is

impounded to treat stormwater runoff, changes to the biotic and abiotic characteristics can occur.

For example, hydrologic disturbance of a wetland can cause a shift from a function as a sink for

nutrients and metals toward a function as a source of these materials, thereby affecting other

functions within the wetland and in downstream communities (Brinson, 1988).

Because wetlands are transition zones between uplands and aquatic systems, they can serve

as exporters of organic materials and sinks for inorganic matter (Mitsch and Gosselink, 1993).

Because of this transitional position in the landscape, some wetlands have high biodiversity,

whereas others are very productive in terms of biomass. Wetlands typically provide habitat to a

variety of microbial and plant species due to presence of ample water. The diversity of physical

and chemical interactions that occur in wetlands results in a continuum of flora and fauna from

the smallest of microbes to large trees. Interactions resulting from the biological diversity in

wetlands results in greater diversity, more complete utilization of energy inflows, and ultimately

the emergent properties of the wetland ecosystem (Kadlec and Knight, 1996). The biological

communities that become established in wetlands are typically made up of a rich mixture of

microbes, plants, and animals.

The established biological community in a particular wetland exists in a state of dynamic

equilibrium with the physical and chemical properties associated with that wetland. Actions that

upset the established balance found in the biological community, such as changes in the

hydroperiod, volume of runoff, or water quality, lead to significant changes in the functions of a

wetland. For example, increasing the volume of stormwater runoff that enters a wetland can

stress indigenous vegetation and allow more flood-tolerant species of vegetation (e.g., Typha) to

take over a wetland.

In wetlands, microbes are major transformers of organic and inorganic materials. The

population of microbes in a wetland varies according to many factors, but usually it is composed

of aerobic species at the surface of the substrate and shifts to anaerobic species as the depth

increases. As facilitators for the many biochemical reactions that occur in wetlands, wetland

microbes have adapted to a wide range of substrate conditions. Aerobic bacteria colonize areas

around plant roots to take advantage of the oxygen-rich rhizosphere surrounding the roots of

wetlands vegetation. Other anaerobic microbes play important roles in the chemical reactions

that produce methane, nitrogen gas, and hydrogen sulfide. Mychorrhizial fungi facilitate nutrient

uptake, reduce stress, enhance salt tolerance, and increase the initial growth and survival of

wetland plants (USDA-SCS, 1992).

Wetland vegetation comes in many forms, including floating, rooted, emergent,

submergent, herbaceous, and woody. Wetland plants transport oxygen from their leaves to the

rhizosphere surrounding their roots. This soil oxygenation process is important for many of the

Page 2-6
Animals

Site-Specific Conditions

Factors to Consider When Selecting BMPs

microbial reactions that take place in wetlands. Other functions of wetland vegetation include

trapping sediment and removing nutrients or other pollutants from the water column and

substrate (USDA-SCS, 1992). Wetland plants provide habitat for a variety of fish and wildlife. All

species of fish and wildlife need habitat-food, water, and cover-for survival. The habitat value

of a particular wetland site depends on the quantity, quality, diversity, and seasonality of the food,

water, and cover that it offers (PSWOA, 1990).

Wetlands support many different types of animals, including invertebrates, fish,

amphibians, reptiles, birds, and mammals. Because of the transitional nature of wetlands,

both aquatic and terrestrial animals live in wetlands. Wetlands provide food sources,

protection from weather and predators, resting sites, reproductive sites, and molting grounds

for wildlife (Cooper, 1989). Wetlands provide this habitat function for many species of fish

and wildlife, including some that are threatened or endangered. Many species of animals

that are not typically considered to be wetland species spend a part of their life-cycle or

fulfill daily requirements in wetlands. Other species like the beaver and muskrat can alter

wetlands as a result of their activities (USDA-SCS, 1992).

Although wetlands in rural or undeveloped areas might be relatively pristine, they can be

affected by agricultural activities, particularly sedimentation and drainage. Wetlands in previously

developed urban areas can be affected by changes in surface water and groundwater hydrology or

water quality. In drier areas, some existing urban wetlands are hydrologically dependent on

treated wastewater inputs, which are subject to variable water use practices. Wetland plant

communities can be altered as a result of hydrologic or physical disturbances. Exotic or invasive

plant species, which become established more easily in disturbed ecosystems, might be present,

affecting the existing plant species and habitat functions of the wetland. Also, natural buffer

areas surrounding urban wetlands might have been eliminated, lowering the diversity of the

wetland system and reducing areas for wildlife refuge.

Wetlands in temperate climates undergo seasonal variation in biological activity, which is a

major factor in many wetland processes involving the retention or transformation of pollutants.

Some wetland types can serve as a sink for nutrients during the growing season and as a source at

other times of the year (Mitsch and Gosselink, 1986), making consideration of the seasonal

distribution of runoff important.

Soils

Soils and their characteristic properties develop as the result of interactions between parent

material, climate, plant and animal life, relief, and time. The degree of influence of each of the five

factors generally varies from place to place. In a given location one factor can dominate in the

formation of a soil and determine most of its properties (Smith and Matthews, 1975).

Soils that form in a wetland environment are classified as hydric and have morphological

characteristics that result under wet conditions. Hydric soils are defined by the Natural Resources

Page 2-7
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Conservation Service (NRCS) as soils that are saturated, flooded, or ponded long enough during the

growing season to develop anaerobic conditions in their upper part. Hydric soils are classified as

either organic or mineral soils based on the percentage of organic material in their upper part (see

Table 2-3). General differences in physicochemical characteristics between organic and mineral soils

include percentage of organic content, pH, bulk density, porosity, hydraulic conductivity, water

holding capacity nutrient availability, and cation exchange capacity (see Table 2-3).

Changes in the characteristics of a soil during its formation result from processes that include

additions, removals, transfers, and transformations (Hall and Matthews, 1974). Modifying existing

processes by placing BMPs adjacent to or upstream of a wetland can result in changes in wetland soil

characteristics. For example, changes in the textural characteristics of a wetland soil can result from

changes in the amount, type, and/or particle size of sediments that enter a wetland. The modification

of soil textural characteristics can result in changes in the drainage characteristics of the wetland. For

example, the percentage of coarse-grained sediments deposited in a wetland could be reduced by a

stormwater BMP, resulting in a reduction of the soil’s permeability over time. The reduced

permeability could result in a reduction in the soil’s ability to infiltrate water, thereby

changing the character of the wetland.

The placement of BMPs adjacent to wetlands can result in changes to the chemical

characteristics of the wetland soil if stormwater is not adequately treated prior to its

discharge to the wetland. Suspended organic and inorganic particles tend to adsorb pollutants,

such as heavy metals, nutrients, hydrocarbons, and bacteria (Stockdale, 1991). If the suspended

particles are deposited in the wetland, the pollutants can become incorporated into the soils.

Over a period of time pollutants that have accumulated in the soil can appear throughout the

wetland environment via chemical transformations, vegetative uptake, or resuspension.

Additional changes to the chemical and morphological characteristics of a wetland soil can

occur as the result of alterations to the natural factors affecting the soil’s development. Changes

to the natural characteristics (e.g., hydrology or vegetation) of a wetland can result in changes to

Table 2-3. Comparison of Mineral and Organic

foils in Wetlands

Parameter Mineral Soil organic soil

Organic content Less than 20%-35% Greater than 20%-35%

pH Usually circumneutral Acid

Bulk Density High LOW

Porosity LOW (45%-55%) High (80%)

Hydraulic Conductivity High (except for clays) Low to high

Water Holding Capacity LOW High

Nutrient Availability Generally high Generally low

Cation Exchange Capacity low, dominated by major cations High, dominated by hydrogenion

Typical Wetland Type Riparian forest, some marshes Northern peatland

Source: Adapted from Mitsch and Gosselink, 1993.

Page 2-8
Climate

Factors to Consider When Selecting BMPs

the chemical transformations and nutrient cycling in a wetland soil. Redox potential, cation

exchange capacity, pH, porosity, hydraulic conductivity, and the organic content of a soil can

change as a result of altering the natural conditions within, or affecting, a wetland. Conversely,

changes in the chemical and morphological characteristics of the soil in a wetland affect the

overall characteristics of the existing wetland habitat.

Climate is defined as the average state of the atmosphere during a period of time-days,

weeks, years, etc. (Rasmusson et al., 1993). Solar radiation is the primary external source of

energy However, other external natural events (e.g., volcanic eruptions) and human-induced

changes (e.g., land surface changes) also can affect climate (Rasmusson et al., 1993). Naturally

occurring quantities and variations in rainfall and runoff are essential to the maintenance of

many wetland types. Both the amount and seasonal distribution of rainfall and resulting runoff

can play a role in determining the species composition, soil characteristics, and ecological functioning of inland wetlands. Factors such as precipitation patterns, including the frequency,

intensity, and duration of storm events, determine the quantity and timing of runoff (Hammer,

1992). Other climatic factors, such as temperature, winds, relative humidity, and incident solar

radiation, also affect wetlands.

Because hydrology is a particularly important factor, wetlands in arid and semiarid climates

require water source investigations before a stormwater pretreatment strategy can be chosen.

Whether wetlands in arid or semiarid climatic regions receive water from groundwater sources or

from surface flows, maintaining adequate and natural inundation periods is crucial to their

survival. Despite the significant reduction of hydrologic flows to wetlands by agricultural

diversions, climate determines the fate of most aquatic habitats in arid and semiarid regions

(Hutchinson et al., 1992). In arid and semiarid regions, precipitation should be considered a

variable rather than a constant when planning surface water controls. Arid and semi-arid climates

are largely responsible for the three distinct types of wetlands found in the American Southwest:

ciengas, playas, and riverine wetlands.

Landscape Position

The location of a wetland in the landscape plays a role in the natural hydroperiod of the

wetland, its retention of pollutants, and the effects of increased stormwater inputs. Brinson

(1988) defined three major geomorphic wetland types based on location in the watershed:

l Basin -Wetlands typically in headwater regions that capture drainage from small areas and

may receive precipitation as the primary source of water. Basins are characterized by

fluctuations of the water table, a long hydroperiod, low hydrologic energy, and low nutrient

levels. Plant communities usually consist of concentric zones of similar vegetation.

Riverine -Wetlands that occur throughout the landscape and are primarily influenced by

water flowing downstream. Riverine wetlands typically have short hydroperiods, high

hydrologic energy, and high nutrient levels. Plant communities are usually arranged

parallel to the direction of flow.

l Fringe -Wetlands that are usually located at the base of a drainage basin and adjacent to a

large body of water, including estuarine areas. They generally have a long hydroperiod,

Page 2-9
Cienegas

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

high hydrologic energy, and variable nutrient loads. Fringe wetlands are often influenced

by frequent flushing by bidirectional flow. Zonation of vegetation is usually perpendicular to the direction of water flow.

Descriptions Of Specific Watland Types

Pocosin Wetlands

Pocosin wetlands occur along the Atlantic seaboard’s lower coastal plain, from southern

Virginia to northern Florida. Approximately 70 percent of pocosins are located in North Carolina.

Pocosin, an Algonquin Indian word, literally means “swamp on a hill,” which is an accurate

description because pocosin wetlands are found in ridge and swale topography, as well as in flat

areas of the lower coastal plain, in depressions of the Carolina Bays, in areas of springs and seeps

in the upper coastal plain, and in the floodplains of streams. Pocosins contain dense evergreen

plant communities, consisting of small broad-leaved evergreen trees (pondpine) and scrub shrubs

(fetterbush and inkberry), which can occur either on highly organic soils, such as mucks or peats,

or on very poorly drained mineral soils. Locally, there is wide species diversity. The soils of

pocosins are acidic and low in nutrients and minerals. (Phosphorus is the limiting agent due to

phosphorus-reducing microbes.) Pocosins occur in many different shapes and can vary tremendously in size from less than an acre to several thousand acres. These wetlands are important to

birds and animals such as migratory waterfowl, herons, egrets, and muskrats.

Pocosin wetlands provide very favorable groundwater storage due to the differing

permeability properties of their organic layers. Macropores in the upper layers make the soil

very permeable, allowing for high retention of rainfall. Conversely, the reduced permeability

of the lower layers, due to smaller pore spaces, prohibits the stored rainwater from draining

very quickly. Because the base of a pocosin is not very permeable, the groundwater beneath

the pocosin, which has a high mineral content, does not come into contact with the lowmineral-content water and soil of the pocosin. Water movement occurs as seepage at the

pocosin’s margins that flows to streams, or as direct flow to salt marshes in estuarine areas.

These two principal properties of pocosins - attenuation of flow and continuous release of fresh

groundwater- are essential to the estuarine ecology of the southeast Atlantic coast. These two

properties also make pocosins particularly vulnerable to the adverse effects of stormwater

discharges in the many areas of the lower coastal plain that are experiencing development.

Cienega is a term that usually applies to mid-elevation (1,008 to 2,000 m), or (3,281 to 6,562 ft)

wetlands characterized by permanently saturated, highly organic, reducing soils (Hendrickson and

Minckley, 1984). These warm, temperate habitats were most often termed cienegas by Hispanic and

later explorers and settlers, and appear to be distinctive habitats (Hendrickson and Minckley 1984).

The word cienega comes from the Spanish cien aqua, meaning “hundred waters.” Cienegas are

perpetuated by permanent, scarcely fluctuating sources of water, and are rarely subject to harsh

winter conditions.

At mid-elevations of in semidesert grassland, cienegas are usually associated with perennial

springs and headwater streams. They are near enough to headwaters that the probability of

scouring from flood is minimal. Often, many meters of organic sediments have been deposited.

Page 2-10
Playa Lakes

Factors to Consider When Selecting BMPs

These wetlands are dominated by semiaquatic sedges, rushes, and grasses. Trees are scarce and

immediate surroundings are saline as a result of capillarity and evapotranspiration (Hendrickson

and Minckley, 1984). Historically grazed, more than 95 percent of the original cienegas have been

lost (Hendrickson and Minckley, 1934). Many have been drained for development or destroyed

by upstream pumping of the groundwater sources.

The term playas generally refers to areas occupied by temporary shallow lakes that have

internal drainage, usually in arid to semi-arid regions. They are not part of an integrated surface

drainage system, but are related to geologic fracture areas. Playas are shallow (typically less than 1

lm (3.28 ft) deep), circular basins averaging 15.5 acres (6.3 hectares) in surface area (Haukos and

Smith, 1992). Playa floors are plate-like with relatively constant water depth throughout much of

the basin. Because very few playas are directly associated with groundwater, playas can usually fill

only from precipitation and irrigation runoff. Most playas are dry during one or more periods of

each year, usually late winter, early spring, and late summer. Several wet-dry cycles during one

year are not uncommon for a playa and depend on precipitation and irrigation patterns (Haukos

and Smith, 1992). Soils of the playa are predominantly clays, differing from the loams and sandy

loams of the surrounding uplands (Haukos and Smith, 1992). The climate of the region containing

most of the playa lakes in the United States (southern Great Plains) is semi-arid in the west to

warm temperate in the east. Vegetation in dry playas resembles upland vegetation and includes

species such as summer cypress, ragweed, and various prairie grasses. Moist and flooded conditions

in playas favor vegetation representative of other North American wetlands: barnyard grass,

smartweed, bulrush, cattail, spikerush, arrowhead, toothcup, and dock (Haukos and Smith, 1992).

Although playas occur throughout the West, the following discussion focuses on a group of

playas occurring in the High Plains of eastern New Mexico and northern Texas, and in an area

south of the Arkansas River and north of the Canadian River. The playas in Texas are small marshlike basins, 5 to 15 acres (2 to 6 hectares) in size, and are typically underlain by clay or fine sandy

loam soils that are hydric. These shallow, circular lakes have individual watersheds of about 80 to

120 acres; the size of the watershed determines the size of the playa. The topography is flat to

gently rolling, containing approximately 20,000 to 30,000 separate playa watersheds. The “wet”

period of playas is seasonal, and their size and wet period depend on the intensity, duration, and

frequency of precipitation and infiltration. Vegetation is diverse because it is influenced by

varying salinity and depth and duration of saturated conditions. Tpically, playas demonstrate a

pattern of concentric plant zonation of submerged and emergent aquatic species, such as

pondweeds, arrowheads, and cattails, and lowland plants in wet meadows that surround the lakes.

Many of these lakes are important migratory bird and songbird habitat.

Precipitation, ranging from 22 to 12 inches from east to west, is the major input since there

are no permanent rivers and streams in the area. Excessive rainfall produces surface runoff in late

spring and early fall. Other inputs, such as groundwater from deep aquifers and irrigation water,

contribute to the permanence of standing water. Such groundwater input is uncommon because

most playas are situated above the regional groundwater table. Because there is no surface water

outflow, playas lose their water by evaporation, seepage, and irrigation use. However, an

abundance of inflow of surface runoff in large enough quantities can result in some recharge to

the High Plains aquifer. This occurs at the margins of the impermeable playas where more

permeable sediments are found.

Page 2-11
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Since many of the playa watersheds function as cropland and rangeland, their vegetation

serves an important purpose, helping to reduce excess nutrients from runoff and thereby

improving the quality of surface water. In an area where water is not abundant, any addition to

the groundwater will have economic significance, whether it be from irrigation water or recharge.

Where playa watersheds receive stormwater discharges, the potential exists for adverse impacts to

the playa itself or for degradation of the quality of the local and/or regional groundwater

resources.

Riverina or Riparian Wetland Areas of the Southwest

Riverine or riparian wetlands exist along the margins of rivers, behind natural levees, in

oxbows and floodplains. Riverine wetlands in arid climates are limited shoreward by desert and

riverward by water depth and scouring. These wetlands are transitory They develop rapidly only

to be removed by channel-straightening floods, or proceed toward an upland community after

drying. In the American Southwest, riverine marshes are located in broad alluvial valleys distantly

bounded by mountains. Like cienegas, riparian lands have been impacted by depletion of baseflow

sources or by direct diversions upstream (Hawkins, 1993). A number of riparian wetlands exist,

but some rely on other water sources such as treated upstream wastewater. The quality of the

wastewater discharging to these wetlands plays a more important role in maintaining wetland

functions than do the effects of stormwater runoff.

Prairie Potholes

The prairie pothole region of the northern United States consists of North Dakota, western

Minnesota, and northeastern South Dakota. This region also extends into southern Canada.

Pothole is defined as a surface depression occurring in glacial sediments, containing water from

precipitation, surface runoff, and groundwater. Vegetation characteristics include cattails and

various species of grasses, sedges, and rushes such as bulrushes. More ephemeral potholes are

characterized by meadow grasses and sedges. Prairie potholes are shallow wetlands in a region

that is fairly flat to rolling; they can occur at many different elevations. These saucer-shaped

depressions have an average depth of about 2 to 5 feet (0.6 to 1.5 m). Their appearance is

dependent on the size and shape of the original stagnant ice block that formed them and on

the effects of wind-induced wave erosion. Individual potholes can range in size from a few

hundred square yards up to several thousand square miles.

Potholes are not usually associated with any regional network of stream channels, but they

are related to local and regional groundwater systems. Water input is from groundwater inflow

(discharge), direct precipitation, and occasionally from surface inflow from excess stormwater or

snowmelt runoff. The hydroperiods in wetlands range from temporarily to permanently flooded.

These differences cause the development of diverse vegetation zones such as wet meadow,

shallow marsh, and deep marsh. Prairie potholes lose water through evaporation, transpiration,

and seepage to groundwater.

Prairie potholes are extremely important wetland resources in a region with few rivers,

lakes, or other productive wetland types. Approximately 50 to 75 percent of all North

American waterfowl use this region for breeding and for resting during migration. Other

birds and mammals, such as blackbirds and deer, are also common to the pothole region.

Drainage of these wetlands for commercial cropland production threatens them as limited

Page 2-12
Sand Hills Wetlands

Factors to Consider When Selecting BMPs

water resources. Degradation of prairie potholes from stormwater discharges is a growing

concern where potholes occur in urban or urbanizing areas.

The Sand Hills wetlands account for about 5 percent (1.3 million acres or 0.5 million

hectares) of the Sand Hills area, which consists of central and eastern Nebraska and a portion of

South Dakota. Fifteen percent (28,021 acres or 11,340 hectares) of the original wetlands were lost

before 1970. These wetlands are a result of hilly topography in conjunction with permeable

geologic formations. Small lakes, marshes, and wet meadows occur in the interdune areas.

Approximately 194 species of grasses, sedges, rushes, floating leaved, and submerged plants,

such as Japanese brome, spreading bentgrass, and fox-tail barley (Segelquist et al., 1990),

dominate these wetlands. These wetlands are important migration sites for waterfowl,

shorebirds, and songbirds. Approximately 80 percent of the Sand Hills wetlands are less than

10 acres in size. The following wetland types are typical:

l Seasonally flooded basins are flooded during spring and well drained the rest of the

year.

l Fresh (wet) meadows have no standing water but have waterlogged soils and root zone

during the growing season; vegetation consists of sedges and grasses.

l Subirrigated meadows have plant roots in contact with the water table.

l Shallow fresh marshes have waterlogged soils for most of the year; marsh areas have

standing water and emergent aquatic vegetation.

l Deep fresh marshes have a flooding depth of up to 3 feet in spring and early summer.

l Open freshwater lakes and ponds are typically perched above local groundwater

levels, or where topography is below the water table level; a small change in depth yields

a large change in water area because of very shallow lakes. In the westernmost region of

the Sand Hills, lakes and ponds are alkaline and have less diversity of wetland plant

species.

l Wind pump wetlands are small wetlands caused by overflowing wind-powered pumps

that tap underlying groundwater.

Most of the wetlands are influenced by local hydrogeology. There is negligible groundwater

inflow from areas beyond the Sand Hills. Annual precipitation ranges from 16 inches in the west

to 24 inches in the east, and is the principal source of water. Highly permeable soils and grassy

dune vegetation promote high rates of water infiltration. Within the interdune valleys, the

accumulation of fine sediments and organic material has reduced permeability Therefore,

snowmelts and spring rains result in the wetland formations described previously. The hydrology

of each wetland type is dependent on the rate of water input and the rate of downward

infiltration. Other factors influencing groundwater recharge are soil characteristics, geology,

and water table depth. These “subirrigated” meadows are unique because they have more

consistent precipitation and infiltration rates than other wetland types with more seasonal

variations and their water level is almost permanently at ground level. Many have a fairly

constant hydrologic input from groundwater. This constant inflow continues even in drier

years.

Page 2-13
Bottomland Hardwoods

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The Sand Hills wetlands are an integral part of the Sand Hills hydrologic system. The

meadowlands have economic significance because of hay production, as well as ecological

significance related to lakes and marshes. Although the wetlands themselves play a relatively

minor role because they constitute only 5 percent of the land surface, the Sand Hills area is

important for recharge of water to the underlying Ogallala High Plains aquifer, which extends

into other portions of Nebraska, as well as parts of Kansas, Oklahoma, and Texas.

Peatlands of the North-central States

The peatlands of the north-central states include the Red Lakes Peatlands of northern

Minnesota, one of the largest areas of peatlands in the country Peatlands in this area have low

topographic relief and have a depth ranging from 3 to 10 feet. Peatland describes wetlands that

have soils composed of partially decomposed remains of plants. The decomposition rate is low

because of low oxygen concentrations and saturated soils. Bogs and fens are the predominant

types of wetlands found in the peatlands of the north-central states.

Bogs have acidic, fibrous, spongy, nutrient-poor organic soil (phosphorus and potassium are

the limiting factors), whose organic plant material consists mostly of sphagnum moss. Because of

their location at or above the local groundwater table, bogs acquire most of their water from

precipitation and primarily support the growth of acid-tolerant trees and shrubs such as the

tamarack, the black spruce, and the leatherleaf. Fens represent a transitional stage between

marshes and bogs. Fens obtain water not only directly from precipitation, but also by surface

runoff and groundwater seepage. Fens support diverse plant communities consisting of sedges,

grasses, reeds, and some woody vegetation. Both areas contain a vast number of invertebrates,

insects, and amphibians.

Water chemistry determines the development of different wetland types. Acidic water with

a very low mineral content is typical of bogs, while the fens are characterized by the reverse.

These water chemistry differences are related to water origins. Mineralized fen water originates

from groundwater, whereas precipitation produces the high-acidity, low-mineral water content of

a bog.

Peatlands have a hydrogeologic flow system independent of regional groundwater

movement. Some limited groundwater recharge might occur in the sandy former shorelines

of glacial lakes, where more permeable sediments would permit the percolation of water.

Some examples of particular groundwater interactions are spring fens and groundwater

mounds. The former result from upward seepage of regional groundwater, and the latter are a

result of the mounding of the water table. Also, because of increased elevation of water in

groundwater mounds, a gradient is created, thereby resulting in a return of flow downward.

As a result of increased agricultural cultivation over the last 100 years, many of the

peatlands in the north-central states have been drained. The increase in impervious surfaces that

results from development associated with urbanization has the potential to adversely impact

certain peatlands, particularly fens due to their receiving surface water flows.

Bottomland hardwoods are forested wetlands in the river valley floodplains of the Atlantic

Coastal Plain (extending south from Virginia to Florida), and of the Gulf states of Alabama,

Page 2-14
Factors to Consider When Selecting BMPs

Mississippi, and Louisiana. They occupy the broad floodplains, seldom exceeding a width of

5 miles. Since the settling of America, 60 to 80 percent of the original area of these wetlands has

been lost. Bottomland hardwoods consist of flood-tolerant species of oak, gum, cypress, elm, and

ash. These species are adapted for survival in areas that are flooded between 20 to 150 days a year.

Vegetational characteristics are determined by the overall extent of seasonal flooding. This region

is also home to a diverse number of animal and bird species such as deer, raccoons, owls, and

hawks. Forested wetlands like the bottomland hardwoods are important wood duck breeding

habitat.

This seasonal hydrology also affects surface water and groundwater movement. In drier

seasons, floodwaters and lateral groundwater movement serve as the dominant inputs. Other

input sources include overbank flooding from the main channel, flooding from small tributary

streams, lateral overland flow from valley sides, lateral groundwater flow from valley-side rock

formations, and movements of groundwater parallel to the main river channel. Where there are

permeable rock formations in the local geology like limestone, groundwater helps maintain

wetland characteristics through seepages and springs. Recharge can also occur in the form of bank

storage. As water levels rise, water can move laterally from the channel to the adjacent floodplain.

During floods, bottomland hardwoods trap, filter, and attenuate inputs of sediments and

nutrients. In instances of high rainfall conditions they filter upslope surface runoff. They can also

provide continual recharge to the aquifer, raising groundwater levels up to hundreds of feet away

from the channel.

Swamps and Bogs of the Northeast

Two wetland types common to the Northeast are swamps and bogs. Swamps and bogs occur

in the Northeast in Pennsylvania, New Jersey, New York, and New England. Swamps consist of

woody vegetation occurring on poorly drained lowlands. Generally, they are found in valleys and

valley-side depressions that are periodically flooded. They are associated with surface drainage

systems and periodically can have standing water. Their size ranges from small depressions of less

than an acre to many acres. Northern floodplain swamps have an abundance of hardwoods. Other

swamps, not bordering a river, may contain a mixture of evergreen and deciduous trees. Trees

common to the areas are the white cedar and the red maple. Bogs are a type of wetland dominated

by peat soils, which are nutrient-poor acidic soils dominated by sphagnum moss. Bogs can occur

on flatland, on slopes, or as raised bogs as is the case in northern Maine. Bogs can support only

hardy, acid-tolerant trees and shrubs, heath species, and sedges such as the black spruce, the

tamarack, orchids, and insect-eating plants. Depending on the dominant vegetation, bogs can be

described as forested, scrub-shrub, or moss-lichen types. Both areas in this region harbor animals

and birds such as deer, rabbits, grouse, and owls. In addition, swamps and bogs are home to a

diverse array of rare plants.

The hydrology of swamps and bogs differs greatly. Groundwater, floodwaters, and tidal

innundations provide input to swamps, while rainfall provides hydrologic input to bogs.

Swamps collect groundwater from valley-side seepage, from the soil of downslope depressions, and through fractures in bedrock. Discharge leaves the swamp as stream flow and/or

seepage. Groundwater is not a major hydrologic component of bogs, although the water that

bogs hold is considered groundwater. Bogs in the Northeast are hydrologically self-contained

and are referred to as ombotrophic; there is little inflow or outflow of either surface water or

groundwater. They are isolated from the high mineral content of groundwater and are therefore

Page 2-15
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

very acidic. Although water is not released to stream systems, it can be released as seepage during

times of surplus precipitation. This lateral movement, however, is very slow.

The functions of both wetlands also vary Water stored in swamps attenuates the movement

of water through the complex integrated hydrological systems involving groundwater, wetlands,

rivers, and lakes. During storm flooding in a dry era, the flooding of a wetland serves as a recharge

source to adjacent aquifers. Bogs, because they retain water so well, act as giant sponges and do

not let much water leave as seepage. What little water is released does not necessarily increase dry

stream flow or recharge aquifers.

Cypress Dome Wetlands

Cypress dome wetlands occur in southern Georgia and in the Florida wetlands. The term

cypress dome, also referred to as “cypress pond” and ‘cypress head,” is defined as a hardwood

forested wetland occurring in seasonally or permanently wet saucer-shaped depressions. These

wetlands are small in scope, usually not exceeding 25 acres (10.1 hectares) and are dominated by

pond cypress trees, some of which are over 400 years old. If enough light penetrates the canopy,

understory vegetation like the wax myrtle can grow. Viewed from the side, these trees assume a

characteristic dome-shaped profile, with the smaller trees toward the edges and the larger trees in

the middle. The arrangement of the trees in this manner is due to the occurrence of wildfire,

which often burns only the outer, smaller trees. These domes contain acidic water and organic soil

that is thickest in the middle and thinner toward the edges of the domes. Snakes, alligators, and

nine species of frogs are common in this region.

Cypress domes occur in flat areas where the water table is close to the surface; this surface

water is connected to shallow aquifers. Movement of water from cypress domes proceeds in a

lateral direction. Primary hydrologic inputs to cypress dome wetlands are rainfall and surface

water inflow. Water is lost through evapotranspiration and seepage to groundwater systems. The

deciduous leaves of cypress trees seasonally influence the water budget due to the changes in the

amount of interception of rainfall and transpiration. In the summer months of maximum rainfall,

a net inflow into the wetlands results. The reverse occurs during drier times, providing some

recharge. Groundwater recharge/discharge is influenced by the geologic formation beneath the

cypress domes. Cypress dome wetlands located above sinkholes can create permeable pathways

between the wetland and the aquifer and are capable of recharging deeper limestone aquifers.

Cypress dome wetlands have been used for the natural treatment of effluent.

Permafrost/Tundra Wetlands

Permafrost/Tundra wetlands are situated in the interior of Alaska and are the western

extension of the wetland complexes of northern Canada. Severe frost is the most important

characteristic that distinguishes the hydrology of these wetlands. Water is frozen in the ground

year-round, resulting in impermeable layers known as permafrost. Permafrost encompasses over a

half-million square miles in Alaska. This condition is continuous in the north, but scattered in

regions farther south. Permafrost areas are very sensitive to minute changes in vegetation cover

and drainage. For instance, color, thickness, and degree of saturation of the wetland determine the

thermal properties of the wetland, which in turn determine summer thaw depth and winter

freeze depth. Thawing occurs at a maximum of 3 feet, and freezing can extend up to hundreds of

Page 2-16
Factors to Consider When Selecting BMPs

feet. Wetlands produced by permafrost are seasonal thaw ponds, shallow emergent wetlands,

partially drained lake basins, and wetlands in wet and dry tundra. The term muskeg means

peatland, and it constitutes the organic content of these wetlands. A brief summer growing

season produces limited vegetation consisting of mosses, lichens, and sedges. Mosses fill a particularly important ecological niche because of their role in peat formation; the rate of which is about

one inch per 300 years primarily due to the cold temperatures.

The water budget of the permafrost/tundra wetlands of Alaska varies from site to site.

Precipitation in the Alaskan interior yields less than 12 inches (30.5 cm) per year. However,

because of limited evapotranspiration, there is a net surplus of water available. Both snowmelt

and rainfall are very important water sources for wetlands. Precipitation is the main water input

because of impermeable conditions created by permafrost. Very little water is lost or received to

or from stream and groundwater flow, although there are exceptions. Groundwater recharge can

occur in certain instances where summer snowmelt and precipitation percolate through frozen,

but dry surfaces, or on the warmer southern-facing slopes that have permafrost-free zones

allowing for infiltration. In warmer areas where there is groundwater circulation, more

mineralized water can emerge, resulting in the formation of arctic fenlands. Icings and icy

mounds are wetland features that are the result of springs that continue to flow in early winter.

The timing and amount of summer rain and snowmelt have a significant impact on the

characteristics of individual wetland areas.

Stormwater Factors

Stormwater Quantity

Changes in land use within a watershed usually result in changes to stormwater runoff

volume and quality. For example, urbanizing watersheds are characterized by increases in

impervious surfaces, which include roads, sidewalks, parking lots, and buildings, as compared to

rural land uses. Increased imperviousness leads to increased runoff volumes and velocities and

higher pollutant loads. Moreover, natural stormwater conveyances tend to be replaced with hard

structures such as concrete gutters or swales because of the increases in erosion that often

accompany increased runoff amounts and velocities.

Runoff and Peak Flow

Land use changes alter the established rainfall-runoff relationship that exists in a

watershed. The most common effects are reduced infiltration and subsequent reduction in

the time of concentration (which is the time it takes surface runoff from the most distant

point of a watershed to reach the first swale, gutter, sewer, or channel) (Maidment, 1993).

Travel time, the time it takes flow to move through various conveyance elements to the next

inlet or design point, may also be decreased by urbanization. Both of these factors can

significantly increase peak discharges and runoff (USDA-SCS, 1986). Runoff volumes are

primarily determined by the amount of precipitation and by the infiltration characteristics

of an area. For a given location, some of the factors that determine infiltration characteristics are

more likely to be influenced by human intervention than others. The amount and type of

precipitation for a given location can be quite variable, but are not likely to be modified by

Page 2-17
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

human actions. The infiltration characteristics are a function of soil type, soil moisture,

antecedent rainfall, cover type, impervious surfaces, and surface retention (USDA-SCS, 1986).

Activities that increase imperviousness, decrease surface retention, or modify cover type can lead

to increases in surface runoff or peak discharge.

As mentioned above, travel time is the time it takes runoff to travel from the point where

sheetflow enters a recognizable conveyance element (e.g., culverts, swales, over land), through the

various conveyance elements, to a specified point in a watershed (Urbonas and Roesner, 1993).

Travel time is principally a function of slope, length of the flow path, depth of flow, and the

roughness of the flow surfaces(USDA-SCS, 1986). As land uses in a watershed become smoother

(e.g., imperviousness increases or forested areas decrease), the velocity of runoff increases, which

decreases the travel time (Urbonas and Roesner, 1993).

Peak discharge changes are often good indicators of changes in land use within a watershed that

will affect the hydrology of natural wetlands. The relationship between runoff volume, watershed

drainage area, relative locations of urbanized areas, effectiveness of flood control structures or other

storage, the time distribution of rainfall during a storm event, and travel time determines peak

discharge (USDA-SCS, 1986). The estimation of peak flows on small (16.1 miles2

 or<25.9 km2) to

medium-sized (321.9 mile2 or <518 km2

) watersheds is a very common application of stormwater

runoff estimation (Pilgrim and Cordery, 1993).

Mathematical relationships, or models, are used to approximate the relationship of rainfall

to runoff. The results from modeling approximations used to predict runoff from a particular area

are generally much better at indicating changes in runoff, rather than absolute runoff volumes.

For the purpose of determining impacts to wetlands from stormwater runoff, estimating relative

changes in runoff volume and peak discharge is sufficient.

A variety of methods exist to determine runoff volume or peak discharge for sizing and

designing conveyance systems and detention facilities. Pilgrim and Cordery (1993) and

Maidment (1993) describe several different approaches for predicting runoff volume and peak

discharge. Some of the modeling approaches focus on runoff and others on the loss, the part of the

rainfall that does not run off. The assumptions of the different approaches are summarized below:

Loss (and conversely runoff) is a constant fraction of rainfall in each time period, or for

storms with constant rainfall intensity, a simple proportion of the total rainfall. An

example method using these assumptions is the rational formula.

l Runoff is the residual after a selected constant loss rate or infiltration capacity is

fulfilled. Examples include use of probable maximum flood computations and the

prediction of hydraulic conductivity (assuming sufficient soils data are available).

l Initial loss and continuing constant loss rate index models are similar except that the initial runoff

is zero until an initial loss capacity is met regardless of the rainfall rate; then runoff is a constant

rate.

l Runoff is estimated by an equation that represents a function of the capacity rates of loss

decreasing with time. The equations may be based on empirical relationships or

physically based models. An example is the Green and Ampt (1911) equation.

l Runoff is represented by rainfall-runoff relationships, such as the U.S. Soil Conservation

Service TR-55 method, a runoff curve (CN) method.

Page 2-18
Rainfall

Factors to Consider When Selecting BMPs

Rainfall and snowmelt are the basis for stormwater runoff and are variable in space and

time. In the estimation of runoff or peak flows, rainfall is represented by a hyetograph, which is

the time pattern of rainfall intensity When data are available, recorded rainfall can be used to

determine the hyetograph, which may be assumed to be constant for the entire watershed if

sufficient spatial data are not available. In the absence of sufficient local data, regional design

rainfall of average intensity (found in national intensity-duration-frequency information) can be

used (Pilgrim and Corder-y, 1993). National precipitation data are published in Climatological Data

andHourly Precipitation Data by the National Climatic Data Center, which is part of the National

Oceanic and Atmospheric Administration in the Department of Commerce.

Storm Frequency refers to the time between rainfall events of equal intensity (return periods).

Storm (and flood) frequency can also be expressed as a probability For example, a 25-year frequency

storm has a 4 percent chance of happening in any year. Storm intensity is typically defined as a volume

of rain in a given time period, Maps are available that show rainfall for durations from 30 minutes to

24 hours and return periods of 1 to 100 years (Hershfield, 1961). The frequency and intensity of storm

events vary regionally and seasonally. For example, storm events in the central and southwestern

United States typically occur less frequently than those in the East, but may occasionally produce large

volumes of runoff. Some areas may receive the bulk of their annual precipitation as snowfall, and

snowmelt would be a major contributor to streamflow and runoff in such regions. In a summary of

several studies related to urbanization in a watershed, the largest changes in runoff were associated

with 2-year storm events, not l00-year events (Urbonas and Roesner, 1993).

Stormwater Quality

Runoff can be characterized by the use of the land from which the runoff comes. For

example, the constituents of runoff from farmland are likely to be different from those in urban

runoff. Agricultural runoff tends to be high in nitrogen, phosphorus, bacteria, and suspended

sediments. The principal types of pollutants found in urban runoff include sediment, oxygendemanding substances, nutrients (phosphorus and nitrogen), heavy metals, pesticides,

hydrocarbons, increased temperature, and trash or debris (Woodward-Clyde Consultants, 1990).

The source of sediments in stormwater might be erosion of bare soil in the watershed or

channel scouring due to increased stormwater volumes and velocities. Sediments in surface water

may settle in wetlands because of the effects of wetland morphology and vegetation on the

lowering of water velocities. Some wetland types, such as tidal and riverine wetlands, might

benefit from settling of some sediments and particulates, while other wetland types might be

adversely affected by even low sediment loadings. High sediment loadings might affect plant

communities or reduce fish spawning habitats in a wetland (Canning, 1988).

Another effect of urbanization is generally higher runoff water temperatures in the summer and

colder temperatures in the winter, primarily because of a reduction in vegetative cover and resulting

rapid drainage (Galli and Debose, 1990). Higher summer water temperatures are associated with

decreased dissolved oxygen levels in surface waters, which affect the aquatic faunal community

Pollutants found in stormwater runoff are not transported in the same form; for example,

phosphorus and metals are primarily transported bound to sediments, and nitrogen is often a

dissolved pollutant. Also, the levels of pollutants in runoff can vary according to season and land

use in a watershed (Hickock et al., 1977). Urban wetlands can be affected by increased loadings of

pollutants in runoff in comparison to predevelopment levels.

Page 2-19
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Wetlands that receive stormwater discharges with high sediment levels from sources such as

uncontrolled construction sites can be impacted by excessive silt loads or altered flow patterns.

Large flow volumes, high velocity, and long-term pollutant loads delivered by stormwater discharges can alter or destroy stable wetland ecosystems (USEPA, 1995).

The Nationwide Urban Runoff Program, or NURP (USEPA, 1983), although limited in scope

and purpose, is still considered by the Agency to be the most comprehensive national assessment

of pollutants in urban runoff. The major focus of NURP was to characterize the water quality of

runoff from residential and commercial areas and from industrial park sites. The program

evaluated data from 81 sites in 22 cities and covered more than 2,300 individual storm events.

Because the industrial park category did not include heavy industrial activity, data from the

industrial parks were merged with the data collected from the commercial areas. It should also be

pointed out that the sites evaluated in NURP were selected in part for their low probability to be

influenced by pollutant contributions from construction sites, heavy industrial activities, illicit

connections, or other confounding influences.

The NURP study provides insight on what can be considered background levels of pollutants

for runoff from residential and commercial land uses (USEPA, 1995). The majority of samples

collected under NURP were analyzed for seven conventional pollutants (biochemical oxygen

demand, chemical oxygen demand, total suspended solids, total Kjeldahl nitrogen (TKN), nitrate plus

nitrite, total phosphorus, and soluble phosphorus) and three metals (total lead, total copper, and total

zinc). Median values for the NURP pollutants are reported in Table 2-4, along with their

corresponding coefficients of variation. The original NURP data presented in Table 2-4 are reported

for four land uses: residential, mixed, commercial, and open space. Table 2-5 summarizes the event

mean concentrations as composite results for the same four NURP land use categories.

