United States Environmental Protection Agency EPA-822-R-06-001

Office of Water May 2006

 

Office of Research and Development

FRAMEWORK FOR DEVELOPING 

SUSPENDED AND BEDDED SEDIMENTS (SABS) 

WATER QUALITY CRITERIA
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EPA-822-R-06-001 

May 2006 

 

Framework for Developing Suspended 

and Bedded Sediments (SABS) Water 

Quality Criteria 

Office of Water (OW) 

Office of Science and Technology (OST) 

Health and Ecological Criteria Division (HECD) 

Ecological and Health Process Branch (EHPB) 

Washington, DC 

Office of Research and Development (ORD) 

National Center for Environmental Assessment (NCEA) 

Washington, DC 

National Exposure Research Laboratory (NERL) 

Cincinnati, OH 

National Health and Environmental Effects Research Laboratory (NHEERL) 

Research Triangle Park, NC 

National Risk Management Research Laboratory (NRMRL) 

Cincinnati, OH 
TABLE OF CONTENTS

List of Tables ................................................................................................................................ iv 

List of Figures .................................................................................................................................v 

Note to Reader/Disclaimer ............................................................................................................ vi 

List of Acronyms .......................................................................................................................... vii 

Acknowledgments ......................................................................................................................... ix 

Executive Summary ...................................................................................................................... xi 

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

I.A. Purpose of This Document ......................................................................................1 

I.B. The Need for SABS Criteria ...................................................................................2 

I.B.1. Suspended and Bedded Sediments (SABS) ................................................3 

I.B.2. Summary of the Ecological Effects of SABS .............................................4 

I.B.3. State Needs Survey .....................................................................................6 

I.B.4. Application of this Framework for Developing Water Quality 

 Criteria and Standards .................................................................................7 

I.B.5. U.S. EPA-OW/OST Standards and Criteria Strategy .................................8 

I.C. Current Water Quality Criteria Related to SABS ...................................................9 

I.C.1. Existing / Current U.S. EPA Criteria ..........................................................9 

I.C.2. State Criteria ...............................................................................................9 

I.D. Recommendations of the U.S. EPA Science Advisory Board ..............................10 

II. Programmatic Elements of SABS Criteria Development ...........................................13 

II.A. Possible Uses of this Framework...........................................................................13 

II.B. Resources for Framework Implementation ...........................................................13 

II.C. Integration of the SABS Framework with Existing State Programs ....................14 

II.D. Implementation of SABS Criteria and Standards .................................................15 

II.D.1. Management Options ................................................................................17 

 II.D.2. Evaluation .................................................................................................19 

III. Technical Elements of SABS Criteria Development ....................................................21 

III.A. Need for a Technical Discussion in This Framework ..........................................21 

III.B. Process for SABS Criteria Development ..............................................................21 

III.B.1. Step 1 Review Current Designated Uses and Criteria for a Set 

 of Waterbodies .........................................................................................23 

III.B.2. Step 2 Describe SABS Effects on the Waterbodies’ 

 Designated Uses ......................................................................................25 

III.B.3. Step 3 Select Specific SABS & Response Indicators ..............................25 

III.B.4. Step 4 Define Potential Ranges in Value of SABS and 

 Response Indicators .................................................................................28 

III.B.5. Step 5 Identify a Response Indicator Value that Protects the 

 Designated Use ........................................................................................29 

III.B.6. Step 6 Analyze and Characterize SABS/Response Associations ............30 

III.B.7. Step 7 Explain Decisions that Justify Criteria Selection .........................31 

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III.C. Cross-Cutting Concepts ........................................................................................32 

III.C.1. Classification of Waterbodies .................................................................32 

III.C.2. Indicators - Exposure and Response Measurements ...............................34 

III.C.3. Integration and Synthesis of Multiple Methods.......................................37 

III.D. Methods Applicable within the Framework .........................................................37 

III.D.1. Measurements of SABS; Applicable in Step 3 of the Framework ..........40 

III.D.2. Waterbody Classification; Applicable in Step 4 of the Framework ........46 

III.D.3. Associating Suspended and Bedded Sediments with Response...............52 

III.E. Hypothetical Examples of the Synthesis of Methods within the Framework .......69 

III.E.1 Example: Northeastern Headwater Streams.............................................73 

 III.E.2 Abbreviated Examples .............................................................................81 

REFERENCES CITED ............................................................................................................. 85

APPENDICES 

A Glossary of Terms................................................................................................. 95 

B Impacts of SABS................................................................................................... 99 

C State Needs Survey, Conducted in 2004............................................................. 105

D SABS-Related Criteria for Surface Water Quality ............................................. 111 

E Consultation with the Science Advisory Board.................................................. 141 

F Conceptual Models of SABS Sources and Effects............................................. 147

iii
LIST OF TABLES

1. Ranks of SABS stressors among all stressor types .............................................................2 

2. Sequential elements of a SABS management program ....................................................16 

3. Issues and management options for addressing SABS imbalances by 

 waterbody type...................................................................................................................18 

4. Suitability of SABS indicators by waterbody type ............................................................35 

5. Summary of Chesapeake Bay water clarity criteria for application to 

shallow-water bay grass designated use habitats...............................................................60 

6. Advantages and disadvantages of methods used in SABS criteria development ..............70 

7. Specific applications of the methods used in the hypothetical model for criteria 

development and application .............................................................................................72 

8. Decision rationale for selecting a suspended sediments criterion .....................................78 

9. Decision rationale for selecting a bedded sediments criterion...........................................80 

iv
LIST OF FIGURES

1. Conceptual diagram of SABS effects in estuaries. ..............................................................5 

2. Activities and outputs of the SABS criteria development process....................................22 

3. Seven steps of the SABS criteria development process and relationship 

to four activities in Figure 2...............................................................................................24 

4. Conceptual linkages among sources of sediment stress and aquatic ecosystem health.....26 

5. Suspended sediment transport curves for South Fork Forked Deer and Hatchie River ....41 

6. RBS in streams of the Coast Range ecoregion of Oregon and Washington 

as a function of a relative disturbance gradient in hard volcanic and soft 

 sedimentary geologies........................................................................................................45 

7. RBS in streams of the Coast Range ecoregion in relation to EPT taxa richness...............45 

8. Turbidity in Oregon streams by reference status and erodibility.......................................50 

9. Various stream type succession scenarios .........................................................................52 

10. Quantile regression of the 90th percentile of intolerant invertebrate taxa over a 

full range of percent fines in Minnesota streams in two groups of ecoregions ................57 

11. Availability of light for underwater grasses is influenced by water column and 

at-the-leaf surface light attenuation ...................................................................................58 

12. Mid-Atlantic region of the U.S. with EMAP wadeable stream sampling sites. ................65 

13. Reverse cumulative distribution function (CDF) for percent fines in the substrate 

for stream miles across entire area (all), and reverse conditional CDFs of stream

miles for impacted benthic conditions, unimpacted benthic conditions,

and reference conditions....................................................................................................66

14. Probability of observing EPT taxa richness <9 in mid-Atlantic streams if 

specified value of percent fines in the substrate is exceeded ............................................67 

15. Conceptual model for the Northeastern headwater stream example .................................74 

v
NOTE TO READER 

This document is designed as a framework with a recommended process and methods for 

developing suspended and bedded sediment criteria. It is not a substitute for the CWA or U.S. 

EPA’s regulations; nor is it a regulation itself. The Framework does not impose legally binding 

requirements on U.S. EPA, states, tribes, territories or the regulated community, and the 

recommendations may not apply to some particular situations. U.S EPA, state, tribal, and 

territorial decision-makers retain the discretion to adopt methods on a case-by-case basis that are 

appropriate to their SABS needs. As research results and new information become available, 

U.S. EPA expects to revise this document. 

vi
LIST OF ACRONYMS 

BPJ Best Professional Judgment 

BMP Best Management Practice 

CCC Criterion Continuous Concentration 

CCDF Conditional cumulative distribution function 

CDF Cumulative distribution function 

CI Confidence interval 

CMC Criterion Maximum Concentration 

CPA Conditional probability analysis 

CSREES Cooperative State Research, Education, and Extension Service 

CWA Clean Water Act 

DIN Dissolved inorganic nitrogen 

DIP Dissolved inorganic phosphorus 

EMAP U.S. EPA Environmental Monitoring and Assessment Program 

U.S. EPA U.S. Environmental Protection Agency 

EPT Ephemeroptera, Plecoptera, and Trichoptera metric of mayflies, stoneflies, and 

caddisflies 

GIS Geographic Information System

HDI Human Disturbance Index 

HQ U.S. EPA Headquarters 

IBI Index of Biotic Integrity 

LA Load Allocations for non-point sources of pollution 

LANDSAT Land Remote-Sensing Satellite 

MPRSA Marine Protection, Research, and Sanctuaries Act 

NAWQA USGS National Water Quality Assessment Program

NMFS NOAA National Marine Fisheries Service 

NOAA National Oceanic and Atmospheric Administration 

NPDES National Pollutant Discharge Elimination System

NRCS Natural Resources Conservation Service 

NTU Nephelometric turbidity units 

vii
ODEQ Oregon Department of Environmental Quality 

ORD U.S. EPA Office of Research and Development 

OST U.S. EPA Office of Science and Technology 

OWOW U.S. EPA Office of Wetlands, Oceans, and Watersheds 

PLL Percent Light-at-the-Leaf 

PLW Percent Light-through-Water 

RBS Relative Bed Stability 

RIVPACS River Invertebrate Prediction and Classification System

RTAG Regional Technical Advisory Groups 

SABS Suspended and Bedded Sediments 

SAV Submerged Aquatic Vegetation 

SRI Sediment Risk Index 

SSC Suspended-sediment concentration 

STC Sediment Transport Curves 

TMDL Total Maximum Daily Load 

TSS Total suspended solids 

UAA Use Attainability Analysis 

USDA U.S. Department of Agriculture 

USFS U.S. Forest Service 

USFWS U.S. Fish and Wildlife Service 

USGS U.S. Geological Survey 

WARSSS Watershed Assessment of River Stability and Sediment Supply 

WLA Waste Load Allocation for point sources of pollution 

WQC Water quality criteria 

WQS Water quality standard 

viii
ACKNOWLEDGMENTS

The U.S. EPA Science Advisory Board is acknowledged for valuable input during an October 

2003 consultation. The Board consisted of scientists and technical experts that met to review and 

discuss potential methods for developing water quality criteria for suspended and bedded 

sediment (SABS) as described in a discussion paper prepared and presented by U.S. EPA staff. 

We greatly appreciated states and staff who responded to a survey of states’ needs regarding 

SABS criteria. GLEC, Inc. and Tetra Tech, Inc. provided contractual support for this document. 

Ben Jessup of Tetra Tech was responsible for much of the editing and document compilation. All 

inquiries about this document should be directed to Robert Cantilli by e-mail at 

Cantilli.Robert@epamail.epa.gov. 

Primary Authors 

HECD-OST-OW, HQ 

Robert Cantilli* 

Rick Stevens 

William Swietlik 

AWPD-OWOW-OW, HQ

Douglas Norton 

ORD-NHEERL 

Walter Berry (Narragansett) 

Phil Kaufmann (Corvallis) 

John Paul (Research Triangle Park) 

Robert Spehar (Duluth) 

ORD-NRMRL

Susan Cormier (Cincinnati) 

Contributing Authors 

ORD-NHEERL 

Debra Taylor (Duluth) 

ORD-NRMRL 

Christopher Nietch (Cincinnati) 

Tetra Tech, Inc.

Benjamin Jessup 

Peer Review

U.S. EPA (Chesapeake Bay) Iowa Department of Natural Resources 

Richard Batiuk Mary Skopec 

United States Geological Survey The Center for Computational Hydroscience 

John Gray and Engineering 

 Sam Wang

ix
Technical Support and Document Review

HECD-OST-OW, HQ 

George Gibson 

Steve Potts 

Randy Wentsel 

SHPD-OST-OW, HQ 

Thomas Gardner 

Robert Shippen 

ORD-NHEERL 

Brian Hill (Duluth) 

Brian Melzian (Narragansett) 

Norman Rubinstein (Narragansett) 

OWOW-AWPD

Katie Wolff 

ORD-NCEA

Michael Griffith (Cincinnati) 

Kate Schoffield (HQ) 

ORD-OSP

Erik Winchester 

OGC (HQ)

Peter Ford 

U.S. EPA Region 4

Jim Harrison (Atlanta) 

U.S. EPA Region 8

Mitra Jha (Denver) 

Jim Luey (Denver) 

Ministry of Water, Land, and Air Protection, 

Victoria, BC 

Charles Newcombe 

Idaho (DEQ)

Don Essig 

Oregon Dept. of Environmental Quality 

Doug Drake 

GLEC, Inc.

Doug Endicott 

Tetra Tech, Inc.

Abby Markowitz 

Michael Barbour 

ECflex Inc.

Elizabeth Evans Fryer 

McNicholas High School

Claire K. Racine 

*Principal U.S. EPA contact 

Cover Photograph 

Iron River, WI, (1999) near its confluence with Lake Superior 

Courtesy of Anett Trebitz and John Morrice 

U.S. EPA 

Mid-Continent Ecology Division 

Duluth, MN 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

EXECUTIVE SUMMARY 

Suspended and bedded sediments (SABS) occur naturally in all types of waterbodies. In 

appropriate amounts, sediments are essential to aquatic ecosystems (e.g., in appropriate amounts, 

SABS can contribute to essential habitat for aquatic species’ growth and reproduction). 