Because the NURP sites represent average runoff conditions from a mix of residential,

commercial, and industrial park sites, loading estimates based on NURP concentrations will be

influenced by loadings from some of the sources considered in the industrial and commercial

analysis that were located in the catchments monitored (USEPA, 1995). It is, therefore, important

to consider the land use from which runoff originates, as well as other watershed-specific

conditions, when evaluating BMPs to treat stormwater quality for protecting wetlands. Table 2-6

shows different types of land use, the pollutants expected in runoff from those land uses, and the

potential effects of those pollutants on wetlands. This table can be used as a basis to start

evaluating stormwater quality when determining potential impacts to wetlands.

Page 2-20
Table 2-4 Results of the Nationwide Urban Runoff Median Event Mean Concentrations for All Sites by Land Use Category

Factors to Consider When Selecting BMPs

Residential Mixed

Open/

Commercial Nonurban

Pollutant Median CV Median CV

BOD (mg/L) 10.0 0.41 7.8 0.52

COD (mg/L) 73 0.55 65 0.58

TSS (mg/L) 101 0.96 67 1.14

Total Lead (mg/L) 144 0.75 114 1.35

Total Copper (mg/L) 33 0.99 27 1.32

Total Zinc (mg/L) 135 0.84 154 0.78

TKN (mg/L) 1900 0.73 1288 0.50

Nitrate plus Nitrite (mg/L) 736 0.83 558 0.67

Total Phosphorus (mg/L) 383 0.69 263 0.75

Soluble Phosphorus (mg/L) 143 0.46 56 0.75

Source: USEPA. 1983 Note: CV = coeffcient of variation.

Median cv

9.3 0.31

57 0.39

69 0.85

104 0.68

29 0.81

226 1.07

1179 0.43

572 0.48

201 0.67

80 0.71

Median cv

- -

40 0.78

70 2.92

30 1.52

- -

195 0.66

965 1.00

543 0.91

121 1.66

26 2.11

Table 2-5. Summary of Event Mean concentrations

from NURP for Selected Pollutants

Composite of All Land use Categories

90th Coefficient of

Median Percentile Variability

Mean Site Site for Event

BOD (mg/L) 12 9 15 0.5-1

COD (mg/L) 94 65 140 0.5-1

TSS (mg/L) 239 100 300 4-2

Total Lead (mg/L) 0.24 0.14 0.35 0.5-1

Total Copper (mg/L) 0.05 0.03 0.09 0.5-1

Total Zinc (mg/L) 0.35 0.16 0.50 0.5-1

TKN (mg/L) 2.3 1.5 3.3 0.5-1

Nitrate plus Nitrite (mg/L) 0.86 0.68 1.75 0.5-1

Total Phosphorus (mg/L) 0.50 0.33 0.70 0.5-1

Soluble Phosphorus (mg/L) 0.15 0.12 0.21 0.5-1

Source: USEPA, 1983, 1995.

Page 2-21

Constituent
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Table 2-6. Effects of Pollutants from Different

Land Uses/Sources on Wetlands

Land Uses/Sources

Agricultural runoff (cattle)

grazing land, manure)

Typical Pollutants Effect on Wetland

Bacteria (coliform, Contamination of shellfish, rendering them

streptococcus) inedible

Sediment Clogged bottom sediments, interfering

with fish spawning and benthic

invertebrates

Nutrients Increased vegetative productivity, resulting

in increased standing stocks of vegetation,

followed by increased rates of vegetative

decay and higher Community respiration

rates

AgriculturaI runoff feedlots)

Organic matter

Pesticides, salts

Nitrogen, phosphorus

Greater oxygen demand/depletion

Alteration of species distribution

Increased vegetative productivity, resulting

In increased standing stocks of vegetation

followed by increased rates of vegetative

decay and higher community respiration

rates

Commercial stormwater

runoff

Total nitrogen Increased vegetative productivity resulting

In increased standing stocks of vegetation,

followed by Increased rates of vegetative

decay and higher community respiration

rates

Heavy metals

(Pb, Zn, Cu, Cd)

Petroleum residues

Residential stormwater runoff Total nitrogen

low to moderate density)

Alteration of Species distribution

Decreased growth and respiration rates

(Chronic toxicity)

Increased vegetative productivity, resulting

In increased standing stocks of vegetation,

followed by increased rates of vegetative

decay and higher community respiration

rates

Bacteria (coliform) Contamination of shellfish, rendering them

Inedible

Heavy metals

(Pb, Zn, Cu, Cd)

Petroleum residues

Alteration of species distribution

Decreased growth and respiration rates

(chronic toxicity)

Urban runoff

(developing Areas)

Pesticildes (diazinon)

Suspended solids

Alteration of specks distribution

Clogged bottom sediments. lnterfering

with fish spawning and benthic

Invertebrates (smothering)

Nitrogen, phosphorus Increased vegetative productivity, resulting

In increased standing stocks of vegetation,

followed by increased rates of vegetative

decay and higher community respiration

rates

lead Alteration of species distribution; decreased

growth and respiration rates

(chronic toxicity)

Highway stormwater runoff BOD

Sheet flow blockage by

embankments

Greater oxygen demand/depletion

Sheet flow reduced by embankments,

decreasing the sediment supply to wetlands

and making the waters more likely to stagnate when fully flooded.

Page 2-22
Tabe 2-6. (continued) Land use/Source Typical Polluants Effect on Wetlands

Factors to Consider When Selecting BMPs

Highway Stormwater

runoff (cont.)

Multifamily residential area Nitrogen, Phosphorus Increased vegetative Productivity. resulting in

Stormwater runoff Increased standing stocks of Vegetation,

followed by increased rates of vegetative decay

and higher community respiration rates

Urban stormwater

runoff (developed)

Pasture stormwater

runoff

Cultivated land

stormwater runoff

Industrial area runoff

Alternation of me hydrologic regime, sediment

loading, and direct wetlands removal;

hydrologic isolation, decreased salinity in

tidal marshes, and increase in vegetative cover;

nutrient retention and signs of eutrophication

Oil and grease; polyaromatic Reduced species diversity

hydrocarbons

Heavy metals (Pb, Zn) Alteration of species distribution and replaceand deicing salt/sand ment of sensitive species with tolerant species;

Decreased growth and respiration rates

(chronic toxicity)

Suspended solids

BOD

Clogged bottom sediments, Interfering with

fish spawning and benthic invertebrates

(smothering)

Greater oxygen demand/depletion

Bacteria (coliform) Contamination of shellfish,

rendering them inedible

Heavy metals

Ku. Pb, Zn, NI, As, Be)

Organics (bls-2-

ethylhexyl phthalate)

Pesticides (a-BHC)

Nitrogen, phosphorus

Reduced species diversity

Replacement of sensitive species with

tolerant species.

Alteration of species distribution

Decreased growth and respiration rates

(chronic toxicity)

Increased vegetative productivity, resulting in

increased standing stocks of vegetation,

followed by increased rates of vegetative decay

and higher community respiration rates

BOD Greater oxygen demand/depletion

Suspended solids Clogged bottom sediments, interfering with

fish spawning and benthic invertebrates

Heavy metals (Pb, Zn, Cu, Cd) Alteration of species distribution

Suspended solids Clogged bottom sediments, interfering with

fish spawning and benthic invertebrates

(smothering)

Nitrogen Increased vegetative Productivity, resulting in

Increased standing stocks of vegetation,

followed by increased rates of vegetative decay

and higher community respiration rates

Suspended solids

Hydrocarbons

Clogged bottom sediments, interfering with

fish spawning and benthic invertebrates

Reduced species diversity; replacement of

sensitive species with tolerant species; alteration

of species distribution; decreased growth and

respiration rates (chronic toxicity)

BOD Greater oxygen demand/depletion

COD Greater oxygen demand/depletion

Suspended solids Clogged bottom sediments. lnterfering with

fish spawning and benthic invertebrates

(smothering)

Sources: USEPA, 1983 1993, 1995.

Page 2-23
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Factors contributing to the variability of pollutant types and loadings from similar land uses

could include the following (Driver and Tasker, 1988):

Physical and Land-Use Characteristics

Total contributing drainage area - a factor in determining the amount of runoff

Percentage of total drainage area that is impervious - a factor in determining the

amount of rainwater that runs off as opposed to being absorbed into the ground

Percentage of total drainage area that is industrialized - a factor in determining the

types of constituents likely to be present in runoff

Percentage of total drainage area that is commercialized - a factor in determining

the types of constituents likely to be present in runoff

Percentage of total drainage area that is residential - a factor in determining the

types of constituents likely to be present in runoff

Percentage of total drainage area that is nonurban - a factor in determining the

types of constituents likely to be present in runoff

Population density - a factor in determining the amount of pollution per unit area that

might be expected

Stream flow - an influence on the amount of likely dilution

Climatic Characteristics

l Total storm rainfall - a factor in determining the amount of rain available to run off

l Duration of each storm - a factor affecting the amount of rain running off balanced by

the amount that can be retained in the ground or channeled into another water body in a

given amount of time

l 2-year maximum daily precipitation - a factor explaining the expected climatic

pattern for a geographic area

l Mean annual rainfall - a factor in determining the amount of rain available to run off

l Mean annual nitrogen load in precipitation - a factor explaining some of the sources

of pollution to wetlands

l Mean annual January temperature - a factor explaining the expected climatic pattern

for a geographic area

l Surface water hardness - an influence on the toxicity of certain hazardous substances

(Owe et al., 1982)

Pollutant loadings-nitrogen, phosphorus, sediment, and lead-from urban, agricultural,

and open space land uses were evaluated and plotted to aid in the selection of stormwater BMPs.

Figures 2-2 through 2-5 show the median, maximum, and minimum pollutant loadings reported

for several locations around the United States. Although these figures cannot be used to replace a

thorough evaluation of site-specific conditions, they can be used initially to screen BMPs to

shorten a list of potential BMPs to protect a wetland. For example, a wetland that is downstream

from a predominantly urban area could potentially need to be treated for lead, whereas if the

Page 2-24
Factors to Consider When Selecting BMPs

predominant land use were forest, lead would presumably not be a problem. Sediment

loadings would be an important consideration for all land uses, but loading rates can vary

widely within a land use category. The above-mentioned factors could account for the ranges

of pollution from different land uses and from within the same land use category, as shown

in Figures 2-2 through 2-5.

Figure 2-2. Sediment loading rates for various land uses.

Urban

Figure 2-3. Nitrogen loading rates for various land uses.

Page 2-25
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Figure 2-4. Phosphorus loading rates for various land uses.

Figure 2-5. Lead loading rates for various land uses.

Sources for Figures for 2-2 through 2-5: Novotny and Chesters, 1981: Shahane, 1982; Sweeten and Melvin. 1985; USEPA 1983.

Page 2-26
Overview of BMP Capabilities

Factors to Consider When Selecting BMPs

Assessing the Ability of a BMP to Protect a Wetland

Wetlands can provide water quality benefits that should be considered when developing or

implementing watershed planning. However, because natural wetlands are waters of the United

States they must be afforded the same protection from degradation as any other receiving water.

The wide variability of wetland types and the range of potential impacts from runoff make it

very difficult to recommend a particular methodology to protect wetlands. EPA believes, however,

that the use of natural wetlands for control of runoff should be avoided.

Different wetland types vary in their ability to handle the changes caused by stormwater

flows and pollutant levels. Where runoff is specifically channeled or routed to wetlands, BMPs

should be implemented to maintain the natural functions of the wetland. This might require the

use of BMPs for water quality improvement, techniques to minimize changes in the natural

hydrology of a system, or both. The principal question to be answered is whether the BMP is

providing the level of protection necessary to ensure that the wetland retains its natural health

and functions. Therefore, unlike other manuals that use end-of-pipe approaches, this manual

focuses attention on the resource. To the resource manager this approach could be viewed by

standing in the wetlands.

A variety of physical, chemical, morphological, and biological wetland functions could serve

as appropriate indicators of the wetland’s continued health and sustainability. These include:

l Groundwater quality and recharge

l Groundwater discharge

l Flood flow alteration

l Shoreline stabilization

l Sediment/toxicant retention

l Nutrient uptake, transformation, and removal

l Vegetative diversity, biomass production, and export

l Aquatic diversity and abundance

l Terrestrial wildlife diversity and abundance for breeding, migration, and wintering

l Stable recreational opportunity, uniqueness, heritage

The wetland’s continued function and sustainability should be assessed. If it can be

determined that the wetland is healthy, this might also be an indication that the proper BMP has

been selected, has been well designed for the site and specific application, and has been well

maintained (assuming other objectives of the BMP are being achieved, such as water quality). If

there is some problem with the wetland (i.e., its function, health, or sustainability), the cause of

the problem should be evaluated. Any combination of a number of causal factors could be

responsible for the problem. These include, among others, choice of BMP, design, operation, and

maintenance.

Page 2-27
Nonstructural Controls

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The evaluation should follow a logical, decision-tree-type sequence, working in reverse

order (selection, design, operation, and maintenance). For example, if the improper BMP was

selected for the site, none of the other factors would be likely to solve the problem, although they

might help to some degree. Or, it might be determined that the proper BMP was selected but the

design was not tailored to the site conditions (i.e., considering stormwater discharge factors and

wetland factors like hydrology, soils, and vegetation). In other cases, an operational flaw might be

altering the wetland’s hydrology, or perhaps the BMP is not being maintained in the manner best

suited to ensuring the continued health and function of the wetland.

It is likely that the same decision makers and technical personnel will be responsible for

implementing both stormwater BMPs that discharge to wetlands and BMPs that do not discharge

to wetlands. Therefore, these considerations should be emphasized to the appropriate staff so that

the aspects of stormwater BMP selection, design, operation, and maintenance unique to practices

used to protect wetlands are not inadvertently disregarded.

Although a number of manuals describe BMPs to be used to address stormwater runoff, this

manual is a first attempt at addressing the specific water quality concerns related to wetlands. It

is intended for use by anyone addressing potential impacts to wetlands from stormwater runoff,

and it presents a wide range of planning approaches as well as specific BMPs that can be employed

in a variety of situations. Although these are all discussed as BMPs for the purposes of this manual,

some approaches might be more relevant and useful for large-scale planning efforts, whereas

others are more appropriate for very specific localized problems.

Nonstructural controls are techniques used to manage stormwater runoff that do not

require physical alteration of the land (USEPA, 1993). The prevention and minimization of

pollutant loadings through source reduction and watershed planning are preferred over treating

the unavoidable loadings that occur following urbanization. Watershed planning can help to

reduce the need for expensive construction and maintenance of permanent structures if

development in the watershed is accomplished in an environmentally sensitive manner that

minimizes impacts. Obviously, opportunities for watershed planning will be limited by the

current level and pace of development in a given watershed.

Nonstructural control practices applicable to wetlands include:

. Pollution prevention

l Watershed planning

l Advance identification of wetlands

l Permitting programs

l Preventive construction techniques (minimal impact development)

l Retaining open spaces, vegetated natural buffers, and riparian areas

l Inspection and maintenance of existing stormwater and erosion controls

l Education programs

Page 2-28
Factors to Consider When Selecting BMPs

Watershed Planning

Watershed planning involves the development of a watershed management plan, often as

part of a comprehensive plan, The watershed management plan that describes existing patterns of

environmental quality and community life in a watershed (including demographic trends,

housing, infrastructure, economic activity, natural resources, and wildlife) and recommends goals

and policies (including protection of drinking water sources and control of land uses) to manage

future development to minimize impacts on water resources. A watershed management plan

consists of maps of the watershed and its resources and text that explicitly addresses conflicts and

trade-offs among development, environmental protection, social issues like as affordable housing,

transportation, and many other factors. Watershed management plans also consider alternative

actions and methods of measuring progress (CTIC, n.d.). Special-purpose planning, e.g., wetlands

management planning, is one component of a watershed plan (USEPA, 1992c). Other components

are wellhead protection and Class V (underground injection) well management.

Resource inventory and information analysis provide the basis of watershed management

planning. For a plan to be effective, it should have measurable goals describing desired outcomes;

for example, “Reduce loads to wetlands and surface waters by 25 percent.” The process of

developing a watershed plan should also identify how wetland protection goals and other

concerns of the plan will be addressed, and should identify information gaps. Coal setting must

then be followed by developing means of measuring progress. For example, sediment input and

specific pollutant loads can be assessed to determine whether the plan is being successfully

implemented.

Watershed planning also allows stormwater managers to determine how best to control the

quality and quantity of surface waters within a watershed after development has commenced.

Ideally, this process will attempt to replicate, to the extent possible, the predeveloped hydrology

of the watershed, including how wetlands function for flood storage as well as their water quality

functions. Watershed planning is an opportunity for wetland managers to assess wetland

protection needs, develop wetland restoration goals, plan mitigation strategies, and determine

impacts from land use changes to wetland resources. When wetland resources are identified on a

watershed (or landscape) scale, factors such as location of individual wetlands with respect to

other wetlands, adjacent land uses, or water bodies can be factored into the decision-making

process of a wetland resource assessment and the design of appropriate controls (structural or

nonstructural) for preventing or treating stormwater discharges to natural wetlands.

Some increase in impervious surfaces, resulting hydrological changes, and a related addition

of pollutant sources are inevitable results of urban and suburban development. BMPs attempt to

mitigate these hydrological modifications and pollutant inputs. Without BMPs, wetlands

receiving flows of uncontrolled runoff would likely become severely degraded. Therefore, the

changes in hydrology rather than the BMPs are the cause of the problem. Nonetheless, where

wetlands occur within a watershed, planning for BMPs needs to consider the impact of each BMP

on wetlands and related groundwater resources.

A modeling mechanism may be incorporated into the watershed management plan. Such a

model shows the cause-and-effect relationships within a watershed and can be used to test various

land use/stormwater control scenarios to determine which option best preserves overall wetland

functions or improves the health of a degraded wetland system.

The Maryland Nontidal Wetlands Program calls for watershed management plans that

contain, at a minimum, a functional assessment of nontidal wetlands within a watershed; the

Page 2-29
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

location of potential mitigation sites; and plans for the protection of nontidal wetlands, limiting

cumulative impacts, water supply management, and flood management (MDDNR, 1991). An

effective wetlands watershed management plan may also include wetlands and floodplain

protection ordinances, river corridor programs, sewer overflow provisions and siting controls,

control of septic systems, requirements for pumpout stations for small boats, designing and siting

of wastewater treatment facilities, surface water and groundwater quality controls; and nonpoint source pollution controls (USEPA, 1992c).

Once wetland resources and existing land use designations have been identified and the

goals for wetland protection have been determined, implementation strategies can be developed

to guide activities in the watershed. Nonstructural control practices (as opposed to structural

practices) are the preferred technique for protecting wetlands because they are based on pollution

prevention and reduction. Nonstructural control practices can be used within four program areas:

permitted uses, preventive construction techniques, operation and maintenance, and education.

Permitting Programs

The goals of a watershed management plan, such as wetland protection and water quality

improvement, can be implemented through various permitting programs such as land-use

planning and zoning, natural resource/wetland protection ordinances, stormwater permitting

programs, and other pollution control programs. Land development regulations may also require

natural performance standards such as limiting rates of runoff, soil loss, or pollutant loadings into

wetlands and the completion of environmental impact assessment statements prior to

construction plan approval.

Preventive Construction Techniques

Stormwater quality and wetland protection can be improved through the implementation

of numerous nonstructural preventive construction techniques for new development and

redevelopment that help to minimize impacts, such as:

l Limiting the amount of impervious surface

l Requiring setbacks from wetlands, riparian areas, and surface waters

l Preservation of natural vegetation

l Open space requirements and slope restrictions

l Siting infrastructure so as not to adversely affect wetland and water resources

l Discouraging development in environmentally sensitive areas that are critical to

maintaining water quality

l Site plan review procedures

l Performance standards for stormwater and wetlands

Operation and Maintenance

Maintenance of existing stormwater controls ensures continuing operation, effective

pollutant removal, and the protection of wetland and surface water resources. Maintenance, such

as the removal of sediments from detention and infiltration devices, the replanting of vegetation

as upkeep within buffer and open space areas, and the maintenance of erosion and sediment

control structures, is essential to the success of most structural and vegetation-dependent NPS

Page 2-30
Factors to Consider When Selecting BMPs

pollution controls. Maintenance programs should require the prior designation of an entity or

individual who is responsible for maintenance, and should stipulate the funding source or sources.

Outreach and Education Programs

Outreach programs can be designed to reduce individual contributions to stormwater

problems and improve program implementation by maintenance personnel and government

officials. Training programs and educational materials for public officials, contractors, and the

public are also crucial to implementing effective urban runoff management programs. Contractor

certification, inspector training, and competent design review staff are important to the success

of a stormwater management program. The states of New Jersey, Virginia, Maryland, Washington,

Delaware, and Illinois; NRCS; and the city of Alexandria, Virginia, have developed manuals and

training materials to assist in implementation of urban runoff requirements and regulations

(USEPA, 1993).

Education programs should be implemented in homes, in residential communities, and at the

workplace. At a minimum, they should educate and encourage the public to participate in and

support local pollution prevention programs. Such programs might include storm drain stenciling,

used oil and hazardous chemical recycling, litter control, street sweeping, lawn management and

landscaping, safe use and disposal of household hazardous materials and chemicals, correct

operation of onsite disposal systems, including the danger of industrial wastewater discharges to

septic systems, proper disposal of pet excrement, and water conservation.

Structural Controls

Structural controls are methods for managing stormwater that involve altering the flow,

velocity, duration, and other characteristics of runoff by physical means (USEPA, 1993).

Structural controls can be used for both stormwater volume control and water quality

improvement. A fundamental consideration for design or selection of a particular BMP is whether

the wetland hydrology is dependent on surface water flow, groundwater flow, or some

combination of the two. Most structural controls are engineered structures that require regular

maintenance. Structural controls that can commonly be used to protect wetlands include:

l Infiltration basins

l Infiltration trenches

l Sand filters

Level spreaders (may be associated with gabions)

l French drains

l Grassed swales

l Vegetated filter strips

l Open spaces

l Extended detention dry basins

l Wet ponds

l Constructed wetlands

Page 2-31
BMPs In Series

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Less common controls may be used in special situations and for special purposes, usually to

improve stormwater quality. These controls generally have limitations regarding applicability and

maintenance. For example, untreated stormwater directed to a separator, dry well, or other

shallow disposal system will eventually find its way to a water-table aquifer. Examples of these

less commonly used controls include:

l Porous pavement and concrete grid pavement

l Oil/grit separators or water quality inlets

l Dry wells or roof downspout systems

l Exfiltration trenches

BMPs in series incorporate several stormwater treatment mechanisms in a sequence to

enhance the treatment of runoff where determined necessary. By combining treatment

mechanisms in series rather than using a single method of treatment for stormwater runoff, the

overall levels and relability of pollutant removal can be improved. Some examples of serial BMPs

include the use of multiple pond systems, the combination of vegetated filter strips with grassed

swales and detention ponds, and the combination of grassed swales or vegetated filter strips with

infiltration trenches. (For more information, see the fact sheet “BMPs in Series” in Section 4 of

this manual.)

BMP Maintenance Requirements

When properly designed and located, BMPs can protect wetlands by providing preliminary

treatment of stormwater to (1) restore or maintain predevelopment hydrology and hydroperiod

by providing a balance between infiltration and detention or retention, (2) reduce fluctuations in

nutrient levels, and (3) remove excessive levels of nutrients and sediments. The ability of

stormwater pretreatment systems to provide these functions depends on both the effectiveness

and reliability of individual BMPs or BMPs in series. Regular inspections and maintenance are

essential to good performance for all BMPs (Washington State Department of Ecology, 1991).

Failure to provide proper maintenance can result in reductions in the pollutant removal

efficiency or reductions in hydraulic capacity of stormwater treatment systems (Washington

State Department of Ecology, 1992).

If stormwater BMPs are not functioning properly due to inadequate maintenance, the result

can be flooding problems and in some cases even an increase in the pollutant load of stormwater

discharges (Washington State Department of Ecology, 1992). Effective maintenance can be

ensured by clearly defining maintenance responsibilities and performing regular inspections to

determine maintenance needs (Washington State Department of Ecology, 1992). Apart from

achieving the required effectiveness and reliability, BMP maintenance and longevity are

important considerations in the selection of a BMP not only because longevity varies

considerably between treatment options, but also because maintenance costs may be high, in

some cases rivaling construction costs over the design life of the BMP (Schueler et al., 1992).

Page 2-32
Maintenance Factors

Factors to Consider When Selecting BMPs

Maintenance and maintenance costs can be reduced if maintenance needs are anticipated in

the design stage (Schueler, 1987). The need for incorporation of maintenance provisions in

facility designs is especially important when anticipating removal of sediment and debris from

basins. Two specifics to be incorporated into site plans are access for maintenance equipment and

easements. Easements are necessary around the perimeter of stormwater facilities to allow for

maintenance and to provide a buffer from encroachment (Washington State Department of

Ecology, 1992).

Maintenance is necessary to ensure that the storage and infiltrative capacity of the BMP is

not compromised so that the BMP can effectively buffer wetlands from the detrimental effects of

stormwater. The temporary storage and infiltration functions of pretreating stormwater can be

partially accommodated by the wetland if not provided by the BMP, but not without potential

damage to the wetland. Furthermore, stormwater might not be sufficiently treated before it

enters the wetland. Regular maintenance is used to ensure that the BMP continues to function

according to design specifications. Specific design variables that regular maintenance is intended

to maintain include the detention time of pond systems; the flow path of stormwater to, from,

and within the BMP (preventing erosion); the water level; and vegetative cover in and

surrounding the device. Frequent problems that maintenance is targeted to address include

clogging of infiltrative surfaces; blockage of inlet or outlet structures by debris; erosion of pilot

channels, side slopes, embankments, and emergency spillways; sedimentation; accumulation of

pollutants; overgrown or patchy vegetation; and nuisance insects.

The major mechanism by which pollutants are removed by BMPs is through sedimentation

of sediment particles and pollutants attached to sediments. The more efficient a BMP is at

removing sediments, the more frequently sediments and pollutants that have accumulated in the

treatment device will need to be removed to ensure that the system continues to function

properly (Washington State Department of Ecology, 1992). It is beneficial not to allow sediments

to stand in the system for long because the longer the wastes accumulate in the system the more

likely they are to become contaminated to the point where they might no longer be accepted for

disposal at a landfill (Washington State Department of Ecology, 1992). Frequent sediment

removal from catch basins, detention vaults, pretreatment inlets, oil/grit separators, vegetative

BMPs, and pond forebays prevents sediments from being scoured by storms, which could result in

shock loadings to receiving waters or clogging of a downstream BMP if BMPs occur in series. Pond

systems require less frequent sediment removal; however, flooding can result if pond capacity is

reduced by accumulated sediment. Infiltration devices that become clogged with sediment can

also cause flooding.

The degree and type of maintenance required depend on the BMP type, design, management

objectives, climate, and surrounding land use. For instance, infiltration BMPs, although effective

in removing pollutants, are usually less reliable than other types of BMPs due to poor longevity

(Schueler et al., 1992). Specific management requirements for each of the stormwater

pretreatment systems described in this document are provided in Section 4.

The type of maintenance depends on management objectives. For instance, pond systems

composed of wet meadow or wetland marsh and constructed stormwater wetlands, adjacent to

natural wetlands, may be managed for the dual purpose of promoting wildlife habitat and

removing pollutants. Creation of wetland habitat within a stormwater treatment pond is

Page 2-33
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

especially important in areas where the value of natural wetlands has been diminished by

construction of stormwater treatment systems adjacent to or in natural wetlands (South Carolina

Coastal Council, 1988). Benefits of wetland creation include removal of soluble pollutants,

provision of wildlife habitat, and disguise of unsightly debris and sediment deposits (Schueler,

1987). When a constructed wetland is placed adjacent to a natural wetland, the two wetlands

form an integrated system, the function of which is significantly influenced by the management

of the constructed wetland (DeVoe and Baughman, 1986). Management for waterfowl, the most

common natural habitat objective, may employ some combination of water level manipulation,

bed disturbance, and salinity manipulation in coastal areas. The goal of these practices is to

promote the growth of aquatic plants that attract migrating waterfowl. The degree and timing of

exchange of water between adjacent creeks, the constructed wetland, and the natural wetland

influence dissolved oxygen, temperature, and aquatic species (such as fish and crayfish)

recruitment (DeVoe and Baughman, 1986). Usually water levels of ponds and wetlands

exclusively managed for waterfowl are maintained in the spring and fall for waterfowl migration.

During the late spring, water is drained so the beds can be plowed in June. In October, the beds are

flooded again (DeVoe and Baughman, 1986). There might be conflict of use between the need to

maintain low water levels to capture stormwater and the need to maintain higher water levels to

attract waterfowl. In addition, an objective might be to discourage waterfowl from using the

constructed wetland if pollutant concentrations are expected to be high.

Mosquito control and frequent mowing will not be as important in an area managed for

wildlife as in a residential neighborhood. Mosquitoes are a problem in wet meadows because

rainfall pools in areas, allowing mosquito eggs to develop and hatch. Constructed wetlands and

pond systems can be managed to minimize the production of mosquitoes by maintaining a system

of ditches or canals for drainage. An aquatic weed control program can control mosquitoes by

preventing an overgrowth of vegetation in the pond. Fish stocks can be maintained in the

permanent pool of retention ponds (South Carolina Coastal Council, 1988). A pond that is

scheduled to be filled for waterfowl use can be filled and emptied first to flush out resident

mosquito populations (DeVoe and Baughman, 1986).

Implementation

Frequently, more attention is placed on design and location of structures than on

maintenance. In addition, many jurisdictions do not have required BMP maintenance programs

to ensure the adequate performance of BMPs (Schueler et al., 1992). The lack of routine

inspection and maintenance is especially evident in the case of small, privately owned local

disposal facilities, such as grassed swales, infiltration trenches, and infiltration basins, that are too

small to justify a full-time staff person. The long-term effectiveness and reliability of BMPs can

be enhanced through implementation of a maintenance and operation schedule for each BMP that

explains routine and nonroutine maintenance tasks and identifies the party (or parties)

responsible for performing them (Washington State Department of Ecology 1991). A

maintenance plan developed for the life of the stormwater treatment facility can be required

before the certification of a project (South Carolina Coastal Council, 1988). Inspectors need to be

trained to know how the stormwater treatment system is designed to function and what the early

warning signs of problems are. In addition to the brief overview of maintenance requirements of

various types of BMPs, specific information is provided in Section 4 for each BMP to assist

managers in developing their operation and maintenance plans.

Page 2-34
Factors to Consider When Selecting BMPs

Development of an Effective Maintenance Plan

Development of an effective maintenance plan requires site-specific information and a

considerable amount of planning and foresight, beginning with the establishment of broad goals

and objectives and ending with the scheduling of staff and equipment. Activities involved in

designing an effective maintenance program include developing goals, reviewing existing policies,

assigning responsibilities, planning the frequency of inspections, scheduling inspections,

determining staffing needs, and determining enforcement procedures (Washington State

Department of Ecology, 1992). Each component of the planning phase is discussed separately.

An effective maintenance plan reflects the specific priorities and goals of the community

served by the stormwater treatment program, as well as watershed characteristics and existing

policies within the jurisdiction (Washington State Department of Ecology, 1992). Therefore,

development of a management plan begins with arriving at policies that outline who should be

responsible for maintaining BMPs on private and public lands and how these policies will be

enforced. The goal-setting stage differs from the final stages of maintenance plan development in

that here utility officials should not constrain themselves to consideration of goals limited by

current practices and policies but rather should consider how maintenance ideally should be

performed, looking beyond the next 5 to 10 years to anticipate how decisions made now will

affect future courses of action and alternatives (Washington State Department of Ecology, 1992).

Existing policies within a jurisdiction can either facilitate or impede an effective

maintenance program. Once the goals of the maintenance program are identified, managers

should review existing statutes, ordinances, and policies to assess how these complement the

established goals of the maintenance program. In this manner, options for revising these policies

where shortfalls are uncovered can be identified early (Washington State Department of Ecology,

1992). Design requirements for maintenance (e.g., access, clean-out traps, sediment disposal areas)

should be included in ordinances and policies.

During the planning stage of the maintenance plan, staffing needs and limitations should be

considered prior to deciding who will be responsible for performing maintenance tasks,

specifically whether they will be performed privately or by the local government. Some

distinctions may be made between routine and nonroutine maintenance activities or between

facilities located on rights-of-way and those on private lands. If private individuals or

organizations will perform the maintenance, an ordinance that requires owners to be informed of

operation and maintenance frequency, schedules, procedures, responsibilities, and enforcement

will be necessary For example, an ordinance might require that new owners be notified at the

time of sale that they are owners of a stormwater treatment device and that they be provided

with the operation and maintenance instructions (Urbonas and Stahre, 1993). An ordinance

might not be required if local government will perform the bulk of the maintenance. If an

ordinance is not used to assign responsibilities, consideration should be given to staffing needs

and limitations, merits of alternative funding mechanisms, provisions for intergovernment

cooperation, and specific needs or limitations (Washington State Department of Ecology, 1992).

Maintenance inspections need to be planned, including inspection frequency, scheduling,

and staffing needs. In general, BMPs should be inspected and maintained once a year, at the very

least, to remove debris, sediment, and vegetation that threaten the function or capacity of the

facility and to replant damaged vegetation on grassed swales, vegetated filters, and buffer strips

(Washington State Department of Ecology, 1992). The frequency of inspection depends on the age

of the stormwater BMP, the occurrence of large runoff events that could damage the BMP, the

history of problems encountered, and whether inspectors will perform routine maintenance.

Page 2-35
Fees

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Real estate transfer taxes are assessed as a percentage of property values when property is

sold. These taxes are imposed on property buyers, sellers, or both. Funds raised by such taxes can

be dedicated to help purchase environmentally sensitive lands or to support resource conservation

programs.

The Prince William County,

Virginia, watershed management

study is a project that is attempting

to develop an innovative

stormwater management plan

through the use of BMPs and the

restoration of riparian habitats. A

5-year, multimillion-dollar program

to study the three urban Watersheds is being funded through a

federal-state-local cost-sharing

approach. The Prince William

County government Is funding 50

to 60 percent of the entire

project. The remainder of the

funding is being provided by the

U.S. Fish and Wildlife Service, the

U.S. Geological Survey, the Army

Corps of Engineers. and the

Environmental Protection Agency.

The Prince William County

government is helping to fund the

project through a stormwater

utility fee. Utility taxes can be

imposed on property owners

based on a variety of factors, such

as the amount of runoff generated on a piece of property. (The

fee can be calculated by the

percent of the property that Is

impervious.) Impact fees are

usually collected at one time and

can based on factors such as new

land development.

(See case study on P. 3-11 for

more information.)

Commodity taxes are charged on specific items (commodities) such as

gasoline, liquor, or cigarettes. The money raised could be targeted for

environmental programs or services. A tobacco tax helps finance Washington

State’s water quality protection plan.

Tax surcharges are fees added to established tax rates. They are often

used for sudden unforeseen events. A tax surcharge on residential sewer bills,

for instance, might be used to finance the replacement of stormwater

retention basins destroyed during a hurricane.

Stormwater utility taxes are imposed on property owners to pay for

stormwater treatment. The charge can be based on the amount of runoff

generated from the property, the amount of impervious area (hard surfaces)

on the property, or the assessed value of the property There are more than 100

stormwater utilities in the United States. Methods of determining

stormwater utility charges vary considerably around the country, depending

on local stormwater management goals and conditions. In general, utilities

are either publicly owned and operated enterprises or privately owned

enterprises whose ability to profit from providing public services is regulated

by a public agency. Utilities provide a more reliable source of funds for local

stormwater management than do property taxes.

Tax incentives and disincentives refer to a tax system set up to encourage

or discourage certain behaviors by offering tax reductions or increases.

Incentives often take the form of state tax credits, deductions, or rebates. A tax

credit for the use of low-flow plumbing fixtures, for example, can encourage

water efficiency. Disincentives often take the form of fees, taxes, or price

increases. A tax or fee, for example, can discourage the inefficient use of a

product.

User fees are the most common way of recovering the costs of providing a service. These

fees can tie directly to the users of a resource or facility (sportfishing license fees, for example).

User fees are particularly useful at the local level, where user groups are easily identified.

An innovative example of a user fee is the State of Maryland’s license plate program to fund

its Chesapeake Bay Trust. More than 40,000 "Treasure the Chesapeake” license plates have been

sold, raising over $4 million. Baltimore, Maryland, area Ford dealers offered Bay license plates at

no cost to their new car and truck owners by paying the $10 fee from June through July 1991,

raising $20,000 for the Trust.

Plan review fees are assessed by a local government to conduct a review of development

plans to ensure that they meet certain requirements. This technical review includes determining

Page 2-38
Capacity Credits

Fee-in-Lieu 

Factors to Consider When Selecting BMPs

the adequacy of stormwater management facilities, setback requirements, and wetland

protection. These fees help cover the cost of conducting plan reviews and inspections.

The myriad programs that have

been established to preserve and

restore wetlands in the Chesapeake

Bay watershed are an example of

a multi-stakeholder federal, state,

local, and private citizen partnership. Private organizations and

public agencies, such as the

Chesapeake Bay Foundation and

the Environmental Protection

Agency and the states of Pennsylvania, Maryland, and Virginia, are,

in certain instances, pooling their

resources to fund projects and

create policies regarding the

Chesapeake Bay watershed. For

example, the Sea Grant College

Chesapeake Bay Studies Program,

which researches fish stocks, fate

and transport of toxic pollutants,

and remote sensing, is funded

through a research grant from the

National Oceanic and Atmospheric

Administration. Remote sensing has

been used successfully for

identifying wetlands and dellneating the wetland/upland boundaries

in the Chesapeake Bay region.

Onsite inspection fees are charged to cover the costs of activities to make

sure that development plans are properly implemented. These activities can

include erosion and sediment control; BMP siting, implementation, and

maintenance; and wetland protection. This approach defrays the cost of

conducting inspections.

Impact fees transfer the costs of infrastructure services (roads, sewers,

stormwater treatment) needed for private development directly to

developers or property owners. Unlike user fees, which recover costs over the

life of a project, impact fees are usually collected in one lump sum at the

beginning of a project. These fees are particularly attractive to local

governments because they relieve up-front financing pressures on local

budgets. In California, for example, several wastewater treatment plants have

been financed with fees paid by developers on the basis of the demands for

treatment that their projects are expected to generate. Impact fees could be

used for building regional stormwater management facilities.

The state governments of Maryland

and Virginia have implemented

Iicense Plate programs that provide

part of the proceeds of the plates

to a Chesapeake Bay Trust. Private

citizen associations, such as the

Herring Run Watershed Association

in the Baltimore, Maryland, area

can also receive funding from

beyond their local membership.

The Herring Run restoration

project is a community. state, and

federal partnership that Includes

school curricula for ‘adopting’ and

inventorying land use, planting

trees, and caring for the existing

forest buffers. The Maryland

Department of Natural Resources

recently accepted a grant of

$22,300 from the U.S. Forest

Service’s Chesapeake Bay Program

to help fund this effort to improve

conditions within the Herring Run

watershed.

Capacity credits are a form of financing in which private interests

(usually developers) purchase future capacity in a public facility such as a

stormwater treatment facility Applicants are guaranteed future access to the

additional capacity of that particular facility When enough credits have been

sold, work on the project begins.

Fee-in-lieu is a method of easing environmental impacts on a regional or

watershed basis. If a county or municipality determines that wetland

restoration is too costly for an individual site, a fee can be charged to the

property owner in lieu of implementing the restoration. The funds collected

could be used to restore a more valuable wetland elsewhere in the watershed.

Bonds/Debt Financing

Bonds or debt financing raises up-front capital and distributes the

burden of repayment for capital projects over the life span of the project and

among those who benefit from it. Typically, bonds can be used only to

finance projects that have both known and proven life expectancies. Shortterm bonds are usually payable within 1 year. Establishing short-term debt

provides interim funding of projects waiting to receive long-term financing.

Long-term bonds traditionally match the term of financing with the life expectancy of the

project. A stormwater treatment facility, for example, might be expected to perform adequately

for 30 years; therefore, the community could issue up to a 30-year bond.

Page 2-39
Grants

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

State Revolving Funds

State Revolving Funds (SRFs), which have been established since the Clean Water Act

Amendments of 1987 by grants from EPA and state matching funds, can provide states with funds

to finance NPS projects. They are generally operated by the state and provide long-term, lowinterest loans to localities for major capital investments, such as stormwater retrofit projects.

SRFs may also provide credit enhancement or, to a limited degree, grants. The designated state

institution receives an initial flow of capital from EPA; local user fees are established to cover

operation and maintenance costs and to repay loans and interest rates. As repayments

accumulate, the SRF is able to make more loans using those repayments. The State of California,

for example, uses its SRF for nonpoint source purposes. The fund is administered by the State

Water Board, which developed a flexible program to evaluate and select for funding a wide variety

of nonpoint source pollution projects. Eligible projects include construction of demonstration

projects, retention/detention basins, and a variety of BMPs to reduce or remove pollutants. The

nonpoint source program for the SRF also permits the establishment of substrate revolving funds

that can provide funding to private individuals to finance new onsite septic systems.

Grants are sums of money awarded to state and local governments or nonprofit

organizations that do not need to be repaid. Grants are awarded for the purpose of financing a

particular activity or facility. EPA grants are federal grants that provide state and local

governments funding to meet national environmental quality goals. Criteria for receiving grant

money are established by EPA and must be met before the funds can be used for a specific activity

or program. For example, section 6217 of the Coastal Zone Act Reauthorization Amendments of

1990 (CZARA) requires states to establish coastal nonpoint source control programs, which must

be approved by both the National Oceanic and Atmospheric Administration (NOAA) and EPA.

Once approved, the programs will be implemented through changes to the state nonpoint source

pollution program approved and funded by EPA under section 319 of the Clean Water Act and

through changes to the state coastal zone management program approved by NOAA under section

306 of the Coastal Zone Management Act. Section 604(b) of the Clean Water Act requires an

allotment of funds to provide grants to states to carry out water quality management planning.

Section 314 of the Clean Water Act provides funding for project grants to states for assessing the

water quality of publicly owned lakes, developing lake restoration and protection plans,

implementing these plans to restore and preserve the lake, and performing postrestoration

monitoring to determine the longevity and effectiveness of restoration.

Leases

Leases are contracts that allow another person to use land or a building for a specific time,

usually in return for repayment. Leasing obligations are not considered debt in most states and

voter approval for financing is not required. Lease-purchase agreements (municipal lease) give the

person holding the property lease, the lessee, the option of applying lease payments to the

purchase of the facility. The lessee is responsible for paying taxes. These agreements can be used to

finance wetland restoration projects or to purchase riparian areas or other environmentally

sensitive areas. Sale-leaseback arrangements allow private investors to purchase public facilities or

equipment on behalf of the community. Since the investors are entitled to tax benefits, they can

lease the property back to the municipality at a lower cost.

Page 2-40
Hydrology

Factors to Consider When Selecting BMPs

Matching Wetland/Stormwater Factors to BMP Design

Preliminary Treatment of Stormwater

The level of treatment needed to protect a wetland that receives urban stormwater is

dependent on the type and condition of the wetland; on the quality, quantity, and distribution of

runoff; and on what levels of impacts to the wetland are considered acceptable. Ideally, all

pollutants and sediments not present prior to watershed development should be removed before

the stormwater is discharged to wetlands; however, some wetland types might be able to

assimilate higher levels of certain pollutants. Some regions, such as southern Florida, parts of New

England, and the Southwest, have soils with high infiltration rates, and a major concern related to

urban stormwater might be the potential contamination of aquifers. Instituting stormwater

treatment might be part of a larger effort to protect or restore wetland and downstream

ecosystems and might involve analysis of stormwater dynamics at the watershed level and a

variety of actions aimed at runoff quality maintenance or enhancement.

Matching Wetland Characteristics to BMP Design

Wetlands should be characterized with a classification system such as that of Cowardin and

others (1979) prior to introducing additional stormwater or modifying the characteristics of

existing stormwater inflows with BMPs. The general characteristics of a wetland, used to

determine its placement in a classification system, should be considered when determining the

type and placement of BMPs adjacent to or upstream of a wetland. In addition to considering

general classification characteristics, site-specific evaluations of wetlands should be made. The

modification of existing stormwater characteristics due to development or the type of BMPs used

should be compatible with the characteristics of the existing wetlands in a system. Table 2-7

shows a general comparison of various BMPs and the benefits to protecting wetland functions

that they might offer. This table is intended to be used as a preliminary screening device to

identify potential wetland protection BMPs to treat stormwater runoff.

In addition to considering wetland type and conditions, the nature of stormwater

discharges must be evaluated to determine the best practices for protecting urban wetlands. Both

the quantity and quality of urban runoff are significantly affected by watershed development.

Increased impervious area, removal of trees and other vegetation, and soil compaction in a

watershed can increase runoff volume (Schueler, 1987), altering the natural hydroperiod of

receiving wetlands. Reduced infiltration of stormwater can reduce baseflow and alter the

groundwater hydrology of some urban wetlands. Known hydrologic impacts to wetlands

associated with increased stormwater runoff include changes in wetland response time, changes

in water levels in the wetland, and changes in the detention time of the wetland. Increased

runoff volumes are also associated with greater water level fluctuations in receiving wetlands,

which can adversely affect wetland plant and animal communities (Azous, 1991; Cooke, 1991).

Large amounts of water entering a wetland at once can cause disturbance through changes in

circulation and flushing characteristics and through possible erosion of wetland soils.

Page 2-41
Table 2-7. Potential Benefits to Wetland Functions from Various BMps

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Page 2-42
Climate

Factors to Consider When Selecting BMPs

The natural hydrologic characteristics of a wetland are of concern when designing

stormwater management systems. In areas where natural wetlands are relatively unimpacted, the

existing hydroperiod of wetlands should be maintained, while in areas where wetlands have been

deprived of water, BMPs can play a role in enhancing wetland ecosystems through restoration of a

more natural hydroperiod.

The source of water in a wetland is also important in designing a stormwater management

system. In wetlands where the source of hydrology is primarily in the form of surface water

runoff, the use of BMPs that incorporate infiltration into the soil as the method for stormwater

treatment (e.g., infiltration trenches or infiltration ponds) might change the natural hydroperiod

of adjacent or downstream wetlands. As mentioned, changes in the natural hydrologic

characteristics can adversely affect the structure and functions of these wetlands. Stormwater

treatment systems that treat stormwater by temporary detention or retention (e.g., extended

detention ponds, wet ponds), when properly designed, can help to restore the predevelopment

hydrologic conditions in this type of wetland. Conversely, the use of detention or retention

systems adjacent to or upstream of groundwater wetlands can adversely affect their hydroperiod

by altering natural baseflow conditions.

Local climatic conditions determine the quantity, frequency and intensity of stormwater

runoff events. Under natural conditions, development of wetland types and functions is based

largely on these climatic conditions. In fact, in the United States, climate variation has

contributed to the formation of distinctly different wetland types, and climate is the second

major controlling factor that leads to the formation of regional wetland types. Therefore, climatic

conditions, precipitation, and storm events all need to be analyzed prior to selecting a

stormwater pretreatment strategy The placement of BMPs to treat stormwater or to protect

existing wetlands from stormwater impacts can actually harm the systems if the practices are not

designed based on the local conditions and the natural wetland characteristics. Likewise, the

selected BMP type and design should be based on both design storm requirements and adjacent

wetland characteristics.

For example, stormwater in the Southwest is similar to that in other areas of the country.

Some qualifications would include the following: (1) no major sodium chloride components in

runoff from deicing salts as found in snow zones; (2) an increased dust component; (3) higher

first-flush pollutant concentrations arising from a longer accumulation time between storm

events; (4) suspended sediment sources masked by a high natural background; and (5) the

desiccation of organic material on the landscape, especially domestic animal feces (Hawkins,

1993). Many urban areas in the Southwest lack storm sewers; streets and other land surfaces act

as a conduit for stormwater, which enhances street runoff and contact with contaminants

(Hawkins, 1993).

Any BMPs that require regular rainfall or a moist climate would not be appropriate for

southwestern arid land conditions (Hawkins, 1993). Runoff is not frequent, stored stormwater is

subject to high evaporation rates, and cover is naturally sparse. Traditional retention-type BMPs

are used in the region, however, for peak flow reduction. Most of the water quality BMPs being

proposed for southwestern cities stress dust and soil control, catch basin cleaning, debris removal,

street sweeping, hazardous waste disposal, and other similar pollution prevention practices

(Hawkins, 1993).

Page 2-43
Water Quality

Monitoring

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Natural nutrient levels within a particular wetland vary widely among wetland types, and

the potential effects of loadings from stormwater must be evaluated with consideration of the

type of receiving wetland. Wetlands can vary in their ability to absorb or transform these

compounds due to variations in hydrologic, soil, and vegetative characteristics of the wetlands,

and they might be only temporary sinks for some compounds. Although nitrogen can be removed

from wetland soils as nitrogen gas through the process of denitrification, phosphorus can be held

in wetland soils until a wetland’s natural storage capacity is reached, beyond which the wetland

might no longer function as a sink or might even become a net exporter of phosphorus to

receiving waters (Richardson, 1989).

Pretreatment of stormwater flow prior to its inflow into existing wetlands can help in

attenuating fluctuations in nutrient levels. The pretreatment of stormwater through the

incorporation of BMPs can also reduce the amount of sediment that enters a wetland. If incoming

sediment loads are high, the wetland’s storage capacity could be reduced over time and its ability

to function could be affected (Marble, 1992). While the increased levels of nutrient and sediment

loading to wetlands associated with stormwater can adversely affect wetland functional

characteristics, the removal of most or all suspended particulates through the placement of BMPs

can also result in wetland degradation. Reductions in the natural levels of sediment deposition in

a wetland can result in the embedding of downstream wetland substrates in some wetland types

or in erosion in other types and potentially in erosion and channel scouring in associated

downstream systems. In some systems the resuspension of downstream floodplain sediments can

occur. Natural soil and sediment conditions should be considered in a wetland or wetland system

when determining the feasibility, design, and types of BMPs to be used.

One strategy for determining the performance of a BMP - its effect on the wetland’s

water quality, health, and functions -is through monitoring. Even though monitoring is beyond

the scope of this manual, it is worthwhile to discuss the fundamentals of a monitoring project.

During the BMP planning process, the appropriate level of monitoring should be determined so

that resource requirements can be identified and factored into the overall project. Proper

planning targets monitoring efforts at key elements of the project that will indicate the degree

of success and the potential need or opportunity for improvement in a particular system.

A monitoring plan should be developed based on the objectives of the BMP project and on

documented literature or readily available monitoring results of similar projects (Kusler and

Kentula, 1990; USEPA, 1992). The wetland functions of concern should be identified and the

current level of those functions established relative to reference wetlands. For an existing

wetland, functions that might be threatened by stormwater runoff (e.g., sediment retention and

long-term water storage) should be documented. Where stormwater might be used to restore a

severely degraded wetland, the desired functions of the wetland should be evaluated so progress

can be measured.

The first step in any monitoring effort, establishing baseline data, is important in

evaluating the long-term effectiveness of the BMP. Obtaining as much information as possible

about the resource to be protected or restored will allow progress or degradation to be measured.

As soon as construction of the BMP is completed, monitoring of the project should begin. For a

thorough monitoring effort, the boundaries of the watershed in which the BMP was constructed

Page 2-44
Factors to Consider When Selecting BMPs

should be determined and the exact location of the project within that watershed should be

indicated on a map. Variables that might be included in a monitoring effort include the following

(North Carolina Cooperative Extension Service, 1995; USEPA, 1992a):

l Morphometry (area, slope, and perimeter-to-area ratio)

l Hydrology (water depth, flow rates, flow patterns, and indirect indicators)

. Substrate (soil depth, color, texture, source, organic matter, sediment flux)

l Vegetation (species, coverage, survivorship)

l Fauna (observations, habitat evaluation, species- or community-specific sampling)

l Water quality (pH, DO, temperature, metals, turbidity, TSS, BOD, N, P)

Monitoring strategies might range from simple visual assessments of a wetland to full

evaluations including ambient water quality analyses in the wetland and a BMP inlet/outlet

efficiency assessment. In some cases, the simple, visual assessments (e.g., looking at the

vegetation and hydrologic changes) might be enough monitoring to determine whether the BMP

is performing efficiently When this simple monitoring does not provide adequate information,

more elaborate analysis is needed.

It is advisable to identify and take into account other existing information that might be

available, such as meteorological data, data obtained from monitoring conducted under an

NPDES or state permit, or volunteer monitoring data. A sampling regime including set (or

randomly selected) sampling sites and specific times to repeat the sampling (e.g., in wet and dry

seasons) should be established. A site can be monitored through routine inspections or more

comprehensive, quantitative sampling events. Routine inspections are “spot checks" and are

conducted as often as daily or weekly. These assessments allow the investigator to identify

problems as they develop. Generally routine inspections are less costly and not as damaging to

the wetland or BMP because these inspections are less intrusive (i.e., they require less data

collection and less equipment to obtain the data).

Quantitative sampling events, in comparison, are periodic assessments conducted annually

for several years after the BMP is constructed. This type of monitoring indicates the degree to

which the goals of the project have been met (Kusler and Kentula, 1990). Comprehensive

assessments typically require more equipment and skilled personnel and therefore are more

costly and often more damaging to the wetland than are routine inspections.

Reports of monitoring efforts should include photographs of each sampling effort, a

description of the project and project site, an explanation of site preparation, and a summary of

what was conducted and the results. These data, once evaluated, will allow for improvements in

design guidelines for future BMP projects.

The data quality of monitoring efforts must be scientifically acceptable. Five quality

assurance components of assessments have been identified: precision of the measurements of the

same variable, accuracy of the measurements, completeness of the collected data versus what was

expected, representativeness of the variable’s characteristics, and comparability of one data set to

another (Sherman et al., 1991, cited in USEPA, 1992a).

Page 2-45
Summary

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Best management practices used for the treatment of urban stormwater are commonly

located in low topographic positions adjacent to or within existing wetlands. They can be used

primarily to treat or pretreat stormwater or to protect existing wetlands from the effects of

stormwater runoff. The above examples represent only a few of the variables that should be

considered when placing BMPs within or adjacent to wetland systems. When designing BMPs,

the treatment of stormwater is not the sole consideration. For BMPs that are incorporated into

systems where wetland protection and optimal stormwater treatment are both objectives, the

characteristics. of the existing wetlands must also be considered. It is most desirable to consider

protecting wetland resources from a holistic perspective. This can be accomplished through the

use of a variety of nonstructural BMPs including watershed planning, public education, and

preventive construction techniques.

Page 2-46
References

Factors to Consider When Selecting BMPs

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Cooke, S.S. 1991. The effects of urban stormwater on wetland vegetation and soils - A long-term ecosystem

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Puget Sound Water Quality Authority

Cooper, D.J. 1989. A citizen’s handbook for wetland protection. U.S. Environmental Protection Agency, Region

8, Denver, CO.

Cowardin, L.M., V. Carter, EC. Golet, and E.T. LaRoe. 1979. Classification of wetlands and deepwater habitats

of the United States. Biological Services Program Report FWS/OBS-79/31, U.S. Department of the Interior,

Fish and Wildlife Service, Washington DC. Reprinted 1992.

DeVoe, M.R., and D.S. Baughman, eds. 1986. South Carolina coastal wetland impoundments: Ecological

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Carolina Sea Grant Consortium, Charleston, SC.

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constituent concentrations in urban watersheds in the United States. (200)R290 No. 88-191. U.S. Department of

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Galli, J., and R.D. Dubose. 1990. Thermal impacts associated with urbanization and stormwater management best

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Department of the Environment, Baltimore, MD.

Green, WH., and G.A Ampt. 1911. Studies on soil physics I. Flow of air and water through soils. Journal of

Agricultural Science, vol 4.

Hammer, D. 1992 Creating freshwater wetlands. Lewis Publishers, Chelsea, MI.

Haukos, D.A., and L.M. Smith. 1992. Waterfront management handbook: Ecology of playa lakes. Fish and

Wildlife Leaflet 13.3.7. U.S. Department of the Interior, Fish and Wildlife Service, Washington, DC.

Hawkins, R.H. 1993. Draft: Reconnaissance review of ‘Best Management Practices for Stormwater

Discharges to Natural Wetlands.” The University of Arizona, Tucson, AZ.

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Hershfield, D.M. 1961. Rainfall frequency atlas of the United States for durations from 40 minutes to 24 hours and

return periods from 1 to 100 years. Technical Paper 40. U.S. Weather Bureau, Washington, DC.

Hickock, E.A., MC. Hannaman, and M.C. Wenck. 1977. Urban runoff treatment methods: Vol. I. Non-structural

wetland treatment. EPA 600/2-77-217. U.S. Environmental Protection Agency, in cooperation with Minnehaha

Creek Watershed District.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Hutchinson, C.F., P. Warshall, E.J. Arnould, and J. Kindler. 1992. Development in arid lands. Environment

34(6):16-43.

Kadlec, R.H., and R.L. Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, FL.

Kusler, J.A., and M.E. Kentula, eds. 1990. Wetland creation and restoration: The status of the science. Island Press,

Washington, DC.

Maidment, P.R., ed. 1993. Handbook of hydrology. McGraw-Hill, Inc., New York, NY

Marble, A.D. 1992. A guide to wetland functional design. Lewis Publishers, Boca Raton, FL.

MDDNR. 1991. A guide for developing nontidal wetlands watershed management plans in Maryland. Maryland

Department of Natural Resources, Water Resources Administration, Annapolis, MD.

Mitsch, W.J., and J.C. Gosslink 1986. Wetlands. Van Nostrand Reinhold Co., New York, NY.

Mitsch, W.J., and J.G. Gosselink 1993. Wetlands. 2nd ed. Van Nostrand Reinhold, New York, NY.

National Research Council. 1994. Ground water recharge using waters of impaired quality. ISBN 0309-05142-E.

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North Carolina State University College of Agriculture & Life Sciences.

Novotny, V., and C. Chesters. 1981. Handbook of nonpoint pollution; sources and management. Van Nostrand

Reinhold Co., New York, NY

Iverson. 1982. Contaminant levels in precipitation and urban surface runoff. Water Resources Bulletin

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Hill, Inc., New York, NY.

PSWOA. 1990. Protecting fish and wildlife habitat in Pugct Sound. Puget Sound Water Quality Authority,

Seattle, WA.

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Richardson, C.J. 1989. Wetlands as transformers, filters and sinks for nutrients. In Freshwater wetlands:

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Shahane, A.N. 1982. Estimation of pre- and post-development nonpoint water quality loadings. Water

Resources Bulletin 18(2):231-237.

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Environmental Research Laboratory, Corvallis, Oregon. Cited in USEPA, 1992a.

Smith, H., and E.D. Matthews. 1975. Soil survey of Harford County area, Maryland. U.S. Department of

Agriculture, Soil Conservation Service, in cooperation with the Maryland Agricultural Experiment Station,

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Protection Agency, Office of Water, Washington, DC.

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Page 2-49
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Washington State Department of Ecology. 1992. Stormwater program guidance manual. Vol. II. Prepared by the

Washington State Department of Ecology, Olympia, WA.

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Page 2-50
Case Study-BMP Fact sheet Correlation

Case Studies

Section 3

Case Studies

o illustrate how BMPs have been incorporated with wetlands into urban stormwater

management systems, several case studies are presented. The purpose of the case studies

is to illustrate measures that can be taken to prevent adverse impacts to wetlands from

stormwater runoff. In most of the case studies, wetlands were incorporated into the

rmwater management system for the site. Generally, some type of treatment was provided to

reduce pollutants in the stormwater before its discharge to natural wetlands. Available water

quality data are presented, as well as information regarding habitat change. The case studies are

presented by EPA Region, and by wetland type and BMP applicability. The following list

correlates BMPs used in the case studies to applicable BMP fact sheets in

Section 4.

EPA Region 1

Narrow River Special Area Management Plan

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Preventive Construction Techniques (See BMP Fact Sheet p. 4-12)

Grassed Swales (See BMP Fact Sheetp. 4-32)

Extended Detention Dry-Basins (See BMP Fact Sheet p. 4-43)

EPA Region 2

Freshwater Wetlands Protection Act

Extended Detention Dry Basins (See BMP Fact Sheet p. 4-43)

Contour Terraces

Grassed Swales (See BMP Fact Sheet p. 4-32)

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)

Pollution Prevention (See BMP Fact Sheet p. 4-2)

Page 3-1
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

EPA Region 3

Watershed Management Study

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

Wet Ponds (See BMP Fact Sheet p. 4-47)

Road Culvert Retrofit

Riparian Areas (See BMP Fact Sheet p. 4-18)

EPA Region 4

Hidden River Wetland Stormwater Treatment Site

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

Construction Sedimentation Basins

Grassed Swales (See BMP Fact Sheet p. 4-32)

EPA Region 5

Lake McCarrons Wetland Treatment System

Construction Sedimentation Pond

Level Spreaders (See BMP Fact Sheet p. 4-61)

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

The Phalen Chain of Lakes Watershed Partnership

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)

Grassed Swales (See BMP Fact Sheet p. 4-32)

Open Spaces (See BMP Fact Sheet p. 4-41)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

The Prairie Wolf Slough Project

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)

Constructed Wetlands (See BMP Fact Sheet p. 450)

Open Spaces (See BMP Fact Sheet p. 4-41)

EPA Region 6

Tensas Cooperative River Basin Study

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)

Grassed Swales (See BMP Fact Sheet p. 4-32)

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Case Studies

Water and Sediment Control Basins

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

Pollution Prevention (See BMP Fact Sheet p. 4-2)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

EPA Region 7

Multi-Species Riparian Buffer Strips, Bear Creek Watershed

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Pollution Prevention (See BMP Fact Sheet p. 4-2)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

EPA Region 8

A Watershed Approach to Municipal Stormwater Management

Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Grassed Swales (See BMP Fact Sheet p. 4-32)

Infiltration Basins (See BMP Fact Sheet p. 4-20)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)

Pollution Prevention (See BMP Fact Sheet p. 4-2)

Lemna Nonpoint Source Treatment System

Wet Ponds (See BMP Fact Sheet p. 4-47)

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Constructed Wetlands (See BMP Fact Sheet p. 4-50)

EPA Region 9

Lincoln-Alvarado Project

Oil/Grit Separators (See BMP Fact Sheet p. 4-58)

Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)

EPA Region 10

Sawmill Creek

Riparian Areas (See BMP Fact Sheet p. 4-18)

Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Fencing of Riparian Pasture

Upland Water Troughs for Livestock

Planting of Willow Cuttings

Sublett Creek Restoration Project

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Grazing Allotment Management Plan (AMP)

Planting of Willow Cuttings

Drift Fences

Log Dams

Upland Water Troughs for Livestock

Bear Creek Restoration Project

Sedimentation Basins

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Fencing Riparian Pasture

Riprap

Upland Spring Sites for Livestock

Camp Creek Restoration

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Sedimentation Basins

Fencing Riparian Pasture

Planting of Willow Cuttings

Riprap

Low-rock Structures and Gabions

Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)

The Chewaucan River

Watershed Management Plans (See BMP Fact Sheet p. 4-8)

Riparian Areas (See BMP Fact Sheet p. 4-18)

Riprap

Snag Removal

Fencing Riparian Pasture

Planting of Willow Cuttings

Exclusion of Cattle Grazing

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Case Studies

Regional Case Studies

EPA Region 1

Narrow River Special Area Management Plan, Rhode Island

The Narrow (Pettaquamscutt) River watershed is located in southern Rhode Island in the

towns of North Kingstown, South Kingstown, and Narragansett. The watershed drains into

southwestern Narragansett Bay and encompasses several unique water bodies (Figure 3-l).

Figure 3-1. Location of the Narrow River watershed study area in the State of Rhode Island.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Known use of the river and its resources extends back to at least 3,000 years ago when

Native Americans hunted and gathered along the river. Other uses of the river have included ship

building, agriculture, dairy farming, summer housing, and permanent homes. The Narrow River

watershed is rich in recreational resources such as boating, camping, hiking, fishing, swimming,

and birdwatching, and the river valley is considered one of Rhode Island’s most scenic areas.

Wildlife inhabit Narrow River and its watershed for breeding, nesting, spawning grounds,

and migratory bird routes. Several threatened and endangered species, including species of marsh

grass, osprey, Least Tern, sea cucumber, moonfish, luminescent moss, and several fern species are

known to inhabit the area.

Coastal wetlands in Rhode Island have been altered and destroyed by development

activities, which impact wetlands by filling, removing vegetation, grading, dredging, excavating,

draining, damming, and diverting the hydrologic flows into the wetlands. Alteration of the

adjacent land areas has affected local drainage patterns, thereby altering the sedimentation

processes and salinities of waters that enter wetlands. Building practices, human encroachment,

and other development pressures have caused water quality degradation, impacted critical habitat

areas, reduced public access, and spoiled aesthetic values throughout the watershed.

In response to coastal wetlands loss, the Rhode Island Coastal Resources Management

Council (CRMC) has set goals to protect, preserve, and where possible restore coastal wetlands.

CRMC supports a policy of “no net loss” of coastal wetland acreage and functions and requires a

2:1 mitigation ratio of replacement or creation of coastal wetland to areas permanently altered or

lost. (Wetlands created for stormwater management, erosion control, or waste management are

exempt from mitigation requirements.)

Past management efforts to protect the Narrow River and its watershed were undertaken by

the Narrow River Preservation Association (NRPA), the Narrow River Watershed Advisory

Council, and the Narrow River Land Trust. NRPA, founded in 1970, initiated the first planning

study of the watershed, which resulted in a report describing the development trends and impacts

to the river, and made recommendations for development control. The Narrow River Watershed

Advisory Council, formed in 1981, was a group of representatives from North Kingstown, South

Kingstown, and Narragansett, whose objective was to promote the protection of the watershed’s

values. The Council appointed the Narrow River Watershed Advisory Committee, which

developed a watershed program, recommended policies, and collected and analyzed resource data.

The Narrow River Land Trust, created in 1983, is a nonprofit organization that obtains property

and property rights for protection of natural resources.

Special Area Management plans (SAMPs) have been developed at the local and national

levels as management strategies for environmental planning. SAMPs focus the legislative and

regulatory powers of the CRMC to the specific problems of the designated resource. The effort to

create a SAMP for the Narrow River watershed began in September 1985 as an adaptation of the

SAMP that existed for the salt pond region of southern Rhode Island. It resulted from the general

belief that activities in the Narrow River’s watershed needed stronger management.

One of the first steps in designing the plan was to create a comprehensive characterization

of the watershed. Available research conducted by consulting firms, students, scientists from the

University of Rhode Island, and state agencies and town records were reviewed to determine past

and present problems in the watershed and to develop management strategies and initiatives to

address those problems.

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Case Studies

At the beginning of the planning process, September 24,1985, CRMC imposed a building

moratorium on all development applications within an area 200 ft (60.96 m) inland of mean high

water, or the inland edge of a wetland, bluff, river bank, or other coastal feature. The moratorium

also applied to all CRMC permits required by facilities requiring a parking area (at least 1 acre in

size) and by subdivisions of six units or more. Applications submitted after the end of the

moratorium, December 31,1986, were subject to the guidelines and regulations set forth in the

SAM plan.

The focus of the SAM plan was to address several problems that had not been adequately

addressed in past management efforts: degradation in water quality, development pressures and

human encroachment into areas unsuitable for building, potential loss of wildlife species and

habitat, and loss of aesthetic values. The SAM plan for the Narrow River watershed regulates the

following:

l Land classification for watershed protection

l Watershed controls for stormwater management

l Watershed controls for septic system management

l Watershed controls for erosion and sedimentation

l Lands requiring special considerations (historic/archaeological value)

l Petroleum tanks and oil spills

l Community participation

l Future research efforts

Stormwater management is highlighted here because the SAM plan regulates stormwater as

a means to protect wetlands. The plan defines stormwater management as the quantitative

control of increased volume or rate of runoff and the qualitative control of runoff through a

system of vegetative and structural measures to prevent pollutants from being transported in

runoff.

Stormwater management is required for all new residential developments six units or more,

all facilities and activities requiring 20,000 ft2

 (1,800 m2) or more of impermeable surface area or

resulting in 20 percent or more of the project area being impervious, and all roadway construction

and upgrade projects. Stormwater management is also required for activities that will involve

alteration, maintenance, or improvement to an existing stormwater management structure that

will alter the quality, rate, volume, or location of surface water discharge.

CRMC requires the stormwater management plan to include information on existing

conditions as well as predicted conditions after the activity is implemented. A stormwater

management plan must include maps, charts, graphs, tables, photographs, descriptions, and other

supporting documentation.

The stormwater management plan must provide evidence that structures were planned and

designed and will be constructed to ensure that postdevelopment runoff, hydrodynamic

characteristics of the watershed and groundwater, and wetland functions and values are the same

as predevelopment conditions. Postdevelopment conditions must also prevent increased flooding,

damage, and saltwater intrusion; must protect natural fluctuating levels of salinity in estuarine

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

areas; and must minimize alterations to flora, fauna, and habitat that could result from improper

construction, design, and location of the structures.

Design, construction, and maintenance of stormwater systems may not allow the direct

discharge of runoff into Narrow River and its tributaries. CRMC also prohibits increasing the

volume or rate of runoff or further degrading the quality of existing discharges. Discharges must

be routed through vegetated swales or other structural or nonstructural systems that increase time

of concentration, decrease velocity, increase infiltration, allow suspended solids to settle, and

remove pollutants. These systems should use overland flow and reinfiltration as priority techniques for the treatment of runoff. Detention and retention ponds may not be located in areas

that might cause groundwater contamination.

Stormwater management is only one component of the SAM plan, and CRMC recognizes

that future management improvements and further research efforts are needed to protect the

natural resources of the Narrow River watershed. CRMC has recommended the following areas

for further research:

l Monitoring of the river’s water quality

l Development of a hydrodynamic model of the estuary

l Analysis of bottom sediment (distribution, composition, and transport dynamics)

l Studies of water quality in the northern regions of the watershed

l Determination of the current status of the quality and quantity of groundwater resources

l Initiation of water quality testing in the freshwater systems in the northern regions of

the watershed

l The state and towns collectively undertaking stormwater management techniques to

upgrade or create programs

Reference/Additional Information

Howard-Strobel, M.M., T.G. Simpson, and T.P. Dillingham. 1989. The Narrow River special area management

plan. Coastal Resources Management Council, Wakefield, RI.

Olsen, S., and G.L. Seavey 1993. The State of Rhode Island Coastal Resources Management Program as amended.

Coastal Resources Management Council, Wakefield, RI.

Freshwater Wetlands Protection Act, State of New Jersey

The protection of wetlands has long been a priority in the State of New Jersey, (NJDEP

1995). To protect these vital areas, the New Jersey legislature passed the Wet lands Act in 1970 and

the Freshwater Wetlands Protection Act in 1987. These acts and their corresponding regulations

require approval by the New Jersey Department of Environmental Protection (NJDEP) for a

number of proposed activities that could impact wetlands (both freshwater and saltwater). This

discussion focuses on New Jersey’s Freshwater Wetlands Protection Act and its subsequent rules

regarding stormwater facilities.

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Case Studies

Wetlands receive the same protection granted surface waters under the state’s water quality

standards (N.J.A.C. 13:9B-13 and N.J.A.C. 7:7A-35(a)4). In addition to restrictions protecting the

wetlands themselves, restrictions placed on areas surrounding the wetlands offer further

protection for freshwater wetlands. These areas are designated “transition areas” in the state’s

Freshwater Wetlands Protection Act Rules (N.J.A.C. 7:7A-6.1). The Freshwater Wetlands

Protection Act requires a transition area adjacent to wetlands of “exceptional” or “intermediate”

resource value. Freshwater wetlands of “ordinary” resource value, which constitute approximately

5 percent of New Jersey’s wetland area, do not require a transition area.

The standard width of the transition area adjacent to a freshwater wetland of intermediate

resource value is 50 ft (15.24 m) and for freshwater wetlands of exceptional value is 150 ft (45.72

m). Wetlands of exceptional resource value require an individual permit, and mitigation must be

provided. Further, applicants for activities proposed in wetlands of exceptional resource value

must demonstrate either that there is a compelling public need for the proposed activity which is

greater than the need to protect the wetland or that denial of the permit would impose

extraordinary hardship.

As defined in the Freshwater Wetlands Protection Act Rules, freshwater wetlands of

exceptional resource value are those which exhibit any of the following characteristics:

l Those which discharge into FW-1 waters or FW-2 trout production waters or their

tributaries (FW-1 and FW-2 are water-quality rankings for fresh surface waters in New

Jersey) or

l Those which are present habitats for threatened or endangered species, or those which are

documented habitats for threatened or endangered species, and which remain suitable for

breeding, resting, or feeding by these species during the normal period when these species

would use the habitat.

Freshwater wetlands of ordinary resource value are those which (1) do not exhibit the

characteristics above, (2) are isolated wetlands that are more than 50 percent surrounded by

development, and (3) are less than 5,000 ft2

 (450 m2) in size including but not limited to drainage

ditches, swales, and detention facilities. Freshwater wetlands of intermediate resource value are

those which are not defined as either exceptional or ordinary

The Freshwater Wetlands Protection Act Rules also have requirements related to

pretreatment practices for the protection of wetlands (N.J.A.C. 7:7A-9.2(a) 11, v, ix, and x.)

Under the state’s general permit requirements, pretreatment of stormwater is required for

stormwater flows entering natural wetlands regardless of resource value. All stormwater

discharged into a freshwater wetland from a stormwater outfall must first be filtered or otherwise

treated outside the freshwater wetland (NJDEPE, 1992). Detention basins, contour terraces, and

grassed swales are examples of predischarge techniques that may be required by the NJDEP The

general permit does not authorize placement of detention facilities in freshwater wetlands and

requires compensation for disturbance within the wetland transition area (see Figure 3-2). Other

stormwater facility design restrictions include the following:

l The total amount of riprap or any other material used for energy dissipation at the end of

the headwall placed in the freshwater wetland cannot exceed 10 cubic yards per outfall

structure.

l Excavated areas for the placement of conveyance pipes must be returned to the

preexisting elevation using the original topsoil to backfill from a depth of 18 in (45.72

cm) to the original grade and must be revegetated with indigenous wetland species.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Transition Area Compensation

Transition

Reduction

NJDEP, 1995.

The square footage In the compensation

area is equal to that of the reduction area.

Figure 3-2. Example of a transition area reduction and compensation.

l Pipes used for stormwater conveyance through the wetlands must be designed not to

exceed the preexisting elevation and properly sealed with anti-seep collars at a spacing

sufficient to prevent drainage of the surrounding wetlands.

l If a detention basin is being proposed as the method of pretreatment for water quality

routing calculations must show that the basin has been designed for the l-year storm

event according to the New Jersey Stormwater Management Regulations (N.J.A.C. 7:8).

l If a swale is being proposed to convey stormwater through the wetlands, profiles from

the outlet to the receiving water body, cross-sections, and design support information

must show that the proposed swale will not result in drainage of the wetlands. Swales in

wetlands are permitted only where onsite conditions prohibit the construction of a

buried pipe to convey stormwater to an outfall.

The NJDEP works with property owners on a case-by-case basis to determine the most

appropriate stormwater treatment method to protect wetlands from both physical disturbance

and potential impacts from stormwater discharges. Where new development is proposed adjacent

to freshwater wetlands and preliminary treatment of stormwater is required to meet state water

quality standards, NJDEP staff make the final decisions on the location and design of each BMP.

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Case Studies

References/Additional Information:

NJDEP. 1995. New Jersey Coastal Nonpoint Pollution Control Program: A plan prepared in satisfaction of section

62147 of the Coastal Zone Act Reauthorization Amendments of 1990. Draft. New Jersey Department of

Environmental Protection. April.

NJDEPE. 1992. Freshwater Wetlands Protection Act Rules N.J.A.C. 7:7A (amended March 16, 1994. New Jersey

Department of Environmental Protection and Energy

EPA Region 3

Watershed Management Study, Prince William County, Virginia

Three watersheds in Prince William County, Virginia, are the subject of a 5-year

interdisciplinary, intergovernmental (federal-state-local) watershed management study (see

Figure 3-3). The study includes the protection of wetlands through the use of a variety of BMPs

and the restoration of degraded riparian wetlands following the installation of upstream controls.

The purpose of the project is to develop an innovative stormwater management plan and several

demonstration projects that take a watershed approach to environmentally sensitive decision

making. The headwaters of the three watersheds being studied are located in the Piedmont

physiographic province, cross the fall line, and drain into the tidal portion of the Potomac River

Estuary within the Mid-Atlantic Coastal Plain. The area of study within the watersheds consists

entirely of the portions to the west of Interstate 95 in the Piedmont province.

The northernmost watershed, Neabsco Creek (13,047 acres or 5,284 hectares), experienced

substantial urban/suburban development before stormwater and nonpoint source controls

became a requirement. The large planned community of Dale City is located in the Neabsco Creek

watershed, as is the Potomac Mills shopping complex. The center watershed, Powells Creek

(11,762 acres or 4,764 hectares), is predominantly rural, forested land that is experiencing

development pressure. The southernmost watershed, Quantico Creek (24,636 acres or 9,978

hectares), the majority of which is currently owned by the National Park Service and the U.S.

Marine Corps, is largely undeveloped and is likely to remain so.

All of the watersheds were extensively logged beginning in colonial times, and logging

continued periodically through the 19th century In addition, the Quantico Creek watershed was

the site of both agricultural activities and active pyrite mining for sulfur into the 20th century

Nonetheless, the habitat quality of the streams and wetlands is high throughout the upper

watershed and therefore the Quantico Creek watershed has the potential to be used as a control

site during the study The intention is for the Quantico Creek watershed riparian and wetland

habitats to serve as benchmarks for habitat quality goals established for the Neabsco Creek and

Powells Creek watersheds. Stream rapid bioassessments have been conducted in all three of the

watersheds, allowing comparisons of current habitat conditions. Water quality and quantity

monitoring is also being conducted along all three streams.

Riparian floodplain forests located along the Piedmont streams are the dominant nontidal

wetland type that has been identified in the study area to date. National Wetlands Inventory

maps indicate temporarily flooded (PFOlA) and seasonally flooded (PFOlC) palustrine forested

wetland communities. Because much of the land was in agriculture relatively recently (farming

generally ceased between 25 and 60 years ago), the forests range from successional to mature

communities dominated by red maple (Acer rubrum), sycamore (Platanus occidentalis), and pin oak

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Page 3-12
Case Studies

(Quercus palustris). Common understory species include musclewood (Carpinus caroliniana),

spicebush (Lindera benzoin), Japanese honeysuckle (Lonicera japonica), and greenbriar (Similax

rotundifolia). Emergent wetland communities that have become established in impounded areas,

such as old farm ponds and some stormwater basins, include cattail (Typha latifolia), smooth alder

(Alnus serrulata), soft rush (Juncus effusus), and wool grass (Scirpus cyperinus).

A federal interagency team consisting of the U.S Army Corps of Engineers (Corps), the U.S.

Fish and Wildlife Service (USFWS), and the U.S. Environmental Protection Agency (EPA)

conducted preliminary wetland assessments in 1992 for portions of the Powells Creek and

Neabsco Creek watersheds. The team focused its assessment on forested wetlands and relied on a

combination of the Army Corps of Engineers’ Wetland Evaluation Technique (WET II) and best

professional judgment. Results of the assessment indicated that floodplain forests in both

watersheds have high effectiveness and good potential for floodplain storage, sediment retention,

and nutrient removal functions. Opportunity for these functions to be performed is greater in the

intensely developed Neabsco Creek watershed. Because of the extensive development, the

wetlands in the Neabsco Creek watershed are smaller and more fragmented than those in the

adjacent, relatively undeveloped Powells Creek watershed. The riparian areas and floodplain

wetlands along Powells Creek are larger and more contiguous, providing greater overall wildlife

habitat functions.

The assessment also indicated that deep stream entrenchment caused by increased

frequency, duration, and intensity of stormwater flows in the Neabsco Creek watershed appeared

to be affecting the hydrology of adjacent wetlands. Ironically, despite this degradation, the

Neabsco Creek wetlands were determined to have high educational and recreational value because

of their proximity to population centers. The U.S. Fish and Wildlife Service, in cooperation with

the Prince William County Public Works Department, is working on several stream/wetland

restoration projects along Neabsco Creek.

The structural stormwater management facilities being evaluated as part of the study

include onsite and regional BMPs. Nonstructural BMPs include riparian buffers and stream

restoration techniques. Several of these practices are currently protecting downstream wetlands

from the impacts of urban stormwater discharges.

A regional wet pond is located immediately upstream from a substantial riparian

wetland area along Neabsco Creek adjacent to a shopping center. The BMP pond, which

controls a drainage area of approximately 300 acres (122 hectares), is intended to protect

the downstream wetlands from erosive velocities and to improve water quality A

restoration plan has been prepared for approximately 1 mi (1.6 km) of stream channel, 6

acres (2.4 hectares) of associated riparian forest, and 20 acres (8.1 hectares) of emergent

wetland habitat, which are located immediately downstream of the regional BMP pond.

A "road culvert retrofit BMP” that essentially functions as an extended detention BMP

facility has been established on an unnamed tributary on Neabsco Creek. The upstream

drainage area is more than 200 acres (81 hectares) and is intensely developed with

residential and commercial land uses. The immediate area includes a shopping center

located adjacent to the stream upstream of the culvert. A riser was initially constructed

upstream of a wing wall (concrete apron) built in front of the existing road culvert (see

Figure 3-4). The design is being modified to incorporate a small permanent pool behind

the wing wall and the use of a hydraulic jump to provide the outlet for the 2-year storm

rather than the use of the riser. The design modifications were necessary because during

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Existing Road Culvert

BMP Riser

Low Flow Channel

Prince William County, 1994.

Figure 3-4. Isometric view of the Neabsco Creek tributary road culvert retrofit BMP.

the winter of 1994 the riser became clogged with debris and local officials perceived the

ponded area to be too large.

The road culvert retrofit BMP works by ponding the more frequent storms, which cause

sediment-laden water to overflow the stream banks in the backwater area and deposit its

solids load in the riparian floodplain. This BMP protects downstream riparian wetlands

from the erosive peak velocities and durations associated with frequently occurring

storm events. The specific water quality benefits of the BMP are being studied as part of

the comprehensive 5year watershed program. Automatic sampling and flow-gauging

equipment has been installed and is providing data on hydrology and pollutant transport.

The water quality monitoring information that will be collected and analyzed by the

Virginia Polytechnic Institute and State University (Virginia Tech) includes:

Flow

Nutrients: total phosphorus, soluble reactive phosphorus, soluble aluminum, total

Kjeldahl nitrogen, and oxidized nitrogen

Dissolved oxygen, pH, conductivity, alkalinity and hardness

Trace metals

Biochemical oxygen demand and chemical oxygen demand

Total suspended solids

Total organic carbon

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Case Studies

Prince William County intends to install additional road culvert retrofit BMPs in other

areas of the county during the program. Watersheds of about 80 acres (32 hectares) are being

targeted for these BMPs. The BMPs will allow the floodplain forests that are inundated to realize

the high potential effectiveness for sediment retention and nutrient removal functions identified

by the WET II/BPJ analysis described above. Another potential benefit of this innovative BMP is

to minimize the impact on wetlands. If provided in series throughout a watershed, these BMPs

have the potential to provide substantial water quality improvements and possible wetland

protection with a minimum of disruption to the natural ecosystem (i.e., displacement of natural

wetlands by large stormwater management ponds).