However, imbalanced sediment supply has repeatedly ranked high as a major cause of 

waterbody impairment (U.S. EPA 2003a). The quantity and characteristics of SABS can affect 

the physical, chemical, and biological integrity of streams, lakes, rivers, estuaries, wetlands, and 

coastal waters. Excessive SABS (and in some cases, insufficient SABS) can impair waterbody 

uses such as navigation, recreation, and drinking water filtration. An imbalanced sediment 

supply resulting from human activities impacts ecological integrity at several scales and trophic 

levels. 

In 2003, the U.S. EPA Office of Science and Technology (OST) within the Office of Water 

(OW) issued a document titled “Strategy for water quality standards and criteria: setting 

priorities to strengthen the foundation for protecting and restoring the Nation’s waters” (U.S. 

EPA 2003a). After a wide-ranging review of the existing water quality standards and criteria 

programs within the context of all clean water programs and after extensive discussions with 

Water Quality Standards stakeholders, U.S. EPA identified 10 priorities for improving the 

quality of the Nation’s waters. Development of SABS criteria was among the top priorities. The 

U.S. EPA developed this document in support of states, tribes and territories’ efforts to establish 

SABS criteria that protect the ecological integrity and beneficial uses of water resources, which 

are major goals of the Clean Water Act (CWA). 

This Framework describes a process that states, tribes, and territories can use to develop SABS 

criteria to support water quality standards and protect designated uses. The Framework is 

intended to provide a consistent, defensible process for developing SABS criteria that also allows 

flexibility for regional and local application and interpretation. The major chapters of the 

Framework include both programmatic and technical elements. The programmatic elements 

section contains discussions of resources, integration with state programs, and implementation of 

criteria and standards. The technical elements section provides analytical methods for SABS 

criteria development. Examples are provided to illustrate how the Framework can be applied. 

Neither the process nor the methods are meant to be mandatory. 

Purpose of Document

The U.S. EPA understands that states, tribes, and territories have an interest in adopting 

consistent scientifically defensible SABS criteria. Towards this goal, the U.S. EPA is 

providing this Framework, with possible methods that states, tribes, and territories can 

use to develop SABS criteria to support water quality standards and protect designated 

uses. This Framework describes what is known and what can be done relative to 

developing SABS criteria and will evolve as research results and new information 

become available. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

This Framework does not intend to prescribe a priority of activities that should be 

undertaken for developing SABS criteria. Nor does this Framework intend to suggest that 

states, tribes, territories, or other water resource managers need to change their existing 

priorities (e.g., switching priorities from one program area to SABS). U.S. EPA is 

providing information that water resource managers could use in developing their SABS 

criteria. 

How Can States, Tribes, and Territories Use this Document? 

States, tribes, and territories that desire to develop and implement SABS criteria may use the 

process and methods described in this Framework. The Framework is flexible, allowing many 

variations in the combination of indicators, classifications, and analytical methods. This 

flexibility allows resource managers to customize the criteria development approach to specific 

needs and capacities. It also encourages justification for the choices made in customizing the 

process. While these methods and processes are explained individually, in practice they will be 

applied simultaneously or in combination. 

With this Framework, states, tribes, and territories are presented with scientifically valid tools 

and technical elements needed for developing criteria, adopting criteria into standards, and 

managing and evaluating performance management actions to support attainment of SABS 

standards. Adopting criteria into standards could proceed in phases (i.e., going from a planning 

phase, to adoption of improved narrative criteria, and then to adoption of improved numeric 

criteria). Management for acceptable SABS conditions and evaluation of SABS criteria 

performance are complimentary processes that can be accomplished by monitoring SABS 

conditions and designated use attainment. 

The Framework for SABS Criteria Development

The Framework for SABS criteria development can be expressed as a seven-step process, 

described as follows. 

1. Review current designated uses and criteria for a set of waterbodies. 

2. Describe SABS effects on the waterbodies’ designated uses. 

3. Select specific SABS criteria and biological response indicators. 

4. Define potential ranges in values of the SABS and biological response indicators. 

5. Identify a response indicator value that protects the designated use. 

6. Analyze and characterize SABS/response associations. 

7. Explain decisions that justify criteria selection. 

The most significant aspect of the Framework is that it ties SABS criteria to levels that protect 

the many uses of waterbodies (e.g., fishing, recreation, swimming, navigation, agricultural uses, 

drinking water supply, and aquatic life). The Framework recognizes that SABS are naturally 

occurring and are often altered by human activities that are not necessarily well managed but 

could be. It recognizes that the level of SABS that is appropriate for one waterbody type, say a 

lake, may not be appropriate for the Mississippi River. To accommodate the range of variability 

in waterbodies, their uses, and natural sediment regimes, the Framework describes methods for 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

classification of waterbodies, measurement of SABS, and measurement of effects. Then criteria 

are selected in an analytical fashion that is scientifically defensible. The criteria are linked to 

human values and are readily understood by a lay audience. No single study or analytical method 

is used or recommended. Rather, the Framework consists of a step-wise process that allows for 

the integration of information from different data sets and different perspectives, thereby 

increasing confidence in the criteria.

Several appropriate technical aspects to the Framework are discussed, including measures taken 

within the water column (e.g., Secchi depth, turbidity, suspended sediment concentration, and 

total suspended solids), within bedded sediments (e.g., percent of fine sediments by extent or 

composition at depth), and within the waterbody environment (channel, shoreline, and 

bathymetric measures). Indicators of designated use impairment (biological response indicators) 

are also discussed, especially biological indicators of SABS impairment. Key determinants of 

appropriateness for indicators are their variability and relative distinction between impaired and 

unimpaired waterbodies and their demonstrated relationship to desirable characteristics and uses 

for those waterbodies. 

Classification of Waterbodies 

SABS conditions vary naturally among broad types of waterbodies such as lakes, rivers, 

wetlands, estuaries, and coastal waters. Furthermore, within each type of waterbody, the supply 

and movement of sediment varies with physiographic, climatic, and geologic characteristics. To 

establish appropriate criteria for sediment, these naturally occurring processes should be 

characterized in as much detail as possible. Natural features such as geology, watershed 

topography, stream gradient, waterbody morphology, vegetative land cover, climate, soil 

erodibility and other landscape characteristics contribute to the variability in sediment supply and 

transport. Development of SABS criteria should take into account the natural conditions and 

variability of the water. Regardless of the method used to derive criteria, the outcome should not 

be beyond the natural expectations. In addition, criteria must protect designated uses. However, 

SABS conditions that reflect pristine conditions may not be necessary to fully protect designated 

uses (i.e., aquatic life and recreation goals may be fully supported by SABS conditions that are 

different than pristine conditions). Criteria will vary with waterbody type and with other natural 

waterbody features with respect to designated uses. The Framework recognizes the potential 

need for different criteria based on classification of waterbodies and natural sediment regimes. In 

fact, the need for classification is addressed in the first step in the Framework and is evaluated 

again in steps 4 and 6, with iteration back to step 1 when refinement is necessary. 

Illustration of Methods for Use in Criteria Development 

The Framework suggests methods that can be used for SABS criteria development. These 

methods are presented to illustrate how states, tribes, and territories may identify appropriate 

indicators, link sediment measures with biotic responses, establish expectations for specific 

waterbodies, define impairment, and evaluate adequacy of SABS models. The methods that are 

presented in this Framework are listed below: 

xiii
Framework for Developing SABS Water Quality Criteria U.S. EPA

(1) Measurement of Suspended and Bedded Sediment 

• Readily Available Measures 

• Sediment Transport Curves 

• Relative Bed Stability 

(2) Waterbody Classification 

• Empirical Classification of Reference Sites 

• Fluvial Geomorphology 

(3) Associating Suspended and Bedded Sediment with Response Indicators 

• Controlled Experiment 

• Field Observational Studies 

– Percentile Analysis (including Reference Condition Methods) 

– Exposures and Effects Analysis 

– Conditional Probability Analysis

• Waterbody Use Functionality 

While each of these methods can be described separately, U.S. EPA recommends that they be 

used together in the Framework to take advantage of the strengths of each. In some cases, a 

method is only useful for one step in the Framework. For instance, basic statistical methods for 

classification of streams are essential for step 1 of the Framework but inadequate to select 

protective criteria. Fluvial geomorphology will alert a resource manager to potential impairment 

and reveal the evolution of changing stream morphology, but will not necessarily provide a 

measure of sediment or impacts to a designated use. Likewise, indicators of the physical 

processes moving sediment supply, such as the Relative Bed Stability method, provide an 

understanding of the deviation from natural conditions but do not tell if the designated use is 

impaired when there is 5% or 50% more sediment. Similarly, whereas the Controlled 

Experiment, Field Observational Studies, and Waterbody Use Functionality methods have the 

potential to link desired designated uses with sediment regimes, they do not automatically enable 

classification. 

During an October 3, 2003 consultation on setting SABS criteria, the U.S. EPA Science 

Advisory Board recommended that the U.S. EPA develop a synthesized approach. This synthesis 

has become the Framework. The Framework includes examples of criteria development 

illustrating the potential synthesis of methods that could be applied to various waterbody types 

and with different designated uses. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

Chapter I. INTRODUCTION 

I.A. Purpose of this Document 

 I. Introduction

 

Suspended and bedded sediments (SABS) occur naturally in all types of waterbodies. In 

appropriate amounts, they are essential to aquatic ecosystems. However, imbalanced sediment 

supplies have repeatedly ranked high as a major cause of waterbody impairment (U.S. EPA 

2003a). The quantity and characteristics of SABS may affect the physical, chemical, and 

biological integrity of streams, lakes, rivers, estuaries, wetlands, and coastal waters. Excessive 

SABS (and in some cases, insufficient SABS) can impair waterbody uses such as aquatic life 

navigation, recreation, and filterable sources of drinking water.

In response to evidence that imbalanced sediment 

supplies have negatively affected water resources 

throughout the United States (U.S. EPA 2000a), the 

U.S. Environmental Protection Agency (U.S. EPA) 

is providing the tools that could support the states, 

tribes, and territories in their efforts to establish 

SABS criteria in water quality standards that protect 

the ecological integrity and beneficial uses of water 

resources. 

This document describes a scientific process for 

establishing SABS criteria that are protective of national water resources and their designated 

uses. This Framework includes (1) an introduction to SABS criteria issues, (2) programmatic 

elements for the SABS criteria development effort, and (3) technical elements for developing 

SABS criteria. The Framework can be implemented by states, tribes, and territories at the local 

and regional levels to meet their specific requirements. 

The Agency is providing the 

tools that could support state, 

tribe and territory efforts to 

establish SABS standards that 

protect the ecological integrity 

and beneficial uses of water 

resources. 

While preparing this document, U.S. EPA consulted various resources, including U.S. EPA 

Water Quality Reports and current state and U.S. EPA criteria for SABS-related measures as 

well as the U.S. EPA Science Advisory Board and state water quality resource managers. The 

results of this preliminary work, along with background on SABS criteria issues, are contained in 

Chapter I (Introduction). Chapter II covers the programmatic elements of the Framework, 

including the actions U.S. EPA may take towards providing additional information and 

implementing the Framework. Chapter III focuses on the technical elements of SABS criteria 

development. This chapter illustrates the direction that the scientific research is taking, or could 

take. The Framework is described as a process that includes distinct activities and steps, concepts 

inherent to the Framework, and methods that can be used within the Framework. The 

Framework is illustrated with actual and hypothetical examples for SABS criteria development. 

1
Framework for Developing SABS Water Quality Criteria U.S. EPA

I.B. The Need for SABS Criteria

The imbalanced loading of SABS to aquatic 

systems is considered one of the major causes of 

water quality impairment in the Nation (U.S. 

EPA 2003a). The 305(b) Water Quality Reports 

have consistently listed turbidity, suspended 

solids, sediment, and siltation as dominant 

polluting factors in rivers and streams, lakes, 

reservoirs, ponds, wetlands, and ocean shoreline 

waters (Table 1). In 1998, approximately 40% 

of assessed river miles in the U.S. had problems 

arising from sediment stress (U.S. EPA 2000a). 

We use the term ‘SABS 

imbalance’ to connote significant 

changes in normal SABS 

loading to aquatic systems (i.e., 

changes in comparison to 

natural patterns that typically 

result in increases or reductions 

in sedimentation). 

 I. Introduction

Table 1. Ranks of SABS stressors among all stressor typesa

 (Modified from Berry et al. 2003). 

Waterbody Type Pollutant/Stressor 1994 1996 1998 2000

Siltationb 2c of 7d Rivers & Streams 1 of 8 1 of 8 2 of 8 

Suspended Solids 7 of 7 7 of 8 

Lakes, Ponds, & Siltation 2 of 7 3 of 7 3 of 7 3 of 7 

Reservoirs Suspended Solids 5 of 7 6 of 7 5 of 7 

Sediment 1 of 9 

Wetlands Sedimentation & 

Siltation 

1 of 8 1 of 7 1 of 6 

Estuariese Siltation, Suspended 

Solids, Sediment, or 

Turbidity 

0 of 7 0 of 7 0 of 7 0 of 7 

Turbidity 4 of 7 2 of 8 2 of 7 3 of 7 

Siltation 5 of 7 

Ocean Shoreline 

Waters

Suspended Solids 5 of 8 4 of 7 4 of 7 a Comparisons of 305(b) National Water Quality Inventory Reports by year and waterbody type. 

b

 For streams, siltation is synonymous with increased embeddedness and percent fines. c

 Rank among Pollutants/Stressors 

d

 Total number of Pollutants/Stressors. As an example, Siltation was ranked second out of the 

seven Pollutants/Stressors found on the table for Rivers & Streams in the 1994 Report. e Note that Siltation, Suspended Solids, Sediment, and Turbidity were not on the estuary lists for 

the 1994, 1996, 1998, and the 2000 305(b) Reports. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

Effects of sediment loading in natural, pristine ecosystems are complex, multi-dimensional and 

not fully understood. Changes in sediment loading caused by human activity – SABS imbalance 

– add further complexity. We use the term ‘SABS imbalance’ to connote significant changes in 

normal SABS levels in aquatic systems (i.e., changes in comparison to natural patterns that 

typically result in increases or reductions in sedimentation). SABS stresses result from changes 

in sediment loads originating from within the watershed that ultimately compromise the 

ecological integrity of the aquatic environment (Nietch et al. 2005). Waterbody impairment due 

to SABS is commonly recognized when aquatic life is impaired. While the biotic effects are the 

focus of much of the criteria development effort, other designated uses such as navigation, 

drinking water sources, recreation, and agriculture are also vulnerable to impairment by SABS 

and are addressed by this Framework. 