Riparian wetland areas have been identified and delineated in the Powells Creek watershed.

BMPs designed for the improvement of water quality and the protection of riparian wetlands

have been planned and installed to protect some of these wetland areas. These include numerous

onsite BMP ponds in residential and commercial developments throughout the watershed, a

regional pond currently in design, stream restoration plans, and two farm pond retrofit projects.

The multiple stakeholders, the interdisciplinary approach, and the long-term aspects of the

program are unique. The comprehensive approach being taken in the project contains elements

that cut across traditional federal and local roles. For example, program elements include flood

protection, stormwater management, erosion and sediment control, wetland preservation, water

quality and terrestrial as well as aquatic habitat quality. Prince William County is funding more

than 50 percent of the project. The U.S. Geological Survey (USGS) is involved in the stream

gauging and water quality monitoring components of the project. In addition to the USGS, the

Corps, the USFWS, and EPA are providing federal agency involvement and funding to varying

degrees. The Virginia Department of Environmental Quality and the Chesapeake Bay Local

Assistance Department (a state agency that implements Virginia’s Chesapeake Bay Preservation

Act) are providing funding and/or monitoring and other technical support. Two state universities,

George Mason and Virginia Tech, are providing technical support in the form of bioassessments

and water quality monitoring, respectively

Initial data collection for the project will continue through 1997. An environmental history

of the watersheds will be compiled using baseline water quality monitoring data, land use

information, and an evaluation of data collected on terrestrial and aquatic resources. Traditional

and innovative BMPs for stormwater and nonpoint source controls will be tested and evaluated.

The design of stormwater management facilities will attempt to replicate the hydrologic

characteristics of the watershed based on modeled predevelopment conditions. (These results

could ultimately be compared to field data collected in the Quantico Creek watershed, for the

“predeveloped case.“) Ultimately, the project is attempting to document the cumulative impacts

that result as urbanization degrades water resources and ways in which sound watershed

management might mitigate water quality problems and related habitat problems. The results of

this comprehensive approach to preserving the environmental integrity of a developing watershed

should be useful to all stakeholders. Prince William County will benefit by being able to use the

data to determine the best approach for managing its other watersheds.

References/Additional Information:

Everett, R., and T. McCandless. 1994. New watershed approach in Prince William County. In Watershed

Events, Summer 1994, pp. 9-12. EPA 840-N-94-002. U.S. Environmental Protection Agency, Office of Water,

Washington, DC.

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EPA Region 4

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Getlein, S., R.S. Karalus, A Spingam, and F. Pasquel. 1993. Balancing development, water quality, and

wetlands protection in a Mid-Atlantic watershed. In Proceedings of Watershed '93, A National Conference on

Watershed Management, March 21-24, 1993, Alexandria, VA, p. 823. EPA 840-R-94-002. U.S. Environmental

Protection Agency, Office of Water, Washington, DC.

Pasquel, RF., MR. Mohan, and S.P. Cetlein. 1993. Comprehensive stormwater management planning. In

Engineering Hydrology, Proceedings of the American Society of Civil Engineers Hydrology Symposium, July 25-30,

1993, San Francisco, CA, pp. 832-837.

Hidden River Wetland Stormwater Treatment Site, Tampa Florida

Hidden River Wetland is a natural wetland located in the Hidden River Corporate Park in

Tampa, Florida. The 3-acre (1.2 hectares) wetland receives runoff from a mostly impervious

drainage basin approximately 15 acres (6 hectares) in size that includes an office park complex,

parking lots, and a central roadway The wetland-to-upland ratio of the stormwater treatment site

is approximately 15 or 20 percent (i.e., about 80 percent of the treatment site is upland). Annual

precipitation in the region is about 52 in (132.08 cm) per year. Water leaving the wetland flows

into the Hillsborough River via an alluvial floodplain. Water quality of the Hillsborough River is

good near Hidden River; however, it becomes degraded downstream at Tampa because of factors

not related to this site.

Hidden River Wetland is a freshwater, herbaceous marsh, classified as a palustrine emergent

wetland. In southwest Florida there are many isolated wetlands of this type, known locally as

Florida flag marshes. These wetlands have highly reduced organic soils. Hidden River Wetland has

95 percent vegetation cover; the plant community is dominated by maidencane (Panicum

hemitomom), pickerelweed (Pontederia cordara), and waterlily (Nymphaea odorara). The wetland was

undisturbed prior to site development. Construction of a roadway filling a portion of the south

end of the marsh necessitated the construction of a small mitigation area to the east side of the

marsh. The north rim of the marsh is protected by a buffer of native vegetation.

Runoff enters the system through two inlets and undergoes preliminary treatment in two

sedimentation basins that were built in 1987 as part of the stormwater management system to

protect the wetland. The east sediment basin consists of approximately 0.2 acre (784.08 m2

) of

open water, while the west basin, which is usually dry, covers about 0.07 acre (274.43 m2

) and is

vegetated with cattails (Typha latifolia) and other plant species. The west basin has a very wide,

brief water level fluctuation. Rain events of over 0.5 in (1.27 cm) generally produce flows into

the wetland for less than a day; however, discharges from the wetland do not occur until July and

then are continuous until September. Wetland outflow is treated in a grassed swale before it

enters a lower detention pond. After passing through a forested alluvial floodplain, the outflow

enters the Hillsborough River.

After several years of use, Hidden River Wetland continues to have a beneficial effect on

water quality. Generally, inorganic nitrogen, phosphorus, and suspended solid concentrations are

lower in the wetland outflow than in the inflows. Water in the wetland maintains lower pH,

dissolved oxygen, and reduction/oxidation potential than the inflowing waters. Fluctuations in

water quality are much greater in the sedimentation basins than in the wetland. Water temperatures in the wetland are as much as 10 degrees Celsius lower than those in the sedimentation

basin.

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Case Studies

Although a plant survey was not conducted prior to sedimentation pond construction and

site development, a comparison of aerial imagery from 1984 and 1992 suggests that the discharge

of pretreated stormwater to the wetland has caused a reduction in open water area of the wetland

but has had little effect on which plant species are present. The typical seasonal variation of water

level in Florida flag marshes, including a dry winter period, has been maintained. The pH of the

wetland is slightly acidic rather than the circumneutral pH typical of Florida flag marshes, which

might be due to acidic groundwater influences. Conductivities are also lower than usual for flag

marshes. Where the edge of the wetland vegetative community was disturbed by landscaping

activities, cattails (Typha latifolia) and primrose willow (Ludwigia peruviana) have invaded.

Sedimentation of the preliminary treatment pond has not yet been a problem, possibly as a result

of the close attention paid to construction-related sediment control and site landscaping.

Continuing research on the Hidden River Wetland Treatment Site will include

investigations into the wetland’s hydrologic interactions with groundwater, analyses of soils and

sediments, and continued analyses of water quality at wetland inlets and the outlet.

References/Additional Information:

Rushton, B. 1991. Variation in field parameters in a native wetland used for stormwater treatment. In

Statewide Stormwater Management Workshop, October 2, 1994, ed. B. Rushton, J. Cunningham, and C.

Dye. Southwest Florida Water Management District, Brooksville, FL.

Rushton, B. 1992. Evaluation of a wetland used for stormwater treatment: Preliminary data. Southwest

Florida Water Management District, Brooksville, FL. Unpublished report.

Rushton, B. Southwest Florida Water Management District. Interview, November 1992.

Rushton, B., and C. Dye. 1991. Hidden River stormwater treatment. In Annual report for Stormwater

Research Program, fiscal year 1989-1990. Southwest Florida Water Management District, Brooksville, FL.

EPA Region 5

Lake McCarrons Wetland Treatment System, Roseville, Minnesota

The Lake McCarrons Wetland Treatment System was built in 1985 in Roseville, Minnesota,

a suburb of St. Paul. About 85 percent of the runoff in the Lake McCarrons watershed is routed to

the wetland for treatment prior to discharge to the lake. The portion of the Lake McCarrons

watershed draining to the wetland is approximately 636 acres (258 hectares) in size with

17 percent impervious surface. Normal annual precipitation in the area is about 26 in (66.04 cm).

Lake McCarrons is a eutrophic lake with a surface of 81 acres (33 hectares) and a mean depth of

25 ft (7.62 m). In summer the dominant phytoplankton are blue-green bacteria and the lake’s

deeper waters become anoxic.

The two goals of the project are the improvement of the quality of stormwater runoff

entering Lake McCarrons and the restoration of an existing degraded palustrine wetland. A

sedimentation pond upstream of the wetland serves both as a moderator of stormwater peak

flows to the wetland and as a primary pollutant removal system for water entering the wetland.

The baseflow in the pond/wetland system was recorded as between 0.05 and 0.20 ft3/s (0.0014

and 0.0057 m3

), derived from groundwater inflows including natural springs and some storm

sewer leakage. The sediment basin was intended to reduce pollutant and sediment loads to the

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

wetland, allowing the wetland to serve a “polishing” function and to restore some of the original

wetland functions.

Low berms (12 to 18 in (30.48 to 45.72 cm) high with 12-in culverts) were installed,

dividing the wetland into five consecutive chambered wetlands between the sedimentation pond

and Lake McCarrons (see Figures 3-5 and 3-6). An entrenched channel in the wetland, a result of

increased runoff volume and velocity due to urbanization of the watershed, was filled. These

modifications brought the wetland’s hydrology closer to a natural state and allowed stormwater

entering the wetland to spread out as sheet flow through wetland vegetation and over the peat/

mineral soils for greater removal of pollutants. The resulting wetland is described as a palustrine

emergent marsh similar to the original marsh with a smaller palustrine scrub/shrub border than

that present before construction.

Figure 3-5. Lake McCarrons Wetland Treament System.

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Case Studies

Figure 3-6. Cross section of Luke McCarrons wetland treatment system.

Lower pollutant removal efficiencies were recorded for the wetland than for the sediment

pond, probably because of removal of the most easily settled particulates in the pond and the high

sorption capacity of newly exposed peat soils in the pond. Table 3-1 shows the results of water

quality monitoring for the pond, wetland, and combined system. Although the pond-to-watershed

area ratio is only 0.5 percent, the pond performed well in the reduction of pollutants monitored.

The pond/wetland treatment system did result in substantial reductions in phosphorus loadings

to Lake McCarrons. However, no change in lake water quality has been detected, probably

because of the high internal phosphorus loadings that remain in the lake.

Among problems encountered are the loss of effective pond treatment when the pond is

ice-covered and washouts of wetlands directly below the culverts through berms. Over a 7-year

period (1985-1992) there was a loss of pond storage capacity due to sedimentation, with pond

depth decreasing from 6 to 2 ft (1.83 to 0.61 m). In retrospect, a design including a drain valve for

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

easier pond maintenance and graveled spillways over wetland berms would have been desirable.

Wildlife was described as abundant and the plant community was found to be very diverse in the

modified wetland after 3 years; after 7 years cattails (Typha sp.) had increased substantially,

Since the completion of the original study in 1988, a sedimentation pond has been added to

provide preliminary treatment of runoff entering the lowest wetland chamber. Some road runoff

that previously entered the wetland as sheet flow over a grassed area, however, has now been

routed directly to the wetland without preliminary treatment. A report presenting the results of a

renewed 2-year study on the Lake McCarrons Wetland Treatment System will be completed in

the spring of 1997.

References/Additional Information:

Oberts, G.L. Metropolitan Council of the Twin Cities Area. Interview, November 1992.

Oberts, G.L., and R.A. Osgood. 1988. Lake McCarrons Wetland Treatment System: Final report on the function of the

wetland treatment system and the impacts on Lake McCarrons. Publication no. 590-88-095. Metropolitan

Council of the Twin Cities Area, St. Paul, MN.

Oberts, G.L., and R.A. Osgood. 1991. Water-quality effectiveness of a detention/wetland treatment system

and its effect on an urban lake. Environmental Management 15(1):131-138.

Wotzka, P., and G. Oberts. 1988. The water quality performance of a detention basin-wetland treatment

system in an urban area. In Nonpoint pollution: 1988-Policy, economy, management, and appropriate

technology, pp. 237-247. American Water Resources Association, Edina, MN.

The Phalen Chain of Lakes Watershed Project, Ramsey and Washington

Counties, Minnesota

The Phalen Chain of Lakes watershed covers about 23 mi2 (36.8 km2) in Ramsey and

Washington Counties. It includes five major lakes, 950 acres (385 hectares) of wetlands, and

several connecting creeks called county ditches.

The watershed is the land area that drains to the five major lakes-Kohlman, Cervais, Keller,

Round, and Phalen. The watershed includes parts of seven communities (Figure 3-7)-Little

Canada, Maplewood, North St. Paul, and smaller portions of Oakdale, St. Paul, Vadnais Heights,

and White Bear Lake. The lakes follow the ancient bed of the preglacial St. Croix River. The area is

considered unique and is heavily used for its recreational resources by local residents and the East

Metro area. The Chain of Lakes watershed is also part of a major flyway for migratory waterfowl

and songbirds, and it provides significant habitat for other birds and wildlife in an urban setting.

From settlement in the 1850s until World War II, the watershed was dominated by

vegetable and dairy farming. Farmers drained wetlands, channelized creeks, and constructed early

roads. In the 1970s, construction of Interstate 35E and large commercial areas like Maplewood

Mall accelerated urban development in the watershed.

Urbanization has affected natural resources in the watershed in many ways. First,

settlement has nearly eliminated the native vegetation of the area, replacing it with buildings,

paved surfaces, and lawns. Habitat diversity and the varieties of birds and animals that inhabit the

area have been much reduced because of these changes. Non-native species like loosestrife have

also gained a foothold in the watershed and become problems.

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Phalen Chain of lakes Watershed

Figure 3-7. Phalen Chain of Lakes watershed.

Second, the natural drainage in the watershed has been altered. Soils, vegetation, and

wetlands present at settlement easily absorbed much of the water that fell on the land. Urban

development has increased soil compaction, paved surfaces, channelized creeks, and eliminated

over half the wetlands in the watershed. These changes cause more water to run off the land at a

faster rate, creating flooding and erosion problems.

Higher volumes of runoff carry pollutants and nutrients to lakes, wetlands, and creeks,

causing declines in water quality, and a reduction in the quality of fish and wildlife habitat. Algae

blooms on area lakes are evidence of these changes. It is apparent that without conscious efforts

to manage land and water resources differently, ongoing development in the watershed will

continue the following trends:

l Increasing volumes of stormwater runoff, with additional sediments and nutrients

transported to wetlands, creeks, and lakes.

l Loss of aquatic vegetation and reduced habitat for fish and other aquatic organisms.

l Increasing fragmentation of upland and wetland habitat and loss of plant and animal

diversity

l Loss of open space.

In early 1993, a partnership was formed to address concerns about declining natural

resources in the watershed. The partnership included local city governments, developers and

businesses, the University of Minnesota, and the Minnesota Department of Natural Resources.

The partnership received a grant to develop a comprehensive plan for the watershed. A Steering

Committee, including representatives of all interested groups in the watershed, completed the

plan in April 1994.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The comprehensive watershed plan includes seven major goals, BMPs, and many

recommended action steps to protect, restore, and manage natural resources in the watershed in

the short term and long term. Major goals of the seven-point Action Plan for the Watershed

include the following:

l Improve, restore, and protect surface water quality.

l Restore, enhance, and protect wetlands and creeks.

l Protect the groundwater resources of the watershed.

l Develop and support a connected system of “green corridors” to protect water resources,

enhance fish and wildlife habitat, and provide natural resources recreation and education

opportunities.

l Restore and expand forest cover and diverse native vegetation.

l Increase public awareness and involvement in natural resources management in yards,

public and private lands, and all of the watershed.

l Establish a local natural resources board to coordinate implementation of the watershed

plan.

During the summer of 1994, the Watershed Project partners, local residents, cities,

businesses, and others in the watershed improved natural resources through a variety of projects,

including the following:

l Developing an innovative BMP to control stormwater in Maplewood. It will let

stormwater infiltrate within a neighborhood and eliminate the need for new storm

sewers that would empty into Lake Phalen. This neighborhood will serve as a model for

stormwater management in other urban areas.

l Working with the City of St. Paul and District 2 community to obtain funding for the

Phalen Wetland Park restoration as part of the Phalen Village Small Area Plan.

l Implementing projects to restore aquatic shoreline vegetation, and working with parks

departments and landowners to manage vegetation and use BMPs around wetlands and

lakes to benefit fish, wildlife, and water quality

l Completing a watershed-wide wetlands plan, based on the functions and values of

wetlands in the watershed, that will help the watershed district and local governments

set priorities for purchase, protection, or management of wetlands.

l Completing field work to identify the remaining natural areas and prairie fragments,

and inventorying open-space areas to assist in development of the “green corridors”

network for the watershed.

l Completing restoration projects at the H.B. Fuller Company Willow Lake Nature

Preserve to restore aquatic vegetation and other natural communities.

l Developing a workshop for teachers in five local school districts on watershed issues and

identifying student projects to benefit natural resources.

l Working with neighborhood and citizen groups on creative plantings and projects to

benefit natural resources in parks and residential areas of the watershed.

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The Phalen Project Committee will continue to work with local governments, businesses,

citizens, and natural resources agencies to identify projects and opportunities to benefit land,

water, plants, animals, and local communities.

The Prairie Wolf Slough Project, Chicago, Illinois

The Prairie Wolf Slough is one of several projects aimed at addressing natural resource issues

along the 156-mile-long (249.6-km) Chicago River corridor. The 25-acre (10.1-hectare) project

involves the ecological restoration of a wetlands/prairie/savanna complex along the Middle Fork

of the North Branch of the Chicago River and the creation of an interpretive nature trail.

The key component of the restoration is the creation of a wetland vegetation complex that,

in the past, was drained by an agricultural drainage tile system. Sediments and other

contaminants used to enter the stream via a gully created by the outlet of the drainage system.

After the tiles were removed and the gully was filled, water naturally returned to the floodplain.

The restored wetlands help to eliminate sediments, nutrients, and residues from farm chemicals

used on the property, which is leased by a local farmer for row crops.

Water drains onto the site from a corporate complex and a shopping center, which

contribute pollutants typical of urban runoff, such as lawn chemicals, road salts, and oil and

grease. Ponds just downstream provide some physical removal of sediment, but most of the

organic toxics and dissolved nutrients are not removed. The project diverts water from the two

upstream sources into the wetland system, which provides secondary biological treatment of the

runoff. The water from the site will eventually percolate back into the river, but it will have been

purified by the restored wetland, absorbing waterborne sediments and nutrients that reach the

river. The native wetland vegetation will also function as a filter medium to assist in removal of

deleterious waterborne metals.

The restored wetlands will have a beneficial impact during flood events. By restoring a

cover of dense native vegetation to the 25-acre (10.1 hectare) parcel, many beneficial wetland

functions would be restored. These include an improvement in the retention of precipitation. A

dense matrix of native plants would filter and hold more water than would a traditional crop

field. Increased water retention time translates into an increased ability for soil water absorption

and, therefore, decreased surface erosion.

The restoration will benefit many surrounding jurisdictions. The communities will benefit

from the enhanced site aesthetics, improved wildlife habitat, and increased recreational

opportunities for walking and nature observation. The parcel of land is a logical link with a

proposed riverside trail system and is also a part of a larger greenway that follows the Middle Fork

of the North Branch of the Chicago River. This corridor provides vital habitat, foraging sites, and

nesting locations for neotropical migratory birds, in addition to providing habitat for migratory

waterfowl. Local grade and high schools and a nearby college will also use the site for

environmental education activities and the promotion of environmental awareness. The

beneficial qualities of the wetlands will also be used by the Friends of the Chicago River to help

focus public attention on the importance of water quality, fisheries, wildlife habitat, and open

spaces along the river. The volunteer and environmental education components will build

interest and a constituency for protecting the river and its upper reaches.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Tensas Cooperative River Basin Study, Louisiana

Background

The cumulative impacts of human activities have led to the reduction of bottomland

hardwood forests and wetlands, and their associated wildlife habitat, in the Tensas River

Basin in northeastern Louisiana. Historically, over 90 percent of the 718,000-acre

(290,790 hectares) basin was forested with bottomland hardwoods. Approximately 350,000

of these acres (141,750 hectares) were irregularly to permanently flooded forested wetlands.

Today, an estimated 85 percent of these forests have been cleared and converted to row crop

agriculture, and the basin now contains only 135,000 acres (54,675 hectares) of bottomland

hardwood forests. The accelerated conversion of forestland to cropland during the 1960s and

1970s has resulted in increased environmental and social problems in the basin. The natural

ecosystem can no longer sustain acceptable water quality levels, provide adequate flood

storage functions, or offer the habitat diversity needed for many wildlife species.

In November 1991, various agencies met with the Natural Resources Conservation Service

to devise a strategy for resolving water quality impairment and wetland habitat loss and decline.

The group determined that an overall plan was needed for the entire basin to avoid a “piecemeal”

approach to protecting the area’s natural resources. As the main sponsor of the study, the Natural

Resources Conservation Service realized that for the study to be effective, a broad selection of

participants should be included in the process. Participants in the study included the following:

U.S. Environmental Protection Agency; U.S. Fish and Wildlife Service; U.S. Army Corps of

Engineers; U.S. Geological Survey; U.S. Forest Service; Louisiana Department of Agriculture and

Forestry; Louisiana Nature Conservancy; Louisiana Cooperative Extension Service; Louisiana

Office of Soil and Water Conservation; East Carroll, Madison, Tensas-Concordia, and Northeast

Soil and Water Conservation Districts; Fifth Louisiana Levee District; National Fish and Wildlife

Foundation; and farmers of the Tensas Basin. The study began in October 1992.

The objectives of the study were to facilitate and coordinate the orderly conservation and

management of the basin’s land and water resources, particularly bottomland hardwood

wetlands. Specific objectives include:

l Describe the ecological, economic, cultural, and social resources of the Tensas River Basin.

l Provide a broad-scale analysis of ecological, economic, cultural, and social problems in the

basin.

Describe solutions to the basin’s problems that are environmentally, economically, and

socially sound and acceptable to local residents.

l Identify various federal, state, and local agencies and organizations that provide

technical and financial assistance for implementing solutions to water and related land

resource problems.

Physical Setting

The study area is located in northeastern Louisiana in portions of East Carroll, Madison,

Tensas, and Franklin Parishes and encompasses the watershed of the Tensas River from Lake

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Case Studies

Providence to its confluence with Bayou Macon. The Tensas River Basin is in a subtropical,

transitional climatic region that is affected alternately by cool, dry air flowing southward and

warm, moist air flowing northward. Winters are usually mild with an average temperature of 47

degrees Fahrenheit (0F), and the average summer temperature is 81 0F The average annual

precipitation is 55 in (139.7 cm), most of which occurs between December and May.

The Tensas River Basin is located in the Mississippi River alluvial valley, which was formed

during the early Pleistocene epoch. Following the glacial retreat of the epoch, the Mississippi

River became deeply incised within the basin area, creating a broad, entrenched valley that

gradually filled with alluvial deposits. Elevations average from about 100 ft (30 m) above sea level

along the northern boundary to less than 50 ft (15 m) along the southern boundary The major

landforms resulting from meanders in the course of the Mississippi River can be divided into five

categories: abandoned courses, abandoned channels, natural levees, point bars, and back swamps

(see Figure 3-8). Forested wetlands can be found in all of the major landforms except the natural

levees, which are elevated above the floodplain.

l Abandoned courses are lengthy segments of a river abandoned when the stream forms a

more hydrologically efficient course in the floodplain. They can vary from a few miles to

tens of miles in length, but they always contain more than one meander loop. The

abandoned courses gradually fill in with sediment and are often occupied by a smaller

stream or bayou.

l Abandoned channels are cut-off bends of meandering streams, commonly called oxbow

lakes. A sediment plug forms in the abandoned channel immediately below the point of

cutoff. If the parent stream remains in close proximity, the oxbow quickly becomes

partially or wholly filled with fine-grained sediments and is replaced by vegetated

wetlands in a few centuries. If the river channel rapidly meanders far away from the

oxbow, however, sediment filing is slow and open water conditions often prevail.

Point bars are crescent-shaped ridges consisting principally of sand and silt on the inside

of meander loops as the stream migrates toward the concave bank. As the process

continues, a succession of bars can be formed, the height of which can be as much as 10 ft

above the mean low water level. The shape tends to conform to the curvature of the

channel in which they were created. The low areas between point bars constitute what

are known as swales. They develop dense willow growth that traps fine sediments, and

in time they are filled with silts and clays. Many of the remaining regularly flooded

forested wetlands in the basin occur in swales.

Backswamps are low, flat, featureless areas bordering natural levees and point bars.

Backswamp deposits consist of fine-grained sediments laid down in broad, shallow

slackwater basins during stream flooding. Historically, backswamps would remain

flooded for months during high river stages and periods of heavy rainfall due to

inefficient channels and low gradients. Today, most of these areas have been converted to

row crop farms.

The regularly or permanently flooded bottomland hardwood forests are composed of

baldcypress (Taxodium distichum), drummond red maple (Acer rubrum drummondii), swamp

blackgum (Nyssa sylvatica), and buttonbush (Cephalunthus occidentalis). Seasonally and irregularly

flooded bottomland hardwood forests are composed of overcup oak (Quercus lyrata), bitter pecan

(Carya aquatica), green ash (Fraxinus pennsylvanica), willow oak (Quercus phellos), cedar elm

(Ulmus crassifolia), waterlocust (Gleditsia aquatica), boxelder (Acer negundo), and hackberry (Celtis

laevigata.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Figure 3-8. Geomorphologic features in Tensas Basin,

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Case Studies

The social and economic resources of the Tensas River Basin were also reviewed and

incorporated into the study. The economy of the region is based primarily on row crop agriculture

(see Figure 3-9). Timber harvesting has diminished since there have been no large reforestation

efforts. The area experiences chronic unemployment problems and lack of job diversity and,

consequently, has been undergoing an emigration of people in search of job opportunities. For

example, prices for farm inputs have increased 46 percent more than prices received for raw

agricultural products, and unemployment in the basin ranges from 10.7 to 24.1 percent. These

combinations result in fewer dollars being circulated in the local economy and thus reduced job

opportunities in the retail and service industries in the rural, farm-based economies.

Problem Identification and Treatment Options

A series of public meetings were held throughout the basin to identify problems and

potential solutions. Problems identified include long-term viability of row crop production,

bottomland hardwood wetland decline, impaired water quality, flooding, limited recreational

opportunities, reduced fish and wildlife habitat, and socioeconomic concerns. Regarding the

bottomland hardwood wetland decline, the major sources of problems are habitat fragmentation,

excessive sediment loading, and nutrient and pesticide loading. Throughout the analysis and

planning process, it became apparent that the problems were usually interrelated. Water quality

was also being impaired due to excessive sediment loading and nutrient and pesticide loading,

which was reducing the profit margin for the agricultural operations. Limited recreational

opportunities and reduced fish and wildlife habitat were tied to the forested wetland decline.

Flooding is also a major problem because there are fewer wetlands to provide floodwater storage

and control.

Based on the identified problems, two primary methods for addressing these issues were

evaluated: BMPs and bottomland hardwood restoration. Due to the agricultural nature of the

region, row crop BMPs were determined to be the most effective. Only BMPs deemed by the

study group to be cost-effective, efficient, and acceptable to the residents were included in the

final plan. Row crop BMPs are categorized as follows: (1) soil management, (2) water

management, and (3) nutrient and pesticide management.

Soil Management BMPs

Soil erosion was determined to be linked to many of the problems identified in the basin,

including the decline of bottomland hardwood wetlands. Soil particles often act as carriers of

nutrients and pesticides, which further add to water pollution problems. Soil erosion can be

reduced by maintaining a protective cover of plants or plant residue, reducing the number of

tillage operations, and improving soil structure. The following BMPs were determined by the

Tensas River Basin study to be the most effective measures in reducing soil erosion: (1) chiseling

and subsoiling, (2) conservation cropping sequences, (3) conservation tillage systems, (4) contour

farming, (5) cover crop, and (6) crop residue use.

Water Management BMPs

Water management practices are applied in the fields where the crops are grown and at the

field edges where water enters and exits a field. BMPs applied in the crop field to facilitate plant .

growth and to reduce sediment and water from leaving the fields include (1) land leveling,

(2) irrigation water management, and (3) crop row arrangement. BMPs applied to minimize

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Protecting Natural Wetlands: A Guide to Stormwater Best Managemant Practices

Figure 3-9. Main land uses in Tensas Basin.

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Case Studies

environmental impacts before or after water reaches a field are (1) filter strips, (2) grassed

waterways, (3) irrigation tailwater recovery, (4) water and sediment control basins, and

(5) water control structures.

Nutrient and Pesticide Management BMPs

Nutrient and pesticide runoff is closely tied to soil and water management. However, in

many instances excess nutrients and pesticides do not need to be applied. Prudent application of

nutrients and pesticides enables the producer to reduce expenses while having a positive impact

on the surrounding wetlands. Proper nutrient management requires periodic soil testing and use

of fertilization rates within a recommended range. Pesticide management requires the use of field

scouting, safe handling and mixing procedures, and nematode assay to determine if and when

pesticides should be applied.

Bottomland Hardwood Restoration

Approximately 350,000 acres (141,750 hectares) of hydric soils occur in the Tensas River

Basin. On some hydric soils, profitable row crop production might be limited over the long term

and therefore the most prudent land use for these soils would be hardwood production because it

would allow the floodplain to function naturally Bottomland hardwood restoration would

reduce the impacts of flooding and would improve water quality. It would improve fish and

wildlife habitat while providing a higher economic return. Although not always considered a

BMP to protect natural wetlands, the restoration of the forested wetlands would enhance the

existing wetlands by enlarging the resource as well as providing additional buffer zones.

Implementation

The Natural Resources Conservation Service will use the Tensas River Basin Study to

develop detailed watershed plans for implementation of BMP measures and to target potential

bottomland hardwood restoration sites. Solving the environmental and social problems of the

Tensas River Basin will require a concerted effort by private landowners, federal and state

agencies, local governments, and organizations. Implementation of land treatment options, to a

large extent, is dependent on the voluntary efforts of local landowners. However, by

demonstrating that protection and restoration of bottomland hardwood wetlands not only will

improve environmental quality but also will provide economic and social benefits for the

landowners, this transition should be more easily accomplished. Probably the most beneficial

aspect of the basin study was the consensus building. The diversity of the participants ensured

that a variety of viewpoints were considered, and the result is a plan that relates protection of

bottomland hardwood wetlands to the overall health of the watershed, including the

socioeconomic health.

References/Additional Information:

USDA/NRCS. 1995. Tensas Cooperative River Basin Study. U.S. Department of Agriculture, Natural

Resources Conservation Service, Alexandria, LA.

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EPA Region 7

Multi-Species Riparian Buffer Strips, Bear Creek Watershed, Iowa

Background

Most agricultural landscapes are a mosaic of croplands and residences superimposed on areas

that were previously natural prairie, wetland, and forest ecosystems. In the Corn Belt of the

midwestern United States, most of these natural ecosystems have been cleared for agricultural

purposes. In Iowa, for example, 99 percent of the prairie and wetlands have been converted to

other uses. Many of the remaining riparian wetland systems are heavily impacted by nonpoint

source (NPS) pollution. BMPs in the Midwest that include the protection of riparian wetlands as

an objective must also address enhancement and restoration of riparian wetlands. An example of

this type of BMP is a multi-species riparian buffer strip (MSRBS) system designed and placed

along Bear Creek in central Iowa by the Iowa State Agroforestry Research Team.

The Bear Creek Watershed is located in north-central Iowa within the Des Moines Lobe, the

depositional remnant of Wisconsinan glaciation in Iowa. Bear Creek is 2.16 mi (34.8 km) long,

with 17.27 mi (27.8 km) of major tributaries. The creek empties into the Skunk River. The

watershed drains 18,386.4 acres (7,446 hectares) of farmland, most of which has been subjected

to field tile drainage during the last 40 years. About 87 percent of the watershed is devoted to corn

and soybean agriculture.

Two different levels of research activity are taking place in the Bear Creek Watershed. The

Leopold Center for Sustainable Agriculture’s Agroecology Issue Team (AIT) is using the watershed

to study the condition of riparian zones at the watershed level. The AIT is developing a model to

identify critical riparian reaches along the creek that need protection and restoration. The longterm goal of the project is to help farmers who own land along Bear Creek and other streams to

develop riparian zone management systems that protect riparian wetlands and water quality by

removing sediment and agricultural chemicals.

The Iowa State Agroforestry Research Team (IstART) has been working on one farm in the

watershed to develop the MSRBS model system for use along the critical reaches of Bear Creek.

This model has been developed by an interdisciplinary team of researchers with specialists in

forage crops, soils, hydrogeology, forest hydrology, forest ecology, wetland ecology, economics,

biometrics, wildlife management, and extension. The model can be adapted to other waterways

in Iowa and the Midwest.

The MSRBS system is a filter strip 65.62 ft (20 m) wide consisting of three vegetative zones.

The first zone consists of four to five rows of fast-growing trees planted adjacent to the stream.

The second, or central, zone consists of two rows of shrubs. The third zone, planted on the outer

edge of the riparian buffer, consists of a strip of switchgrass 22.97 ft (7 m) wide. The MSRBS

design takes advantage of the different aboveground and belowground structures of each species

to provide maximum year-round interception of sediment and agricultural chemicals from surface

runoff and subsurface water movement. One of the innovative aspects of this design is the use of

fast-growing tree species that can be used as a short-rotation woody crop system. These systems

can produce biomass for energy in 5 to 8 years and timber products in 15 to 30 years. The frequent

harvests help to maintain active nutrient and pesticide sequestering by the woody plant

community. The selected species do not have to be replanted for three to four harvests because the

species reproduce vegetatively by stump or root sprouts. The large root systems allow very rapid

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Case Studies

regrowth, which provides continuity in water and nutrient uptake and physical stability of the

soil throughout the life of the stand.

The MSRBS systems also include native shrubs, which can provide biomass if harvested and

demonstrate coppice regeneration. The shrubs increase species diversity and wildlife habitat,

provide yet another rooting pattern that will hold soil, intercept shallow groundwater nutrients,

and provide organic matter for soil microbes. Finally, the addition of native prairie grasses such as

switchgrass will provide additional species diversity, a very high frictional surface for

intercepting surface runoff, and a deep and fibrous root system that will play an important role

in improving soil quality.

Study Design

The MSRBS system lies along a 3,281-ft (1,000-m) reach of Bear Creek on a private farm

(see Figure 3-10). At this location, the creek is a third-order stream with average discharge rates

varying between 10.59 and 49.44 ft3

/s (0.3 and 1.4m3/s). During the past 5 years, pesticides

applied on the farm have included chlomazone, atrazine, cyanazine, and the herbicide EPTC.

During the past 12 years, impregnated urea pellets have been applied at the rate of 122.83 lb/acre

(134 kg/hectare).

The reach of the creek under study was divided into three blocks: inside bend, outside bend,

and straight reaches. Five 295.29-ft (90-m) plots were located within each block. Treatments

consisting of three combinations of planted trees, shrubs, grass, and two controls were randomly

assigned to the plots within each block. The planted treatments consisted of five rows of trees

planted closest to and parallel to the creek with a 5.91-ft (1.8-m) spacing between rows.

Different species of trees were used in each of the three treatments. One treatment consisted of a

Figure 3-10. Multi-species Riparian Buffer Strip System.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

poplar hybrid (Populus X euramericana Eugenei) that has been extensively tested and is readily

available in Iowa. The second treatment contained green ash (Fraxinus pennsylvanica), and the

third treatment contained a mixture of four rows of silver maple (Acer succharinum) with a center

row of black walnut (Juglans nigra). Upslope from the trees, a row of red-oiser dogwood (Cornus

stolonifera) and a row of ninebark (Physocarpus opulifolius) were planted. The shrubs were planted

with 3.94-ft (1.2-m) spacing between rows. Finally, a strip of switchgrass 23.95 ft (7.3 m) wide

(Panicum virgatum) was planted upslope from the shrubs. Controls consisted of existing pasture

grasses. Most trees are being grown on a 6- to 8-year rotation depending on species, and black

walnut is being grown on a 45 to 55-year rotation.

The plants for this MSRBS were selected to serve multiple purposes. Those purposes

included rapid growth, dense rooting habits, coppice regeneration ability for the trees and shrubs,

stiff stems for the grass, cover and food for wildlife, and a potential for being used as biomass for

energy The desire was to develop an effective buffer in as short a time as possible to effectively

trap sediment and process chemicals and to demonstrate to landowners that a buffer strip with

woody plants could be grown rapidly

In the study area, an existing field drain tile was providing subsurface drainage for one of

the fields and was discharging untreated water into Bear Creek. An approximately 0.12-acre

(500-m2

) wetland was constructed to process field drainage tile water from a 12.11-acre

(4.9-hectare) cropped field. The wetland is 1.64 to 3.28 ft (0.5 to 1 m) deep and is surrounded by a

low berm. The bottom of the wetland was sealed with clay because of the presence of an

underlying substrate of alluvial sand. Organic soil was then placed as the top layer. The

agricultural drainage tile was excavated and rerouted to enter the wetland at the point farthest

from the creek, forcing the water to travel through the wetland before entering the creek. A gated

water level control structure at the wetland outlet provides complete control of the level

maintained within the wetland. Cattail (Typha glauca) rhizomes were collected from a nearby

wetland during the early spring when the shoots had just begun to elongate. The wetland was

planted in early June at a spacing of approximately 1.97 ft (0.6 m) on center. Willow cuttings

were planted on the stream side of the berm, and native grasses and forbs were planted on the

constructed berm for stabilization and to provide vegetation diversity.

Two soil bioengineering structures 262.48- to 328.1-ft (80-to l00-m)-long have been

developed as part of the MSRBS system. These structures used live staking and dead tree fascines

to stabilize severely eroding banks on the outside stream banks. In the spring of 1992 and 1993,

cuttings of dormant willow (Salix spp.) 3.28-ft (1-m)-long and 16.41- to 24.61-ft (5- to 7.5-cm) in

diameter were pounded into the creek bottom along the toe of the bank and into the stream bank.

A dead fascine system using bundles of harvested silver maple was wired together and staked into

the bank to provide protection for the cuttings. Most of the cuttings took root and grew. Record

floods occurred in the watershed in 1993, and the plantings withstood a record 500-year flood.

The resulting plant material reduces the speed of channel flow on the outside of the bend, causes

sediment to be deposited in the plant material, and stabilizes the bank against further collapse.

Results

Survival of the trees, shrubs, and switchgrass in the MSRBS has generally been very good.

Survival of the three fastest growing tree species was above 87 percent. Black walnut survival was

adversely influenced in the second year of growth because of intense grass competition. Ninebark

has grown very well, with heights of 6.56 ft (2 m) at the end of 1993. The red osier dogwood has

shown mixed growth and has been replaced in spots with nanking cherry (Prunus tomentosa). The

Page 3-32
switchgrass is well established and has produced twice as much biomass as that of the pasture

grasses

The MSRBS was evaluated for root biomass production, and preliminary data indicate very

high root production (Figure 3-11). This is important because plant roots increase soil stability by

mechanically reinforcing soil, and they increase the soil microbial activity that aids in the

processing of nutrients and agricultural chemicals. The mixture of trees, shrubs, and grasses

provides a dense matrix of roots throughout the soil column, providing greater stability than

single-species filter strips.

Water movement through the MSRBS reach of Bear Creek is sampled in the vadose zone (the

unsaturated zone of the soil above the water table including the rooting zone), the unconfined

shallow aquifer (located in the alluvium and glacial till), the bedrock aquifers, the drainage tiles,

and the stream channel. Various kinds of sampling equipment, including piezometers and

tensiometers, have been installed to access these different sources of water. Water samples were

analyzed for nitrate nitrogen and atrazine. The present protocol calls for monthly sample

collections between growing seasons and twice-monthly collections during the growing season.

Although early results do not accurately reflect the full remediation capability of the system

when it is mature, the preliminary results demonstrate that a developing MSRBS system can be

effective in reducing NPS pollutants. Results for nitrate nitrogen (NO3-N) and atrazine are

shown in Figures 3-12 and 3-13. As can be seen, the NO3-N concentrations in the MSRBS never

exceeded 2 ppm (2 mg/L) even though background levels of NO3

-N exceeded 12 ppm (12 mg/L) in

the field. The buffer strip also showed adequate removal rates for atrazine. Data from

minipiezometers located at a depth of 9.84 ft (3 m) below the MSRBS confirm that these

chemicals are not moving below the buffer strip.

Preliminary data from the first 4 months of operation of the field drainage tile wetland

indicate that microbial degradation of NO3

-N is taking place. Measurements are greater than 15

ppm (15 mg/L) at the inflow while measurements are less than 3 ppm (3 mg/L) at the outflow.

Under stormflow conditions when residence times are reduced, NO3

-N levels are not as

effectively reduced. Based on this initial research, constructed wetland systems can be used to

protect existing natural wetlands in agricultural settings. Wetland plant species that can tolerate

excessive nutrient loading can be used in the constructed wetland to protect the more susceptible

species that occur in natural wetlands.

Visual observations of sediment movement suggest that no significant sediment has moved

through the buffer strip since the switchgrass, shrubs, and trees have become established.