 I. Introduction

I.B.1. Suspended and Bedded Sediments (SABS) 

SABS are defined as organic and 

inorganic particles that are suspended in, 

are carried by, or accumulate in 

waterbodies. This definition includes the 

frequently used terms clean sediment, 

suspended sediment, total suspended 

solids, turbidity, bedload, fines, deposits, 

or, in common terms, soils or eroded 

materials. This definition of SABS 

includes organic solids such as algal 

material, particulate detritus, and other 

organic material. SABS are natural parts 

of aquatic systems and are not considered harmful until they are out of balance, that is, excessive 

or deficient. SABS may be a cause of impairment if this material diminishes the quality or 

quantity of the aquatic resource by altering the behavior, health, or survival of biota, the 

availability of habitat, the stability of channels and banks, the natural amount and size 

distribution of particles in the water column and on the bottom and banks of waterbodies, or by 

otherwise impairing designated uses of waterbodies. 

SABS are defined as organic and 

inorganic particles that are 

suspended in, are carried by, or 

accumulate in waterbodies. ... SABS 

are natural parts of aquatic systems 

and are not considered harmful until

they are out of balance, that is, 

excessive or deficient.

SABS are further defined in terms of particle sizes, which are related to the mode of action in the 

aquatic environment. They can be defined as fine sediment and coarse sediment. Fine sediment is 

typically (though not rigidly) considered to consist mostly of particles smaller than 0.85 mm and 

coarse sediment is between 0.85 and 9.5 mm. Particles less than 0.063 mm (silt and clay) remain 

suspended in flowing freshwater and are largely the cause of turbidity but may settle during low 

flow in low gradient streams (Idaho DEQ 2003). 

This Framework addresses the physical properties of SABS and intentionally does not address 

the effects of co-occurring contaminants or nutrients. Nutrient criteria have been developed by an 

U.S. EPA supported effort (see National Nutrient Strategy, U.S. EPA 1998). U.S. EPA has dealt 

directly with the toxicity of chemicals in sediments through its work on Equilibrium PartitioningDerived Sediment Benchmarks (U.S. EPA 2003b, 2005a). U.S. EPA does recognize, however, 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

that managing SABS in the aquatic environment will have consequences on the amount of

toxicants and nutrients associated with SABS and these relationships may need to be examined 

further in future efforts. An example of the integrated assessment of sediments and nutrients is 

described in the technical section using criteria development for the Chesapeake Bay (Section 

III.D.3). 

 I. Introduction

I.B.2. Summary of the Ecological Effects of SABS

The Nation’s waters have many designated uses, including drinking water, navigation, 

recreation, agriculture (such as irrigation), aquatic life, and fishing for sport and food. While 

SABS can affect all of these uses, U.S. EPA is currently focused on SABS effects on aquatic life 

for several reasons. First, when SABS diminish the quality of aquatic life by degrading habitat, 

other uses such as recreational or commercial fishing may also be diminished. Second, there is 

evidence that aquatic-life uses are one of the most sensitive endpoints of altered sediment supply. 

Therefore, measuring and monitoring aquatic organisms may provide an early warning that 

SABS may become problematic for a wide range of uses. Early action may prevent other uses 

from being impacted. This premise influenced water clarity criteria development for the 

Chesapeake Bay, where protection of the vegetative habitat was considered equivalent to 

protection of the species that used that habitat and the larger ecosystem (U.S. EPA 2003c). For 

these reasons, this Framework addresses waterbody designated uses but has a strong focus on 

aquatic life uses (e.g., habitat, foraging, refugia). Because of their importance in ecosystem

functions, the imbalance of SABS can have an impact on ecological integrity at several scales

and trophic levels as depicted in the conceptual model (Figure 1). Therefore, a basic premise for 

managing SABS in waterbodies is the need to maintain SABS at levels that are protective of the 

ecological integrity of aquatic systems. 

SABS differ from toxic pollutants in that SABS, including the organic fraction, occur in 

waterbodies in natural or background amounts and are essential to the ecological functioning of a 

waterbody. In addition, SABS transport toxicants, nutrients, detritus, and other organic matter at 

levels that are critical to the health of a waterbody. SABS in natural quantities also replenish 

intermittently mobile bottom sediments and create valuable micro-habitats, such as pools and 

sand bars. 

Sediments can enter waterways through a wide variety of transport mechanisms, including 

surface water transport, bank erosion, and atmospheric deposition. Once in the system, resuspension and deposition can “recycle” sediments so that they exert water column and benthic 

effects repeatedly over time and in multiple locations. Human activities that increase soil erosion 

or alter rates of sediment transport in waterways (e.g., forestry, mining, urban development, 

agriculture, dredging, channel alteration, and dam construction) are among the most pervasive 

causes of sediment imbalance in aquatic systems (Waters 1995; Nietch et al. 2005). Activities 

that decrease sediment to aquatic systems are numerous and varied. A major cause is man-made 

reservoirs that trap sediment that normally would be carried downstream. Excessive sediment is 

a more common cause of sediment imbalance than is sediment deficiency though both can impair 

ecosystems. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

 I. Introduction

Figure 1. Conceptual diagram of SABS effects in estuaries (courtesy of W. Munns, U.S. EPA). 

5
Framework for Developing SABS Water Quality Criteria U.S. EPA

Excessive suspended sediment in aquatic systems decrease light penetration, directly impacting 

productivity that is especially important in estuarine and marine habitats, where trophic 

interrelationships tend to be more complex and marginal when compared to freshwater aquatic 

systems. Decreased water clarity impairs visibility and associated behaviors such as prey capture 

and predator avoidance, recognition of reproductive cues, and other behaviors that alter 

reproduction and survival. At very high levels, suspended sediments can cause physical abrasion 

and clogging of filtration and respiratory organs. 

 I. Introduction

In flowing waters, bedded sediments are likely to have a more significant impact on habitat and 

biota than suspended sediments; while most organisms can tolerate episodic occurrences of 

increased levels of suspended sediments, impacts can become chronic once the sediment is 

settled. When sediments are deposited or shift longitudinally along the streambed, infaunal or 

epibenthic organisms and demersal eggs are vulnerable to smothering and entrapment. In smaller 

amounts, excess fine sediments can fill in gaps between larger substrate particles, embedding the 

larger particles, and eliminating interstitial spaces that could otherwise be used as habitat for 

reproduction, feeding, and cover for invertebrates and fish. A noteworthy example of effects of 

bedded sediments in streams and rivers is the loss of spawning habitat for salmonid fishes due to 

increased embeddedness. Increased sedimentation can limit the amount of oxygen in the 

spawning beds, which can reduce hatching success, trap the fry in the sediment after hatching, or 

reduce the area of habitat suitable for development. Appendix B details many other direct and 

indirect effects of SABS. 

I.B.3. State Needs Survey

In September 2004, a survey was conducted to solicit input from nine states on the status of 

SABS-related impairment and monitoring in their state, as well as technical, budgetary, and other 

needs for developing numeric SABS criteria. Details of the survey are included in Appendix C. 

The results presented below pertain only to those states surveyed and cannot be extrapolated to 

the entire Nation. Three states (Delaware, New Hampshire, and New York) consider SABS a 

minor or lower priority problem, while states in other parts of the country consider SABS a 

major problem. SABS criteria appear to be partially established for most of the states surveyed 

and are a mix of narrative and numeric criteria and standards. 

Wyoming, for example, has numeric criteria for turbidity but narrative criteria for suspended and 

settleable solids. The programs under which states apply SABS criteria/standards include Total 

Maximum Daily Load (TMDL) reporting, National Pollutant Discharge Elimination System

(NPDES), surface water monitoring programs and various state-level programs. The majority of 

states surveyed use turbidity and total suspended solids (TSS) as indicators for suspended 

sediments; North Carolina also uses Secchi depth and Michigan uses light penetration. Bedded 

sediments are most commonly measured with embeddedness, followed by percent fines, 

Wolman pebble counts, substrate stability, best professional judgment using photos, and 

intergravel dissolved oxygen. 

Most respondents felt the need to improve water quality criteria for SABS in their state. The 

Wyoming respondent suggested that there is a greater need for bedded sediment criteria than 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

suspended sediment criteria, which already exist in many places (as criteria for turbidity or TSS). 

All designated uses, except agricultural uses, were considered vulnerable to SABS impairment. 

Each of the states surveyed envision technical and scientific obstacles to SABS criteria 

development. Some pointed out that, in most waterbodies, SABS occur naturally and with 

significant variability, making the development and application of strict numeric criteria 

difficult. Others mentioned the lack of sound scientific data that could lead to numeric criteria for 

threatened and endangered species. In addition to technical and scientific obstacles, states may 

also face political obstacles where SABS sources are mostly non-point, such as from agricultural 

lands. Louisiana was unique in that sediment starvation in their coastal wetlands was the primary 

concern; their criteria should be sensitive to the state’s efforts at arresting wetland subsidence. 

Program elements considered most useful for SABS criteria development include 

personnel/expertise, money/grants and access to data on SABS effects from scientific literature 

as well as from other states. Some elements of the Framework were considered less useful by a 

minority of respondents. 

 I. Introduction

I.B.4. Application of this Framework for Developing SABS Water Quality 

Criteria and Standards

Water Quality Criteria

Water quality criteria (WQC) describe the quality of water that will generally support designated 

use(s). U.S. EPA, under Section 304(a) of the CWA, periodically publishes WQC 

recommendations for use by states, tribes, and territories in developing and adopting water 

quality standards. Water quality criteria published pursuant to Section 304(a) of the CWA are 

based solely on data and scientific judgments on the relationship between pollutant 

concentrations and environmental (and human health) effects and do not consider economic 

impacts or the technological feasibility of meeting the criteria values in ambient water. 

When establishing SABS numeric criteria, states, tribes, and territories can use the process 

described in this document or other scientifically defensible approaches for deriving criteria. 

U.S. EPA’s 304(a) criteria recommendations have been instrumental for states, tribes, and 

territories to control many forms of pollution and improve water quality across the Nation. 

As mentioned previously, in addition to aquatic life uses, waterbodies have other designated uses 

that need to be protected from stressors such as excess SABS. These include recreation in and on 

the water, navigation, drinking water sources, industrial water use, and agricultural water use. 

Waterbodies may have multiple use designations, including those just listed and aquatic life. 

Water Quality Standards

Water quality standards (WQS) consist of three elements: (1) one or more designated uses for a 

waterbody, (2) WQC to protect the designated use(s), and (3) an antidegradation policy. States, 

tribes, and territories adopt WQS to protect public health and welfare, protect designated uses, 

enhance the quality of water, and serve the purposes of the CWA. Section 101(a) of the CWA 

specifies that WQS should provide, wherever attainable, “water quality which provides for the 

protection and propagation of fish, shellfish, and wildlife and provides for recreation in and on 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

the water.” Section 303(c) states that WQS should be established taking into consideration 

waterbody use and value for public water supplies, propagation of fish and wildlife, recreation, 

agriculture, industry, navigation, and other purposes. 

 I. Introduction

Antidegradation provisions specify that all existing uses of a waterbody, that have occurred since 

November 28, 1975, should be maintained, regardless of whether they are specified as 

designated uses. If the water is of a higher quality than necessary to support fishable/swimmable 

uses, then that water quality must be maintained unless important economic and social goals 

dictate otherwise. A three-tiered antidegradation policy is part of each state’s WQS: 

Tier 1 Maintain existing beneficial uses of surface waters and prevent degradation 

that could interfere with those uses. 

Tier 2 Protect water quality in “fishable/swimmable” waters (bodies of water in 

which water meets or exceeds the levels necessary to support the propagation 

of fish, shellfish, and wildlife as well as recreation on and in the water). 

Tier 3 Provide special protection for “Outstanding Natural Resource Waters,” such 

as waters of national or state parks, wildlife refuges, or other waters of 

exceptional recreational or ecological significance. 

I.B.5. U.S. EPA-OW/OST Standards and Criteria Strategy

Recently, U.S. EPA’s Office of Science and Technology (OST) within the Office of Water (OW)

issued a document titled “Strategy for Water Quality Standards and Criteria: Setting Priorities to 

Strengthen the Foundation for Protecting and Restoring the Nation’s Waters” (U.S. EPA, 2003a). 

Working with stakeholders and considering a wide-ranging review of the existing WQS and 

criteria program within the context of all CWA programs, U.S. EPA identified 10 priorities for 

achieving higher WQS on a national basis. These include providing guidance, strategies, or 

approaches for criteria development for several stressors. Producing and implementing a 

Framework for the development of SABS criteria was among the top priorities and is the basis 

for the present work. OST and the Office of Wetlands, Oceans, and Watersheds (OWOW) are 

coordinating efforts with the Office of Research and Development (ORD) to design research and 

develop methods that can be used to support SABS criteria development. 

One of the milestones of the Standards and Criteria Strategy discussed above was a consultation 

with the Science Advisory Board regarding development of SABS criteria. This consultation 

took place on October 2, 2003 and resulted in generally agreed-upon recommendations that are 

presented in Section I.D. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

I.C. Current Water Quality Criteria Related to SABS

I.C.1. Existing/Current U.S. EPA Criteria

 I. Introduction

In “Quality Criteria for Water” (U.S. EPA 1986), the Agency published the following 

recommendations for developing a numeric criterion for suspended solids and turbidity: 

Solids (Suspended, Settleable) and Turbidity - Freshwater fish and other aquatic 

life: Settleable and suspended solids should not reduce the depth of the 

compensation point for photosynthetic activity by more than 10 percent from the 

seasonally established norm for aquatic life.

This criterion has not been frequently adopted or used by states, perhaps because certain methods 

are somewhat difficult to perform. A narrative “free from” aesthetic standard that states have 

occasionally adopted into their water quality standards was published in the same document 

(U.S. EPA 1986), stating: 

Aesthetic Qualities - All waters shall be free from substances attributable to 

wastewater or other discharges that: settle to form objectionable deposits; float 

as debris, scum, oil, or other matter to form nuisances; produce objectionable 

color, odor, taste or turbidity; injure or are toxic or produce adverse 

physiological response in humans, animals, or plants; [or] produce undesirable 

or nuisance aquatic life.

I.C.2. Current State Criteria 

In addition to the more recent needs survey discussed in section I.B.3 above, U.S. EPA 

conducted a study of published SABS criteria in all states in 2001 (Appendix D). Based on the 

study, some form of numeric SABS criteria existed in 32 of the 53 states, tribes, and territories, 

and the District of Columbia. Narrative criteria were identified in 13 states with no numeric 

criteria (and in 23 of the states with numeric criteria as well), leaving eight states with neither 

numeric nor narrative sediment criteria identified. Of these eight states without criteria, five 

listed an alternative or guide for establishing sediment criteria such as effluent controls or 

regional criteria. Additional reviews of state criteria have been compiled by Caux et al. (1997a), 

Singleton (1985), Idaho DEQ (2003), and Rosetta (2005). 

Of the 32 states with numeric criteria, 30 had criteria for turbidity and seven for suspended 

solids. Five of these 32 states listed criteria for both turbidity and suspended solids. Criteria were 

in the form of exceedances over background (e.g., “not more than 10% above background” or 

“no more than 10 NTUs above background”) or absolute values (e.g., “not greater than 100 

NTU”). States have established statewide and/or basin-specific criteria depending on the 

presence of salmonids. In general, concerns are the effects of water clarity and light scattering on 

aquatic life. The majority of states use U.S. EPA method 180.1 to measure turbidity and U.S. 

EPA method 160.2 (40 CFR Part 136) to measure TSS. For example, suspended solids criteria 

vary from 30 mg/L up to 263 mg/L for aquatic life uses and up to 500 mg/L for storm water 

9
Framework for Developing SABS Water Quality Criteria U.S. EPA

pollution control in North Carolina. Florida uses transparency as a criterion (not to be reduced by 

more than 10%). 

States, under pressure to develop and issue total maximum daily loads (TMDLs) for SABSimpaired waterbodies, are moving forward on their own to develop new-and-improved SABS 

criteria from which to develop TMDLs. U.S. EPA believes it is valuable to examine what states 

have done in the past, are currently doing, and plan to do in the future in developing SABS 

criteria as a way to identify methods that may be useful, either directly or with adaptation, for the 

entire Nation. U.S. EPA also believes this same consideration should be given to the SABS 

criteria efforts in other countries. Therefore, promising methods used by some states and other 

countries have been reviewed by U.S. EPA and are included in the Framework. As new methods 

become available, U.S. EPA may review and consider them either for application nationwide or 

for updating this document. Criteria have recently been developed by Idaho, Oregon, and New 

Mexico (United States), British Columbia (Canada), Australia, New Zealand, and the European 

Union (Appendix D). 

 I. Introduction

I.D. Recommendations of the U.S. EPA Science Advisory Board

As part of the current effort to develop national SABS criteria, the U.S. EPA Science Advisory 

Board met on October 2, 2003 to discuss various methods for establishing criteria. This meeting 

resulted in several generally agreed-upon recommendations. It is important to note, however, that 

the Science Advisory Board did not reach consensus and votes were not taken. The general 

recommendations are summarized here and detailed in Appendix E. The specific approaches 

mentioned here are discussed in detail in Section III.D. 

Overall Recommendations

• Consideration should be given to setting criteria from the management perspective, 

classifying by waterbody function and designated uses, while ensuring that resource 

managers know what natural levels of SABS are expected for any given waterbody. 

• Criteria should be developed for each major waterbody type (lakes, estuaries, wetlands, 

rivers, streams, headwaters, etc.) and then tiered by classes of similar waterbody types 

within each of these major categories (e.g., high-gradient vs. low-gradient mountain 

streams). 

• As no single criterion or indicator will work for each major waterbody type and class, 

several different criteria or indicators should be developed to address key distinctions 

in SABS among waterbody types and classes. 

• Criteria should be based on a synthesis of methods that demonstrate the relationship 

between the measurements of SABS and aquatic life or a valued ecological resource. 

The conditional probability and reference condition approaches could be used to meet 

this requirement. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA

• The strengths and weaknesses of each method should be clearly explained for states, 

tribes, and territories. 

• Any uncertainty with respect to ecological theory or statistical model development 

should be clearly documented and considered during criteria selection and 

implementation. 

 I. Introduction

• The problem of SABS imbalance resulting from too little sediment should not be 

overlooked. 

• Recommended methods should be clear and understandable. 

• Work should continue that develops methods and other approaches for establishing 

SABS criteria. Real data should be used in creating examples of a synthesized process. 

• Recommended that there is national consistency in assessment, management, and 

evaluation. 

It has been and will continue to be the intention of the U.S. EPA to consider all of these 

recommendations during the development and implementation of this Framework. For instance, 

the recommendation that actual or available data should be used in creating examples of a 

synthesized approach (or combination of approaches) was interpreted as a need for case studies. 

U.S. EPA initiated a case study that is included as a draft using hypothetical examples (see 

Section III.E). Case studies, using actual state data, are now under development and may be 

included in U.S. EPA SABS documents in the future. The Board did not suggest any new, 

unique, or “silver bullet” methods that would solve all problems or be quickly and easily 

implemented. 

However, U.S. EPA is not taking a supervisory role in defining criteria near jurisdictional 

boundaries but will support the efforts of bordering states and act as a mediator if needed. This 

document is designed to provide a Framework for developing SABS criteria. It is not a substitute 

for the CWA or U.S. EPA’s regulations nor is it a regulation itself. The Framework does not 

impose legally binding requirements on U.S. EPA, states, tribes, territories or the regulated 

community and may not apply to some particular situations. U.S. EPA, state, tribal, and 

territorial decision-makers retain the discretion to adopt methods and approaches on a case-bycase basis that are appropriate to their SABS needs. 

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 I. Introduction

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Chapter II. PROGRAMMATIC ELEMENTS OF 

SABS CRITERIA DEVELOPMENT 

II.A. Possible Uses of this Framework

Using this Framework, states, tribes, and territories could develop new, or review existing, 

SABS criteria (narrative and numeric criteria). These criteria could then be incorporated into 

WQS and implemented in various water quality programs. Criteria development could follow the 

process as described in Chapter III, proceeding first in regions and watersheds where applicable 

data are currently available. Where states have existing SABS criteria, these criteria could be 

reviewed in the context of the overall Framework. 

 II. Programmatic Elements

II.B. Resources for Framework Implementation

For those states developing SABS criteria or beginning the process of addressing SABS, this 

Framework provides several resource elements. For example, components of the Framework

include techniques for sampling, data management, and analysis. The resources include 

professional contacts for technical and administrative issues and communication vehicles. These 

tools and resources are yet to be developed, and the following list is a sampling of possibilities. 

The final list of tools and resources may differ as needs are identified, tools are developed and 

U.S. EPA support evolves. 

U.S. EPA Expertise

U.S. EPA Headquarters, ORD, and Regional staff will be interested in how state, tribal, and 

territorial officials, and other interested parties develop SABS criteria. 

Internet Resources

In support of SABS criteria development, U.S. EPA plans to build and maintain a Web site 

devoted to SABS information and knowledge exchange. This Web site could serve at least three 

functions: (1) as a portal for communication among states, tribes, and territories (2) as a source 

of data on SABS exposures and biotic responses and (3) as a center for distribution of tools for 

SABS criteria development. 

Communication

SABS criteria development will benefit from dialogue among all parties involved, including 

state, tribe, and territorial water resource managers, scientists, National and Regional SABS 

Teams, and U.S. EPA. Moreover, parties will benefit and learn from third-party communication. 

For example, exchange of information between a state scientist and Regional SABS Team

members may be useful to a scientist in another state in the same region. A SABS Web site may 

help facilitate this type of communication, where frequently asked questions can be answered, 

problems and solutions can be posted, virtual brainstorming can occur, and innovative ideas can 

be shared. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

SABS Datasets

As datasets with sufficient data for analysis are identified, they should be made available, for 

example, via a Web site. These datasets may include state monitoring records, academic studies, 

or federal agency research. Perhaps the biggest challenge of SABS criteria development will be 

establishing links between SABS exposures and biotic responses so that effect levels can be 

identified. Reviewing the existing data in the primary scientific literature will help this process 

(e.g., Berry et al. 2003). These reviews may be the starting point for quantifying relationships 

between SABS and biotic responses, which may assist in both setting criteria and monitoring 

management actions. 

 II. Programmatic Elements

Data Management: Storage and Processing

States, tribes, and territories will benefit from consistent and compatible data storage, retrieval, 

and assessment systems to help interpret data so that it is meaningful for management decisions. 

Convenient data storage and modeling programs will enhance data assessment, and also, if 

consistent throughout a region, promote coordinated inter-state surveys and data sharing. The 

U.S. EPA Storage and Retrieval database (STORET) or the U.S. Geologic Survey may be an 

appropriate starting point for data management though other alternatives may exist or be 

developed. 

II.C. Integration of the SABS Framework with Existing State 

Programs

The SABS Framework provides a scientifically defensible process and the necessary methods 

and analytical tools for states, tribes, and territories to develop or adjust numeric SABS criteria 

into their WQS. This Framework could help water quality resource managers support efforts to 

achieve and maintain protective water quality conditions as well as identify impaired waters and 

their causes. Some state, tribal and territorial efforts that may be supported by SABS Framework

implementation and WQS revisions include 

• Total maximum daily loads (TMDLs), waste load allocations (WLAs) for point sources 

of pollution and load allocations (LAs) for non-point sources of pollution 

• Water quality management plans which prescribe the regulatory, construction and 

management activities necessary to meet the waterbody goals 

• NPDES water quality-based effluent limitations for point source discharges 

• Water quality certifications under CWA § 401 for activities that may affect water quality 

and that require a federal license or permit 

• Reports, such as those required under CWA § 305(b), that document current water 

quality conditions and CWA § 303(d) that list impaired waters and 

• CWA § 319 management plans for the control of non-point sources of pollution. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Protection of waterbodies from SABS imbalances may require management actions. SABS 

management is a process that should integrate a number of programs and management

approaches, including but not limited to 

• Non-point and Watershed programs 

• NPDES Permitting programs

• Nutrient and Contaminated Sediment Management 

• Marine Protection, Research, and Sanctuaries Act (MPRSA) permits for ocean dumping 

 II. Programmatic Elements

• CWA permitting for dredge and fill activities 

• Biosolids Management programs 

As the process and methods outlined in this Framework are implemented or utilized, we will 

informally gather and evaluate feedback and experiences from states, tribes, territories, and other 

water resource managers to ensure the SABS Framework works well. Suggestions, comments, 

and input may include data sets, existing analysis or insights into the interactions between SABS 

sources and waterbody conditions and knowledge of SABS conditions and designated use 

attainment. If necessary, we will revise the document accordingly and issue another edition. 

II.D. Implementation of SABS Criteria and Standards

As stated previously, the primary goal of this Framework is to provide useful tools for 

developing SABS criteria. This Framework could also help water quality resource managers 

manage and evaluate SABS through application of criteria and standards. There are some

fundamental management concepts that should apply in most situations. The SABS program

needs to consider what activities will be needed once SABS criteria have been established. 

Possible sequential steps are outlined in Table 2. 

This Framework incorporates all the key elements essential to good management planning, but 

the user might find that some steps can be consolidated or that circumstances necessitate a 

different sequence. With a good database predicated on reliable indicators and the comparable 

analytical methods for development of regional SABS criteria, states, tribes, and territories will 

be capable of assessing the SABS status of their waters, and establishing their criteria as well as 

planning, prioritizing, and evaluating their management responses. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Table 2. Sequential elements of a SABS management program. 

Step Description

1

Identify

Problem

Identify waterbodies where SABS may contribute to non-attainment of aquatic life and

other designated uses based on landscape or mechanistic screening. Collect SABS indicator

measurements from the sites to confirm exceedance of protective SABS criteria. If 

possible, collect biological data or other indicators of designated uses to confirm loss or

reduction of the designated use. If the designated use is not impaired, the level of SABS

may be tolerated at the location and the site need not be listed as impaired. If there is 

reduction or loss of a designated use, the impairment should be addressed. The problem

should be defined in terms that make it possible to seek a solution. Be aware that if the 

designated uses are fully supported but sediment is exported to other waterbodies, these

sites may be a source for sediment that is impairing a different waterbody. 