Recommendations

The Iowa State University Agroforestry Research Team has developed preliminary

recommendations for Multi-Species Riparian Buffer Strips for Iowa based on their research at

Bear Creek. General design recommendations include:

l The general layout should consist of three zones, starting at the stream bank edge; the

first zone should include a strip of trees (four to five rows) 29.53- to 32.81-ft (9- to 10-m)

wide, the second zone should include a strip of shrubs (one to two rows) 9.84- to 13.16-ft

(3-to 4-m)-wide, and the third zone should include a strip of native warm-season grasses

22.97 to 26.25 ft (7 to 8 m) wide.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

DATE (1993)

Schultz et al., 1995.

Figure 3-12. Mean nitrate-nitrogen concentrations in the buffer strip.

Schultz et al., 1995.

DATE (1993)

Figure 3-13. Mean atrazine concentrations in the buffer strip.

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Case Studies

l Fast-growing trees are needed to develop a functioning MSRBS in the shortest possible

time.

l Rows 1 through 3 in the tree zone should include fast-growing, riparian species such as

willow, cottonwood, silver maple, hybrid poplars, green ash, and box elder. Other

moderate-growth species include black ash, river birch, hackberry, shellbark hickory,

swamp white oak, pin oak, Ohio buckeye, and sycamore. The key to tree and shrub

species selection is to observe native species growing along existing natural riparian

zones and select the faster-growing species.

l Shrubs should be included in the design to increase biodiversity and wildlife habitat.

Possible species include ninebark, red osier and gray dogwood, chokecherry, Nanking

cherry, nannyberry, sandbar willow, Bebb willow, peachleaf willow, pin cherry, wild

plum, and blackhaw.

l Switchgrass is recommended because it produces a uniform cover and has dense, stiff

stems that provide a high frictional surface to intercept surface runoff. Other permanent

warm season grass, such as Indian grass, big bluestem, and little bluestem, can be included

as long as switchgrass is the dominant species.

l Native perennial forbs may also be part of the mix, especially if they are seeded in clumps.

If wildlife habitat is an important component of the buffer strip, widths of 98.43 to

295.29 ft (30 to 90 m) would provide a more suitable wildlife corridor or transition zone

between the upland agricultural land and wetland/aquatic ecosystem.

Recommendations for tile wetland construction include:

l A small wetland can be constructed at the end of the field tiles by constructing a basin

at the ratio of 1:100 (1 acre of wetland for l00-acre drainage). Thebottom of the wetland

should be sealed with clay if the soil texture is sandy.

l Clay tile and perforated plastic tile used to drain fields might become plugged by tree and

shrub roots in the buffers. Two possible solutions to this problem exist: (1) replace the

tile passing through the buffer strip with solid tile or (2) plant a strip of warm season

grass above the tile line at a width of 65.62 to 98.43 ft (20 to 30 m) depending on the

woody plants that are planted.

Costs for establishment of the MSRBS system have been estimated at $358 to $396 per acre,

and annual maintenance costs are estimated at $20 per acre. The establishment and maintenance

costs do not include any existing governmental cost-share or other subsidy. Currently, there are

several cost-share programs available that will cover up to 75 percent of the expenses. A good

contact for information on potential cost-share programs is the local office of the USDA Natural

Resources Conservation Service. Overall the MSRBS system seems to function quite well. In

addition to protecting riparian wetlands, the MSRBS system offers farmers a way to intercept

eroding soil, trap and transform NPS pollution, provide wildlife habitat, produce biomass for onfarm use, produce high-quality hardwood in the future, and enhance the aesthetics of the

agroecosystem. As a streamside BMP, the MSRBS system complements upland BMPs and provides

many valuable benefits.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

References/Additional Information:

Schultz, R.C. 1994. Design and establishment of a multi-species riparian buffer strip. Leopold Center for

Sustainable Agriculture, Ames, IA.

Schultz, R.C. 1994. Multiple benefits from constructed multi-species riparian buffer strips. Leopold Center for

Sustainable Agriculture, Ames, IA.

Schultz, R.C., J.P. Colletti, T.M. Isenhart, W.W. Simpkins, C.W. Mize, and M.L. Thompson. 1995. Design

and placement of a multi-species riparian buffer strip system. Agroforestry Systems Journal (29):201-226.

EPA Region 8

Watershed Approach to Municipal Stormwater Management, Fort Collins,

Colorado

Introduction

Fort Collins, a city of 92,000 people, is located in a quickly developing area of Colorado

known as the Front Range. The city, situated at 5,000 ft (1,524 m), has a semi-arid climate with

14 in (35.56 cm) of annual precipitation and an average of 300 days of sunshine. Due to the

pleasant climate, natural areas, and other factors, Fort Collins is experiencing significant growth.

This increase in development led the city to create a Stormwater Utility. Within the municipal

boundaries, three types of wetland communities can be found. The dominant community is

seasonally flooded riparian wetlands consisting of willow (Salix spp.), narrowleaf cottonwood

(Populus angustifolia), plains cottonwood (Populus sargentii), golden current (Ribes aurem), and

chokecherry (Prunus virginiana). The other two wetland communities are seasonally flooded

emergent marshes dominated by broad-leafed cattails (Typha latifolia) and bulrush (Scripus spp.);

and seasonally saturated wet meadows consisting of sedges (Carex spp.) and rushes Juncus spp.).

The Stormwater Utility’s original mission was to create a drainage system that protects

citizens from flooding. The Utility typically manages the stormwater system by drainage basin,

which is the land contributing stormwater runoff to a particular point, usually a stream. The size

of a basin, anticipated rainfall amounts, and the type of land use (i.e., industrial, residential, or

natural) are factors used to calculate the need for flood control improvements. With the

implementation of the National Pollutant Discharge Elimination System (NPDES) permit

program and other programs, water quality became a critical component of stormwater

management and required the Utility to take a new look at how drainage systems are designed

and managed.

Approach

It became apparent to the city that a drainage system designed to convey flood waters can

be planned to meet objectives other than the control of water quantity. For example, drainage

systems are typically along riparian wetland corridors, which provide a multitude of functions

and values such as wildlife habitat and recreation. Consequently, it became critical to look at the

protection and enhancement of these important wetland areas. The city revised the mission

statement for the Stormwater Utility to state the “purpose for the utility is to provide stormwater

facilities for the drainage and control of surface and floodwaters in order that . . . pollution may

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Case Studies

be reduced and the environment should be protected and enhanced.” Based on this new mandate,

the city developed primary and secondary objectives for the Stormwater Utility.

Primary stormwater objectives include:

l Protect Fort Collins from flood waters.

l Protect and enhance water quality in creeks, lakes, and wetlands.

l Protect and restore creeks, lakes, and wetlands as critical wildlife habitat areas.

l Protect water table aquifers from stormwater contamination.

Secondary stormwater objectives include:

l Enhance a sense of community by including citizen participation in protecting local

natural areas.

Create trails to support the use of alternative transportation.

l Promote recreational opportunities associated with trails and natural areas.

To accomplish these objectives, the Stormwater Utility decided to use a watershed

management approach as a holistic method to manage stormwater and drainage basins. A holistic

approach requires looking at all factors that influence stormwater management, including those

factors not typically associated with stormwater management. For example, the Utility realized

that alternative transportation has a direct correlation to stormwater quality A reduction in

automobile use improves air quality and reduces the amount of pollutants that can be

redistributed with precipitation. A reduction in automobile use also reduces the pollutants left on

pavement, which can enter the stormwater system through runoff. Carried to its fullest potential,

a greater reliance on alternative transportation can lead to a reduction in the amount of

impervious surface associated with roads and parking lots, thereby reducing the overall amount of

storm runoff contributed to the system.

Another example of looking at the system holistically is addressing the protection of

riparian wetland corridors along drainage systems. The riparian corridors provide important

benefits such as natural filters of storm runoff, wildlife habitat, and bank stabilization. In

addition, stormwater systems along riparian corridors can be considered as potential

greenway parks. In times when municipal budgets are limited, integrating park facilities and

stormwater systems can be an efficient way of using capital improvement resources.

A final example of how stormwater management and other issues are interrelated is

enhancing a sense of community by encouraging citizen participation in protecting local natural

areas. By raising the public’s awareness of the natural areas along the stormwater system,

educational efforts to encourage people not to pollute (for example, encouraging them not to pour

chemicals down storm drains) become more effective because people realize the ultimate effects

of their actions (for example, they understand where those storm drains discharge). Furthermore,

an awareness of why BMPs are used can decrease the likelihood that they will be vandalized.

To begin applying the watershed approach, the Utility divided the urban watershed into

three primary and interactive components: land, tributaries, and receiving waters. The urban

landscape comprises industrial, commercial, and residential land uses and open space. Tributaries

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Table 3-2. Concept Cost Comparison 04 lssues

Associated with Watershed Grades

Issue Grade A Grade B Grade C Grade D

Land Costs

Construction Cost

Opens Space Provided

Development Potential

(along drainages)

Maintenance Cost

Highest

Lowest

Highest

Lowest

Lowest

Intermediate

Intermediate

lntermediate

lntermediate

lntermediate

Intermediate

lntermediate

Intermediate

lntermediate

Intermediate

Lowest

Highest

Lowest

Highest

Highest

Next Steps

For the Stormwater Utility to fully implement a watershed approach, the following steps

will need to be taken:

l Develop an integrated approach between the various municipal departments

(Stormwater, Natural Resources, Parks and Recreation). Clarify implementation roles

between departments and eliminate cross purposes and redundancies. The city must

realize that the drainage system can play an important role in meeting a variety of city

goals, but the city must also understand and agree on a balance between competing

objectives. Some of these are:

- Aesthetics, groomed vs. natural appearance

- Efficient stormwater flows vs. water and habitat quality

- Regulation vs. private property rights

- Service levels vs. cost

Refine the watershed rating system and develop methods to objectively measure

and rank sections of the stormwater system.

l Adopt individual watershed master plans where the master planning of stormwater

facilities and natural resource areas, including wetlands, is cooperatively completed

through the use of geographic information system (GIS) technology.

l Modify storm drainage design criteria to include a variety of BMPs that protect water

quality and wetlands. Include components of the Natural Areas Mitigation Manual in the

City’s storm drainage design criteria.

l Formalize stormwater education efforts and integrate them with other existing

municipal and county environmental education programs.

The Stormwater Utility is just beginning to create the framework for an integrated

watershed approach to stormwater management. At the municipal level, a successful watershed

approach relies on communication and coordination between all departments to provide for a

cohesive program. It also requires close communication and input from the local citizens. By

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Case Studies

preventing pollution on the land, addressing the ecological effects of providing drainage services,

and preparing sound hydrologic analysis, objectives related to water quality, public safety, and

natural area protection can all be achieved.

References/Additional Information:

McBride, K. 1995. Stormwater quality: A watershed approach. City of Fort Collins, Colorado.

Lema Nonpoint Source Treatment System, Chatfield Reservoir, Colorado

Chatfield Reservoir, located 15 mi (24 km) southwest of Denver, Colorado, impounds water

from the South Platte River drainage, a 2,969 mi2 (7,719.4 km2) watershed. The reservoir is a

flood control structure built and operated by the U.S. Army Corps of Engineers, and it has become

an important recreational facility for the metropolitan region. The developed lower portion of

this watershed system is the Plum Creek subwatershed, which is a 438-mi2 (1,338.8-km2) drainage

area in Douglas County Plum Creek and Chat field Reservoir in the Plum Creek subwatershed are

identified in the Denver Regional Council of Governments (DRCOG) regional Clean Water Plan

as being affected by nonpoint source (NPS) pollution, primarily high phosphorus loading.

The magnitude of the problem is reflected by the total pounds of phosphorus that reach the

reservoir each year. The phosphorus loading of the reservoir is about 53,100 pounds (lb)

(24,086 kg) per year from developed land and about 50,513 lbs (22,912.67 kg) per year from

undeveloped land. The total maximum allowable load that will not exceed the in-reservoir

standard is 59,000 lb (26,762.4 kg). Under normal conditions, about 48,300 lb (21,908.88 kg) of

nonpoint-source-derived total phosphorus will need to be removed from the watershed.

In addition to degrading water quality, the high phosphorus loads are negatively impacting

the fringe wetlands associated with the reservoir and the riparian wetlands along Plum Creek. The

fringe wetlands are seasonally and permanently flooded lacustrine wetland communities with a

mixture of broad-leafed cattails (Typha latifolia), hard-stem bulrushes, (Scripus acutus), sedges

(Carex spp.), and rushes (Juncus spp,), The riparian wetlands are seasonally flooded palustrine

wetland communities with cottonwoods (Populus sargentii), sandbar willows (Salix exigua), and

chokecherries (Prunus virginiana). Excessive phosphorus loads are allowing pollution-tolerant and

invasive species to take over and decrease plant biodiversity. Eutrophication of the reservoir is

promoting algal blooms, which are shading out submergent wetland species.

The Chat field Basin Authority management program has identified many potentially usable

BMPs that could reduce phosphorus loading and offer ancillary benefits such as protection of

existing natural wetlands. The problem facing the Authority is predicting the effectiveness of

these BMPs. The Authority wants highly effective, low-cost, and easily maintained BMPs for the

watershed nonpoint source control program. The placement of small BMP structures at every site

of urban development that generates nonpoint source pollution appears to be a very costly

option. Therefore, a pilot project was selected to evaluate the effectiveness of a low-cost,

biologically based system.

Lemna System

A private corporation has developed a natural biological treatment process that uses aquatic

plants (duckweed) to assimilate nutrients and reduce pollutants in a pond environment.

Duckweed (Lemna sp.) is a small floating plant commonly found in many lakes, ponds, and slowPage 3-41
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

moving streams. It consists of one or more leaves (called fronds) but has no visible stem. Over 35

species of duckweed grow worldwide in a variety of climates. Duckweed is an extremely fastgrowing plant that reproduces primarily by vegetative processes. The biomass can double in less

than 18 hours under optimal conditions. In Colorado conditions, the biomass is anticipated to

double in about 72 hours. Seasonal changes in weather and sunlight affect pond temperature and

thus the growth of duckweed. Optimum growth is achieved at 68 0

F (20°C) to 86°F (30 0C).

Lemna is semi-tolerant of cold temperatures and will continue to grow slowly at temperatures

near 44 0

F (7 0C). Nitrogen, phosphorus, and trace metals are needed to support the growth of

duckweed, with optimum growth possible when there is a balance of available nutrients. Low

levels of either nitrogen or phosphorus result in starved plants.

The use of Lemna has proven effective as a wastewater treatment nutrient removal system,

with the added benefit of reducing metals, biological oxygen demand, and total suspended solids

along with its constituents. The resultant effluents have low phosphorus concentrations (below

1 ppm (mg/L)). The by-product of the Lemna process is plant tissue, which has been used as a food

supplement for feedlots and as a compost product. The Chatfield Basin Authority has

implemented a pilot system using Lemna to determine the system’s effectiveness in removing

nutrients from Plum Creek before it enters Chatfield Reservoir. The pilot system is under

evaluation for 1 year to assess water quality benefits; it will then be monitored longer to assess

the effectiveness under various hydrologic loading conditions naturally encountered in the Plum

Creek subwatershed.

The main pollutant removal pathways are a combination of plant mat uptake and

precipitation. Management of the duckweed system for phosphorus removal maximizes growth

of the plant mat. The primary method for maximizing growth is mat density management. Mat

density management uses harvesting of the biomass to optimize the uptake of phosphorus. A

young duckweed plant population tends to have higher phosphorus uptake rates and grows faster

than an older plant population. Additionally, the water column can contain sufficient

concentrations of ions, which promote precipitation of insoluble salts. Some of the phosphorus,

for example, will precipitate and settle as calcium phosphates. The duckweed also reduces algae

growth by not allowing light into the water. Algae can contribute to increased total suspended

solids within the water and subsequent effluent discharge.

The treatment system consists of three primary components:

l A patented floating-cell system that can be adapted to a wide variety of pond

configurations. This allows the system to be adapted to existing pond structures (e.g.,

gravel operation ponds). The floating cells are designed to contain and control locally

available Lemna plants.

l An on-shore control unit and automatic sensing probes provide nutrient circulation and

assess chemical balance within the pond structure.

l An aquatic harvester is used to inoculate, distribute, and harvest Lemna plants from the

pond surface. A single harvester can be used on many ponds to improve the cost

effectiveness of the system.

The advantages of the Lemna system over other more conventional biologically based

BMPs include:

l Marginal, poor-quality lands can be selected for a site.

l The system can be designed to accommodate the available site.

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Case Studies

l The system hardware is simple and durable, which reduces future maintenance costs.

l The by-product can be used as a high-protein food supplement for feedlots.

l The by-product can be composted and land-applied for beneficial reuse.

The disadvantages of the Lemna system over other more conventional biologically based

BMPs include:

l An energy source is required for the various pieces of hardware, including the pump and

aquatic harvester.

l Personnel are required to maintain and operate the system.

Pilot Scale Description

The Chatfield pilot system is located off-channel of Plum Creek with protective banks to

keep the system from being impacted by floods. The system is designed as a S-shaped pond or

lagoon. The final pond is about 45 ft (13.72 m) wide and 600 ft (182.88 m) long, with an average

depth of 5 ft (1.52 m) and maximum surface acreage of 6.2 acres (2.5 hectares) (Figure 3-15). A

small stilling basin was created near the outflow by placing a sandbag barrier across the pond with

a flow-through pipe and float release valve. Discharge into the system and outflow from the

system pass through similarly designed concrete boxes. These boxes have built-in flow weirs for

measuring flow.

Lemna System Site Plan

DRCOG, 1994.

Figure 3-15. Lemna nonpoint source treatment system.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The pond system is lined with a 20-mil PVC liner. A set of barriers was installed as shown in

Figure 3-15. This barrier system was anchored to the sides of the pond with a cable system and

was designed to keep the duckweed plants evenly distributed across the pond’s surface. A

diversion structure was installed in Plum Creek. The system inflow sump tank and the return

outflow line were installed immediately above and below the diversion structure, thereby

preventing any drying of the stream as a result of this diversion. A small pump with a timer lifts

the water from the sump tank to the pond. Return flow relies on gravity, and the water is

discharged directly into Plum Creek below the point of diversion.

The final cost for the pilot project was $210,510, which was $42,510 more than the original

estimate for the project. The Chatfield Basin Authority anticipates spending an additional $7,500

over the next year to complete its evaluation of the system as a BMP.

Operation and Results

Inoculation with native duckweed is the primary operation necessary for successful start-up

of the system. Sources of duckweed included backwaters of streams and small ponds near

Chatfield Reservoir. The Chatfield system start-up in April 1994 did not produce the desired plant

densities, and additional plant material was collected and added to the system in April and May

1994. It appears that a low-nutrient duckweed system is much harder to inoculate and will require

a longer start-up period. Consequently, additional duckweed plants were added to the system and

undesirable algae were harvested.

Low or unbalanced concentrations of nitrogen or phosphorus can limit growth of

duckweed. Typically, this is not a problem for duckweed systems that rely on wastewater but

seems to be a problem with NPS pollution systems. Plum Creek was experiencing unusually low

nitrogen loading rates during the start-up period, which was resulting in poor duckweed growth.

Nitrogen was applied by spraying fertilizer onto the duckweed mat to compensate for nitrogen

deficiency.

Hand harvesting was used on the pilot system, although large systems usually use a

mechanical harvester. An investigation was made of local markets and disposal options. The plant

tissue is not classified as a biosolid, and the Chatfield Basin Authority has identified no apparent

disposal problems. The biomass can be composted onsite by mixing it with a carbon supplement

such as sawdust or wood chips.

Flow rates through the pilot duckweed system were designed at 23 days. The low stream

flows in Plum Creek and low nutrient loads required changes to the flow rate through the system.

The flow rate was shifted to a l0-day retention time. Based on a l0- day retention time and a

typical growing season extending from April to November, the duckweed system can process

about 24 pond volumes per year. Monitoring data at the end of the first growing season suggest

that the flow rate could be reduced to 5 days. Flow rate evaluation studies will be done by the

Chatfield Basin Authority during the 1994-1995 monitoring program.

The preliminary data from the 1994 growing season monitoring program show that the

system is reducing total phosphorus on the average of 71 percent per pond volume with an average

influent concentration of 0.1 ppm (0.1 mg/L) and a discharge concentration of 0.02 ppm (0.02

mg/L). The range of total phosphorus removal varied from 50 to 98 percent as shown in Figure

3-16. The preliminary water quality data suggest that a duckweed system used as a BMP could

achieve consistent 50 percent removal of nonpoint source phosphorus as required in the Chatfield

Basin Control Regulation.

Page 3-44
Summer Growing Season

DRCOG. 1994.

Figure 3-16. Range of total phosphorus removed by the Lemna system.

Conclusion

Although results of this project are preliminary, it appears that a scaled-up Lemna system

could function as a regional water quality enhancement and wetland protection system by

processing stream flows directly from Plum Creek or the South Platte River. The next steps the

Chatfield Basin Authority will take with the Lemna project include detailed water and biological

quality monitoring, cost-effectiveness evaluation of the system, a study of harvest material

disposal options, other research applications, and implementation of a full-scale nonpoint source

management system. When completed, the study will be submitted to the Urban and

Construction Subcommittee of the Colorado Nonpoint Source Task Force for consideration as a

Colorado Best Management Practice.

References/Additional Information:

DRCOG. 1994. Lemna nonpoint source treatment system: Final report and operation and maintenance manual.

Denver Regional Council of Governments, Denver, CO.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

EPA Region 9

Lincoln-Alvarado Project, Union City, California

A piece of property in Union City, California, consisting of 69 acres (28 hectares) of upland

habitat and approximately 12 acres (4.8 hectares) of wetland habitat, was proposed for a

multiphase warehouse/distribution complex. A section 404 permit was required from the Corps of

Engineers, San Francisco District, because 12.5 acres (5 hectares) fell within section 404

jurisdiction. The landowners proposed that 9 acres (3.6 hectares) would be developed and the

remaining 3 acres (1.2 hectares) would be incorporated into a 5-acre (2-hectare) onsite mitigation

area consisting of one-third marsh, one-third seasonal wetland, and one-third upland. After

extensive review by the Corps and other federal agencies and negotiation with the applicant, the

project was approved with the following requirements that included pretreatment of runoff: (1)

rainwater flow from the roofs of major buildings would be directed to grease/sediment traps and

then to wetlands, (2) 12 acres (4.8 hectares) of jurisdictional wetland would be preserved, (3) a

1.18-acre (0.47-hectare) buffer would be established, and (4) funding for the permanent

maintenance would be provided by assessments on a ‘benefits district” of all properties in the

subdivision (Association of Bay Area Governments, 1991).

References/Additional Information:

Association of Bay Governments. 1991. San Francisco Estuary Project. Status and trends report on wetlands and

related habitats in the San Francisco Bay Estuary. Third draft. Prepared under cooperative agreement with U.S.

Environmental Protection Agency. Agreement No. 815406-01-0. Association of Bay Area Governments,

Oakland, CA.

EPA Region 10

Riparian Area Wetland Restoration Project, Sawmill Creek, Idaho

Sawmill Creek is located in the Bureau of Land Management’s (BLM) Big Butte Resource

Area, 37 mi (59.2 km) northwest of Howe, Idaho. Sawmill Creek resides within a 200,000-acre

(81,000-hectare) watershed that drains a high-elevation (6,400 ft (1,950 m)) desert valley

surrounded by mountains. Soils are derived from alluvial deposits consisting of limestone and

volcanic debris. The climate is semiarid, with hot summers and cold winters. Annual precipitation

averages 100 to 114 in (254 to 289.56 cm); 66 percent occurs as snow. Cattle grazing is the

primary land use activity along the creek, and fishing and camping activities are steadily

increasing.

Prior to 1986, the combined effects of flooding, wildfires, channelization, and fall grazing

had degraded the riparian area along Sawmill Creek, causing bank instability, lateral degradation

of the stream channel, and reduced fish habitat. In response, the BLM and the Idaho Department

of Fish and Carrie (IDFG) initiated the Sawmill Creek Project to restore the riparian zone and

improve channel morphology Specific project objectives included (1) improved growth, vigor,

and regeneration of the riparian zone; (2) increased bank stability; (3) increased fish populations;

and (4) improved channel morphology.

Pretreatment surveys conducted by the BLM and the IDFG enabled these agencies to

identify critical areas and develop a riparian restoration plan. Approximately 8 mi (12.8 km) of

Sawmill Creek were treated by implementing the following BMPs.

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Case Studies

l Installation of 8 mi (12.8 km) of fencing along the creek, creating an upstream and a

downstream riparian pasture. The upper 5 mi (8 km) of riparian pasture has been fencedoff and allotted for spring grazing only, while the lower 3 mi (4.8 km) has been excluded

from grazing for up to 15 years. The previous grazing plan allowed season-long grazing

throughout the riparian zone.

l Establishment of upland troughs for off-site livestock water. Planting of willow and

cottonwood cuttings in the lower half of the riparian pasture.

Photodocumentation was effectively used to monitor habitat improvement in the

treatment area. Project monitoring and evaluation included (1) established photo points, (2)

reconnaissance inventories every 3 years, (3) a willow survivability inventory, (4) infrared aerial

photographs of the site to be repeated every 10 years, and (5) water quality sampling. The BMP

implementation resulted in increased bank stability in both riparian pastures and expanded

natural riparian vegetation, especially onto gravel bars. However, survival of willow and

cottonwood plantings has been poor. Beavers have moved back into the area, and fish habitat

appears to have improved. Posttreatment response has been slower on the lower pasture

(compared to the upstream pasture) due to greater channel instability and pretreatment

degradation.

Funding for the restoration came from mitigation money from the Little Lost River

Diversion Project supplied by the BLM, USDA Soil Conservation Service, and Butte Soil and

Water Conservation District. Total project costs amounted to $90,000.

References/Additional Information:

Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-

033. U.S. Environmental Protection Agency Region 10, Seattle, WA.

Sublett Creek Restoration Project, Idaho

Sublett Creek is located within the Burley Ranger District on the Sublett Cattle

Allotment in Sawtooth National Forest, approximately 55 mi (88 km) southwest of Burley, Idaho.

The Sublett drainage encompasses approximately 917 acres (371 hectares) of high desert habitat

and is intercepted at its base by an irrigation reservoir. Local topography consists of moderately

dissected mountains; soils are derived from limestone. The local climate is frigid with 17 in (43.18

cm) of precipitation annually; 80 percent occurs as snow. Sublett Creek drains U.S. Forest Service

(USFS) land except for the lower half mile (0.8 km) above Sublett Reservoir, which is on private

land. Because Sublett Creek maintains a popular cold-water fishery, recreational use is heavy.

By 1979, impacts from cattle and camping along Sublett Creek had changed the natural

composition of streamside vegetation from desirable riparian species to Kentucky bluegrass,

thistle, and other undesirable weeds. The creek had widened, becoming more shallow. Willows

were absent along several sections of the creek. Stream bank stability had decreased, increasing

instream sediment loads and reducing gravel beds available for spawning trout. In addition, cattle

were dying (from bloating) after grazing on watercress growing along Sublett Creek. In response

to these disturbances, the USFS and the Idaho Department of Fish and Game (IDFG) surveyed the

stream to inventory fish habitat and developed measures to protect and restore the riparian zone;

the USFS conducted a riparian habitat survey Both surveys indicated that the drainage had been

severely damaged. To protect and enhance the creek, the USFS initiated the Sublett Creek

Restoration Project. Specific project objectives included (1) reducing cattle losses, (2) reducing

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

the impact on canyon bottoms and riparian areas from cattle grazing, (3) stabilizing the stream

channel, (4) reducing siltation, and (5) improving fish habitat.

A new grazing allotment management plan (AMP) was developed in 1983 in conjunction

with the grazing permittee. The old allotment plan consisted of a rest rotation system in which

cattle were allowed to remain in a unit season long. The new AMP consists of a modified fourunit rest rotation system with a 5-year rotation. Each of the units is rested 1 year out of 5 except

along the north fork of Sublett Creek, which is rested 2 years out of 5. Grazing on this section is

now permitted only in the spring. Other BMPs included, (1) establishment of stream bank

protection structures along unstable portions of the creek (willows were planted, but survival has

been poor), (2) construction of several drift fences, (3) installation of log dams to create

downstream pools, (4) installation of two cattle troughs on upland sites, and (5) improvement of

permittee herding and salting practices.

Posttreatment monitoring (since 1987) by the Sawtooth National Forest Riparian Team

includes (1) sampling to obtain cross section measurements, (2) green line measurement, and

(3) measurement of woody-species regeneration within the watershed. Photo points were

established prior to treatment and have been monitored since.

Since implementation of the new AMP, water quality and habitat in Sublett Creek have

improved and the area also looks better. Posttreatment improvements include (1) improved

quality and quantity of spawning gravel, (2) increased stream bank stability (3) increased

productivity of riparian meadows and forage, (4) improved flow duration, (5) narrower and

deeper stream channels, and (6) decreased cattle losses. Monitoring from 1987 to 1990 indicates

that improvements are not continuous throughout all portions of the creek (Chard, 1991).

Drought conditions over the past 5 years might have contributed to the slow recovery on portions

of Sublett Creek during the last few years.

Funding for the project was provided by the USFS and the Sublett Cattle Allotment Grazing

Association. Project costs were split equally between these organizations; total costs amounted to

approximately $70,000, $10,000 of which was invested in the riparian zone.

References/Additional Information:

Chard, Jim. U.S. Forest Service, Burley, ID. Personal communication. July 1991.

Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-

033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.

Bear Creek Restoration Project, Crook County, Oregon

The Bear Creek watershed is located southeast of Prineville, Oregon, in Crook County The

watershed drains to the west from its origin in the Maury Mountains in the Ochoco National

Forest. The Bear Creek watershed drains approximately 55,500 acres (22,478 hectares) of

rangeland habitat; elevations range from 3,400 to 5,532 ft (1,036 to 1,686 m). Local topography

consists of rolling hills and valleys intersected by steep basaltic ridges and incised drainages. Soils

are derived from Columbia River basalt and volcanic ash. The climate is semiarid with 12 in

(30.48 cm) of precipitation annually; 40 to 60 percent occurs as snow. Approximately 75 percent

of the watershed occupies public lands managed by the BLM, and the remaining 25 percent is

owned by cattle ranchers. The primary land use activity is cattle grazing.

Page 3-48
Case Studies

Since the 1860s intensive cattle grazing in the Bear Creek watershed had degraded riparian

areas along Bear Creek, reducing woody riparian species, lowering the water table, destabilizing

stream banks, and increasing instream sedimentation. Fire suppression on upland sites, coupled

with lowered water table levels permitted juniper to invade the watershed and replace native

herbaceous species, resulting in large areas of bare, erosive ground and reducing available forage.

Subsequent to these changes, heavy flooding and overland storm flow within the watershed

accelerated erosion and resulted in heavy sediment deposition in Prineville Reservoir and the

Crooked River. To control and reduce these impacts, the BLM initiated the Bear Creek

Restoration Project. Project objectives included (1) reducing juniper populations and replacing

them with herbaceous species, (2) increasing infiltration of precipitation into the soil, (3)

stabilizing stream banks, and (4) increasing native riparian vegetation and raising the streambottom.

The Bear Creek Project involved 55,490 acres (22,473 hectares), of which 41,260 acres

(16,710 hectares) were administered by the BLM and funded from 1972 to 1978. Juniper trees

were cut on upland sites (approximately 14,000 acres (5,670 hectares)). Then prescribed burns

were used to inhibit further juniper invasion and to aid establishment of herbaceous species.

Thirty mi (48 km) of pasture and enclosure fencing was installed on both upland and riparian

sites, enclosing approximately 2.25 mi (3.6 km) of riparian area. In addition, 16 mi (25.6 km) of

juniper riprap was placed along banks on Bear Creek and several of its tributaries, sediment

catchment dams were installed in the creek to raise the creek bottom, springs were developed on

upland sites for livestock watering, and a new allotment management plan (AMP) was developed

to reduce the impacts of grazing on riparian areas. The old plan allowed season-long grazing on a

rest rotation basis. Under the new plan, allotments were divided into a greater number of

pastures and a deferred grazing system (20-day rotation period) was used. Crazing permittees and

local landowners constructed the pasture fencing and also installed some riprap.

Monitoring activities included (1) photo points on riparian and upland sites, (2) soil surface

factor transects to rate erosive potential, (3) macroinvertebrate analysis, (4) cross section stream

channel measurement, (5) riparian habitat inventories, (6) stream channel evaluation, and

(7) water quality sampling.

Project successes resulted from the watershed approach adopted by the BLM to reduce

sedimentation and restore the health of the entire drainage. Upland juniper populations have

been effectively reduced, and herbaceous species are more prevalent. As a result, less bare ground

now exists, erosion rates have declined, and water absorption has improved, as evidenced by the

appearance of new springs. Seventeen mi (27.2 km) of stream now support vigorous riparian

growth, bank erosion has declined, and sediment deposition behind the catchments has

controlled stream incision by elevating the stream bottom. The new AMP has provided sufficient

protection of the riparian areas to allow their regrowth. In addition, forage productivity has

increased from 70 to 340 animal unit months (AUMs). An AUM is defined as the amount of

forage required to maintain a mature l,000-lb (453.6-kg) cow or the equivalent for a l-month

period (USEPA, 1993).

The BLM funded the project with $650,000. Additional costs were borne by private

landowners and livestock grazers in the watershed.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

References/Additional Information:

Connin, S. 1991. Characreristics of successful riparian restoration project in the Pacific Northwest. EPA 910/9-91-

033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.

USEPA. 1993. Guidance specifying management measures for sources of nonpoint pollution in coastal waters.. EPA

840-D-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

Camp Creek Restoration, Crook County, Oregon

Camp Creek is located 40 mi (64 km) southeast of Prineville in Crook County, Oregon. It

originates in the Maury Mountains of the Ochoco National Forest and drains to the east. The

Camp Creek watershed drains approximately 110,710 acres (44,838 hectares) of rangeland

consisting of sagebrush, juniper, and bunchgrass. This also includes coniferous forest habitat with

elevations ranging between 3,665 and 6,12 1 ft (111 and 1865 m) . The drainage basin consists of

fluvial valleys surrounded by more resistant basalt buttes and hills. Soils consist of highly erodible

bentonitic and montmorillanitic clays. The climate is semiarid with 12 to 14 in (30.48 to 35.56

cm) of precipitation annually; 20 percent occurs as snow. Approximately 59,000 acres

(23,895 hectares) of the watershed are public land, and the remainder is held by private

landowners. Land use within the basin includes livestock and hay production.

Overgrazing, mismanagement of livestock, fire control, and intensive road/logging

development since the late 1800s have accelerated stream bank and upland erosion, channel

incision, dendritic gully spread, and riparian degradation, resulting in a drop in the local water

table. As a result, sagebrush and juniper have since invaded the area, replacing native grasses and

reducing available forage. In response to these disturbances, the BLM initiated the Camp Creek

Restoration Project in 1965. Project objectives included (1) stabilizing the steam channel and the

raising the water table on 31.6 river miles (50.844 km) and 383 acres (155 hectares) of riparian

habitat, (2) improving stream water quality and reducing sediment discharge, (3) restoring the

Camp Creek channel to 60 percent of its potential condition, and (4) increasing the forage

resource base for wildlife and livestock.

In 1964, the BLM developed an initial Camp Creek watershed plan. Plan implementation

included the following: (1) several detention dams were constructed, (2) 2.7 mi (4.34 km) of

Camp Creek were fenced off, (3) 1,000 Russian olive seedlings and willow cuttings were planted

along the upper portion of the creek, (4) severely disturbed areas were reseeded with tall

wheatgrass and sweetclover, (5) stream banks were riprapped with juniper trees, (6) juniper and

sagebrush were removed from several upland sites by cutting, chaining, and burning, and (7) lowrock structures and gabions were installed in the creek to trap sediment and raise the water table.

In 1978 an intensive water quality and macroinvertebrate sampling survey was initiated.

Following continued watershed surveys, a revised watershed plan was drafted in 1985, which

initiated a new rest-rotation grazing plan. (Prior to this, grazing was year-round on open range.)

Private landowners have also removed juniper and placed riprap along the creek on their property.

Monitoring of the Camp Creek restoration project included (1) establishment of permanent

photo points on riparian and upland sites; (2) stream channel studies initiated in 1978 which

included water quality and macroinvertebrate surveys; (3) permanent range condition transects;

(4) upland erosion study plots; and (5) an intensive riparian zone hydrology study, which was

initiated in 1985.

Page 3-50
Case Studies

Success of the riparian restoration varied. Two to eight ft (0.51 to 2.44 m) of sediment was

deposited behind instream structures. One livestock crossing effectively acted as a check dam.

Beaver activity increased sediment deposition. Collectively these treatments have elevated the

stream bottom and raised the water table within the floodplain. Juniper removal and prescribed

burning enabled grasses to reestablish on upland sites, increasing available forage and augmenting

infiltration of precipitation into the soil. Juniper riprapping stabilized stream banks and

increased sediment deposition, allowing reestablishment of riparian plant species. Gabions were

damaged by heavy flooding, however, a year after installation, and Russian olive and willow

plantings were drowned out by the rising water table. Fenced enclosures have been only partially

successful in limiting access of livestock to the creek. Several grazing permittees have failed to

prevent their cattle from damaging fencing and grazing within the enclosures.

Juniper removal and reintroduction of fire into the ecosystem have been essential to the

natural reestablishment of herbaceous plant species. Posttreatment structural maintenance has

been necessary to achieve project objectives. A shift from year-round grazing to spring and late

fall grazing adjacent to the riparian zone will protect fencing from damage incurred as cattle seek

shade and water during the summer months. Greater supervision of the site by the BLM and

grazing permittees will be necessary to keep cattle out of the riparian enclosures. Periodic surveys

and monitoring have revealed unexpected changes in the riparian habitat, allowing the BLM to

adopt new BMPs in response to these changes.

Financial support was appropriated from congressional funds, the Oregon Department of

Fish and Wildlife, Oregon State University, range improvement funds returned from grazing

permits, and local landowners.

References/Additional Information:

Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-

033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.

The Chewaucan River Project, Lake County, Oregon

The Chewaucan River is located in Lake County, Oregon, approximately 10 mi (16 km)

southwest of Paisley, Oregon. The Chewaucan River Watershed drains approximately 30 m2

(78 km2) of grassland/forest habitat with an average elevation of 6,000 ft. The upper portion of

the watershed is a grassland meadow where Dairy Creek and Elder Creek join to form Chewaucan

River. Downstream, the river drains several steep-sided canyons separated by open meadows. Soils

consist of alluvial material derived from adjacent highlands. The climate is semiarid with 20 in

(50.8 cm) of precipitation annually; 50 percent occurs as snow. The river basin is used for cattle

grazing, and several instream irrigation structures are present in the upper meadow (Schrader,

1991).

Overgrazing throughout the drainage basin degraded riparian habitat and reduced stream

bank stability The confluence of Dairy Creek and Elder Creek was very unstable and highly

eroded. Spring flooding accelerated bank erosion throughout much of the upper basin. In 1964, a

flood event deposited flow out of the main stream channel, causing bank blowouts. A new

landowner recognized these problems and enlisted the help of the Soil Conservation Service

(now the Natural Resources Conservation Service) to obtain funding and expertise to rehabilitate

the area. The two groups initiated the Chewaucan River Project. Project goals included

(1) stabilizing stream banks, (2) enhancing riparian vegetation, (3) improving fish habitat, and

(4) eliminating erosion caused by dead snags lodged in the lower portion of the river.

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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

In 1988, approximately 2 mi (3.2 km) of riparian area in the upper meadow, including

portions of Dairy Creek and Elder Creek, and 1 mi (1.6 km) in a downstream canyon were treated.

Best management practices (BMPs) that were implemented included (1) riprapping stream banks

with juniper; (2) riprapping the confluence of Dairy Creek and Elder Creek with stone material;

(3) placing boulders in the river to enhance fish habitat; (4) removing snags from the lower

portion of the river; (5) treating one highly disturbed stream corner with, a geotextile mat, which

was then seeded and watered; (6) fencing 0.25 mi (0.4 km) of riparian pasture in the upper

meadow; (7) planting willows throughout the basin, and 8) excluding the lower pasture from

cattle grazing for 3 years.

Project monitoring was designed to include the establishment of five photo points along the

river to be monitored annually for a period of 10 years. Willow growth is also to be monitored for

10 years.

Project results included increased sediment deposition in back eddies caused by juniper

riprap, with riparian vegetation continuing to colonize the newly deposited sediment. Stream

bank stability increased throughout the treated portions of the river. Stream banks that had

sloughed onto riprapped sections were more sloped than previously. The geotextile mat worked

very well to stabilize the adjacent stream bank; however, it probably will not be used again

because of its expense. Removal of snags in the downstream reach oriented the river back into the

main thalweg, reducing bank erosion. Willow plantings were not as successful as other

treatments. Survivorship in the upper meadow was approximately 10 percent due to beaver

cutting and 40 percent in the lower meadow (Schrader, 1991). No immediate benefits to the

fishery from habitat enhancement have been recorded (Schrader, 1991).

The Chewaucan River Project cost in excess of $50,000, which was provided primarily by

the Governor’s Watershed Enhancement Board with additional help from the Oregon Department

of Fish and Wildlife, Soil Conservation Service, U.S. Forest Service, and owners of the J-Spear

Ranch.

References/Additional Information:

Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-

033. US. Environmental Protection Agency, Region 10. Seattle, WA.

Schrader, Bill. Soil Conservation Service, Lakeview, OR. Personal communication. July 1991.