2 

Investigate 

Background 

Use literature searches, questionnaires, interviews, and other background investigations to

describe the lost designated use due to exceedance of SABS criteria. Compile and analyze 

available data and other information. Develop list of possible sediment loading sources

and/or other factors leading to SABS imbalance. At this and the following two stages, 

identify and characterize fully supported biological and physical reference conditions or

reference sites.

3

Gather Data

Design and conduct a field study to sample physical, chemical, and biological parameters 

and sediment loading sources in the watersheds. This step should be of sufficient duration 

to accommodate seasonal and annual variation and possible storm events. 

4

Confirm

Problem

Conduct a thorough causal assessment of all of the above information. Consider the other 

possible causes for the impairment. If SABS are identified among the probable cause(s), 

estimate sediment loading from all identified sources. 

5

Develop 

Alternative 

Management 

Options 

Develop a list of management alternatives to address each sediment source. Evaluate risk 

associated with each alternative and its impact on present uses with respect to the

likelihood of restoring the designated use, scientific validity, cost-effectiveness, and 

sociopolitical feasibility. Involve local and state-level governments, property owners, 

citizen groups, and public and business interests in discussions about the optimal approach. 

Potential management options for SABS in different waterbodies are presented in Table 3.

6

Detail 

Management 

Plan 

Prepare a plan that discusses how to address each key element of the SABS problem in the 

most effective sequence. Indicate the rationale for selecting a particular course of action. 

Include a stepwise sequence of coordinated activities in detail. Management plans are 

typically written for a five-year period. Changes in SABS ought to be detected in this time 

frame, which is short enough to be accommodated within most budgets. Longer projects 

might require sequential management plans and will be more apt to detect biological 

recovery. 

7

Implement and 

Communicate 

Initiate the management program, including consideration of SABS water quality criteria 

(WQC) and other WQS. Where appropriate, establish SABS limitations in NPDES permits 

and develop TMDLs as elements of the program. Maintain community, interest group, and 

other agency involvement through regular updates on the process. Communications may 

begin at step 4 or sooner but should be emphasized here. 

8

Monitor and 

Review 

Incorporate water quality monitoring before, during, and after the project to demonstrate 

relative response of the system to management efforts. Build in specific intervals for 

management review to allow response to changing circumstances, modifications of

approaches and schedules, and changes in emphasis. 

9

Complete and 

Evaluate 

Determine if the water resource has been protected or improved. Give credit to the 

community and other participants. Report on successes and failures for future applications 

and on lessons that are learned. 

10

Monitor and 

Maintain 

Controls 

Water resource monitoring stations and parameters continue on a reduced scale (e.g., fewer 

sampling stations, fewer parameters, less frequent sampling). Ensure regular maintenance 

of management efforts to preserve the effects achieved. Monitoring provides warning of

any future degradation, allowing resource managers to intervene in a timely, cost-effective 

manner. Close the cycle by returning to step 1. 

 II. Programmatic Elements

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

II.D.1. Management Options

The management of SABS imbalance involves a sequential investigation and decision-making 

process, including a multidisciplinary evaluation of possible mitigating, remedial or other 

alternative actions to address SABS problems and prioritize them and their possible solutions. 

Although not intended to be exhaustive, Table 3 summarizes remediation, protection, and 

management approaches by waterbody type. It is an introductory presentation of some of the 

readily evident options that states, tribes, territories and other responsible parties can use to make 

a positive response to the situations with imbalanced SABS regimes. 

 II. Programmatic Elements

Another management resource is the "Draft Handbook for Developing Watershed Plans to 

Restore and Protect Our Waters" (U.S. EPA 2005b), which is available at 

http://www.epa.gov/owow/nps/watershed_handbook/. The handbook contains in-depth guidance 

on quantifying existing pollutant loads including SABS, developing estimates of the load 

reductions required to meet water quality standards, developing effective management measures, 

and tracking progress once the plan is implemented. As indicated previously, during this pilot 

phase we will informally gather and evaluate feedback and experiences from states, tribes, 

territories, and other water resource managers to ensure the SABS Framework works well. If 

necessary, we will revise the document accordingly and issue another edition. 

In considering the various management options for controlling SABS imbalances (Table 3), the 

resource manager should keep in mind that the different waterbody types described here may 

often be interrelated (e.g., streams draining to and from lakes and rivers entering estuaries and 

coastal waters). Under these circumstances, the resource manager would select management plan 

practices that are protective of downstream resources. For example, biota in high gradient 

streams may tolerate spates of high sediment loads during storms, whereas reservoirs and low 

gradient streams may be overwhelmed as these materials settle. 

It should be noted that activity in upland portions of the watershed could affect all waterbody 

types in the drainage system. Management in upland areas should proceed with consideration of 

the connectivity between land disturbance anywhere in the watershed and effects on the SABS 

loadings to aquatic systems. Watershed approaches to management provide options that consider 

sources and controls for SABS for all connected waterbodies. They offer the advantages of 

allowing communities to focus resources on the most serious sources of excess sediment in the 

watershed. Additional basic management actions can be found in other U.S. EPA documents 

such as Protocol for Developing Sediment TMDLs (1999) and Guidance Specifying Management 

Measures for Sources of Nonpoint Pollution in Coastal Waters (1993). 

An example of an assessment framework to guide sediment management actions for streams is 

the U.S. EPA-funded study called the Watershed Assessment of River Stability and Sediment 

Supply (WARSSS). It is based on geomorphic analysis of current sedimentary states of 

watersheds and stream systems and pertains to development of a sediment assessment framework 

(http://www.epa.gov/warsss). WARSSS is based on modeled associations between SABS 

sources and channel conditions and the models are calibrated on field observations. 

17
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Table 3. Issues and management options for addressing SABS imbalances by waterbody type. 

Issue Area Management Option 

Land use 

Include land use as a separate early warning indicator (i.e., if development is

proposed in a watershed, an environmental impact study should be done to

assess the potential impact on the surrounding watershed). 

Hydrology, hydraulics 

(flow regime, storm water 

management, stream

regulation) 

Identify natural hydrologic regimes and use such information in addressing

runoff control or dam operations to better replicate natural conditions in the 

waterbodies while allowing development, generating power, or preserving

intended reservoir levels. 

Impoundment removal Remove man-made impoundments that have lost their utility and are now 

causes of flow interruption and sources of downstream sediment imbalance. 

Restoration of riparian

and flood plain wetlands 

Implement programs designed to restore riparian and flood plain wetlands.

STREAMS AND RIVERS 

Storm water management Implement storm water BMPs such as constructing ponds, wetlands, 

infiltration and detention basins, and diversions. 

Vegetative buffer zones 

Preserve or reestablish natural, indigenous vegetation (groundcover, shrubs,

and trees) in the riparian zone to intercept sediment runoff before the runoff 

reaches the waterbody. 

Watershed land use 

changes 

Identify critical loading sources and promote changes of these land use 

practices. Examples of practices to promote are implementation of

conservation farming; use of road, commercial and municipal runoff diversions

and detentions; restoration of woodlots in critical drainage areas; and land use 

planning to avoid excessive tiers of lake residences. 

Habitat restoration

Improve lake nursery and spawning areas to restore a diverse aquatic

community and food chain. 

Water level control Initiate winter or other episodic draughts of lake/reservoir waters to augment 

sediment removal or consolidation. 

Restoration and protection

of strategic wetlands 

Restore and protect wetlands located in areas critical to water quality concerns. 

LAKES AND R

ESERVOIRS 

Storm water management Implement storm water BMPs such as constructing ponds, wetlands, 

infiltration and detention basins, and diversions. 

Wetland protection and

restoration 

Preserve and restore wetlands through the implementation of voluntary and

regulatory programs. 

Vegetative buffer zones 

Preserve or reestablish natural, indigenous vegetation (ground cover, shrubs, 

and trees) as buffer zones adjacent to wetlands to intercept sediment runoff 

before the runoff reaches the wetland. 

Watershed land use 

changes 

Identify critical land loading sources and promote changes of these land 

practices. Examples of changes that could be made include the implementation 

of conservation farming techniques; runoff diversions and detentions, filter 

strips, and vegetated drainage ways; the implementation of forestry BMPS; and 

the implementation of controls on urbanization and industrial development.

Land use planning 

Protect wetlands by limiting amounts of impervious surfaces, limiting 

development near waterbodies or steep slopes, and minimizing discharges from

storm water, sewer, and septic systems. 

WETLANDS 

Protect and restore 

streams entering wetland 

Stabilize stream channels and establish riparian buffers to reduce the amount of

sediment entering a wetland. 

Land use and 

development controls

Promote natural vegetative cover in shore areas and zoning restrictions on

dense residential or commercial/industrial development along shoreline areas. 

Restricted 

estuaries/coastal areas 

Protect sensitive waters such as endangered shellfish beds, spawning and

nursery areas, and recovering weed beds. 

Shoreline erosion controls

Implement erosion controls on banks subject to wave or ice damage. Restrict 

access to sensitive shorelines, dune restoration areas, and shorelines susceptible 

to erosion.

EST

UARIES A

ND 

COASTAL WATERS 

Sea grass replenishment 

Restore submerged and emergent aquatic vegetation in estuaries, including

wetland areas. Plant and protect emergent and terrestrial riparian vegetation as 

further protection of tidal zone wetlands from runoff. 

 II. Programmatic Elements

18
Framework for Developing SABS Water Quality Criteria U.S. EPA 

The study considers hillslope and channel processes responsible for changes in erosion and 

sedimentation and related stream channel instability. Two hierarchical levels of assessment are 

included that provide (1) an initial broad overview “screening level” to identify and prioritize 

potentially high risk watersheds or river systems that require a more detailed predictive

assessment for process-specific mitigation and (2) a process-based, quantitative prediction of

potential sediment sources, magnitude of sediment delivery, streamflow changes, and river 

stability related to the nature, extent and location of a variety of land uses. WARSSS includes a 

bank erosion model for quantifying the relative contribution of bank erosion versus hillslope and 

other sources of sediment (Rosgen 2001). A monitoring methodology related to the prediction 

process allows validation of the assessment approach and tracks the effectiveness of 

recommended mitigation to reduce existing excess sediment loading and improve channel 

stability. As an assessment framework rather than a rigid methodology, individual steps in a 

WARSSS assessment are amenable at the user’s discretion to substitution of alternate models or 

measures better suited to the region or waterbody type being assessed. 

 II. Programmatic Elements

II.D.2. Evaluation

When appropriate indicators and criteria have been established, states, tribes, or territories may 

be able to evaluate the effectiveness of management and regulatory approaches. Progress in 

management of SABS imbalance and designated use impairment should be assessed by 

comparing changes in sediment flux from the land, SABS indicators, and designated uses 

through the state’s water quality monitoring programs. Timely evaluation of program

effectiveness allows for successful management approaches and techniques to be shared and 

repeated in similar circumstances elsewhere. Where success has not been achieved, the 

knowledge gained is valuable in developing alternative approaches and in avoiding repetition of 

the same unproductive activity. This information could be shared through correspondence and 

national meetings to enhance management effectiveness. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Chapter III. TECHNICAL ELEMENTS OF 

SABS CRITERIA DEVELOPMENT

III.A. Need for a Technical Discussion in This Framework

This chapter is an introduction to the scientific process, potential methods, and current research 

regarding development of SABS criteria. Inclusion of a technical section is intended to provide 

as much clarity as is possible to those looking for a defensible, transparent approach toward 

setting SABS criteria. The SABS technical workgroup decided that issuing workable scientific 

methods, along with the intent to develop SABS criteria, would expedite implementation. The 

workgroup committee is aware that this technical information does not cover all possibilities but 

believes that these methods provide a starting point to initiate SABS criteria development. The 

Framework may encourage research that could further improve the methods. 

While all the material has been reviewed by the workgroup, which consist of experts in various 

aspects of SABS policy and science and knowledgeable peer reviewers, some of the material 

may still be in an exploratory or developmental stage. This applies especially to some of the 

analytical methods (Section III.D) and the hypothetical example that illustrates how these 

methods can be combined to develop SABS criteria (Section III.E). 

III.B. Process for SABS Criteria Development

 III. Technical Elements 

The basic process for developing SABS criteria, outlined in Figure 2, consists of four types of

activities: (1) gathering information, (2) synthesizing the state of knowledge, (3) analyzing 

available data, and (4) selecting criteria values. The process begins by gathering information 

from the literature, regulations and stakeholders about data sources and possible classifications 

for waterbodies. The information is then synthesized, depicted in a conceptual model, and 

described in text format. From the conceptual model, measurements are selected and the 

rationale for the selection is recorded. Next, available data sets are assembled and analyzed. The 

details of some possible analyses are presented in Sections III.D and III.E. Outputs from the data 

analysis phase may include analysis designs, evaluated classifications, exposure-response 

profiles, background SABS regimes, ranges of protective responses, and probabilities of adverse 

effects. Finally, the outputs from the analysis phase are considered in the decision analysis phase 

where SABS criteria values are selected and the rationale for the selection is described. SABS 

criteria can then be implemented within a comprehensive management plan as described in Table 

2. 

21
Framework for Developing SABS Water Quality Criteria U.S. EPA 

 III. Technical Elements 

Criteria 

Development 

Process

 -Literature 

Sources

 -Stakeholders Gather 

Information

Figure 2. Activities and outputs of the SABS criteria development process. 

Synthesize 

State of 

Knowledge 

Analyze 

Available 

Data 

Select 

Criteria 

Values 

Implement 

Criteria 

Collect 

Additional 

Data 

 -Regulations 

 -State Data 

Revise 

Waterbody 

Classification -Conceptual Models 

-Selected Measurements 

-Selection Rationale 

Outputs

Outputs

Insufficient 

Data 

Outputs

-Decision Rationale 

-Criteria Values 

 -Analysis Design 

 -Evaluated Classification 

 -Exposure Response Profiles 

 -Background SABS Regimes 

 -Range of Protective Responses

 -Probability of Adverse Effects 

22
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Although presented as a sequence of steps, iteration may be necessary. For instance, a set of 

waterbodies may be classified as a group at the beginning of the process, but new information 

may arise and require waterbody types to be assigned to more specific categories. Available data 

may be insufficient and require additional data collection. In all cases, analysis that develops 

SABS associations with response indicators should take advantage of the benefits of comparing 

results from several methods using different data sets, thereby, allowing criteria selection to be 

supported by the strength-of-evidence. 

The four activities can be expanded to reveal the greater detail shown in Figure 3 that presents 

the elements of the SABS Criteria Development Framework (in seven steps). Each of the seven 

steps is described briefly below. In addition, hypothetical examples that illustrate how one could 

implement the seven steps are presented in Section III.E as a synthesis of the methods. The 

methods for classification, analysis, and characterization of SABS/response associations are 

presented in Section III.D along with specific examples. 

III.B.1. Step 1. Review Current Designated Uses and Criteria for a Set of 

Waterbodies 

The development of SABS criteria begins by selecting and characterizing a type of waterbody 

and identifying the specific designated uses for which the local authority desires to set protective 

criteria. Although waterbody type (streams, rivers, estuaries, coastal areas, lakes, or wetlands) 

may be sufficient as a classification variable, more refined classification relevant to SABS is 

usually necessary during this step or in step 4. 

 III. Technical Elements 

Existing designated uses and associated narrative or numeric criteria should be reviewed and an 

initial determination should be made as to whether these are protective of the valued resources. 

Uses are designated to support and protect navigable waterways, industrial, and agricultural uses, 

recreational activities, drinking water sources, and aquatic life. Designated uses may be very 

general (e.g., biotic integrity) or more specific (e.g., high-energy, cold-water streams that 

supports salmonid fisheries). Extremely vulnerable or highly valued waterbody types may have 

their own specific designated uses that provide special protection for valued, threatened and 

endangered species or important ecological functions. With a more specific designated use, the 

SABS criteria will be more defensible. However, it is important to balance the desire for 

defensibility against the need to avoid proliferation of so many specific standards that SABS 

criteria become impractical to implement. Davies and Jackson (2006) discuss the appropriate use 

of biological information to tier designated aquatic life uses in WQS. 

Criteria should be identified for all current designated uses. If these criteria need refinement, or if 

a new criterion is needed for a new designated use, then a general description is required of the 

point of transition between support and non-support of the designated use for a group of 

waterbodies. Initially, the criteria should be described in narrative terms and then quantified in 

subsequent steps. It is important to note that premature declaration of a specific threshold may 

introduce bias into the criteria development process. 

23
Framework for Developing SABS Water Quality Criteria U.S. EPA 

 III. Technical Elements 

Gather 

Information 

1. Review current designated uses 

and criteria for a set of waterbodies 

2. Describe SABS effects on the 

Synthesize waterbodies’ designated uses 

State of 

Knowledge 3. Select specific SABS and 

response indicators 

4. Define potential ranges in value of 

the SABS and response indicators

Analyze 

Available 

Data 

5. Identify a response indicator value 

that protects the designated use 

6. Analyze and characterize 

SABS/response associations 

Select 

Criteria 

Values 

7. Explain decisions that justify 

criteria selection 

Figure 3. Seven steps of the SABS criteria development process and relationship to four 

activities in Figure 2. 

24
Framework for Developing SABS Water Quality Criteria U.S. EPA 

III.B.2. Step 2. Describe SABS Effects on the Waterbodies’ Designated Uses 

SABS criteria should have a strong scientific basis, including both a causal mechanism and 

empirical evidence of association between SABS and the designated use, described in either 

positive terms or in the form of use impairment. A literature review is critical to identify

evidence of causal mechanisms and the current state of knowledge related to the SABS criterion 

under consideration, including examples of exposure-response relationships. An additional 

review of relevant and available data sets would reveal both potential data sources and 

significant data gaps that may affect the course of SABS criteria development. 

The current scientific understanding of the ways that SABS impair the designated use may be 

described in text and conceptual diagrams (Figure 4). The use of both of these communication 

tools helps ensure clarity of thought and consistent logic while developing the SABS criteria. 

Their use also enables easier identification of appropriate indicators (see step 3) and ultimately 

enables the defense of the selected criteria and standards. Most importantly, the underlying 

scientific basis linking SABS with designated uses should be articulated. Sections I.B.2 and 

Appendix B provide some useful documentation of how SABS can impair waterbody types. 

Additional examples of conceptual models can be found in Appendix F and Section III.E.1. 

Associations between SABS and designated use in terms of impairment (through the response 

indicator) should be supported by peer-reviewed literature or confirmed with data sets that the 

state, tribe or territory has compiled and analyzed. For instance, associational analysis 

(correlation, regression) of survey data including measurements of both biota and SABS might 

show the strength of exposure-response relationships. A combination of mechanistic studies and 

correlative associations provide the most defensible rationale for selection of SABS and response 

indicators in step 3. 

 III. Technical Elements 

III.B.3. Step 3. Select Specific SABS and Response Indicators 

Selecting specific SABS and response indicators sets the stage for data analysis in steps 4, 5, and 

6 through selection of the quantitative measurements for SABS (exposure indicators) that are 

believed to reduce the support of a designated use as described in the conceptual model (step 2). 

For example some typical measurements are Secchi distance to measure clarity, suspended 

sediment concentration to measure inorganic particles and percent fines to measure settled 

particles. Composite indicators of sediment movement are calculated from more than one 

measurement (See Relative Bed Stability, Section III.D.1). SABS exposure indicators should 

represent levels of intensity, frequency and duration as well as quantify the attributes of SABS 

that are responsible for impairment as evaluated in step 7. A mechanistic connection between the 

SABS indicator and the response indicator, as described in step 2, is also necessary to support the 

analyses described in step 6. 

25
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Excess

Turbidity

Habitat 

Disturbance

Nutrient/ 

Toxin 

Sorption

Light 

Limitation

Food Web 

Dynamics

Decrease

Biotic

Integrity

Change

Primary &

Secondary

Production

Agricultural 

-Tiling

-Ditching

-Wetland Loss

-Farm/Range 

Practices

Land Use

Silviculture

- Harvests

-Riparian Loss

Urbanization

-Construction

-Imperviousness

-Street Dirt

Hydromodification

Channelization

Damming

Bank-Shoreline

modification

Dredging and 

Boating

In-Channel 

Sediment Load

Soil 

Erosion

Sediment 

Load

Channel 

Instability

Increase 

Runoff

Volume/ 

Duration

Increase

Runoff

Velocity

Change

Stream 

Power

Decrease

Base Flow

Channel 

Hydrograph

Watershed Hydro-Modification

Stream/ Lake/ 

Estuary/ Wetland 

Sediment Stress

Anthropogenic

Activities 

LandBasedWaterBased

Related Ecological 

Parameters/Processes

Ecosystem

Health Effects

Sediment-related Process Alterations

Degraded 

Ecological

Integrity/

Water Quality

Channel

Sediment 

Transport

Embeddedness

Resuspension

Bank Erosion

Bed Aggradation

Excess

Turbidity

Habitat 

Disturbance

Nutrient/ 

Toxin 

Sorption

Light 

Limitation

Food Web 

Dynamics

Nutrient/ 

Toxin 

Sorption

Light 

Limitation

Food Web 

Dynamics

Decrease

Biotic

Integrity

Change

Primary &

Secondary

Production

Agricultural 

-Tiling

-Ditching

-Wetland Loss

-Farm/Range 

Practices

Land Use

Silviculture

- Harvests

-Riparian Loss

Urbanization

-Construction

-Imperviousness

-Street Dirt

Hydromodification

Channelization

Damming

Bank-Shoreline

modification

Dredging and 

Boating

In-Channel 

Sediment Load

Soil 

Erosion

Sediment 

Load

Channel 

Instability

Increase 

Runoff

Volume/ 

Duration

Increase

Runoff

Velocity

Change

Stream 

Power

Decrease

Base Flow

Channel 

Hydrograph

Watershed Hydro-Modification

Stream/ Lake/ 

Estuary/ Wetland 

Sediment Stress

Anthropogenic

Activities 

LandBasedWaterBased

Related Ecological 

Parameters/Processes

Ecosystem

Health Effects

Sediment-related Process Alterations Stream/ Lake/ 

Estuary/ Wetland 

Sediment Stress

Anthropogenic

Activities 

LandBasedWaterBased

Related Ecological 

Parameters/Processes

Ecosystem

Health Effects

Sediment-related Process Alterations

Degraded 

Ecological

Integrity/

Water Quality

Channel

Sediment 

Transport

Embeddedness

Resuspension

Bank Erosion

Bed Aggradation

Embeddedness

Resuspension

Bank Erosion

Bed Aggradation

 III. Technical Elements 

Figure 4. Conceptual linkages among sources of sediment stress and aquatic ecosystem health 

(Nietch et al. 2005).

26
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Also in step 3, the response measures that will be used to define impairment are selected. 

Examples of response measures include abundance of a species, presence or absence of a 

species, and clogging rate of drinking water filters due to source water impurities. In some cases 

the distinction between the SABS and the response indicator can be confusing. For instance, rate 

of stream bank erosion may be a measure of sediment to a stream, a SABS indicator, or it can be 

a measure of aquatic habitat loss or damage to adjacent real estate, a response indicator as 

described for the Waterbody Use Functionality method (Section III.D.3). Care should be taken to 

recognize how the indicator is being used. 

Indicators should be selected that are appropriate for the waterbody type, classification, region, 

and designated use. Furthermore, indicators should be selected that have the following 

characteristics: (1) association with the designated uses, (2) quantifiable with available or 

accessible data, (3) dependable measurement characteristics, (4) appropriate for the specific 

analytical method, and (5) valued by stakeholders. Response indicators should relate directly to 

the designated use and quantify how well the waterbody type is meeting expectations for that 

use. If the designated use is the support of aquatic life, biocriteria such as an index of biotic 

integrity may be the appropriate indicator of response. The best response indicator would have a 

robust relationship with SABS levels. Existing biocriteria probably address general impairment, 

not SABS-specific impairment, and metrics that are more responsive to SABS levels should be 

selected as response indicators if they are available and the responsiveness can be documented. 

For designated uses more specific than “aquatic life” other appropriate entities and attributes 

may be used for defining attainment (U.S. EPA 2003d). 

After the response indicator is selected, the level of protection is defined. This is a value 

judgment. For chemical criteria, the U.S. EPA has defined that level as protecting 95% of the 

tested species. Identifying the level for sediment is challenging. Current knowledge of SABS 

effects does not permit the same type of rigorous calculation for SABS. In the meantime, 

alternative standards can be used. A protective level may be pre-determined if criteria already 

exist in state standards for the designated use selected in step 1. Otherwise, impairment 

thresholds can be determined in step 5. 

 III. Technical Elements 

Data availability and accessibility may be significant factors in the selection of indicators. Many 

state programs are currently collecting and compiling monitoring data for purposes other than 

SABS criteria development. If these monitoring data are sufficient and relevant to the SABS 

criteria development effort, they should certainly be used, eliminating the need for a new and 

specifically designed monitoring program. Sufficiency of existing data should be determined 

through consideration of the program sampling design, sample size, sample frequency and 

timing, performance characteristics of the data (precision, bias, accuracy, representativeness, and 

completeness) and whether the indicators already sampled represent relevant SABS and response 

measures. Existing multi-purpose data would be valuable for preliminary analyses of potential 

value ranges (step 4), protective response indicator levels (step 5), and exposure-response 

relationships (step 6). 

If existing data are found to be insufficient or irrelevant in steps 3-6, then a new and specifically 

designed SABS monitoring program should be implemented. New study designs that incorporate 

sampling of biological assemblages or individual taxa should target the biota that have 

27
Framework for Developing SABS Water Quality Criteria U.S. EPA 

measurable responses to the SABS indicators of interest over the expected range of values as 

recorded in the scientific literature (step 2). The sampling design used to collect the data is very 

important. Data sources and sampling designs can introduce bias and imprecision. Imprecision 

adds noise that limits the ability to reach sound conclusions. Bias clouds our understanding of 

mechanisms but its uniform nature still allows trends to be detected. Interpretation of data should 

assume that both processes are acting to increase uncertainty and that attempts to minimize their 

effects will be necessary. A probability-based design is ideal for quantifying status and trends 

and allows extrapolation of analytical results throughout the geographic area of interest. 

However, a targeted design, including the highest and lowest quality sites, is typically required to 

assure that the full range of exposure and response is represented to develop a complete 

exposure-response model. A hybrid design, a probability-based design augmented with targeted 

sites, combines the advantages of both methods and improves the overall analysis. 

Frequency and timing of sample collection may also be an important consideration in the 

selection of indicators. For instance, some suspended sediment indicators vary with climatic as 

well as geographical variation. Data for such indicators may need to be collected more frequently 

or with prescribed timing in relation to storm events. Both data collection and adjustment of 

expectations can be more complex for some indicators, and investigators should be confident that 

they can collect sufficient data to account for multiple sources of spatial and temporal variability. 