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Best Management Practices

Section 4

Best Management Practices

his section describes some of the best management practices (BMPs) that might be useful

in protecting natural wetlands from the effects of stormwater runoff or useful as part of a

stormwater runoff treatment system that includes a natural wetland. The BMPs are

grouped as follows:

l Nonstructural BMPs

- Pollution Prevention

-Watershed Management Plans

- Preventive Construction Techniques

- Outreach and Educational Programs

- Riparian Areas

l Structural BMPs

- Infiltration Basins

- Infiltration Trenches

- Sand Filters

- Grassed Swales

-Vegetative Filter Strips

-Vegetated Natural Buffers

- Open Spaces

- Extended Detention Dry Basins

-Wet Ponds

- Constructed Wetlands

- Porous Pavement and Concrete Grid Pavement

- Oil/Grit Separators or Water Quality Inlets

- Level Spreaders

- French Drains

- Dry Wells or Roof Downspout Systems

- Exfiltration Trenches

l BMPs in Series

Each BMP is described in a fact sheet that includes specific information about the BMP The

fact sheet for each nonstructural BMP includes a description of the practice and sources of

additional information. The fact sheets for the structural BMPs, unconventional BMPs, and BMPs

in series are more detailed and include a definition and purpose, the scope and applicability of the

BMP, considerations for design criteria, potential impacts to wetlands, maintenance requirements, and sources of additional information, as applicable.

Page 4-l
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The fact sheets are intended to provide information about different BMPs for evaluation

purposes. With information such as where a BMP is most applicable or what the potential impacts

on wetlands might be, a planner or watershed manager can develop a stormwater management

program that is as effective in protecting a wetland and all of its functions as it is effective in

treating stormwater runoff.

It is important to note that the fact sheets are intended to be used as a planning tool and are

not meant to be used in the design of any of the BMPs. Other sources of information, such as

those listed at the end of each fact sheet, should be consulted for design, construction, and

operation and maintenance of the BMPs. It should also be noted that the BMPs included in this

document were selected because they have the potential, in a variety of situations, for reducing

impacts from stormwater runoff to wetlands. There are other BMPs that are not addressed here,

primarily because they might offer only one or two specialized applications to wetlands.

Remember to look at the site-specific conditions and develop a stormwater management

program to protect an individual wetland based on those site-specific needs. Use the information

provided in the first section of this document to help in identifying the particular conditions that

are unique to the site and to choose one or more BMPs accordingly.

Nonstructural BMPs - Pollution Prevention

Definition/Purpose

Pollution prevention is defined as the reduction or elimination of pollutant discharges to

the air, water, or land. Pollution prevention approaches to environmental protection include:

l Elimination of pollutants by substituting nonpolluting chemicals or products (e.g.,

material substitution, changes in product specification), or altering product use.

l Reducing the quantity and/or toxicity of pollutants generated by production processes

through source reduction, waste minimization, and process modifications.

l Recycling of waste materials (e.g., reuse, reclamation).

Pollution prevention measures are used to reduce pollutant discharges and can be implemented to reduce nonpoint source pollutants generated from the following activities:

l The improper storage, use, and disposal of household hazardous chemicals, including

automobile fluids, pesticides, paints, solvents, etc.

l Lawn and garden activities, including the application and disposal of lawn and garden

care products and the improper disposal of leaves and yard trimmings.

l Turf management on golf courses, parks, and recreational areas.

l Improper operation and maintenance of onsite disposal systems.

l Discharge of pollutants into storm drains, including floatables, waste oil, and litter.

l Commercial activities such as parking lots, gas stations, etc.

l Improper disposal of pet excrement.

l Industrial wastewater disposal in septic systems.

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Best Management Practices

Scope/Applicability

Pollution prevention practices can be applied to reduce the generation of nonpoint source

pollution in all areas and for numerous activities (e.g., residential, commercial, industrial,

institutional, transportation, public and private facilities). Pollution prevention is implemented

through various educational, volunteer, and incentive programs and through federal, state, and

local policies and regulations. Pollution prevention practices include the following:

l Promoting public education programs regarding proper use and disposal of household

hazardous materials and chemicals.

l Establishing programs such as Amnesty Days to encourage proper disposal of household

hazardous chemicals.

l Developing used oil, used antifreeze, and hazardous chemical recycling programs and site

collection centers in convenient locations.

l Encouraging proper lawn management and landscaping that includes proper pesticide

and herbicide use, reduced fertilizer applications and proper application timing, limiting lawn watering, xeriscaping, reduced runoff potential, and training, certification,

and licensing programs for landscaping and lawn care professionals.

l Encouraging proper onsite recycling of yard trimmings.

l Encouraging the use of biodegradable cleaners and other alternatives to hazardous

chemicals.

l Managing pet excrement to minimize runoff into surface waters,

l Using storm drain stenciling in appropriate areas.

l Encouraging alternative designs and maintenance strategies for impervious parking lots.

l Controlling commercial sources of NPS pollutants by promoting pollution prevention

assessments and developing NPS pollution reduction strategies and training materials

for the workplace.

l Promoting water conservation.

l Discouraging the use of septic system additives.

l Encouraging litter control.

Promoting programs such as Adopt-a-Stream to assist in keeping waterways free of

litter and other debris.

l Promoting proper operation and maintenance of onsite sewage disposal systems (OSDS)

through public education and outreach programs.

l Encouraging closure of floor drains or shallow disposal wells that direct pollutants to

groundwater.

Potential Impacts to Wetlands

Benefits

l Reduces pollutants at their source, thereby reducing pollutant loads in stormwater and

downstream wetlands.

Page 4-3
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

l Because discharges are prevented, reduces the need for structural BMPs and stormwater

controls designed to remove pollutants from stormwater.

Limitations

l High participation crucial to success.

l Difficult to monitor results.

Sources of Additional lnformation

Alachua County Office of Environmental Protection. 1991. Best management practices for the use and storage of

hazardous materials. Alachua County Office of Environmental Protection, Gainesville, FL.

Broward County, Florida. March 20, 1980. Determining the effectiveness of sweeping commercial parking areas to

reduce water pollution. CPP task no. 13. Broward County Planning Council, Areawide Waste Treatment

Program, Fort Lauderdale, FL.

Cahill Associates. 1991. Limiting NPS pollution from new development in the New Jersey coastal zone. State of

New Jersey Department of Environmental Protection, Trenton, NJ,

California State Water Resources Control Board. 1983. Lake Tahoe Basin water quality plan. California State

Water Resources Control Board, Sacramento, CA.

Carlson, L., and E. Scott. 1988. Final report: An assessment of nonpoint sources of pollution to Rhode Island’s

waters. Rhode Island Department of Environmental Management, Providence, RI.

Page 4-4
Best Management Practices

Chesapeake Bay Local Government Advisory Committee. 1991. Chesapeake Bay Restoration: Innovations at the

local level. U.S. EPA Chesapeake Bay Program, Washington, DC.

Citizen’s Clearinghouse for Hazardous Wastes. Household hazardous wastes fact pack.

Citizens Program for the Chesapeake Bay. 1986. Baybook: A guide to reducing water pollution at home.

Cook College, Department of Environmental Resources. 1989. Watershed management strategies for New Jersey.

Rutgers, the State University of New Jersey, NJ Agricultural Experiment Station. Publication no. H-17505-1-

89.

Delaware Department of Natural Resources and Environmental Control. 1989. Household hazardous waste.

Clean water series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Delaware Department of Natural Resources and Environmental Control. 1989. Oil recycling. Clean water

series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

District of Columbia Department of Consumer and Regulatory Affairs. 1989. Homeowners urban guide on

ground maintenance. District of Columbia Department of Consumer and Regulatory Affairs, Washington,

DC.

Cibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

British Columbia Research Corporation. File No. 2-51-246(242). Prepared for Greater Vancouver Regional

District Municipality of Surrey, British Columbia Ministry of Transportation and Highways, and British

Columbia Ministry of Advanced Education and Training, Vancouver, BC, Canada.

Hansen, R.C., and K.M. Mancl. 1989. Modern composting: A natural way to recycle wastes. Bulletin no. 792.

Ohio State University

Hoffman, E.J. 1980. Waste lubricating oil disposal practices in Providence, Rhode Island: Potential significance

to coastal water quality Coastal Zone Management Journal 8(4).

Jackson, J.E., N.N. Lillquist, A.L. Schaedel, G.B. Sutherland, and R.S. Wood. 1989. Oregon nonpoint source

management plan. Oregon Department of Environmental Quality and the Environmental Quality Commission,

Portland, OR.

Jensen, R. 1991. Indoor water conservation: Toilets, shower heads, washing machines and faucets can all use

less water. Texas Water Resources 17(4): l-6.

King County, Washington. 1990. Local hazardous waste management plan for Seattle-King County. King County

Solid Waste Division, Seattle, WA.

Klein, R.D. 1990. Protecting the aquatic environment from the effects of golf courses. Community and Environmental

Defense Associates, Maryland Line, MD.

La Valle, P.D. 1975. Domestic sources of stream phosphates in urban streams. Water Research 9:913-915.

Land Management Project. Undated. The land management project completion report: LMP publication appendix.

Rhode Island Department of Environmental Management and U.S. Environmental Protection Agency, Providence, RI.

Land Management Project. 1990. Alternative turf The Land Management Project - best management practices series.

BMP fact sheet #7. Land Management Project, Providence, RI.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone:. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section, Florida Department of

Environmental Regulation, Tallahassee, FL.

Page 4-5
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Maine State Planning Office, Maine Coastal Program. 1991. The estuary book: A guide IO promoring understanding and regional management of Maine’s estuaries and embayments. Maine State Planning Office, Augusta, ME.

Minnesota Pollution Control Agency. 1989. Protecting water quality in urban areas. Minnesota Pollution

Control Agency, Division of Water Quality

Myers, J.C. 1988. Governance of nonpoint source inputs to Narragansett Bay: A plan for coordinated action. The

Narragansett Bay Project, Rhode Island Department of Environmental Management and U.S. Environmental

Protection Agency, Providence, RI.

Nassau-Suffolk Regional Planning Board. May 1978. Non-point source controls planning options, areawide

recommendations, legal needs, Summary plan: Interim report series: 7. Prepared pursuant to Section 208, Federal

Water Pollution Control Act Amendments of 1972 (PL 92-500). Nassau-Suffolk Regional Planning Board,

Haupauge, NY

New Jersey Department of Environmental Protection, Division of Water Resources. Pamphlets promoting

solutions and suggestions for citizens concerned about clean water in New Jersey: The clean water book; Clean

ocean information about: litter, plastics, animal waste, and motor oil; New Jersey Water Watch; and others.

New York Department of Environmental Conservation, Division of Water. 1986. Chapter 6: Best management practices, Stream corridor management: A basic reference manual.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annadale, VA.

Northern Virginia Soil and Water Conservation District. 1980. You and your land: A homeowner’s guide for Fairfax

County. Northern Virginia Soil and Water Conservation District, Fairfax, VA.

Northern Virginia Soil and Water Conservation District. 1991. Please don't feed our streams. Northern Virginia Soil

and Water Conservation District, Fairfax, Virginia.

Puget Sound Water Quality Authority. 1986. Issue paper: Nonpoint source pollution.

Ridgley, S. 1987. Hazardous waste from Minnesota households. Minnesota Pollution Control Agency, Household

Hazardous Waste Pilot Collection Project, St. Paul, MN.

Robertson, D.K., J. Akagha, J. Belasco, J. Bullis, C. Byrne, J. DiPatria, W. Fisher, J. Fonzino, J. Hsu, L. Merchan, D.

Oster, J. Rosenberg, S. VonAulock, and B. Vroeginday. 1987. Liquid household hazardous wastes in the United

States: Identification, disposal, and management plan. Environmental Management ll(6): 735-742. Academic

Press Limited.

Robinson, J.H., and H.S. Snyder. Undated. Golf course development concerns in coastal zone management

Unpublished paper.

Salt Institute. 1991. Salt and highway deicing. Series 26, Issue 2. Salt Institute, Alexandria, VA.

Santa Clara Valley Nonpoint Source Pollution Control Program. Undated. Best management practices for

automotive-related industries. Santa Clara Valley Nonpoint Source Pollution Control Program, San Jose, CA.

University of Maryland, Cooperative Extension Service. 1983. Lawn care in Mary/and. Bulletin 171.

U.S. Department of the Interior, Undated. Pollution prevention handbook. Pollution Prevention Series. U.S.

Department of the Interior, Washington, DC.

USDOC, NOAA. 1990. Coastal management solutions to nonpoint source water pollution. Tech. asst. bul. 102.51

U.S. Department of Commerce, National Oceanic and Atmospheric Administration.

Page 4-6
Best Management Practices

USEPA. 1984. Report to Congress: Nonpoint source pollution in the U.S. U.S. Environmental Protection Agency,

Washington, D.C.

USEPA. 1986. Septic systems and ground-water protection: A program manager’s guide and refercnce Book. U.S.

Environmental Protection Agency, Office of Ground-Water Protection, Washington, D.C.

USEPA. 1988. Used oil recycling. EPA/530-SW-89-006. U.S. Environmental Protection Agency, Office of Solid

Waste, Municipal Solid Waste Task Force, Washington, DC.

USEPA. 1989. How to set up a local program to recycle used oil. U.S. Environmental Protection Agency, Office

of Solid Waste and Emergency Response, Washington, DC.

USEPA. 1989. Recycling works: State and local solutions to solid waste management. EPA/530-SW-89-014. U.S.

Environmental Protection Agency, Office of Solid Waste, Washington, DC.

USEPA. 1991. Guides to pollution prevention-The automotive refinishing industry. EPA/625/7-91/ 016. U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH.

USEPA. 1992. Stormwater management for construction activities: Developing pollution prevention plans and best

management practices. EPA 832-R-92-005. U.S. Environmental Protection ,Agency, Office of Water, Washington,

DC.

USEPA. 1993. Guidance specifying management measures for sources of nonpoint pollution in coastal waters. EPA

840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

USEPA. 1993. Urban runoff management information/education products. U.S. Environmental Protection

Agency, Region 5, Water Division, Wetlands and Watershed Section, Watershed Management Unit, Chicago,

IL.

U.S. General Accounting Office. 1990. Water pollution: Greater EPA leadership needed to reduce nonpoint source

pollution. GAO/ RCED-91-10.

Virginia Cooperative Extension Service. 1990. Report of the Virginia Cooperative Extension Service of Virginia

Polytechnic Institute and State University on pesticides and fertilizers in the urban environment. House document

no. 14. Commonwealth of Virginia, Richmond, VA.

Virginia Department of Conservation and Recreation. 1979. Best management practices handbook: Urban.

Virginia Department of Conservation and Recreation, Division of Soil and Water Conservation, Richmond,

VA.

Voorhees, P.H. 1989. Generation and flow of used oil in the United States in 1988. Presented at Government

Institutes/NORA Conference on Used Oil: Management & Compliance, Prepared for U.S. Environmental

Protection Agency, Office of Solid Waste, Economic Analysis Staff, Washington, DC, November 28, 1989.

Washington State Department of Ecology. 1991. Water quality guide: Recommended pollution control practices for

homeowners and small farm operators. #87-30 Washington State Department of Ecology Olympia, WA.

Whalen, J. 1989. Pest management around your home. Water quality: It’s not just a drop in the bucket - You can

make difference. University of Delaware. Fact Sheet NPS 6.

World Wildlife Fund, The Conservation Foundation. 1991. Gettlng at the source: Strategies for reducing

municipal solid waste. World Wildlife Fund, Baltimore, MD.

Young, K., and D.L. Danner. March 31, 1982. Urban planning criteria for non-point source water pollution

control. Department of Civil Engineering, Catholic University.

Page 4-7
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Nonstructural BMPs - WatershedManagement Plans

Definition/Purpose

Watershed planning is a process for determining future activities within a watershed and

should be a first step in implementing an effective stormwater/wetlands management program.

Watershed planning usually involves the development of a watershed management plan that

describes existing patterns of community life in a watershed-including demographic trends,

housing, economic activity, natural resources, and infrastructure. In addition, watershed management plans should recommend goals and policies (including control of land use) to manage future

development that should, in turn, minimize impacts on water resources, including wetlands.

A watershed management plan is based on a series of maps of the watershed and its resources. The watershed management plan also contains text that explicitly addresses conflicts and

trade-offs among development, environmental protection, social issues (such as affordable

housing), transportation, and many other factors. Special-purpose planning (including wellhead

protection, underground injection control, and wetlands management planning) is one component of a watershed plan. A generalized watershed is shown in Figure 4-1.

Figure 4-1. A generalized watershed showing natural and anthropogenic features.

Page 4-8
Best Management Practices

Watershed management plans can be developed for any geographic area and are usually

applied through the use of watershed overlay maps or a geographic information system. Most

watershed management plans are implemented at the state and local government levels.

Figures 4-2 and 4-3 indicate varieties of watershed management planning map resources.

Potential Impacts to Wetlands

Benefits

l Allows for resource inventory, including identifying wetland resources on a watershed

scale.

l Allows for information analysis, including locating individual wetlands with respect to

other wetlands, adjacent land uses, and adjacent water bodies.

l Allows wetland managers to assess wetland protection needs, develop wetland protection and restoration goals, plan mitigation strategies, and determine impacts from land

use changes to wetland resources.

l Serves as a modeling mechanism to be used for testing various land use/stormwater

control scenarios within the watershed to determine options to best preserve overall

wetland function or improve the health of a degraded wetland system.

LARGE

WATERSHED

Adapted from MWCOG, 1993.

Figure 4-2. Watersheds nest within each other. The site indicated lies within both a small watershed

and larger watershed.

Page 4-9
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Adapted from MWCOG, 1993.

Figure 4-3. Overlay zoning adds another measure ofprotection to critical resources.

Limitations

l Watershed boundaries frequently overlap political boundaries.

Sources of Additional Information

Aldrich, J.A., K.A. Cave, J.E. Swanson, and J.P. Hartigan. 1988. Stormwater master planning in urban coastal

areas: The Virginia Beach master plan. In Proceedings of the Symposium on Coastal Water Resumes, American

Water Resources Association.

Alexandria Department of Transportation and Environmental Services. 1992. Alexandria supplement to the

Northern Virginia BMP handbook. Alexandria Department of Transportation and Environmental Services,

Alexandria, VA.

Coffey, S., W. Berryhill, M. Smolen, and D. Miller. 1989. Watershed screening for nonpoint source impacts and

controls. Document No. 87-EXCA-3-8030. North Carolina State University and U.S. Environmental Protection Agency.

Franklin County, Florida. 1987. Chapter 28-22.100, 22.201, Land planning regulations for the Appalachicola

Buy Area Critical State Concern. Franklin County Administration Commission, Appalachicola, FL.

Howard-Strobel, M.M., TC. Simpson, and T.P. Dillingham. 1987. The Narrow River special area management

plan. Rhode Island Coastal Resources Management Council.

Page 4-10
Best Management Practices

Livingston, E.H. 1989. Florida nonpoint source management plan. Vol. II. Nonpoint Source Pollution Management

Programs. Florida Department of Environmental Regulation. Chapter 8.

Marsalek, J., and H.Y.F. Ng. 1989. Evaluation of pollution loadings from urban nonpoint sources: Methodology and applications. Journal of the Gear Lakes Reservoir 15(3).

Martin, S.R. 1988. An urban stormwater retrofit assessment and planning method. In Symposium on Coastal

Water Resources, American Water Resources Association.

Metropolitan Washington Council of Governments, Washington Metropolitan Water Resources Planning

Board. 1983. Urban runoff in the Washington metropolitan area; Final report. Washington D.C. Urban Runoff

Project, EPA Nationwide Urban Runoff Program. Metropolitan Washington Council of Governments,

Washington, DC.

Myers, J.C. 1988. Governance of nonpoint source inputs to Narragansett Buy: A plan for coordinated action. The

Narragansett Bay Project, Rhode Island Department of Environmental Management and U.S. Environmental

Protection Agency, Providence, RI.

New York-New Jersey Harbor Estuaries Program. 1989. Nonpoint source pollution action plan.

Northern Virginia Planning District Commission. 1990. Evaluation of regional BMPs in the Occoquan Watershed.

Northern Virginia Planning District Commission. Annandale, VA.

Oregon Land Conservation and Development Commission. 1989. Chapter 660, Oregon Administrative Rules.

Puget Sound Water Quality Authority. 1989. Managing nonpoint pollution: An action plan handbook for Puget

Sound watersheds. Puget Sound Water Quality Authority

Schueler, TR., J. Galli, L. Herson, P Kumble, and D. Shepp. 1991. Developing effective BMP systems for urban

watersheds. Anacostia Watershed Restoration Team. Metropolitan Washington Council of Governments,

Washington, DC.

South Florida Water Management District. April 1989. Surface water improvement and management (SWIM)

plan for Biscayne Bay. South Florida Water Management District, West Palm Beach, FL.

South Florida Water Management District. 1989. Technical document in support of chapter 40E-61, works of the

district within the Lake Okeechobee Basin.

USEPA. 1990. The lake and reservoir restoration guidance manual. 2nd ed. EPA-440/4-90-006.

USEPA. 1991. Nonpoints Source Watershed Workshop: Seminar Publication. EPA/625/4-91/027. Prepared by

Eastern Research Group for the U.S. Environmental Protection Agency, Office of Research and Development,

Center for Environmental Research Information, Cincinnati, OH.

Wisconsin Department of Natural Resources and Wisconsin Department of Agriculture, Trade, and Consumer

Protection. 1990. A nonpoint source control plan for the Milwaukee River South Priority Watershed Project.

Document no. WR-24590. Ozaukee County Land Conservation District and the Milwaukee River South

Advisory Subcommittee.

Page 4-11
Definition/Purpose 

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Nonstructural BMPs - preventive Construction Techniques

Preventive construction techniques are practices applied to construction sites to control

pollution at the source. Pollution source controls are implemented throughgood management and

housekeeping techniques designed to minimize nonpoint source pollution from the sites. Typically, preventive construction techniques are developed to control runoff volumes and sediment,

but they can also be designed to control other NPS pollutants such as nutrients, oil and grease, and

pesticides.

An overall management plan for the control of nonpoint source pollution on a construction

site that addresses specific control measures to be implemented in an effective manner can be

applied as a preventive construction technique. The construction site pollution control plan

should address specific categories including erosion and sediment controls, equipment maintenance and repairs, waste collection and disposal, storm sewer inlet protection, dust controls,

storage of construction materials, washing areas, demolition areas, sanitary facilities, and pest

controls. Some management and housekeeping techniques applied to these categories should

include the development and implementation of an effective erosion and sediment control plan;

the proper location of activities that can act as a source of pollutants to wetlands, streams, or

stormwater conveyance systems in areas that are not subject to surface water runoff; the placement of filtering devices to protect conveyance systems from settleable pollutants during

construction; the proper use and storage of chemicals; proper collection and disposal of wastes on

a site with adequate and properly located receptacles; and the maintenance of a site in a neat and

orderly condition.

Preventive construction techniques are used to minimize the contamination of stormwater

on a site by reducing the availability of construction-related pollutants that might contaminate

runoff. Where the contamination of runoff water cannot be avoided, pollutants and polluted

water are controlled on site.

Preventive construction techniques can be applied to all construction projects. The planning and management techniques applied to a location should be adapted to the site- specific

characteristics of a project. The

degree of planning and management necessary to prevent or

minimize nonpoint source

pollution on a site will depend,

primarily, on the size and complexity of the project.

See Figure 4-4.

Figure 4-4. Preventive construction

techniques.

Page 4-12
Best Management Practices

Design Criteria Considerations

Develop an overall plan for the control of nonpoint source pollution that addresses

specific measures that can be described and implemented in an effective manner.

Develop a plan that is specific to the characteristics of a site.

Potential Impacts to wetlands

Benefits

l Reduction in the amount of stormwater-associated pollutants entering adjacent or

downstream wetlands.

l Reduction of construction site erosion resulting in a reduction of stormwater sediment

loads to downstream wetlands.

l Reduction in the potential for downstream wetland degradation resulting from erosion

associated with peak stormwater flows.

Limitations

l Possible reduction in the amount of surface water supplied to adjacent or downstream

wetlands as a result of rerouting.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

USEPA. 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.

EPA 840-B-92-002 U.S. Environmental Protection Agency, Office of Water, Washington, DC.

Washington State Department of Ecology 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Nonstructural BMPs - Outreach and Education Programs

Definition/Purpose

Educational programs should improve wetlands protection program implementation by

maintenance personnel and government officials and should reduce individual contributions to

stormwater problems. Training programs and educational materials for public officials, contractors, and the public are crucial to implementing effective stormwater management programs.

Educational programs for public officials, contractors, and the public are also necessary to teach

the value of natural wetlands and the potential impacts of stormwater runoff. Contractor

certification and inspector training are important educational programs that add to the success of

stormwater management programs and their continued effectiveness. Programs for the public can

Page 4-13
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

educate and encourage participation and support for pollution prevention efforts such as storm

drain stenciling, used oil and hazardous chemical recycling, litter control, street sweeping, lawn

management and landscaping, safe use and disposal of household hazardous materials and chemicals, correct operation of onsite disposal systems, proper pet excrement disposal, water conservation, and closure of shallow disposal systems that direct pollutants to groundwater.

Scope/Appilcability

Educational programs can be implemented in homes, residential communities, and at the

workplace. Training and certification programs can be implemented at all levels of government

and through numerous private and public institutions involved in wetland and stormwater

management including developers, contractors, scientists, engineers, and professional associations. The states of New Jersey, Virginia, Maryland, Washington, and Delaware, and the city of

Alexandria, Virginia, are examples of governments whose agencies have developed manuals and

training materials to assist in the implementation of urban runoff requirements and regulations

(USEPA, 1993).

Numerous public and private institutions are involved in or sponsor public education

programs, such as environmental organizations; neighborhood, business, civic, and professional

associations; school systems; churches; Boy Scouts and Girl Scouts of America; and 4-H Clubs. A

common program is storm drain stenciling to enhance public awareness (see Figure 4-5). Educational programs can be achieved through various public outreach media, including newsletters,

magazines, newspaper, audiovisuals, public meetings, or workshops.

Figure 4-5. Stencil spray painting to enhance public awareness.

Page 4-14
Potential Impacts to Wetlands

Best Management Practices

Benefits

l Teaches the public the value of natural wetlands and the positive and negative impacts

of stormwater.

l Teaches the public how pollutants can impact wetlands via stormwater runoff and how

to prevent pollution from entering surface waters and groundwaters.

l Provides opportunities for the public to participate in decision-making activities, to

observe wetlands and other aquatic ecosystems, and to gain “hands on” experience in the

field.

l Prepares government officials and personnel to implement their stormwater and wetland

programs effectively and consistently, to make educated decisions regarding stormwater

controls, and to communicate the goals and objectives of stormwater/wetland policies to

the public.

Limitations

l High participation crucial to the success of many public education programs

l Difficult to monitor results.

l Program results might not be realized for some time.

l Programs require continuous funding and demands on personal time.

Barton, S.S. 1989. Landscape management. Water quality: It’s not just a drop in the bucket - You can make a

difference Fact sheet NPS 10. University of Delaware.

Barton, S.S. 1989. Lawn management for conservation. Water quality: It’s not just a drop in the bucket - You can

make a difference Fact sheet NPS 11. University of Delaware.

Chesapeake Bay Foundation. 1989. Homeowner series: Septic systems and the Bay. Chesapeake Bay Foundation.

Citizen’s Clearinghouse for Hazardous Wastes. Household hazardous wastes fact pack.

Citizens Program for the Chesapeake Bay. 1986. Baybook: A guide to reducing water pollution at home.

Baltimore, MD.

Delaware Department of Natural Resources and Environmental Control. 1989. Detergents and phosphorus.

Clean water series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Delaware Department of Natural Resources and Environmental Control. 1989. Household hazardous waste.

Clean water series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Delaware Department of Natural Resources and Environmental Control. 1989. Oil recycling. Clean water

series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Delaware Department of Natural Resources and Environmental Control. 1989. Septic systems. Clean water

series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Page 4-15
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

District of Columbia Department of Consumer and Regulatory Affairs. 1989. Homeowners urban guide on

ground maintenance. District of Columbia Department of Consumer and Regulatory Affairs, Washington, DC,

Firehock, K. 1991. Virginia’s Erosion and Sediment Control Law: A citizen’s action guide. Virginia Save Our

Streams Program, Izaak Walton League of America.

Hansen, R.C., and K.M. Mancl. 1989. Modern tomposting: A natural way to recycle wastes. Bulletin no. 792.

Ohio State University.

Himelick, K. 1989. Landscape design for water conservation. Water quality: It’s not just a drop in the bucket - You

can make a difference. Fact sheet NPS 8. University of Delaware, Newark, DE.

Himelick, K. 1989. Plant selection for conservation. Water quality: It’s not just a drop in the bucket - You can make

a difference. Fact Sheet NPS 9. University of Delaware, Newark, DE.

Land Management Project. 1990. Biological mosquito control, The Land Management Project - Land use and

water quality series. Fact sheet 87. Land Management Project, Providence, RI.

Land Management Project. 1990. Stormwater and wetlands, The Land Management Project - Land Use and

Water Quality Series. Fact sheet #6. Land Management Project, Providence, RI.

Land Management Project. Undated. The Land Management Project completion report: LMP publications

appendix. Rhode Island Department of Environmental Management and U.S. Environmental Protection

Agency, Providence, RI.

Livingston, E.H. 1989. Florida Nonpoint Source Management Plan. Vol. II Nonpoint Source Pollution Management Programs. Florida Department of Environmental Regulation. Chapter 8.

Livingston, E.H., and E. McCarron. 1992. Stormwater management: A guide for Floridians. Florida Department

of Environmental Regulation, Stormwater/Nonpoint Source Management, Tallahassee, FL.

Maine State Planning Office, Maine Coastal Program. 1991. The estuary book: A guide to promoting understanding and regional management of Maine’s estuaries and embayments. Maine State Planning Office, Augusta, ME.

Mancl, K.M. 1985. Mound system for wastewater treatment. Agricultural engineering fact sheet. Document

No. SW-43. Pennsylvania State University, College of Agriculture, Cooperative Extension Service.

Mancl, K.M. 1985. Septic system failure. Agricultural engineering fact sheet. Document No. SW-41. Pennsylvania

State University, College of Agriculture, Cooperative Extension Service.

Mancl, K., and W.L. Magette. 1991. Correcting septic system pro&/ems. Water Resources Information, Maryland

Water Resources Research Center.

Mancl, K., and W.L. Magette. 1991. Maintaining your septic tank. Water Resources Information, Maryland

Water Resources Research Center.

Mancl, K., and W.L. Magette. 1991. Using septic tank-soil absorption systems in Maryland. Water Resources

Information, Maryland Water Resources Research Center.

Nebraska Department of Natural Resources. Undated. National Resources Districts, unique, progressive

leadership in conservarion.

New Jersey Department of Environmental Protection, Division of Water Resources. Pamphlets promoting

solutions and suggestions for citizens concerned about clean water in New Jersey: The clean water book; Clean

ocean information about: litter, plastics, animal waste, and motor oil; New Jersey Water Watch; and others.

Page 4-16
Best Management Practices

Northern Virginia Soil and Water Conservation District. 1980. You and your land: A homeowner’s guide for

Fairfax County. Northern Virginia Soil and Water Conservation District, Fairfax, VA.

Northern Virginia Soil and Water Conservation District (NVSWCD). 1991. Please don’t feed our streams

Northern Virginia Soil and Water Conservation District, Fairfax, VA.

Oregon Department of Land Conservation and Development. Undated. Oregon Coastal Management Program:

A citizen’s guide. Funded by the Office of Ocean and Coastal Resource Management, National Oceanic

Atmospheric Administration.

Ohio Environmental Protection Agency Division of Water Quality Planning and Assessment. 1991. Nonpoint

Source Education/Demonstration Project evaluation report, nonpoint source pollution abatement in Ohio 1984-1987.

Pitt, D.G., W. Gould, Jr., and L. LaSota. 1990. Landscape design to reduce surface water pollution in residential

areas. Water Resources 32. Water Resources Information, University of Maryland System, Cooperative

Extension Service.

Puget Sound Water Quality Authority 1989. Managing nonpoint pollution: An action plan handbook for Puget

Sound watersheds. Puget Sound Water Quality Authority

Salt Institute. 1983. Deicing salt facts (A quick reference).

Shaver, H.E., and F.M. Piorko. Undated. The role of education and training in the development of the Delaware

Sediment and Stormwater Management Program. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

South Florida Water Management District. April 1989. Surface water improvement and management (SWIM)

plan for Biscayne Bay. South Florida Water Management District, West Palm Beach, FL.

Southwest Florida Water Management District. Undated. A citizens guide to the S.W.I.M. Priority List.

University of Maryland. 1983. Lawn care in Maryland. University of Maryland, Cooperative Extension

Service, College Park, MD. Bulletin 171.

U.S. Department of the Interior. Undated. Pollution prevention handbook. Pollution Prevention Series. U.S

Department of the Interior, Washington, DC.

USEPA. 1988. Used oil recycling. EPA/530-SW-89-006. U.S. Environmental Protection Agency, Office of Solid

Waste, Municipal Solid Waste Task Force, Washington, DC.

USEPA. 1989. How to set up a local program to recycle used oil. U.S. Environmental Protection Agency, Office

of Solid Waste and Emergency Response, Washington, DC.

USEPA. 1991. Nonpoint Source Watershed Workshop: Seminar publication. EPA/625/4-91/027. Prepared by

Eastern Research Croup for the U.S. Environmental Protection Agency, Office of Research and Development,

Center for Environmental Research Information, Cincinnati, Ohio.

USEPA. 1993. Urban runoff management information/education products. U.S. Environmental Protection

Agency, Region 5, Water Division, Wetlands and Watershed Section, Watershed Management Unit, Chicago,

IL.

Washington State Department of Ecology 1991. Water quality guide: Recommended pollution control practices for

homeowners and small farm operators. No. 87-30. Washington State Department of Ecology, Olympia, WA.

Page 4-17
Definition/Purpsoe

Scope/Applicability

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Westchester County, New York. 1981. Water quality management program: Best management practices manual on

highway deicing storage and application methods. Westchester County, White Plains, NY.

Whalen, J. 1989. Pest management around your home. Water quality: It’s not just a drop in the bucket - You can

make a difference. Fact Sheet NPS 6. University of Delaware.

Wisconsin Legislative Council. 1991. Wisconsin legislation on nonpoint source pollution. Report no. 9. Wisconsin

Legislative Council.

Younger, L.K., and K. Hodge. 1992. 1991 International Coastal Cleanup results. Center for Marine Conservation, Washington, DC.

Nonstructural BMPs - Riparian Areas

Riparian areas are vegetated ecosystems along a water body through which energy, material,

and water pass. These areas characteristically have a high water table and are subject to periodic

flooding and influence from the adjacent water body. Riparian areas encompass wetlands,

uplands, or combinations of these areas, and environmental conditions in the zone at times

resemble both wetland and upland. The complex organizations of biotic and abiotic elements that

make up riparian areas can be effective in removing suspended solids, nutrients, and other

contaminants from stormwater runoff.

Maintaining natural riparian areas helps to slow stormwater runoff, trap sediment, and

reduce the volume of runoff by allowing some infiltration to occur. Reducing the velocity of

stormwater runoff attenuates soil erosion processes and increases runoff contact time with soil

and vegetative surfaces. Increased contact of stormwater runoff with the soils and vegetation in a

riparian area can result in the infiltration of runoff and the filtration or uptake of stormwaterassociated pollutants.

Riparian areas are important to both the wetland and the upland as habitat for aquatic and

wetland-dependent wildlife species, as refuges for wildlife species during high-water events, as

seed reservoirs, and as buffers against extreme environmental conditions. Other functions of

riparian areas that contribute to water quality include shading, flood attenuation, and shoreline

stabilization. A typical riparian area is shown in Figure 4-6.

Where natural riparian areas are present, they should be maintained around all wetlands

that might be impacted by stormwater flows. The removal of trees and other vegetation in the

riparian zone should be limited and heavy use should be minimized to reduce the potential for soil

compaction, which could result in decreased infiltration rates.

Page 4-18
Best Management Practices

WETLAND

GROUNDWATER

Figure 4-6. A typical riparian area.

Riparian areas should be a part of a series of BMPs for treating stormwater in densely

developed areas where there are high percentages of impervious surfaces or where discharge rates

are high and flow is concentrated.

Riparian areas should be maintained, when possible, in all areas where they exist and can be

combined with other structural or nonstructural BMPs as part of a stormwater treatment system.

They are useful in separating incompatible land uses, and can be effective in protecting sensitive

habitats such as wetlands, streams, lakes, and shorelines from adjacent land uses.

Design Criteria Considerations

l Maintain natural vegetation.

l Avoid compaction of the soils.

l Consider slope, vegetation, soils, depth to impermeable layers, runoff sediment characteristics, type and quantity of stormwater pollutants, and annual rainfall when determining

widths.

l Increase riparian area width with increased slope, where possible.

l Combine natural riparian areas with other structural or nonstructural BMPs as

pretreatment where discharge rates are high or flows are concentrated.

Potential Impacts to Wetlands

Benefits

l Reduce the amount of stormwater-associated pollutants entering adjacent or downstream wetlands.

l Reduce stormwater sediment loads to downstream wetlands.

l Reduce the potential for downstream wetland degradation resulting from erosion

associated with peak stormwater flows.

Page 4-19
Source of Additional Information

Definition/Purpose

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

l Might result in recharge of groundwater from infiltration, benefiting adjacent baseflowdependent wetlands.

Maintain slope stability adjacent to wetlands and streams.

l Provide a buffer between wetlands and adjacent land uses.

l Provide critical habitat adjacent to wetlands and streams.

l Protect aquatic life by preventing and reducing thermal warming impacts.

Limitations

l Might not adequately attenuate concentrated peak stormwater flows to adjacent or

downstream wetlands.

Brown, M. 1991. Vegetative buffer zones. Prepared for the Southwest Florida Water Management District

Surface Water Improvement and Management Program. Henigar & Ray Engineering Associates, Inc., Crystal

River, FL.

Heraty, M. 1993. Guidance report I: Riparian buffer programs. Prepared for the U.S. Environmental Protection

Agency, Office of Wetlands, Oceans and Watersheds. Metropolitan Washington Council of Governments,

Washington, DC.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

USEPA. 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.

EPA 840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Information Basins

Infiltration basins are stormwater impoundments that detain stormwater runoff and return

it to the ground by allowing runoff to infiltrate gradually through the soils of the bed and sides of

the basin. Infiltration basins are flat-bottomed, have no outlet, and are usually located to collect

stormwater runoff from adjacent drainage areas. Infiltration basins can be designed to control

peak discharges from relatively large design storms.

Infiltration basins can be designed as an off-line system for treating the first flush of

stormwater flows or to treat the peak discharges of the 2-year storm event. They remove both

soluble and fine particulate pollutants, provide groundwater recharge, and preserve the natural

water balance of a site by diverting a signifcant fraction of the annual runoff volume back into

the soil. Infiltration basins can maintain flow levels in small headwater streams during critical

dry-weather periods. They do not produce thermal or low dissolved oxygen impacts to downPage 4-20
Best Management Practices

stream waters as do wet ponds. Infiltration basins can be used as sediment basins during the

construction phase of a site as long as the sediment is removed prior to final grading of the basin.

Scope/Applicability

Infiltration basins are effective at removing both soluble and fine particulates found in

stormwater runoff. (Coarse-grained pollutants should generally be removed before they enter an

infiltration basin.) Unlike other infiltration devices (e.g., trenches), basins can be adapted to

provide full control of peak discharges for large design storms. Infiltration basins can also be

adapted to relatively large drainage areas (up to 50 acres). Depending on the degree of storage/

exfiltration achieved in the basin, significant groundwater recharge, low flow augmentation, and

localized stream bank erosion control can be achieved (Schueler, 1987).

Infiltration basins can be used at locations with sufficient open space and proper topography to allow gravity flow of stormwater to the basin. They are usually used in commercial and

large residential developments. Infiltration basins can serve drainage areas of 2 to 50 acres,

depending on local conditions. An infiltration basin must be located in permeable soils with

infiltration rates greater than 0.5 inches per hour. Soil and water table conditions should be such

that the system can provide for a new volume of storage through percolation or evapotranspiration within a maximum of 72 hours following a stormwater event.

The use of infiltration basins is not recommended in the following situations: ultra-urban

areas, watersheds with risk of chronic oil spills or other contaminant spills, regions with cold

winters and snowmelt/freeze and thaw conditions, arid regions where a dense vegetative cover

cannot be reliably maintained, regions with sole-source aquifers, and areas with predominantly

clay or silt soils. Soils with a combined silt/clay percentage of over 40 percent by weight are

susceptible to frost heave and are not good candidates for infiltration basin applications. Basins

are also unsuitable if the site is located over fill soils that form an unstable upgrade and are prone

to slope failure.

It should be noted that infiltration basins have a high failure rate due to the tendency of the

basin soils to become clogged with sediments. Failure rates for infiltration basins in the midAtlantic region range form 60 to 100 percent in the first 5 years, according to studies conducted in

Maryland (Schueler, 1992). Once a basin has become clogged, it is very difficult to restore its

original function; thus, many infiltration basins have been converted to retention basins or

constructed wetlands.

l Detention of the 2-year, 6-hour minimum storm to 72-hour maximum drawdown time.

l Recommended size of contributing drainage area based on site-specific conditions (e.g.,

soil infiltration capacity or rainfall).

l Pretreatment sediment forebay to dissipate the velocity of incoming runoff, spread the

flow, and trap the sediment.

Page 4-21
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Offsets to waterwells, onsite disposal systems, and fundations are based on hydrologic,

soil, ecologic, and topographic characteristics of the site or existing state or local requirements.

Flat-bottomed basin floor vegetated with dense turf grass, such as reed canary grass or tall

fescue.

Shallow/Basin depth with inlet level with basin floor.

Riprap apron at inlet to prevent incoming runoff from reaching erosive energy levels and

scouring the pipe outfalls and to spread incoming runoff more evenly.