III.B.4. Step 4. Define Potential Ranges in Value of the SABS and Response 

Indicators

 III. Technical Elements 

Once the ecology of the waterbody type is reviewed and SABS and response indicators are 

selected, then it is time to begin the analysis phase. The first step is to analyze the natural and 

altered waterbody characteristics that affect SABS regimes. For instance, SABS regimes may be 

affected by natural differences in responses to SABS variables by region, waterbody size, 

geomorphology, hydrology, lithology, soils, and so on. They may also be affected by land uses 

or modifications to the waterbody itself such as dams, channelization, and water diversion, to 

name a few (see Cross-Cutting Concepts, Section III.C.1, for a more extensive description.). 

Characterization of the natural and disturbed SABS regimes and response indicator values is 

dependent on waterbodies selected in step 1 and the appropriate classification within that 

waterbody type. Classification is typically based on expected, not observed, natural indicator 

levels. Waterbody classifications are evaluated in light of the potential and observed responses at 

step 6. 

The process of classification or stratification identifies waterbody types with shared SABS 

regimens so that variability within a class is minimized compared to the variability among 

classes or variability caused by disturbance. For instance, high gradient streams would be 

expected to have less deposited sediments than low gradient systems where stream power is less 

and, therefore, particles settle. Properly recognizing natural supply regimes is particularly 

important for wetlands, where alteration of sediment supply could mean the difference between 

wetland loss due to accelerated subsidence or loss due to filling. Analytical methods that may be 

used to classify streams for SABS include most statistical tests that allow comparison among two 

or more potential populations. For example, if the central tendencies or distributions for 

28
Framework for Developing SABS Water Quality Criteria U.S. EPA 

measured suspended sediment concentration are different for undisturbed streams from two 

different ecoregions, these two types of streams should be analyzed separately and may require 

different sediment criteria. Issues associated with classification are more fully described in 

Section III.D.2. The sub-classes of waterbody types are then evaluated for existing and nearly 

natural levels of SABS. 

Sediment supply and redistribution are natural processes that can be disrupted, leading to 

impairment of the designated uses of waterbodies. When impairment relates to rates of habitat 

loss or other non-aquatic biological endpoints, natural levels of SABS should be estimated to 

determine appropriate levels that will maintain or restore the designated use. Natural levels of 

SABS can be modeled using site and landscape characteristics or observed within groups of 

reference sites with similar characteristics. The potential natural range of a SABS indicator for a 

set of waterbodies is usually not the same as the observed range of the indicator for the same set 

of waterbodies. Examining the discrepancy between the potential and the observed is an 

instructive exercise in determining the extent and magnitude of SABS imbalances. Like the 

analysis of SABS indicator value ranges, the natural potential and observed ranges of response 

indicator values should also be examined in this step. This exercise will illustrate the extent and 

magnitude of response indicator imbalances. These values may prove useful in determining a 

threshold of non-attainment of designated use in step 5. 

III.B.5. Step 5. Identify a Response Indicator Value that Protects the 

Designated Use 

 III. Technical Elements 

If there is a preexisting criterion for the designated use, for instance, a defined score from a 

benthic invertebrate index, and this criterion is used as the response indicator, then the criterion 

level for attainment identified in step 1 is the value used in subsequent analysis steps. If there is 

no preexisting criterion that is acceptable or if a more specific response indicator is preferred, 

then a response level that protects the designated use should be selected. 

An appropriate transition point may be selected as a threshold of impairment by analysis of

available data. Because natural systems are characterized as responding incrementally to changes 

in exposures, response indicators rarely exhibit an unambiguous inflection between unimpaired 

(or minimally impaired) and impaired conditions. Therefore, threshold levels of impairment 

should be supported with a detailed description of the procedure used to determine the threshold, 

preferably documented with peer-reviewed literature. There are three general ways to set 

thresholds for a given set of analyses on a data set: 

(1) Ad hoc - A subjective approach in which thresholds are arbitrarily set at a specific percentile 

of reference sites, all sites, or some other subset of the data. The result may be biased because it 

depends on how the sites and percentile were selected. In explaining the selected threshold, this 

potential bias and subjective process should be recognized. 

(2) Resource Managers decision – A resource manager sets a threshold that she/he is comfortable 

with - for example, at 90% probability of identifying a degraded resource. Rationale for 

threshold selections can include considerations of costs associated with false positive and false 

29
Framework for Developing SABS Water Quality Criteria U.S. EPA 

negative results. It can also include the resource manager’s preferences regarding acceptable 

uncertainties, tolerable sacrifices, and desirable resource protection. 

(3) Statistical significance – An objective approach that is dependent on the sample size and 

variability. However, subjective decisions must be made in defining a difference to check for, 

perhaps in biomarkers, and the level of significance to use. 

III.B.6. Step 6. Analyze and Characterize SABS/Response Associations 

A specific body of water is impaired when it is not attaining its designated uses. Step 6 describes 

the procedure for identification of the level of SABS that is likely to cause failure to attain a 

designated use. First, it is necessary to show a relationship between the SABS and response 

indicators using one or more of the available quantitative analysis techniques. Analytical 

methods to establish an exposure-response relationship are of two types, based on either 

controlled experiments in the laboratory or field or descriptive analyses of biological and SABS 

indicators as they normally occur in the region, often termed “field observations.” Field 

observations can be analyzed as a continuous or categorical relationship. Next, SABS levels that 

are either detrimental to or protective of the designated use must be identified. This may be 

accomplished by relating SABS indicator values with the transition point for the response 

indicator identified in step 5. 

There is always uncertainty when trying to link exposure levels to an effect, in this case, linking 

SABS levels with use attainment. Awareness of the sources of these uncertainties and 

recognition of assumptions made during study design, data collection, and analysis are 

paramount. Some key issues to consider for dealing with uncertainty are mentioned here. 

Detailed guidance may be more fully described in future technical manuals. 

 III. Technical Elements 

Imbalanced SABS regimes may occur concurrently with other stressors, such as elevated 

nutrients or temperature. In such cases of multiple, simultaneous stressors, it is possible that the 

SABS indicator may be a causal agent of use impairment at only some of the sites used to 

develop the relationship. It is also possible that SABS may indirectly cause effects through an 

intermediate cause, such as settled particles restricting the flow through interstitial spaces in the 

bedded sediments thus reducing food availability, gas exchange, temperature maintenance, and 

waste removal (see Appendix F, Model 2). The SABS would then be considered part of a causal 

pathway that results in a deleterious effect. Controlling for multiple stressors and accounting for 

complex secondary effects is sometimes possible when using controlled experiments (see 

Section III.D.3). However, any correlative association may be confounded and may not be 

causal. These caveats must be considered when applying any of the methods. Nevertheless, the 

SABS indicators should be shown to be associated with a biological response. A SABS criterion 

can then be determined that is likely to result in biological conditions that permit a body of water 

to either attain or not attain its designated use(s). 

Finally, the waterbody classification identified in step 1 and refined in step 4 needs to be 

reevaluated to see if it remains defensible. If further refinement of the classification scheme is 

needed, then the process is reiterated until defensible associations are developed. For example, if

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

classification of streams by size results in similar levels of SABS for non-attainment in each size 

class, then the classification would be unnecessary. However, if classification indicated that 

different levels or measures of SABS would indicate non-attainment, then the classification was 

important in the criteria development process. At this point, a level of the SABS indicator that 

separates attainment from non-attainment for a designated use and waterbody class (the SABS 

criterion) should be established. 

III.B.2. Step 7. Explain Decisions that Justify Criteria Selection 

The scientific basis for setting any SABS criterion should be documented, including the actual 

criterion, magnitude, duration, and frequency variations (if necessary). All the steps used to 

establish this criterion should be recorded as well (including description of the data used). 

Different methods or studies will often indicate different SABS levels. The rationale for 

resolving these differences must be clear, reasonable, and scientifically defensible. Factors that 

may influence the decision may include choosing the most conservative method, selecting the 

method that enables the use of the highest quality data, averaging the results of several methods, 

or incorporating the weight of evidence in other ways. See Linkov et al. (2004) and Stahl et al. 

(2002) for various decisional analysis approaches. 

One way to illustrate options that have been considered is to model expected impacts using 

simulations that reflect various potential SABS criteria. Building models that link criteria with 

impacts for evaluating potential criteria offers a number of advantages. For example, accurate 

predictive models require a thorough working knowledge of a system. If the output of such a 

model does not reflect field observations (e.g., relationships among causes, stressors, and 

responses are not consistent), this might indicate that more information about a system is needed 

to make effective management decisions or that the model needs refinement. Conversely, models 

that accurately reflect the relationships seen in field data may be useful for making management 

decisions. Models also allow virtual manipulation of systems beyond what is typically possible 

via experimentation, and without exorbitant time or cost commitment. For instance, what is the 

effect of setting a criterion at 30% versus 10% fines? If a researcher has developed a model of 

SABS effects on low-gradient streams in forested watersheds with aquatic life designated use, 

then the model could be used to compare the effect on benthic macroinvertebrate assemblages. 

 III. Technical Elements 

Furthermore, if the indicators were collected with a probability-based design, a cumulative 

distribution function can be constructed for the entire resource, known impaired resources, 

known unimpaired resources, and best conditions. Then, various SABS indicator levels can be 

overlaid on these distributions to evaluate the trade-offs of varying criteria levels, giving an 

estimate of error rates associated with the proposed criterion. False positives (identifying a 

waterbody as impaired when it is not) and false negatives (failure to detect truly impaired 

waterbodies) are valuable quantitative indications of uncertainties associated with an established 

criterion. Models can also be used to estimate the costs of remediation to specific criterion levels. 

For instance, what will be the cost of being more protective? What are the accrued societal

benefits at the more protective level? And, what is the cost of having to remediate to a greater 

level as more waterbodies fall within the category not meeting the criterion? 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

III.C. Cross-Cutting Concepts 

III.C.1. Classification of Waterbodies 

As discussed earlier, SABS conditions vary naturally among waterbody types and geographic 

regions because of differences in supply and transport properties. Natural features such as 

geology, watershed topography, waterbody morphology, vegetative land cover, climate, soil 

erodibility and other landscape characteristics contribute to the variability in sediment supply and 

transport (Appendix F, Model 3). Expectations of sediment conditions must be established in the 

context of natural variability before impairment can be assessed. Moreover, certain indicators 

may be much more effective in certain regions or waterbody types than others. The waterbody 

types that form the basic strata are

• Rivers and streams 

• Lakes, ponds, and reservoirs 

• Wetlands 

• Estuaries 

• Coastal marine waters. 

Further classification to account for more complex natural variability in sediment conditions may 

also be needed. Classification to account for natural variability was strongly recommended by 

the U.S. EPA Science Advisory Board.

 III. Technical Elements 

Waterbody types

WQS are typically tailored for different waterbody types. A number of factors, such as flow 

regime, water (and sediment) retention time, sediment input sources, indicator biota, and many 

others make different types of waterbodies distinct. These natural differences imply SABS 

imbalances, and the way that those imbalances are measured and managed, are specific to each 

waterbody type. 

For SABS criteria development, states, tribes, and territories may consider stratifying, at a 

minimum, by the five major waterbody types listed above. Stratifying waterbodies in this way 

will lend organizational and scientific plausibility to the overall criteria development process. 

Approaches for assessing SABS should consider that although waterbody types can be addressed 

separately, they are not independent of one another, but rather, are part of interconnected and 

larger basins or watersheds. The interconnectedness of systems highlights the need for integrated 

assessment and control of SABS for all waterbody types. 

Regions 

Stratification by region may be essential for discerning major locational differences in 

waterbodies (e.g., ecoregions, biogeographic provinces, physiographic/geologic regions, climatic 

regions). For instance, Simon et al. (2004) used ecoregional stratification to produce suspendedsediment ‘reference’ values using the flow that occurs, on average, every one and a half years as

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

a measure of effective discharge for suspended-sediment transport. Regional stratification may 

also serve to simplify the criteria development process by limiting the waterbody types, 

analytical data to be reviewed, and range of classes within waterbody. 

The well-documented “ecoregion” system (Omernik 1995; Omernik et al. 1988) may be a useful 

framework to stratify regions for SABS assessment because it has been used successfully to 

develop biological criteria. If it is found to be appropriate for the development of regional SABS 

criteria, it is encouraged that the scale of ecoregion aggregation and division be determined. The 

degree of variability within each of the ecoregions would determine the final regional scheme. 

Ecoregional stratification does not preclude the use of other classification schemes if they are 

judged to be more appropriate. 

Classification beyond Waterbody Types and Regions

Even after stratifying by waterbody type and region, the variation of natural SABS levels within 

these strata may require finer levels of classification or classification based on other factors. For 

example, streams within one region may have low-gradient and high-gradient classes. A 

measurement of waterbody size (e.g., stream order, lake area, catchment area, discharge) may 

also be used to classify waters. Lakes may be classified by size or retention time. These different 

classes within waterbody types have different levels of naturally occurring SABS and may 

respond differently to an imbalance of SABS. The actual number of classes recognized within a 

stratum depends on a number of factors, including variation among classes in natural levels of 

SABS, similarities and differences among classes in effective response indicators, and data 

available for development of criteria. 

 III. Technical Elements 

The goal of defining classes within strata is to achieve a balance between accounting for the 

natural differences in SABS among individual waterbodies and finding some commonalities 

among waterbodies so that each river or lake does not become a class. One option is to identify 

the waterbody type in the watershed or basin that is less tolerant to shifts in sediment supply. 

Criteria developed for this waterbody type may automatically set the criteria for upstream

waterbodies, which may be sources of sediment but resilient in the face of episodic spates of 

increased sediment loads. Taking this tact may reduce the number of classes and customized 

criteria. It may also enable remediation plans on a basin or watershed scale (see the example for 

the Chesapeake Bay, Section III.D.3). 