Emergency spillway.

Maximum side slopes of 3:l (h:v) to allow vegetative stabilization, easier mowing, and

public safety

Riprap level spreaders.

Uniform ponding depth across entire surface of basin; low spots should be leveled.

Contributing watershed slope less than 20 percent; 5 percent optimal.

Minimum 4-ft clearance between basin floor and bedrock level.

Minimum 4-ft clearance to seasonally high groundwater table.

Minimum 100 ft from drinking water wells.

Minimum 10 ft downgradient and 100 ft upgradient of foundations.

25ft vegetated buffer around the basin perimeter; low-maintenance, water-tolerant

native plant species that provide food and cover for wildlife and act as a screen.

Initial and periodic tilling of basin floor.

Use of lightweight equipment in basin.

Maximum depth low enough to ensure complete drainage of basin within 72 hours;

depends on soil types present.

Design Considerations to Improve Longevity

l Stone trenches.

l Sand surface layer.

l Underdrains below basin floor.

l Shorter dewatering rate (24 hr rather than 72 hr).

Pretreatment forebays to control sediment inputs.

l Small contributing watershed areas.

l Shallow basin depths (standing water appears to promote soil compaction).

l Off-line designs that bypass large storms and sediment inputs.

l More efficient dewatering mechanisms in basins (e.g., stone trenches rather than soil).

l Careful geotechnical investigation of soil conditions prior to excavation.

Page 4-22
maintenance Requirements

Best Management Practices

Potential Impacts to Wetlands

Benefits

l Recharge of groundwater from infiltration basins, benefiting baseflow-dependent

wetlands.

l Reduction of stormwater sediment loads to downstream wetlands.

l Reduction in the potential for downstream wetland degradation resulting from erosion

and hydroperiod changes associated with stormwater flows.

l Reduction in the amount of stormwater-associated pollutants entering downstream

wetlands.

Limitations

l Reduction in the amount of surface water supplied to adjacent or downstream wetlands as the result of rerouting and detention.

l Short life span (5 years or less).

l Might not be applicable in cold or arid climates, areas with impermeable soils, or areas

overlying sole source aquifers.

l Filtering effect of the topsoil can be lost by distributing runoff directly into the subsoil

horizon.

Infiltration basins require relatively frequent inspection and maintenance. Infiltration

basins require inspection, sediment removal, tilling, erosion control, and debris and litter removal. The frequency of sediment removal will depend on whether the basin is vegetated or

nonvegetated, its storage capacity, its recharge characteristics, the volume of inflow, and the

sediment load.

Infiltration basins require more frequent inspections after construction (see Figure 4-7),

with inspections tapering off to twice a year once performance has been verified. Once the basin

is put to use, it should be inspected after every major storm or at least once a month if no major

storm occurs. Inspections include monitoring of water levels for drainage and checking for

accumulation of sediment or signs of erosion or contamination.

Sediment removal from infiltration basins without vegetation should be performed annually or semiannually followed by tilling to maintain infiltration rates. Sediment removal should

be performed when the basin is dry to prevent compaction of the soils and clogging of infiltrative

surfaces. Care should be taken to avoid compaction of the basin floor by using light equipment or

possibly hand raking to remove sediments. After the sediment is removed, the basin should be

tilled. Rotary tillers or disk harrows are normally used, but deep plowing might be necessary if

heavy equipment has compacted the soil. Removal of sediments from vegetated basins might not

need to be performed as frequently because vegetative growth helps to prevent the formation of

impermeable layers on the surface of the soil. Dense vegetative growth on side slopes and buffer

strips will also help to prevent erosion from occurring.

Page 4-23
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Top View

Side View

Back-up Underdrain Pipe In Care of Standing Water Problems

Schueler. 1997.

Figure 4-7. Two views of an infiltration basin.

The basin should be checked annually for structural stability including the erosion of side

slopes, differential settlement, cracking, leakage, or tree growth on the embankments. Erosion

control is very important because the associated sediments can clog the infiltration basin. The

erosion of side slopes can be prevented by the maintenance of a dense turf having extensive root

growth that promotes infiltration through the basin sides, promotes bed stability, and inhibits

weed growth.

Sources of Additional Information

Austin City Council. 1991. Environmental criteria manual. City Council, Austin, TX.

Gibb, A.., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242). March 15.

Land Management Project. 1990. Artificial wetlands. BMP fact sheet #6. U.S. Environmental Protection

Agency and Rhode Island Department of Environmental Management, Land Management Project, Providence, RI.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater

infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of

Natural Resources, Annapolis, MD.

Page 4-24
Defintion/Purpose 

Scope/Applicability

Best Management Practices

Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.

Prepared for South Central Connecticut Regional Water Authority, New Haven, CT

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan watershed. Prepared

for the Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District

Commission, Annandale, VA.

Schueler, T.R. 1987. Controlling urban runoff A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Schueler, T.R., PA.. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices:

Techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Tahoe Regional Planning Agency, 1988. Water quality management plan for the Lake Tahoe Region, Handbook of

best management practices. Vol 2. November 30.

Virginia Department of Conservation and Recreation, USDA Soil Conservation Service, Virginia Department

of Transportation, Virginia Polytechnic Institute and State University College of Urban Design and Department of Civil Engineering, Occoquan Monitoring Laboratory, and the Virginia Water Control Board. 1990.

Best management practices handbook: Urban.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-71. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Infiltration Trenches

An infiltration trench is an excavated trench backfilled with clean, coarse aggregate to

allow for the temporary storage of runoff. Runoff stored in the trench is allowed to infiltrate into

the soil in the trench bottom or is conveyed from the trench by an outflow pipe to downstream

stormwater detention or retention systems. Infiltration trenches are designed to provide temporary storage and infiltration for increased stormwater runoff associated with development.

Infiltration trenches can attenuate peak discharges associated with the design storm and may

replicate predevelopment hydrologic conditions.

Infiltration trenches remove fine particulates and soluble pollutants from runoff by

temporary storage and infiltration into the underlying soil. Pollutant removal from runoff in

infiltration trenches results from adsorption, filtration, and microbial decomposition in the soil.

Temporary storage and partial or complete infiltration of runoff in an infiltration basin can also

reduce downstream bankfull flooding and resultant stream bank erosion and can help to maintain

baseflow conditions. A typical infiltration trench is shown in Figure, 4-8.

Infiltration trenches can be used on small individual sites or can be incorporated into

multiuse sites where open area is restricted. Pretreatment devices such as grassed swales or filter

Page 4-25
Design Criteria Conditions

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Schueler, 1987.

Figure 4-8. Typical infiltration trench.

strips should be incorporated with infiltration trenches to remove coarse particulates from runoff

prior to its entering the trench.

Infiltration trenches should not be located in areas with shallow groundwater or adjacent to

groundwater-maintained wetlands because of the potential for adverse impacts resulting from

pollutants in the stormwater. Potential impacts to the natural hydroperiod of existing surface

water-maintained wetlands resulting from the rerouting of water through infiltration trenches

and away from these systems should also be considered.

Contributing areas should be less than 10 acres in size, and slopes should be less than 5

percent. Infiltration trenches cannot be installed in fill and should not be used in areas with lowpermeability soils. Their use may also be limited in areas where the ground remains frozen at

depth for extended periods of time or in arid areas with sparse vegetative cover.

l Location in suitable soils with sufficient infiltration rates, preferably greater than 0.5

inches per hour.

l Water table offset of at least 3 ft from the bottom of the trench.

l Contributing area of less than 10 acres.

l Contributing slopes of less than 5 percent.

l Detention time of 48 to 72 hours to allow adequate pollutant removal.

l Complete drainage of trench within 72 hours of a storm event to maintain aerobic

conditions

l Pretreatment of stormwater inflow to remove coarse sediments.

Page 4-26
Best Management Practices

l Sizing of trench dependent on the volume of runoff to be controlled.

l Use of observation wells to monitor performance.

l Level trench bottom.

l Offsets to waterwells, onsite disposal systems, foundations, etc. based on hydrologic, soil,

ecologic, and topographic characteristics of the site or existing state or local requirements.

Design Considerations to Improve Longevity

l Field verification of soil infiltration rates and water table location.

l Use of pretreatment systems that provide some degree of storage (e.g., sump pits,

swales with check dams, plunge pools).

l A layer of filter fabric 1 ft below surface of trench.

l Use of a sand layer rather than filter fabric at the bottom of the trench.

l Avoiding construction until all contributing watershed disturbances and construction

activities are completed.

l Rototilling of trench bottom to preserve infiltration rates.

Potential Impacts to Wetlands

Benefits

l Reduction of stormwater sediment loads to downstream wetlands.

l Reduction in the potential for downstream wetland degradation resulting from

erosion associated with peak stormwater flows.

l Reduction in the amount of stormwater-associated pollutants entering downstream

wetlands.

Limitations

Reduction in the amount of surface water supplied to adjacent or downstream

wetlands as the result of rerouting.

l Embedding of downstream wetland substrates as the result of the removal of coarse

sediments.

l Might not be applicable in cold or arid climates, areas with impermeable soils, or areas

overlying sole source aquifers.

l Filtering effect of the topsoil can be lost by distributing runoff directly into the subsoil

horizon.

Page 4-27
Maintenance Requirements

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Infiltration trenches require periodic low-level maintenance. Because trenches are typically

smaller than other BMPs and are buried underground, they might receive little attention from

homeowners or might be relatively inaccessible. Infiltration trenches require continued monitoring and maintenance according to a well-defined schedule that outlines responsibilities and

enforcement. Routine maintenance activities include inspection, buffer maintenance and

mowing, sediment removal, and tree pruning.

Inspections for drainage are typically performed frequently upon completion of construction and annually thereafter. Water level monitoring should be conducted several times within

the first few months of operation. The surface of the infiltration trench should be checked for

standing water after a rainstorm, and water levels in the observation well should be recorded over

several days to check drainage rates. If there is no observation well, a small hole can be dug down

to the first layer of filter fabric to observe the water level in the trench. The monitoring schedule

is reduced to an annual frequency once performance of the device has been verified.

The accumulation of sediments in the top foot of stone aggregate or the surface inlet should

be monitored on the same schedule as the observation well to check for surface clogging. When

infiltrative capacity is significantly reduced, sediment should be removed from the top of the

infiltration trench by removing the stone, replacing the filter fabric, and washing or replacing the

stone. Removal of sediment from the top of the infiltration trench should be required less

frequently if the trench is designed with a pretreatment inlet. Sediment should be cleaned out of

the pretreatment inlet, sediment trap, or grease trap on a regular basis.

Grass buffer strips adjacent to and growing over the infiltration trench should be inspected

annually for lush, vigorous growth. Bare spots should be reseeded or resodded, and eroded areas

should be repaired. Trees adjacent to the trench should be trimmed so that their leaves will not

clog the trench. Pioneer trees that start to grow near the trench should be removed to prevent

puncturing of the trench by their roots,

Sources of Additional lnformation

Gibb, A., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242). March 15.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Maryland Department of Natural Resources, 1984. Maryland standards and specifications for stormwater

infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of

Natural Resources, Annapolis, MD.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

Schueler, TR., P.A.. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Page 4-28

Westchester County Department of Planning, 1984. Best management practices manual for stormwater runoff

control. Westchester County Environmental Management Council, White Plains, NY.
Definition/Purpose

Scope/Applicability

Design Criteria Consideraitions

Best Management Practices

Structural BMPs - Sand Filters

Sand filters are systems of underground pipes beneath a self-contained bed of sand designed

to treat urban stormwater. Runoff from a developed site is routed to the filters, infiltrated

through the sand, then collected in underground pipes and returned back to the stream or channel.

Sand filters are enhanced with the use of peat, limestone, gravel, and/or topsoil layers and may

have a grass cover. Sand filters remove sediment, trace metals, nutrients, BOD, and fecal coliform

from the initial pulse of stormwater from a development site. They provide significant pollutant

removal and are useful for groundwater protection.

Sand filters are adaptable for urban areas. They can be used to treat stormwater from small,

intensely developed sites (e.g., gas stations, convenience stores, small parking lots). Sand filters

have been used to retrofit existing stormwater management systems by locating them at the end

of existing stormwater outlet pipes. Sand filters are an off-line system (i.e., they should be located

outside the stream channel or drainage path). Sand filters are more costly to construct than

infiltration trenches by a factor of 2 or 3, but they have lower regular maintenance costs.

Sand filters are designed to treat stormwater quality, not quantity They have a limited

ability to reduce peak discharges and do not provide detention for downstream areas such as

wetlands. Average removal rates of 85 percent for sediment, 35 percent for nitrogen, 40 percent

for dissolved phosphorus, 40 percent for fecal coliform, and 50 to 70 percent for metals have

been reported for sand filters. Two views of a sand filter design developed by the City of Austin,

Texas, are presented in Figure 4-9.

l Sand filters can be used in areas with thin soils, high evaporation rates, low soil infiltration rates, and limited space.

l Drainage areas can be as great as 50 acres; however, most sand filters will function well

with contributing watersheds ranging from 0.5 to 10 acres.

l Two to 4 ft of head are needed for proper operation.

l Using a peat or limestone layer in the filter bed and a grass cover can increase the pollutant removal efficiency

l Minimum design depth of the filter should be 18 inches.

l Filters designed with a long drawdown time (24 to 40 hours) can increase the pollutant

removal efficiency

Page 4-29
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

TO STORMWATER

DETENTION BASIN

SEDIMENT CHAMBER PLAN VIEW

ENERGY DISSIPATORS FILTRATION BASIN

STONE RIPRAP

FILTRATED OUTFLOW

CROSS SECTION

FILTRATED OUTFLOW

UNDERDRAIN PIPING SYSTEM

City of Austin, Texas, 1991.

Figure 4-9. Two views of a sand filter design.

Design Considerations to Improve Longevity

l Quarterly maintenance of the sand filter to maintain porosity aids in keeping the filter

operating efficiently

l Designs that include a flow splitter can help to prevent clogging.

l Pretreatment to remove sediment will help to prevent clogging.

l Designs that allow for access to the filter aid in maintenance and inspection of the

filter.

l Regular removal of surface sediment increases the longevity of the filter.

Potential Impacts to Wetlands

Benefits

l Reduction in the amount of stormwater-associated pollutants entering downstream

wetlands.

Limitations

l Primarily function as a water quality BMP and might not adequately attenuate concentrated peak stormwater flows to adjacent or downstream wetlands.

l Might adversely affect downstream sediment or nutrient-depleted wetlands.

Page 4-30
Best Management Practices

Maintenance Requirements

Sand filters require relatively frequent yet simple inspection and maintenance to maintain

performance. When a predetermined headloss is reached, the top layer of sand is removed and

replaced to restore the filtration capacity of the filter. The frequency of sediment removal

depends on the solids content of the water being filtered. To extend the life of the filter, system

designs incorporate a wet pool that is used to trap the coarse sediments before they reach the

filter. Sand filters require raking, surface sediment removal, and the removal of trash, debris, and

leaf litter. Peat-sand filters that have vegetation growing on their surface require vegetation

maintenance including periodic mowing. Mowing the grass short removes nutrients absorbed by

the plants and maintains a neat filter appearance.

Sand filters require monitoring for hydraulic conductivity. Routine inspections are also

needed for sediment accumulation in the wet pool, health of the vegetative cover, and the removal

of trash deposited in the wet pond. The vegetative cover can be damaged by salt if the system is

not shut down over the winter season. Managers should select hardy vegetation that is resistant

to damage by salt, disease, and flooding.

Sources of Additional Information

City of Austin, Texas. 1991. Design guidelines for water quality control basins, Public Works Department,

Austin, TX.

Galli, J. 1990. Peat-sand filters: A proposed stormwater management practice for urbanization areas. Prepared for

the Coordinated Anacostia Retrofit Program and the Office of Policy and Planning, DC Department of Public

Works, Washington, DC.

Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).

Land Management Project. 1990. Artificial wetlands. BMP fact sheet #5. U.S. Environmental Protection

Agency and Rhode Island Department of Environmental Management, Land Management Project, Providence, RI.

Metcalf & Eddy, Inc. 1979. Wastewater engineering: Treatment disposal reuse. 2nd ed. McGraw-Hill Book

Company, New York, NY.

Milone & MacBroom, Inc. 1991. Urban stormwater qualify management for public water supply watersheds.

Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.

Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning

and designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,

Annandale, VA.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occcquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

Schueler, T.R., P.A. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Page 4-31
Definition/Purpose

Scope/Applicability

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Grassed Swales

Grassed swales are channels lined with grass or erosion-resistant plant species that are

constructed for the stable conveyance of stormwater runoff. They use the ability of vegetation to

reduce the flow velocities associated with concentrated runoff. Grassed swales are not usually

designed to control peak runoff loads independently and are often used in combination with

other best management practices. Where slopes are excessive, grassed swales can include excavated depressions or check dams to enhance runoff storage or to decrease flow rates.

Grassed swales are primarily stormwater conveyance systems designed to channel and

transport stormwater without the resultant erosion associated with high-velocity runoff. The

reduction in flow velocities resulting from the conveyance of surface runoff through dense

vegetative cover can result in a reduction of peak discharges. Pollutants can be removed from

stormwater by filtration through the vegetation, by deposition, or in some cases by the infiltration of soluble nutrients into the soil. The degree of pollutant removal in a swale depends

primarily on the residence time of water in the swale and the extent of its contact with vegetation and the soil surface. The incorporation of excavated depressions or check dams into grassed

swales can enhance pollutant removal by increasing detention/retention times. An example of a

grassed swale is shown in Figure 4-10.

Grassed swales can be used in large-lot single-family subdivisions and on campus-type office

or industrial sites in place of curbs and gutters. They are useful for runoff conveyance in highway

medians and are often combined with other best management practices. They can be used in all

areas of the country where the climate and soils allow for the establishment of dense vegetative

covers. Grassed swales have a limited ability to control runoff from large storms and shouldnot

be used in areas where flow rates exceed 1.5 ft per second.

Design Criteria Considerations

l Longitudinal swale slope of less than 2 percent or use of check dams or excavated depressions where slopes exceed 4 percent.

l Wide and shallow parabolic shape with side slopes of less than 3:1.

l Development and maintenance of dense vegetation.

l Greater than a 2-ft offset to the water table.

Page 4-32
Best Management Practices

Swales Slopes

as Close to

Zero 16 Drainage

Will Permit

Stone Prevents

Downstream Scour

Schueler. 1987.

Figure 4-40. Grassed swale.

l Use of underdrains if well-drained conditions are required.

l Discharge of runoff to wetlands or adjacent BMPs at nonerosive velocities.

Potential Impacts to Wetlands

Benefits

l Potential creation of wetlands and wetland habitat in low-slope areas.

l Potential for groundwater recharge in low-flow storm events, benefiting adjacent

baseflow-dependent wetlands.

Limitations

l Reduction in the amount of surface water supplied to adjacent or downstream wetlands

as a result of the rerouting of surface water.

l Potential for the introduction of pollutants to downstream wetlands during peak storm

events if conveyance is to the wetlands.

Maintanance Requirements

Maintenance requirements for grassed swales are relatively minimal. These include

cleanout of sediment trapped behind check dams, mowing, litter removal, and spot vegetation

repair. The most important objective in the maintenance of grassed swales is the maintaining of a

Page 4-33
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

dense and vigorous growth of turf. Usually in residential subdivisions, homeowners adjacent to

the swales maintain the grass and remove litter. Education of homeowners is recommended

because the type of maintenance sought to maximize pollutant removal is somewhat different

from that used to maintain the average homeowner’s lawn. For example, grass should not be cut

too short, excessive fertilizers should not be used so that contamination of receiving waters or

groundwater is avoided, and ditches should be kept free of lawn debris.

Periodic cleaning of vegetation and soil buildup in curb cuts is required so that water flow

into the swale is unobstructed. Sediments should be removed when they accumulate to 6 inches or

more at any spot or when they interfere with the grassed swale operation. During the growing

season, swale grass should be cut no shorter than the level of the design flow. Cuttings should be

removed promptly. Swale maintenance at the end of the growing season depends on whether the

objective is to remove nutrients or particulates. Grasses and wetland plants are mowed or cut to a

low height at the end of the growing season to promote nutrient removal; for other pollution

control objectives, such as sediment removal, plants are allowed to stand at a height exceeding the

design water depth by at least 2 inches at the end of the growing season. These plants will act as a

filter to screen out particles by slowing the velocity of water so that particles can settle.

Gibb, A.., B. Bennett, and A. Birbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242).

Khan, Z., C. Thrush, P. Cohen, L. Kulzer, R. Franklin, D. Field, J. Koon, R. Horner. 1992. Biofiltration swale

performance, recommendations, and design considerations. Municipality of Metropolitan Seattle Water Pollution

Control Department, Seattle, WA.

Land Management Project. 1990. Artificial wetlands. BMP fact sheet #2. U.S. Environmental Protection

Agency and Rhode Island Department of Environmental Management, Land Management Project, Providence, RI.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section, Florida Department of

Environmental Regulation, Tallahassee, FL.

Long Island Regional Planning Board. 1984. Nonpoint source management handbook. Long Island Regional

Planning Board, Hauppauge, NY.

Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater

infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of

Natural Resources, Annapolis, MD.

Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning

and designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,

Annandale, VA.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

Schueler, T.R., P.A. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments.

Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments.

Page 4-34
Best Management Practices

Structural BMPs - Vegetative Filter Strips

Definition/Purpose

Vegetative filter strips are densely vegetated sections of land designed to convey runoff in

the form of sheet flow from adjacent developed sites. Level spreaders can be incorporated into the

design of vegetated filter strips to increase their effectiveness by distributing runoff over the full

length of the strip. Vegetative filter strips primarily function as water quality BMPs and do not

provide adequate detention or infiltration to reduce peak discharges to predevelopment levels.

Vegetative filter strips direct runoff in the form of sheet flow across grassed or forested

surfaces (see Figure 4-11). Reduction in flow velocities resulting from the conveyance of surface

runoff through dense vegetated cover results in the removal of particulate contaminants through

sedimentation, enhanced infiltration into the soil, and a reduction in the potential for downstream channel degradation. Vegetative filter strips may also reduce runoff volumes and contribute to groundwater recharge. Maximum water quality benefits of vegetative filter strips can be

obtained if the strips include the use of native vegetation (preferably undisturbed or conserved

natural areas).

A recent variation of vegetative filter strips is a technology referred to as bioretention. This

approach can be suitable for managing runoff from small drainage areas using a mixture of upland

plant materials and enriched soil composition. Bioretention can maximize nutrient uptake,

evapo-transpiration, infiltration, microbial degradation of metals and carbon-based pollutants,

and storage to help reduce peak flows from the drainage area served to predevelopment levels. It

should be noted, however, that bioretention methods require modification of existing site grading

practices to provide sheet flow as a runoff conveyance rather than traditional pipe inlet systems.

Schueler,l987.

Figure 4-11. Vegatative filter strip between developed area and sensitive aquatic habitat.

Page 4-35
Scaope/Applicability

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Vegetative filter strips can be used on low- and medium-density residential and campus-type

office or industrial sites where the percentage of pervious area is sufficient to promote infiltration and filtering. They are often used to convey sheet flow runoff to other conveyance or

detention systems. Contributing drainage areas should be less than 10 acres in size with gentle

slopes so that runoff arrives at the site in the form of overland sheet flow.

Vegetative filter strips are useful as buffers between developed areas and sensitive aquatic

habitats such as wetlands, streams, and lakes and can be useful in stabilizing stream banks.

Vegetative filter strips are adaptable to most climates and are effective where dense vegetation

can be sustained on a year-round basis. They are not feasible in densely developed urban areas,

where there are high percentages of impervious surfaces, or where discharge rates are high and

flow is concentrated. A vegetative filter strip used for protecting a natural waterway in a commercial construction setting is shown in Figure 4-12.

Design Criteria Considerations

l Contributing areas of less than 10 acres.

l Uniform, even contributing slope of less than 5 percent.

l Length of no less than 50 to 75 ft with an additional 4 ft for every increase in slope of 1

percent.

l Width of no less than 20 ft.

l Development and maintenance of dense erosion-resistant vegetation species.

l Use of a level spreader at the top of the filter strip to distribute flow easily.

l Layout of the top edge of the filter strip on contour.

l Use of native vegetation.

Diversion -

Natural

vegetative

Filter Strip

Existing Waterway

Page 4-36

Adapted from 

Figure 4-12. Vegatative filter strip.
Sources of Additional Information

Best Management Practices

Potential Impacts to Wetlands

Benefits

l Reduction of stormwater sediment and pollutant loads to adjacent and downstream

wetlands.

l Potential recharge of groundwater, benefiting adjacent baseflow-dependent wetlands.

l Provide a buffer between wetlands and adjacent development.

Limitations

l Primarily function as a water quality BMP and might not adequately attenuate concentrated peak stormwater flows to adjacent or downstream wetlands.

Maintenance Requirements

Frequent inspections and maintenance are required in the first few years after filter strip

construction while vegetation becomes established. Watering, fertilizing, and reseeding might be

required during the initial establishment of the strip to maintain a dense vegetative cover.

Established filter strips should be inspected on an annual basis for foot or vehicular damage.

Inspectors should note encroachment, gully erosion, density of vegetation, and evidence of

concentrated flows through or around the strip. A filter strip and its associated level spreader,

when used, should be inspected periodically during storms to ensure that flow is not concentrating and short circuiting through the strip.

Vegetated filter strips require periodic repair, regrading, and sediment removal to prevent

channelization. Sediments accumulating near the top of the strip should be removed to maintain

the original grade. Longer buffer strips present the option of management as a lawn, or as a

succession of vegetation types from grass, to meadow, to second-growth forest. ‘Natural” filter

strips require less maintenance than grass lawns; however, corrective maintenance is still required

to prevent the formation of concentrated flows. Shorter strips are managed as a lawn or as a short

grass meadow and are mowed two or three times a year to suppress weeds and woody growth.

Gibb, A.., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District, File no. 2-51-246(242).

Maine Department of Environmental Protection. 1992. Environmental management: A guide for town official,

best management practices to control nonpoint source pollution. Maine Department of Environmental Protection,

Augusta, ME.

Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater

infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of

Natural Resources, Annapolis, MD.

Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds

Prepared for South Central Connecticut Regional Water Authority, New Haven, CT

Page 4-37
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occcquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning

designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,

Annandale. VA.

Prince George’s County. 1993. Design manual for use of bioretention in stormwater management. Prepared for

Prince George’s County Government, Watershed Protection Branch, Landover, MD, by Engineering Technologies Associates, Inc., and Biohabitats, Inc.

Schueler, T.R. 1987. Controlling urban runoff A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Schueler, T.R., P.A. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

USEPA. 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.

EPA 840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

Virginia Cooperative Extension Program. 1994. Easy reference to sustainable landscape management and water

quality protection. Publication 426-612. Virginia Cooperative Extension Program, Blacksburg, VA.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Vegetated Natural Buffers

Vegetated buffer areas are barriers of natural or established perennial vegetation managed to

reduce the impact of development on the water quality of adjacent areas. They are effective in

separating incompatible land uses and in displacing activities that represent potential sources of

nonpoint source pollution from adjacent wetlands or water bodies. Vegetated buffer areas can be

spatially arranged in linear strips or as free forms depending on site characteristics.

Vegetated buffer areas function primarily as water quality BMPs and usually do not provide

adequate detention to reduce peak discharges to predevelopment levels. They reduce the velocity

of surface runoff from adjacent developed sites and provide area for infiltration of runoff into the

soil. Reduced flow velocities result in the removal of particulate contaminants through sedimentation and reduce the potential for channel erosion or degradation. Vegetated buffer areas can also

reduce runoff velocities and contribute to groundwater recharge.

Vegetated buffer areas can be used in large-lot, medium- to low-density single-family

subdivisions or campus-type office or industrial sites where the percentage of pervious area is

sufficient to promote infiltration. Vegetated buffer areas should be located in areas with gentle

Page 4-38
Best Management Practices

slopes where runoff is conveyed in the form of sheet flow. They are useful in separating incompatible land uses, and they can be effective in protecting sensitive habitats such as wetlands,

streams, lakes, and shorelines from the impacts of adjacent development. Vegetated buffer areas

are also useful in combination with other structural BMPs. An example of a vegated buffer is

shown in Figure 4-13.

Design Criteria Considerations:

l Avoid compaction of the soils.

l Consider slope, vegetation, soils, depth to impermeable layers, runoff sediment characteristics, type and quantity of stormwater pollutants, and annual rainfall when determining

buffer widths.

l Combine vegetated buffer areas with other structural or nonstructural BMPs as pretreatment where discharge rates are high or flows are concentrated.

l Slope of less than 5 percent.

l Increased buffer width as slope increases.

l Intermixed zones of vegetation (particularly, native vegetation) including grasses,

deciduous and evergreen shrubs, and understory and overstory trees.

Potential Impacts to Wetlands

Benefits

l Reduction of stormwater sediment and pollutant loads to adjacent and downstream

wetlands.

l Potential recharge of groundwater, benefiting adjacent baseflow-dependent wetlands.

l Provide a buffer between wetlands and adjacent land uses.

l Provide critical habitat adjacent to wetlands.

Adapted from State of Maine, DEP. 1992.

Figure 4-13. Vegetated natural buffer.

Page 4-39
Maintenance requirements

Sources of Additional Information

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Limitations

l Primarily function as a water quality BMP and typically do not adequately attenuate

concentrated peak stormwater flows to adjacent or downstream wetlands.

The inspection and maintenance of vegetated buffer areas are most important during the

period of initial establishment. Maintenance requirements during the first few years of establishment include weed suppression and rodent protection in forested areas. Extra watering, fertilizing, and grass reseeding or tree replacement might also be necessary Trees might need to be staked

to increase their survival rates. The condition of vegetated buffer areas should be inspected

periodically, especially after heavy runoff events, during the first few years after buffer area

creation to ensure that vegetation is healthy and that channelized flows are not developing.

Maintenance requirements are relatively minimal once a vegetated buffer area is estab

lished. Routine maintenance is designed to promote the growth of dense, vigorous vegetation and

includes mowing, litter removal, repair of eroded areas, and spot vegetation repair. Sediments that

accumulate more than 6 inches at any spot should be removed. Watering and possible fertilization

might also be required periodically.

Established buffer areas should be inspected on an annual basis for foot or vehicular damage.

Inspectors should note encroachment, gully erosion, density of vegetation, and evidence of

concentrated flows through or around the vegetated buffer area. A plan view of the use of natural

vegatated buffers to protect riparian wetland areas is shown below in Figure 4-14.

Brown, M. 1991. Vegetative buffer zones. Prepared for the Southwest Florida Water Management District

Surface Water Improvement and Management Program. Henigar & Ray Engineering Associates, Inc., Crystal

River, FL.

Chesapeake Bay Local Assistance Department. 1989. Local assistance manual. Chesapeake Bay Local Assitance

Department, Richmond, VA.

Heraty, M. 1993. Guidance report I: Riparian buffer programs. Prepared for the U.S. Environmental Protection

Agency, Office of Wetlands, Oceans and Watersheds. Metropolitan Washington Council of Governments,

Washington, DC.

Maine Department of Enviromental Protection. 1992. Environmental management: A guide for town officials,

best management practices to control nonpoint source pollution. Maine Department of Environmental Protection,

Augusta, ME.

Schueler, T.R., P.A. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Virginia Cooperative Extension Program. 1994. Easy reference to sustainable landscape management and water

quality protection. Publication 426-612. Virginia Cooperative Extension Program, Blacksburg, VA.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Page 4-40
Scope/Applicability

Best Management Practices

Schueler, 1987.

Figure 4-14. A plan view ofnatural vegatated buffer use.

Structural BMPs - Open Spaces

Definition/Purpose

Open spaces are grassed or wooded areas located within development sites to increase

pervious area. Open spaces function primarily as water quality BMPs and usually do not provide

adequate detention to reduce peak discharges to predevelopment levels.

Open areas reduce the velocity of surface runoff, resulting in an increased contact time of

sheet flow with the soil and vegetative surfaces. Reduced flow rates result in the removal of

particulate contaminants through sedimentation and reduce the potential of channel erosion or

degradation. Reduced flow velocities can improve water quality by increasing infiltration,

filtration, and adsorption of stormwater runoff on a site. Groundwater recharge can also occur as

the result of increased infiltration in open areas.

Open areas can be used in locations with gently sloping topography where runoff is conveyed in the form of sheet flow. They should be located in well-drained or moderately welldrained soils where offsets to the water table or bedrock exceed 4 ft. Open areas can be incorporated into lightly used recreational areas, or they can be maintained as meadows or wooded areas.

Open areas should not be located in heavily used areas because of the potential for soil compaction, which could result in decreased infiltration rates on the site. An example of the use of open

space to maximize the preservation and protection of wetlands and other aquatic resources is

shown in Figure 4-15.

Page 4-41
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Design Criteria Considerations:

l Contributing slopes of less than 5 percent.

l Conveyance of runoff in the form of sheet flow.

l Locate in well-drained or moderately well-drained soils.

l Minimum water table and/or bedrock offset of 4 ft.

l Adequate size of open area to provide sufficient levels of treatment.

Potential Impacts to Wetlands

Benefits

l Reduction of stormwater sediment and pollutant loads to adjacent and downstream

wetlands.

l Potential recharge of groundwater, benefiting adjacent baseflow-dependent wetlands.

l Provide a buffer between wetlands and adjacent development.

Limitations

l Primarily function as a water quality BMP and might not adequately attenuate concentrated peak stormwater flows to adjacent or downstream wetlands.

Figure 4-1.5. A plan view for maximizing the preservation and protection ofwetlands.

Page 4-42
Maintenance Requirement

Scope/Applicability

Best Management Practices

The maintenance of open spaces is minimal once the vegetation is established. Frequent

inspections are required during the first few years to ensure a healthy, dense growth of the desired

forms of vegetation. Extra watering, fertilization, and reseeding might be required. Forested areas

might require weed suppression, rodent protection, watering, or staking to increase the survival of

trees and shrubs during the first few years after establishment. Cutting and spraying with approved herbicides might also be necessary to remove unwanted vegetation.

Open spaces should be inspected on an annual basis for damage by foot or vehicular traffic,

encroachment, gully erosion, and vegetation density. The effectiveness of the open space will

decrease over time as sediments accumulate. Inspectors should look for accumulated sediments so

that they can be removed before they damage vegetation. Routine maintenance includes removal

of trash and debris, repair of eroded areas, spot repair of vegetation, and mowing of the grass.

Sources of Additional Information

Chesapeake Bay Local Assistance Department. 1989. Local assistance manual. CBLAD, Richmond, VA.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared for

Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission,

Annandale, VA.

Northern Viginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning designing

best management pratices in Northern Virginia. Northern Vi Planning District Commission, Annandale, VA

Structural BMPs - Extended Detention Dry Basins

Definition/Purpose

Extended detention dry basins temporarily store stormwater runoff from a site and release it at

a controlled rate by use of a fixed outlet. They are designed not to have permanent standing water

and are usually dry between storm events. Extended detention dry basins control water quantity by

temporarily detaining stormwater, and they reduce downstream channel erosion by reducing the

frequency of bankfull and subbankfull flooding events. Extended detention dry basins provide some

water quality benefits by removing pollutants primarily through the settling of suspended solids.

They are designed and located to collect stormwater runoff from drainage areas and to control peak

discharges for one or more design storm frequencies.

Extended detention dry basins can be used in locations with sufficient open space and

without backup into surrounding areas. They can be used in combination with Permanent Pools,

proper topography to allow gravity flow of stormwater to the basin and sufficient storage

or they can incorporate shallow marsh habitat in the normally inundated areas near their outlet

ing drainage areas of over 30 acres and are not usually practical for areas less than 10 acres in size.

pipes to enhance pollutant removal. Extended detention dry basins are best suited for contributThe natural hydrologic conditions and characteristics of adjacent or downstream wetlands shou1d

Page 4-43
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

be considered in the design and placement of extended detention dry basins so that impacts to

these existing systems can be minimized. See Figure 4-16.

Design Criteria Considerations

Detention of the 2-year, 24-hour design storm for at least 40 hours with release at a rate

no greater than 50 percent of the predevelopment peak rate.

l Sufficient storage for sedimentation to be effective before water leaves the basin.

l Length-to-width ratio of 3:l if possible.

l Sufficient pond depth and cross-sectional area to establish low flow velocities.

l Minimum slope of 2 percent on basin floors.

l Minimum resuspension by reducing inflow velocities.

l Native plants.

Potential Impacts to Wetlands

Benefits

l Potential recharge of groundwater from extended detention ponds, benefiting baseflow

dependent wetlands.

l Reduction of stormwater sediment loads to downstream wetlands.

l Potential reduction in the amount of stormwater associated pollutants entering downstream wetlands.

l Reduction in the first-flush impact of stormwater runoff to downstream wetlands.

Adapted from MWCOG, 1992.

Figure 4-46. Schematic of an enhanced dry extended detention pond system designed to

accommodate protection ofexisting wetlands.

Page 4-44
Best Management Practices

l Elimination of the need for a permanent pool with habitat destruction potential.

l Potential for the creation of high marsh or wet meadow wetlands within the extended

detention ponds through the incorporation of micropools.

l Potential for the incorporation of complex boundaries and microtopography in the

pond design to enhance diverse vegetation and habitat.

l Reduction in the potential for downstream wetland degradation resulting from erosion

associated with peak stormwater flows.

Limitations

l Reduction in the amount of surface water supplied to adjacent or downstream wetlands as the result of rerouting and detention.

l Embedding of downstream wetland substrates as the result of the removal of coarse

sediments.

l Changes to adjacent natural wetland hydroperiods.

l Smothering of wetlands incorporated into extended detention ponds as a result of

increased sedimentation.

l Thermal impacts to downstream wetlands resulting from the discharge of water from

extended detention ponds.

l Low habitat diversity and limited structure of wetlands created in extended detention

ponds.

Extended detention dry basins can have relatively high maintenance burdens and costs.

Extended detention dry basins will not achieve their intended purpose unless routine and nonroutine maintenance tasks are performed on schedule. Responsibilities for maintenance need to

be clearly defined, maintenance schedules enforced, and regular inspections performed. Routine

maintenance includes mowing, debris and litter removal, erosion control, and the control of

nuisances.

Extended detention dry basins should be inspected on an annual basis to ensure that they

continue to operate as designed. The inspector should measure and record the drainage rate of

water after a storm to check that the design detention times are met. The flow control device

should be inspected regularly for evidence of clogging or too rapid release. In general, the extended detention dry pond should be inspected for structural soundness, sediment accumulation,

broken or missing parts, and trash and debris accumulation. The side slopes should be inspected

for rodent holes, tree growth, subsidence, erosion, and cracking. The spillway should be inspected

for clogging or missing rocks. The pilot channel to the upper stage, the flow path to the lower

stage, and the channel upstream and downstream of the basin should be checked for erosion

damage. The forebay/riser should be checked for sediment accumulation. Figure 4-17 indicates

typical locations for necessary maintenance access.

Trash and debris should be removed from the site. Trash should be removed from the debris

barriers when greater than 20 percent of the openings in the barrier are plugged, and it is especially important to remove floatable debris to prevent clogging of the control device or riser.

Page 4-45
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

The grass/ground cover of basins located in nonresidential areas should be moved at least

twice a year to control weeds and to discourage the growth of woody vegetation. Extended

detention dry basins located in residential areas require more frequent mowing. Dense vigorous

growth should be maintained on the bottom as well as on the sides of the extended detention dry

pond. The side slopes, emergency spillway, and embankment might also require periodic stabilization from erosion damage.

Nonroutine maintenance includes the removal of accumulated sediments from the basin.

Accumulated sediments reduce the performance of an extended detention dry basin by gradually

reducing its capacity to treat stormwater, and by clogging the orifice or filter medium. After

sediments are removed, the area should be stabilized immediately with vegetation to prevent

sediments from clogging the control device. Other nonroutine maintenance activities include the

eventual replacement of the inlet, outlet, and riser works.

Sources of Additional Information

Gibb, A.., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).

Land Management Project. 1990. Artificial wetlands. BMP fact sheet #5. U.S. Environmental Protection

Agency and Rhode Island Department of Environmental Management, Land Management Project, Providence, RI.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.

Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan watershed. Prepared

for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

PLAN PROFILE

Adapted from Milone & MaBroom, Inc.. 1991.

Figure 4-17. Schematic of dry pond showing maintenance features.

Page 4-46
Scope/Applicability

Best Management Practices

Schueler, TX., P.A.. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Washington State Department of Ecology. 1992. Stormwater Management Manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs- Wet Ponds

Definition/Purpose

Wet ponds are depressions constructed by excavation and embankment procedures to store

excess runoff temporarily on a site. After a runoff event, overflow from the pond is released at a

controlled rate by an outlet device designed to release flows at various peak rates and elevations

until the design elevation of the pool is reached Wet ponds maintain a permanent pool of water

between storm events. Wet ponds are located to collect stormwater inflows from adjacent

drainage areas and are usually designed to control peak discharges from relatively large design

storms.

Wet ponds regulate stormwater runoff from a given rainfall event by the temporary storage

of peak flows in order to mitigate quantity and quality impacts to downstream systems. Pollutant

removal in wet ponds results from the gravity settling of sediments/pollutants, the chemical

transformation and biological uptake of nutrients while water is detained in the pond, and the

infiltration of soluble nutrients through the soil profile. Extended detention time in the permanent pool of wet ponds allows for increased sedimentation, transformation, and flocculation of

pollutants in the system. Decreased runoff rates from wet ponds reduce downstream channel

erosion and resultant sediment pollution. Wet ponds have been shown to be the most efficient

means of water quality protection when compared with other conventional BMPs.

Wet ponds can be located in areas that have topographic conditions that allow for the

gravity flow of stormwater and enough open space to allow sufficient sizing of the structure so

that it can adequately treat expected flows. Wet ponds can be used in low- and high-visibility

locations where contributing watersheds are greater than 10 acres in size or where continuous

baseflows exist to ensure dry-weather flow. They are not useful in arid regions where evapotranspiration exceeds rainfall, and their use is limited in areas where space is a constraint such as

densely developed urban localities. Wet ponds have been used in combination with wetlands and

other extended detention treatment methods. An extended detention wet pond is shown in

Figure 4-18.

design Criteria Considerations

l Extended detention of a l-inch storm for 24 to 40 hours.

l Permanent pool volume of at least 2.5 times the runoff volume generated by the mean

storm.

Page 4-47
Potential Impacts to Wetlands

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Sufficient volume in the permanent pool to allow for low-energy settling of sediments

between storms.

Use of pond liners in high-permeability soils.

Length-to-width ratio of 3:1 with a wedge shape.

Watershed area greater than or equal to 10 acres.

Access for maintenance equipment.

Enhanced conditions for biological treatment between storms (i.e., native vegetation in

shallow ponds).

Inlet and outlet pipes set to discharge at or below the permanent pool surface.

Stone riprap lining, plunge pools, energy dissipators, or other acceptable means should be

used below the pond outlet to prevent scouring.

Benefits

l Potential for the creation of emergent and high marsh-wetlands within the wet pond.

l Reduction of stormwater sediment loads to downstream wetlands.

l Potential for the incorporation of designs to enhance diverse vegetation and habitat.

l Reduction in the potential for downstream wetland degradation resulting from erosion

associated with peak stormwater flows.

Limitations

l Changes to the natural hydroperiod of adjacent natural wetlands.

l Reduction in the amount of surface water supplied to adjacent or downstream wetlands

as the result of rerouting and detention.

Adapted from Schueler. 1992.

Figure 4-18 Conceptual cross section view of an extended detention wet pond.

Page 4-48
Maintenance Requirement

Best Management Practices

l Potential for the introduction of pollutants to downstream wetlands during peak storm

events.

l Embedding of downstream wetland substrates as the result of the removal of coarse

sediments.

l Strong shifts in the trophic status of downstream communities.

l Thermal impacts to downstream wetlands resulting from the discharge of water from

wet ponds.

l Low habitat diversity and limited structure of wetlands created in wet ponds.

Maintenance requirements for wet ponds are relatively modest. Long-term performance

will be degraded, however, by the buildup of sediments. Therefore, a firmly established maintenance and inspection program is required. Routine maintenance includes inspections, mowing of

the embayment and buffers, and the removal of trash and debris from the forebay.

Wet ponds should be inspected on an annual basis to ensure that they continue to operate as

designed. The inspector should monitor the water level after a storm to compare pond performance against the design detention time. Other factors that contribute to the performance of the

pond that should be inspected are related to structural soundness, sediment accumulation,

appearance, security, and the ease of maintenance. The side slopes should be inspected for rodent

holes, tree growth, subsidence, erosion, and cracking. The barrel, spillway, and drain should be

inspected for clogging, and the forebay/riser should be checked for sediment accumulation. The

adequacy of the erosion protection measures for the channel upstream and downstream of the

basin should be noted, as well as any modifications that have occurred to the contributing

watershed or pond structure.

Trash and debris should be removed from the site as part of the periodic mowing regimen.

Maintaining a neat appearance at the site helps to discourage vandalism and illicit dumping. All

floatable debris around the riser should be removed, and the outlet should be checked for possible

clogging.

Mowing of the upper stage, side slopes, embankment, and emergency spillway is required at

least twice a year to prevent woody growth and the excessive growth of weeds. More frequent

mowing is required if the wet pond is located in a residential neighborhood. A dense vigorous

growth of grass or ground cover should be maintained around the wet pond. The side slopes,

emergency spillway and embankment might also require periodic stabilization from slumping and

erosion damage.

Nuisances associated with problem wet ponds include insects, weeds, odors, and algae. Algae

and mosquitoes can be controlled by the introduction of fathead minnows and other fish. This

practice is preferred over chemical application, especially in the case of ponds that discharge to

wetlands. Excessive growth of emergent, floating, and submerged vegetation can be mechanically

harvested or controlled with herbicides.

Nonroutine maintenance includes the removal of accumulated sediments from the basin.

Accumulated sediments reduce the performance of a wet pond basin by gradually reducing its

capacity to treat stormwater. Wet ponds require sediment removal when the storage capacity of

the permanent pool is significantly reduced.

Page 4-49
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Actual sedimentation rates depend on the size, degree of construction, and land use in the

watershed. Other nonroutine maintenance includes structural repairs and the replacement of

various inlet/outlet and riser works.

Sources of Additional Information

Gibb, A.., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Long Island Regional Planning Board. 1984. Nonpoint source management handbook. Long Island Regional

Planning Board, Hauppauge, NY.

Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Schueler, T.R., P.A.. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Washington State Department of Ecology 1992. Stormwater management manual for the Puget Sound Basin

Publication no. 91-735. Washington State Department of Ecology, Olympia, WA.

Westchester County Department of Planning. 1984. Best management practices manual for stormwater runoff

control. Westchester County Environmental Management Council, White Plains, NY.

Structural BMPs - Constructed Weltands

Definition/Purpose

Constructed wetlands are shallow pools constructed on nonwetland sites as part of the

stormwater collection and treatment system. They provide growing conditions suitable for the

growth of emergent marsh plants. These systems are designed primarily for the purpose of

stormwater management and pollutant removal from surface water flows. They are essentially a

type of wet pond with greater emphasis placed on vegetation and depth/area considerations.

Constructed wetlands are often used in sequence with a sediment basin, a forebay, or some type

of stormwater pond.

Constructed wetlands are designed to maximize removal of pollutants from stormwater

through physical, chemical, and biological mechanisms. They can be designed to store stormwater

runoff temporarily, thereby lowering stormwater quantity and quality impacts on receiving

systems including lakes, water supply reservoirs, streams, wetlands, and recharge aquifers for

water supply wells. Physical mechanisms of pollutant removal include sedimentation, filtration,

and volatilization. Chemical mechanisms include precipitation, adsorption to sediments, flocculation, and transformations such as reduction. Biological mechanisms include plant and bacterial

nutrient uptake. Constructed wetlands can also be designed to allow for a wide diversity of plant

species and improved wildlife habitat.

Page 4-50
Scope/Applicability 

Best Management Practices

Constructed wetlands can be used in locations with sufficient open space and appropriate

topography to allow gravity flow of stormwater and sufficient sizing of the structure to adequately treat expected flows. They can be applied to most sites, including those with large

pollution and runoff loads, provided sufficient baseflow is available to maintain proper hydrology

to support wetland vegetation. Constructed wetlands might be useful as a retrofit for older dry

stormwater basins. It is important to remember that the hydrology of the watershed draining to

the constructed wetland must be capable of supporting the wetland. A schematic of a constructed

wetlands pond is shown in Figure 4-19.

Design Criteria Consideration

l

Volume should accommodate at least a 6-month, 24-hour storm for the watershed’s

developed condition.

Wetland area should be greater than or equal to 2 percent of the watershed area.

Watershed of 5 acres or more.

Length-to-width ratio of 3:l or greater; if this is not feasible, use baffles.

Vary water depth, with approximately 50 percent of the area about 0.5 ft deep and with

some open water, to provide diverse habitat.

Dry season baseflow must be adequate for vegetation maintenance, with evapotranspiration considered.

Minimize short circuiting by using baffles, islands, and peninsulas to ensure a long

distance from inlet to outlet.

Incorporate islands to provide habitat and refuge for birds.

Plant and soil pollutant removal effectiveness may vary with season.

Consider soil permeability and groundwater conditions. Lining may be necessary.

Organic soils provide best nutrient retention and plant substrate.

Vegetation should be selected for hydroperiod, climate, resistance to contaminants, stem

density (to promote sedimentation), and habitat value. Consider native vegetation.

Consider plant uptake/release of nutrients and contaminants, and possible plant harvesting.

Use of forebay or other controls in “treatment train” design to pretreat runoff.

Erosion control should be employed in the forebay and at the outlet, preferably with

vegetation.

Design for easy maintenance.

Provide access for maintenance equipment.

Page 4-51
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Schueler. 1992.

Figure 4-19. Schematic design ofconstructed wetland for stormwater control with an enhanced shallow

marsh system.

Potential Impacts to Wetlands

Benefits

l Reduction of flooding and erosive velocities and stormwater sediment loads to adjacent

and downstream wetlands.

l Potential for the incorporation of designs to enhance diverse vegetation and wildlife

habitat in urban areas.

l Reduction in the potential for downstream wetland degradation resulting from erosion

associated with peak stormwater flows.

Limitations

l Changes to the natural hydroperiod of adjacent natural wetlands.

Reduction in the amount of surface water supplied to adjacent or downstream wetlands

as the result of rerouting and detention.

l Smothering of vegetation in constructed wetlands resulting from sedimentation.

l Potential for the introduction of pollutants to downstream wetlands during peak storm

events.

l Embedding of downstream wetland substrates as the result of the removal of coarse

sediments.

l Thermal impacts to downstream wetlands resulting from the discharge of water from

constructed wetlands.

Page 4-52
Maintenance Requirements

Best Management Practices

l Potential takeover of vegetation by invasive aquatic nuisance plants.

l Potential for blocking fish passage if constructed in stream channel.

Maintenance requirements for constructed wetlands receiving stormwater are high during

the first several years while vegetation is being established. Reinforcement planting and erosion

control BMPs might be necessary. Maintenance during the establishment phase involves frequent

inspection for erosion damage or subsidence on the embankment or spillway. Rills formed

through erosion should be filed and thoroughly compacted. It is important that the vegetated

cover on the embankment and spillway be dense and healthy Mowing and fertilizing help

promote vigorous growth of plant roots that resist erosion. Mowing also prevents the growth of

unwanted woody vegetation.

Another type of maintenance that might be necessary during the initial growing season is

protection of the first year wetland vegetation growing at the water’s edge and on the side slopes

from birds. Birds often feed on the carbohydrate-rich shoots of the young vegetation, a problem

referred to as “eat-out.“The problem can be addressed by surrounding the open water area of the

constructed wetland with wire to limit access to the vegetation from the water, which is how the

birds get to the vegetation. The wire should be maintained until the wetland vegetation is well

established, which is usually by the second growing season.

Periodic inspections are necessary to ensure that the constructed wetland is operating as

designed. Constructed wetlands should be inspected after major storms during the first year of

establishment for the stability of banks and for flow channelization. For example, debris on

plants or dead vegetation that has fallen over should be removed to minimize damage to other

wetlands vegetation. Excessive accumulation of sediments in any part of the system should be

noted as well as any changes to the contributing watershed. The inspector should pay special

attention to the proper operation of pumps and water control structures, sealing, water level,

flow distribution, and density of vegetation during the first years of operation. Water level is the

most critical aspect of wetland plant survival within the first year after planting. Too much water

is often a greater problem than too little because the roots of plants do not receive enough oxygen.

Routine maintenance of constructed wetlands includes repair of fences, mowing of sod/

ground cover on embankments, and removal of trash accumulated in trash racks, outlet structures,

and valves. Burrowing animals may damage embankments and spillways. They can be discouraged

by including a thick layer of sand or gravel on the fill or by installing a wire screen to inhibit

burrowing. Organic matter accumulating in the wetland will eventually limit storage capacity

and the capacity to treat runoff. Accumulation of organic matter can be reduced by harvesting of

vegetation or seasonal drawdown to allow organic material to oxidize. Periodic sediment removal

from the forebay is necessary

Mosquito problems are one of the more frequently cited drawbacks of constructed wetlands. Mosquitoes can be more of a problem in wetlands with tall cattails and bulrushes than

those with lower-growing vegetative forms due to the protection from predators afforded by the

taller plants. Cattails can be controlled by flooding for several weeks during the growing season

after the stems have been cut (stems need to be cut below the water level). Biological control of

mosquitoes can be enhanced by stocking the wetland with fish that are tolerant of low dissolved

oxygen conditions. Mosquitoes can also be controlled through judicious application of mosquito

larvicide using the optimum dosage level and applying only when larval density is high.

Page 4-53
Sources of Additional Information

Definition/Purpose

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Davis, L. 1995. A handbook of constructed wetlands, A guide to creating wetlands for: Agricultural wastewater

domestic wastewater, Coal mine drainage, and stormwater in the Mid Atlantic region. 5 vols. U.S. Department of

Agriculture, U.S. Environmental Protection Agency, and Pennsylvania Department of Environmental Resources.

Gibb, A.., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242).

Hammer, D. A. 1992. Creating freshwater wetlands. Lewis Publishers, Boca Raton, FL.

Kadlec, R. and R. Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, FL.

Land Management Project. 1990. Artificial wetlands. BMP fact sheet #3. U.S. Environmental Protection

Agency and Rhode Island Department of Environmental Management, Land Management Project,

Providence, RI.

Schueler, T.R. 1987. Controlling urban runoff A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs- Porous Pavement and Concrete Grid

Pavement

Porous pavement is an alternative to conventional pavement designed to minimize surface

runoff. It may be constructed of asphalt or concrete and is similar to regular paving material

except that a larger-sized aggregate is used in the asphalt or concrete mixture to provide a highvoid course. Porous pavement is composed of four layers: the pavement course, the upper filter

course, a stone reservoir, and a lower filter course and filter fabric lining over the underlying soil

(see Figure 4-20).

A similar practice is concrete grid pavement, where modular, interlocking concrete blocks

having openings are used (see Figure 4-21). Runoff that permeates the porous pavement surface

enters an underground stone reservoir and gradually exfiltrates from the reservoir into the

surrounding subsoil.

Porous pavement can help to restore or maintain predevelopment hydrology by reducing the

volume of stormwater runoff produced after development relative to runoff volumes generated

from roads and parking lots paved with conventional surfaces. By increasing the amount of

infiltration, porous pavement can provide groundwater recharge, low flow augmentation, and

stream bank erosion control through reduction of peak discharges. Pollutants are removed by

absorption, straining, and microbial decomposition as stormwater seeps through the subsoil.

Sediments and particulate-associated pollutants are removed in the underground stone reservoir.

The use of porous pavement has added advantages in that it reduces land consumption, reduces or

eliminates the need for curb and gutters and conveyance systems, and reduces the tendency of

vehicles to hydroplane and skid. Other benefits can include storm detention and preservation of

water supplies to the vegetation around parking areas.

Page 4-54
Best Management Practices

Scope/Applicability

The use of porous pavement is constrained to sites having deep and permeable soils, slopes

less than 5 percent, restricted truck traffic, and suitable adjacent land uses. The use of porous

pavement can also be restricted in regions with colder climates, arid regions or regions with high

wind erosion rates, and areas having sole-source aquifers. It is generally used only for parking lots

(between 0.25 acre and 10 acres in size) and lightly used access roads. Porous pavement is used

when the size of the development, or the lack of available space, limits the use of other BMPs. It

has limited retrofit capability because most soils in urbanized areas have been previously modified

to the extent that they are not capable of providing adequate infiltration rates. Porous pavement,

designed with an underdrain, can be used in areas where underlying soils, groundwater depth, or

bedrock restrict the ability of runoff to be disposed of by infiltration. Porous pavement reservoirs

with underdrains serve as underground detention facilities.

Schueler. 1992.

Detail of cross section.

Filter Course (Gravel, 2

Filter Fabric Layer

Undisturbed Soil

Porous Pavement Course

(2.5-4.0 lnches Thick)

Filter Course

(0.5 Inch Diameter Gravel,

1 .0 Inch Thick)

Stone Reservoir

(1.5-3.0 Inch

Diameter Stone)

Depth Variable Depending

on the Storage Volume

Needed, Storage Provided

by the Void Space Between

stones

Deep)

Schueler, 1992.

Figure 4-20. Schematic cross section of a porous pavement system with storage reservoir.

Page 4-55
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Design Criteria Considerations

l Field-verified infiltration rates greater than or equal to 0.5 inch per hour.

l Site area of less than 10 acres with minimal contributions of runoff from the surrounding

watershed.

l Slopes less than 5 percent.

l Minimum clearance of 3 ft from the bottom of the system to the groundwater table.

l Filter fabric lining to prevent the upward piping of underlying clays.

Reservoir of variable depth containing clean, washed, l- to 2-inch-diameter stone.

l Overlying filter course of 0.5- to l-inch gravel.

l Use of underdrains if well-drained conditions are lacking at a site.

l 20-ft-wide grass buffer around the pavement to filter pollutants from runoff contributed

by adjacent areas, if applicable.

Castellated Unit

Poured-in-Place Slab

Lattice Unit

Modular Unit

State of Washington, 1992.

Figure 4-21. Variations of concrete grid pavement.

Page 4-56
Maintenance

Potential Impacts to Wetlands

Limitation

Best Management Practices

Porous pavement requires quarterly vacuum sweeping and/or jet hosing to maintain porosity and prevent clogging. Sediments will accumulate where water is concentrated. These can be

removed by a vacuum cleaning street sweeper equipped with a brush followed by jet hosing.

Porous asphalt and concrete require no more additional maintenance than conventional paving

materials. Buffer strips surrounding the pavement will need mowing. Surfaces paved with

modular concrete blocks with open lattice might require mowing of grass growing up between the

lattice. Mowing is seldom required in areas of frequent traffic. Poured-in-place concrete grid

pavements can be plowed as long as the plow blade is set high enough to prevent damage to grass.

Fertilizers and deicing chemicals should not be used on concrete grid pavement because these

chemicals can damage the concrete. The application of abrasive material, such as sand or ash, in

times of heavy snowfall should be avoided due to the potential for clogging of the surface.

Cleaning techniques are effective only in restoring porous pavement that has reductions in

permeability of less than about 25 percent. Clogging may also be alleviated by drilling 0.5-inch

holes through the pavement every few feet. If severe clogging should occur, complete replacement

is required. Potholes and cracks can be repaired using conventional nonporous patching compounds as long as the cumulative area being patched is minimal.

Porous pavement should be inspected several times in the first few months after construction and annually thereafter. Inspections of the pavement should be scheduled after major storms

so that areas of standing water can be identified. Water standing on the pavement might indicate

local or widespread clogging. The condition of the buffer strips adjacent to the pavement should

also be checked at the time of inspection.

Benefits

l Reduction in the amount of stormwater-associated pollutants entering adjacent wetlands.

l Reduction of stormwater sediment loads to adjacent wetlands.

l Reduction in the potential for adjacent wetland degradation resulting from erosion

associated with peak stormwater flows.

l Potential recharge of groundwater from infiltration, benefiting adjacent baseflowdependent wetlands.

l Might not adequately attenuate concentrated peak stormwater flows to adjacent

wetlands.

l Possible reduction in the amount of surface water supplied to adjacent surface-flowdependant wetlands as a result of rerouting.

l Not appropriate for high traffic areas or surfaces receiving frequent heavy vehicle traffic.

Page 4-57
Definition/Purpose

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Sources of Additional Information

Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia

Department of Conservation and Recreation, Division of Soil and Water Conservation. Richmond, VA.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and wafer management. Stormwater/Nonpoint Source Management Section FIorida Department of

Environmental Regulation, Tallahassee, FL.

Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Schueler, TR., P.A.. Kumble, and M.A.. Harity. 1992. A current assessment of urban best management practices:

Techniques for reducing non-point source pollution in the coastal zone. Technical guidance to implement section

6217(g) of the Coastal Zone Management Act. Prepared for the U.S. Environmental Protection Agency,

Office of Wetlands, Oceans, and Watersheds, Washington, DC.

Urbonas, B., and P. Stahre, 1993. Stormwater: Best management practices and detention for water quality,

drainage, and CSO management. PTR Prentice Hall, Englewood Cliffs, NJ.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

An oil/grit separator or water quality inlet is an underground concrete vault that can have

from one to three chambers. These structures are designed to remove sediments and hydrocarbons

from stormwater runoff associated with roads and parking lots before it is discharged into the

storm sewer system or an infiltration BMP. Several different designs, which vary in their purpose,

removal mechanisms, space requirements, and stormwater retention capacities, are used. Some

are designed simply for spill control and have limited capacity to treat the dispersed oil found in

stormwater runoff from parking lots. Spill control oil/water separators consist of a chamber with

a submerged orifice that allows the oil to float at the top of the chamber, where it can be removed.

Other separator designs have multiple chambers and use sophisticated equipment to remove

oil from the surface and particles settled at the bottom. The American Petroleum Institute (API)

oil-water separator and the Coalescing Plate Separator (CPS) are two designs used in the State of

Washington. The hydraulic conditions for oil removal by the API separator are promoted by

baffles. The CPI separator contains a series of fiberglass or polypropylene plates that promote the

process of oil separation. Three-chambered oil/grit separators typically contain permanent pools

of water and are designed to remove oils by providing long contact times with particles so that

sorption onto particles will take place and the subsequent removal by gravity settling will occur.

A recently developed design in Canada includes a built-in diversion (bypass) structure. This

feature allows 80 to 90 percent of all rain hours (typically considered to capture most "first flush”

events) to enter the treatment chamber. The larger, problem-causing (flushing) storms (10 to 20

percent of all rain hours) are diverted around the treatment chamber.

Page 4-58
Scope/Applicability

Maintenance

Best Management Practices

Oil/grit separators are used to remove oil, grease, trash, and debris from runoff originating

from heavily trafficked areas such as gas stations, public works, transportation maintenance

facilities, industrial yards, loading areas, or other areas where hydrocarbon pollutant loads are

expected to be significant. Water quality inlets are frequently used to pretreat runoff before it is

conveyed through the storm drain network, or before treatment by a local infiltration BMP such

as an infiltration trench. Oil/grit separators provide minimal groundwater recharge, low flow

augmentation, peak runoff attenuation, or stream bank erosion control benefits. Figure 4-22

shows two views of a typical oil/grit separator.

Oil/grit separators, when used alone, are restricted to highly impervious catchments of small

size (less than or equal to 2 acres) such as service stations, parking lots, convenience stores, and

fast food outlets. Oil/grit separators are adaptable for use in all regions of the country and are

frequently used as part of a series of BMPs. They are commonly used as pretreatment devices for

infiltration BMPs. Oil/grit separators can also be used as a pretreatment device for pond-type

BMP systems, to prevent oily sheens from developing on pond surfaces, and to remove trash.

Design Criteria Considerations

Typically serve an area of less than 1 acre.

Horizontal velocity less than 3 ft per minute or 15 times the rise rate, whichever is

smaller.

Depth 3 to 8 ft.

Width 6 to 16 ft.

Use of baffles to prevent resuspension.

Removal covers that allow access for observation and maintenance.

Maximum pool volume in three chambered separators in the first and second chamber.

Chambers should be sized to provide at least 400 ft of wet storage per contributing acre.

Use of trash racks welded to the end plates between the first and second chambers in

multiple-chambered separators.

Upstream flow control to prevent the flushing of accumulated pollutants during major

storms.

Although the structural failure rate of water quality inlets is very low relative to other

stormwater treatment devices, regular removal of accumulated sediments and debris is critical to

achieving any degree of pollutant removal effectiveness. Material that accumulates in the oil/grit

separator must be removed promptly or it might be flushed from the device during the next storm,

resulting in a pulse of highly concentrated contaminants to receiving waters. Cleanouts should be

performed at least twice a year, and weekly inspections are recommended. Separators should be

cleaned in time for the rainy season and after the first storm of the season.

Page 4-59
Sources of Additional Information

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Side View

Schueler, 1987.

Figure 4-22. Two views of an oil/grit separator.

Limitations

l Primarily function as a water quality BMP and might not adequately attenuate concentrated peak stormwater flows to adjacent wetlands.

l Possible reduction in the amount of surface water supplied to adjacent surface-flowdependent wetlands as a result of rerouting.

l Potential negative impacts to adjacent or downstream wetlands from pollutants

associated with improperly maintained separators.

Gibb, A.., B. Bennett, and A.. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.

Prepared for the Greater Vancouver Regional District, the Municipality of Surrey, British Columbia Ministry

of Transportation and Highways, and British Columbia Ministry of Advanced Education and Training.

Document no. 2-51-246 (242).

Romano, F. 1990. Oil and water don’t mix: The application of oil-water separation technologies in stormwater quality management. Published by the Office of Water Quality, Municipality of Metropolitan Seattle,

Seattle, WA.

Schueler, T.R., P.A.. Kumble, and M.A.. Harity. 1992. A current assessment of urban best management

practices: Techniques for reducing non-point source pollution in the coastal zone. Technical guidance to implement

section 6217(g) of the Coastal Zone Management Act. Prepared for the U.S. Environmental Protection

Agency, Office of Wetlands, Oceans, and Watersheds, Washington, DC.

Page 4-60
Definition/Purpose

Scope/Applicability

Best Management Practices

Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Ontario Ministry of Transportation and National Water Research Institute, Environment Canada. 1994.

Stormwater management facilities inventory study. Burlington, Ontario.

Washington State Department of Ecology. 1992. Stormwater management manual for de Puget Sound Basin.

Publication no.91-75. Washington State Department of Ecology, Olympia, WA.

Strutural BMPs -Level Spreaders

A level spreader is a hydraulic device used to convert channelized flows from an outlet pipe or

culvert to sheet flow by causing the stormwater to spread out through a rock-lined trench before

discharging over a berm, thereby dissipating energy that could cause erosion of downstream areas.

The trench or channel is lined with filter fabric and covered with riprap, gabions, or a slope mattress

to retard flow and provide turbulence. Energy is dissipated as stormwater spreads out over the rocks

and then over the top of the berm. The berm is usually covered with riprap. Higher runoff velocities

may be treated by placing gabions in the trench instead of riprap.

Level spreaders are located at the outlet of channels or culverts and are used to protect a

receiving channel or downstream area from erosion by dissipating fluid energy. Level spreaders

can be used to attenuate erosive flow velocities in stormwater discharges before they reach a

vegetated BMP. They provide a moderate amount of coarse sediment removal and infiltration, but

they are primarily a flow control device rather than a stormwater treatment system. A level

spreader is shown in Figure 4-23.

Level spreaders are used for moderate flows in small drainage areas. One of their primary

applications is to convert channelized flows from culverts to sheet flows upstream of a vegetated

filter strip or grassed swale. They should be constructed in undisturbed soils and discharge to

stabilized areas.

Design Criteria Considerations

l Grass-lined trench used for flows up to 5 ft per second (ft/s).

l Riprap used for flows between 5 and 12 ft/s (median stone size of 8 inches, minimum

thickness of 1 ft used for 5 to 8-ft/s flows; median stone size of 16 inches, minimum

thickness 2 Et used for 8- to 12-ft/s flows).

l Riprap-lined channel not suitable for velocities greater than 12 ft/s or pipe diameters

greater than 3 ft.

l Gabion rock mattress or slope mattress required to transmit flows of very high energy

(between 12 and 20 ft/s).

l Adjust dimensions for varying pipe sizes, flows, and velocities.

Page 4-61
Maintenance

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Level spreaders require inspection and possible repair after large storms.

Potential Impacts to Wetlands

Benefits

l Reduction in the potential for adjacent wetland degradation resulting from erosion

associated with peak stormwater flows.

l Possible reduction of stormwater sediment loads to adjacent wetlands.

l Possible reduction in the amount of stormwater-associated pollutants entering adjacent

wetlands.

Limitations

l Primarily a flow control device and might not adequately improve the water quality of

stormwater flows to adjacent wetlands.

l Might not adequately attenuate concentrated peak stormwater flows to adjacent

wetlands.

Adapted from Milone & MacBroom, Inc.. 1991.

Figure 4-23. Two views of a level spreader.

Page 4-62
Scope/Applicability

Best Management Practices

Sources of Additional Information:

Chow, VT. 1978. Open channel hydraulics. Bureau of Reclamation. Hydraulic design of stilling basins and energy

dissipators. Document No. EM 25.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

/and and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds: A

guide to nonpoint source pollution and mitigation. Prepared for the South Central Connecticut Regional Water

Authority, New Haven, CT.

U.S. Army Corps of Engineers. 1970. Hydrauric design of flood control channels. Document no. EM 1110-2-

1601.

U.S. Department of Transportation, Federal Highway Administration, 1983. Hydraulic design of energy

dissipators for culverts and channels. Hydraulic Engineering Circular no. 14.

Washington State Department of Ecology. 1992. Stormwater management manual fir the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - French Drains

Definition/Purpose

A French drain is a type of exfiltration system that consists of a perforated pipe drain placed

in a deep pit or trench that is filled with coarse open-grade rock. The trench is lined with filter

fabric and can be extended out laterally from the roadway to increase its water holding capacity

Water exfiltrates from the trench and into the surrounding soil. Dutch drains are similar to French

drains except that water enters the Dutch drain through a cast iron grate at the trench surface

instead of from a perforated pipe. Both French drains and Dutch drains are used to store runoff

until it can percolate into the ground.

French drains require permeable, well-drained soils. Soil permeability should be sufficient to

provide a reasonable rate of infiltration, and the offset of the water table from the base of the

trench facility should be enough to prevent pollution of the groundwater. Like other infiltration

practices, installation of a catch basin ahead of the drain will help prevent clogging by coarse

sediment and debris.

French drains are typically used in areas where space is restricted. They are normally used to

catch runoff from parking lots, roadways, and roof drains. They are not recommended where

runoff contains a high volume of suspended materials. Presettling, filtering, and oil and grease

separators are recommended for use with French drains if high volumes of suspended materials are

present in the runoff.

Page 4-63
Design Criteria Considerations

Maintenance

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

l Location in suitable soils with infiltration rates of at least 0.5 inch per hour.

l Clearance of 6 to 10 inches between the trench bottom and the seasonal high groundwater level.

l Overflow pipe capable of handling at least a 25year storm event.

l Sediment traps located at least every 150 ft for a French drain.

l Complete drainage within 3 days after a storm to maintain aerobic conditions in the

trench.

l Presettling or filtering of stormwater to remove coarse sediments.

l Sizing of the trench based on volume of runoff to be controlled.

l Use of observation wells to monitor performance.

Newly constructed French drains should be inspected quarterly after initial installation and

after large rainstorms. The frequency of inspections may be decreased after the performance of

the drain is verified, but inspections should be conducted on at least a yearly basis. Observation

wells should be monitored to observe the functioning of the drain. If a filter strip precedes the

drain, it should be inspected for patchy vegetation and erosion or signs of channelized flows.

Sediment that accumulates in the top foot of stone or at the inlet should be checked at the

time of inspection and removed if infiltration rates have been reduced. Sediment that has collected in the sediment trap or pretreatment inlet should be removed periodically

Potential Impacts to Wetlands

Benefits

l Reduction in the amount of stormwater-associated pollutants entering adjacent wetlands.

l Reduction of stormwater sediment loads to adjacent wetlands.

l Reduction in the potential for adjacent wetland degradation resulting from erosion

associated with peak stormwater flows.

l Potential recharge of groundwater from infiltration, benefiting adjacent baseflowdependent wetlands.

Limitations

l Might not adequately attenuate concentrated peak stormwater flows to adjacent

wetlands.

l Possible reduction in the amount of surface water supplied to adjacent surface-flowdependant wetlands as a result of rerouting.

Page 4-64
Definition/Purpose

Scope/Applicability

Best Management Practices

Sources Of Additional Information

Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia

Department of Conservation and Recreation, Division of Soil and Water Conservation.

Dennis, J., J. Noel, D. Miller, C. Eliot. 1989. Phosphorus control in lake watersheds: A technical guide to

evaluating new development. Maine Department of Environmental Protection, Augusta, ME.

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Tahoe Regional Planning Agency. 1988. Water quality management plan for the Lake Tahoe Region: Handbook of

best management practices. Vol. 2.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Dry Wells or Roof Downspout Systems

Dry wells are infiltration pits used primarily to collect rooftop runoff from residential or

commercial buildings, although they can be used to drain small parking lots. Dry wells may be

constructed similar to infiltration trenches, using a filter fabric-lined pit filled with gravel, or

they can consist of an underground perforated concrete tank lined with gravel. The interior of the

perforated concrete structure can be filled with coarse gravel to provide structural stability Some

dry well designs incorporate an outlet pipe leading to a drain field.

Dry wells can be used to reduce the amount of runoff collected at storm sewers and stormwater treatment facilities, especially when runoff from roofs is expected to be relatively clean.

Dry wells increase infiltration and therefore help to recharge groundwater, provide base flow in

streams, and reduce peak runoff volumes and stream bank erosion.

Dry wells are suitable for use in areas where the subsoils are sufficiently permeable to

provide reasonable infiltration rates and where there is sufficient offset to the groundwater. Their

use is restricted to small sources of runoff such as from roof drains, small parking lots, and tennis

courts. Roof downspout systems may be used to replace direct connections to sanitary sewers or

storm sewers. They are adaptable to retrofitting in subdivisions because they are small, inexpensive, and relatively simple to install. Because dry wells provide minimal treatment of roof runoff,

they should not be used in areas where air deposition of pollutants constitutes a major portion of

the nonpoint source pollutant loads. A typical dry well/infiltratrion pit is shown in Figure 4-24.

In areas where runoff contains high concentrations of suspended materials, a method of settling

or pretreating runoff that filters out particles should be provided. Dry wells may be installed

under pavement if they are equipped with a small yard drain or grate-covered catch basin to

channel any overflow away from the overlying pavement.

Page 4-65
Maintenance

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Design Criteria Considerations

l Location in suitable soils having sufficient infiltration rates, preferably greater than 0.5

inch per hour.

l Water table offset of at least 3 ft from the bottom of the well.

l Detention time between 48 to 72 hours to allow for adequate pollutant removal.

l Complete drainage of well within 3 days to maintain aerobic conditions.

l Use of an observation well to monitor performance.

l Filter fabric wrapped completely around the aggregate rock.

l Length not to exceed 100 ft from the inlet sump.

Line pits for precast concrete dry wells with a minimum of 1 ft of 0.75inch stone.

l Avoid placement under pavement whenever possible.

l Overflow drain for wells that are located beneath the pavement.

Dry wells and infiltration pits should be inspected frequently for proper drainage upon

completion of construction and annually thereafter once performance of the device has been

verified. Maintenance and inspection practices differ between dry wells and infiltration pits. Dry

wells require periodic maintenance and inspection to prevent clogging and eventual failure.

Filtering the stormwater through a fine mesh geotextile material will remove sediments and

prevent premature clogging. The cap on a perforated concrete dry well can be removed for water

level inspection and sediment removal. If the dry well becomes clogged, the rocks inside the

concrete well will need to be removed. Sediments blocking the openings in the perforated lining

should also be removed. After the rocks are removed, the well should be tested for drainage. If

drainage rates are unsatisfactory, the precast concrete well might have to be removed. The pit

itself might need to be enlarged if the soil adjacent to the well has become clogged. The dry well

should then be rebuilt using clean rocks.

The maintenance of dry wells and infiltration pits is similar to that for an infiltration

trench. An observation well installed in an infiltration pit will facilitate the inspection of water

levels after storms. Frequent inspections are required during the rainy season. The accumulation

of sediments in the top foot of stone aggregate or the surface inlet should also be monitored on

the same schedule as the observation well to check for surface clogging. Clogging of the device is

usually due to the accumulation of sediments between the upper layer of stone and the protective

layer of filter fabric. When infiltrative capacity is significantly reduced, sediment should be

removed from the top of the infiltration pit by removing the stone, replacing the filter fabric, and

washing or replacing the stone.

Potential Impacts to Wetlands

Benefits

l Reduction in the potential for adjacent wetland degradation resulting from erosion

associated with peak stormwater flows.

Page 4-66
Best Management Practices

Side View

Adapted from Milone & MacBroom. Inc., 1991.

Figure 4-24. Dry well/infiltration pit.

l Possible reduction in sediment transport to adjacent wetlands resulting from reduced

overland flow.

l Potential recharge of groundwater from infiltration, benefiting adjacent baseflowdependent wetlands.

Limitations

l tight not adequately attenuate concentrated peak stormwater flows to adjacent wetlands.

l Possible reduction in the amount of surface water supplied to adjacent surface-flowdependent wetlands as a result of rerouting.

l May not adequately improve the water quality of stormwater flows to adjacent wetlands.

Sources of Additional lnformation

Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia

Department of Conservation and Recreation, Division of Soil and Water Conservation.

Page 4-67
Definition/Purpose

Scope/Applicability

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Livingston, E., E. McCarron, C. Cox, and P Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Schueler, T.R. 1987. Controlling urban runoff A practical manual for planning and designing urban BMPs.

Metropolitan Washington Council of Governments, Washington, DC.

Urbonas, B., and P. Stahre, 1993. Stormwater: Best management practices and detention for water quality,

drainage, and CSO management. PTR Prentice Hall, Englewood Cliffs, NJ.

Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.

Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.

Structural BMPs - Exfiltration TrencheS

Exfiltration trenches are a series of underground slotted pipe sections that temporarily store

stormwater while it exfiltrates into the underlying soil through perforations or slots in the pipe. A

restrictor plate is placed at the end of the exfiltration pipe that controls the flow of water out of

the pipe by using a high-level overflow device or a restrictive orifice. Exfiltration trenches require

pretreatment of runoff to remove large particles of sediment and debris that may clog the pipes.

Exfiltration trenches are used to provide groundwater recharge and a modest amount of

temporary runoff storage. They are frequently used under parking lots to save space and have the

advantage over infiltration basins of being hidden from sight. They can be used in situations where

basins are visually unacceptable. Exfiltration trenches provide some reduction in peak flows especially if they are oversized to store runoff. Pollutants are filtered out as water passes through the soil

under the system. Exfiltration trenches may be applied in moderately and well drained soils on low

to moderate slopes. Two views of an exfilteration system are shown in Figure 4-25.

SLOTTED PIPE SECTION

OR SLOTS

END SECTION

Adapted from Milone & MacBroom, Inc. 1991.

Figure 4-25. Two views of an exfiltration system.

Page 4-68
Maintenance

Best Management Practices

Design Criteria Considerations

l Two- to 4-ft offset from the pipe invert to groundwater.

l Two- to 4-ft offset to bedrock.

l Settle or filter runoff to remove solids.

l Level placement of pipes with no slope.

l Size for 0.5inch runoff minimum before overflow.

l Use in combination with a stone bed to increase storage capacity.

Exfiltration trenches require preventive maintenance to function effectively. Frequent

cleanout of sediment traps and the maintenance or replacement of settling or filtering measures

might be necessary If clogging of the facility occurs, replacement of the exfiltration trench might be

required.

Potential Impacts to wetlands

Benefits

l Reduction in the amount of stormwater-associated pollutants entering adjacent wetlands.

l Reduction of stormwater sediment loads to adjacent wetlands.

l Reduction in the potential for adjacent wetland degradation resulting from erosion

associated with peak stormwater flows.

l Potential recharge of groundwater from infiltration, benefiting adjacent baseflow dependent wetlands.

Limitations

l Might not adequately attenuate concentrated peak stormwater flows to adjacent wetlands.

Possible reduction in the amount of surface water supplied to adjacent surface-flowdependent wetlands as a result of rerouting.

Sources of Additional Information

Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound

land and water management. Stormwater/Nonpoint Source Management Section Florida Department of

Environmental Regulation, Tallahassee, FL.

Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds: A guide

to nonpoint source pollution and mitigation. Prepared for the South Central Connecticut Regional Water Authority,

New Haven, CT

Page 4-69
BMP in Series

Scope/Applicability

Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices

Definition/Purpose

BMPs in series incorporate several stormwater treatment mechanisms in a sequence to

enhance the treatment of runoff. Some examples of serial BMPs include the use of multiple pond

systems, the combination of vegetated filter strips withgrassed swales and detention ponds, and

the combination of grassed swales or vegetated filter strips with infiltration trenches.

By combining structural and/or nonstructural treatment mechanisms in series rather than

using a single method of treatment for stormwater runoff, the levels and reliability of pollutant

removal can be improved. By using serial BMPs, a single desired facility that might not provide the

necessary level of stormwater treatment without sequencing can be used. The effective lifetime

of a BMP can be increased by combining it with a pretreatment device, such as a grassed swale, to

remove suspended particulates prior to treatment in the downstream unit. Sequencing of BMPs

can also reduce the potential for resuspension of deposited sediments by reducing flow energy

levels or by providing longer flow paths for runoff. An example of using BMPs in series is shown

in Figure 4-26.

The feasibility of using serial BMPs on a site depends on the characteristics of the individual

components in the sequence.

Top View Side View

Adapted from Schueler, 1991.

Figure 4-26. Example of BMPs in series.

Page 4-70
Sources of Additional Information

Best Management Practices

Design Criteria Considerations

Design criteria considerations depend on the requirements of the individual BMPs. The

least expensive and most easily maintained component should be placed at the most upstream

position in the series.

Maintenance Requirements

The maintenance requirements for serial BMPs depend on the requirements of the individual components of the system. (Refer to the individual BMP fact sheets.) A firmly established

maintenance and inspection program that addresses both routine and nonroutine tasks is necessary to ensure that the system functions as designed.

The placement of the least costly and most easily maintained BMP at the most upstream

position in the series can reduce the maintenance requirements for the downstream components

in the system. If the overall system is designed properly, the cost for maintenance of the individual components of the system can be reduced.

Potential Impacts to Wetlands

The potential impacts resulting from the placement of serial BMPs above, adjacent to, or

within wetlands will depend on the components of the system. The potential positive or negative

impacts of the individual components should be considered. The potential impacts of the individual components of the serial BMP should then be evaluated as a whole to determine their

possible impact to adjacent or downstream wetlands.

Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared

for Occcquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission, Annandale, VA.

Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning

designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,

Annandale, VA.

Schueler, TR., P.A.. Kumble, and M.A.. Heraty. 1992. A current assessment of urban best management practices,

techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington

Council of Governments, Washington, DC.

Page 4-71