Classification requires defining likely classes and describing indicator ranges among proposed 

classes. Classification should progress using data from waterbodies that are unimpaired. Splitting 

into more refined classes has possible drawbacks. There may not be enough sites to perform a 

statistical evaluation or enough resources to collect data from the field. Too many classes may 

make it difficult to know which criteria to apply in a particular case. Classification using 

stochastic or deterministic models does not require as many data points per class as classification 

methods based exclusively on statistical analysis of field data. However, the cost (in terms of 

dollars and time) of initiating a new model development effort may be excessive. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

III.C.2. Indicators - Exposure and Response Measurements

The selection of indicators is a major element within the Framework and is a key step in defining 

impairment and monitoring management actions. When attempting to meet WQS, resource 

managers rely upon narrative or numeric criteria to determine whether a designated use is being 

protected. In many cases, resource managers select specific, measurable variables, or indicators, 

to express a narrative standard in terms of the pollutant of

concern. A numeric target value for the variable is a 

threshold between the impaired and unimpaired designated 

use of the waterbody. The most effective indicators are 

quantitative measures that can be used to establish the 

relationship between pollutant sources and their impact on 

water quality. 

An ideal indicator is

measurable, quantifiable, 

reproducible, and 

comparable.

There are many indicators of SABS-caused impairment. Most fall into one of five discrete 

categories: (1) water column measures, (2) substrate measures, (3) channel/bathymetric 

characteristics, (4) biotic response measures, and (5) functional measures. The first three 

categories are types of exposure measures; the last two are measures related to effects and 

designated uses. Indicators should be appropriate to the waterbody type (Table 4) and allow 

analysts to efficiently discriminate impaired from unimpaired conditions. 

When adopting a particular indicator or suite of indicators, it is important to consider various 

technical, practical, and socioeconomic considerations. An ideal indicator is measurable, 

quantifiable, reproducible, and comparable. In addition, it is important to weigh the costs of 

obtaining data compared against the value of the information produced. Each potential indicator 

has specific measurement methods, appropriate applications, precedent uses as indicators, and 

ranges of possible criterion values. When applied properly and judiciously, indicators can 

provide the requisite understanding of SABS processes to show the link to biological resources 

or designated uses and to identify the management actions with the highest likelihood of success. 

In practice, selection of appropriate indicators will require investigation into measurement 

techniques, specific applicability, and performance characteristics that cannot be completely 

reviewed in this Framework. 

 III. Technical Elements 

Exposure Measures 

There are three main classes of sediment-exposure indicators: (1) water-column measures, (2) 

substrate measures (including bedload), and (3) channel/bathymetric characteristics. Each can be 

characterized by one or more metrics tailored to the specific indicator. For example, metrics 

associated with suspended sediment and turbidity tend to be more effective in identifying watercolumn impairments in still or slow-moving water, such as in lakes, estuaries, and some coastal 

areas, and some rivers at sluggish flows. In faster-moving waters, bedded sediments and bedload 

may have relatively greater impacts on habitat and biota than water column impairments. This is 

in part due to the episodic nature of suspended sediment flux in faster-moving waters, in which 

most aquatic organisms have adaptive characteristics for withstanding short-term exposures to 

turbid waters. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Table 4. Suitability of SABS indicators by waterbody type. z = appropriate application,  = 

limited applicability, { = not appropriate 

Rivers and 

Streams 

Lakes, Ponds,

and Reservoirs Wetlands Estuaries

Coastal Marine

Waters 

Suspended Sediment 

Turbidity z     

Total Suspended Solids z     

Suspended Sediment

Concentration z z z   

Light Penetration  z  z  

Water Clarity z z  z z 

Bedded Sediment 

Bedload Sediment z { {  { 

Percent fine sediment at

surface z z z z { 

Percent fine sediment at

depth z  z z { 

Sedimentation rate z z z z  

Embeddedness z z {  { 

Suspendable Solids z z  z { 

Particle size distribution z z z  { 

Particle size geometric 

mean 

z z z  { 

Substrate Stability z  {   

Relative Bed Stability z { { { { 

Bottom Deposit Depth  z z z z 

Residual Pool Volume z { z  { 

Bank Stability z z z z { 

Waterbody Dimensions z z z z { 

Bathymetry z z z z z 

Riffle/Pool ratios z { { { { 

Gradient z {  { { 

Sinuosity z { { { { 

Incision z { z { { 

Response Indicators 

Biological Measures z z z z z 

Eroding Banks z z { z z 

Reservoir Filling Rate z z z z { 

Filter Clogging z z { { { 

 III. Technical Elements 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Suspended sediments reduce water clarity and light penetration. The particles can be abrasive, 

clogging biological and man-made filters. If the particles are organic or algal, they may also alter 

water quality via decomposition and shift in community structure (such as an altered food 

source). Suspended sediments also have the potential to settle. No single indicator measures 

exposures that would be adequate to reflect all of these effects. Therefore, it may be judicious to 

measure a suite of indicators. 

Physical measures associated with substrate or bedded sediments include embeddedness, percent 

coverage or percent volume of fine sediments, and substrate stability indices. Bedload transport 

is largely responsible for changes in channel morphology and habitat. 

Channel/bathymetric characteristics are measures associated with the morphological stability that 

change near-shore or wetted basin physical characteristics. They can reveal effects of erosion, 

transport, and deposition on channel morphology and habitat conditions. Channel/bathymetric 

characteristics can be used to infer past, present, and potential future erosional and depositional 

processes. A process-based understanding of the fluvial system can lead to development of 

causative links to management practices aimed at remediation of sediment problems. 

Biotic Response Measures

The existing biomonitoring programs in many states, tribes, and territories sample aquatic life 

that may be sensitive to SABS. Biological metrics can provide discriminating indicators for 

SABS associated with impairment of the aquatic conditions. Aquatic organisms may be 

measured in the water column as well as in or near the sediment or substrate. Because the 

presence, diversity, and productivity of aquatic organisms can be used to infer habitat suitability, 

biological indicators can complement physical 

exposure indicators in SABS criteria 

development as well as provide information 

on overall biological integrity. Biotic 

responses may be measured or calculated in 

numerous ways, including metrics of taxa 

assemblages or presence and abundance of 

specific taxa such as threatened, endangered, 

invasive, or exotic species. For example, 

researchers have assigned sediment tolerance values to specific organisms in stream

environments, allowing calculation of metrics that may prove uniquely responsive to SABS 

effects (Relyea et al. 2000; Yuan 2006). 

 III. Technical Elements 

Biological metrics can be 

discriminating indicators for SABS 

associated with impairment of the 

aquatic conditions though they 

may not be sufficiently specific for 

diagnosis of SABS impairment. 

It is important to note that biological measures may not always indicate or diagnose SABS 

impairment. An excess of SABS may result in a predictable change in the biota. However, any 

given change in the biota may not be attributable definitively to SABS. SABS is only one of 

many stressors in aquatic systems that can cause similar responses in the biota.

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

III.C.3. Integration and Synthesis of Multiple Methods

One conclusion of the U.S. EPA Science Advisory Board was that no single method would 

suffice for complete criteria development in every situation and that multiple methods applied 

simultaneously (synthesized) may be more appropriate for criteria development. This conclusion 

recognizes the complexity of natural SABS settings, the variable applicability of methods in 

those settings and the flexibility required by states, tribes, and territories to use their SABS data 

to their best advantage. Various methods are described in Section III.D, organized by groupings 

that are appropriate for measuring and calculating SABS indicators, for classifying waterbodies, 

and for developing associations between indicators of SABS with indicators of designated uses. 

A key element is that the methods and resulting evidence are best used in combination. Results 

from different methods can provide independent collaboration of scientific findings. They are 

best applied when interpreted in terms of a watershed or interconnected waterbodies. In other 

words, the evidence should be evaluated in such a way that upstream criteria protect not only the 

immediate waterbody but downstream designated uses as well. Examples of how these methods 

could be used in combination (a synthesis of methods) are described in Section III.E. 

III.D. Methods Applicable within the Framework

At this time, U.S. EPA has been examining various methods for use in developing water quality 

criteria for SABS that are applicable within this Framework. Some of these methods are 

presented here as they relate to three activities: (1) measuring suspended and bedded sediments, 

(2) evaluating water body classification, and (3) associating suspended and bedded sediments 

with designated uses. These methods are generally applicable in steps 3, 4, and 6 of the 

Framework, respectively. The presented statistical methods can often be applied to more than 

one activity. Some methods are well developed, whereas, others may have been tested in only 

certain classes of waterbodies. All these methods need to be evaluated and applied to local 

situations. The Framework is flexible, allowing many variations in the combination of indicators, 

classifications, and analytical methods. This flexibility allows resource managers to customize 

the criteria development process to specific needs and capacities. It also encourages justification 

for the choices made in customizing the process. While these methods are explained 

individually, in practice they will be applied simultaneously or in combination. 

 III. Technical Elements 

(1) Measurement of Suspended and Bedded Sediment (Step 3) 

• Readily Available Measures 

• Sediment Transport Curves 

• Relative Bed Stability 

(2) Waterbody Classification (Step 4) 

• Empirical Classification (Reference Condition) 

• Fluvial Geomorphology 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

(3) Associating Suspended and Bedded Sediment with Response Indicators (Step 6) 

• Controlled Experiment 

• Field Observational Studies 

– Percentile Analysis (including Reference Condition Methods) 

– Exposures and Effects Analysis 

– Conditional Probability Analysis 

• Waterbody Use Functionality 

Brief examples of some of these methods are included with the descriptions below. The 

examples use data sets generously provided by the state of Oregon, the Chesapeake Bay 

Program, and the U.S. EPA Environmental and Monitoring Assessment Program (EMAP). These 

example analyses demonstrate that acceptable data sets may be already available or can be 

developed within a few years. 

To select a SABS indicator value that is protective of a designated use, common sense and clear 

thinking are indispensable. This section will provide some analytical methods and a few tips, but 

the investigators should provide the clear thinking and rationale for each of their choices. 

Choices of indicators and thresholds require reliance on assumptions regarding mechanisms, 

modeled relationships, bias, measurement precision, and other analytical elements. Selection of a 

protective response level requires a trade-off between full protection and what the public will 

support and implement. These assumptions and compromises should be examined transparently 

and often during the criteria development process. The four elements that have the strongest 

impact on criteria development include selection of endpoints and measurements, classification, 

methods for demonstrating associations, and selection of criteria values. 

 III. Technical Elements 

Selection of endpoints and measurements should support the goal of showing a causal 

relationship between SABS and an impaired designated use. The most mechanistically plausible 

relationships are those that are specific rather than general, rely on few classifications, and make 

direct association with few intervening steps. 

• Specific indicators are better than general ones. The association of stoneflies, a type of 

benthic invertebrate, and silt free substrates is more definitive than an invertebrate index 

or even the number of ephemeroptera, plecoptera, and trichoptera (EPT) taxa with silt 

free substrates. This is because most stoneflies have very narrow habitat and water 

quality requirements, whereas benthic macroinvertebrates occupy many niches. EPT, a 

metric of mayflies, stoneflies and caddisflies, includes mayflies that burrow in sediment 

and caddisflies that thrive on fine particulate matter. Indices are designed to detect a wide 

range of causes rather than impacts of SABS alone. 

• Indicators are better if they rely on few classifications. Relative Bed Stability is a 

measure that inherently uses channel characteristics in calculation of the metric. Because 

the channel characteristics incorporate the same determinants that might be used to 

classify sites, more sites can be lumped into a single class, with individual site 

differences accounted for in the metric. This reduces the chances of a categorical error in 

site classification, though some gross and easily recognized class may still be needed 

(e.g., wadeable streams within a single ecoregion). 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

• Indicators with direct associations are better than those with indirect pathways. An 

association of suspended sediment concentration (SSC) and extent of eelgrass bed is 

more readily demonstrated than SSC and blue crab catch. This is because the catch is 

dependent on effort as well as abundance, and sediment does not directly affect the crab 

as much as it affects eelgrass beds. Therefore, there is an indirect association rather than 

a direct one. In a conceptual model there would be multiple boxes and arrows to make 

the connection. 

Classification is a statistical method for removing variation due to factors other than SABS that 

affect the SABS and response indicators. It is most appropriate and necessary for observational 

field survey data. Classification may be unnecessary if assessment endpoints are specific. If field 

data are plotted for the presence of brook trout and total suspended solids, the classification is de 

facto for those streams with brook trout. Classification is explicit in controlled experiments, 

where the laboratory conditions or experimental setting defines the class. Classification is 

looking as much for similarities as it is for differences. No two sites are the same. However, by 

placing different sites in the same class, we are recognizing their relative similarity among all 

sites in the data set. In doing so, we allow for potential bias and error (some sites are not as 

similar as others) and simplify criteria application (by not expecting definition of site-specific 

criteria). 

Methods for demonstrating associations between the SABS measurement and the response 

measurement can show that an adverse effect is likely to occur given some level of SABS. To 

demonstrate an association, it is recommended that one use at least two methods that rely on 

different assumptions, different data sets, and different statistical methods. For instance, results 

from controlled experiments can be compared with characterizations based on independent field 

observations. 

 III. Technical Elements 

When SABS are characterized with respect to reference sites or acceptable physical conditions, it 

is possible to describe deviation from the reference conditions in terms of SABS measurements 

alone. These deviations may be interesting and perhaps even indicate increased human activity in 

the watershed, but it is possible that they are also insignificant to the function and attainment of 

the designated use. Until the SABS indicators are linked to the response indicator (selected 

because it represents the designated use), changes in the SABS indicator cannot be interpreted in 

the criteria setting context. 

Selection of a criterion value is often a value judgment that can be somewhat distanced from

scientific methods, especially when clear inflection points are not evident in stressor-response 

curves. Despite the many uncertainties, one can determine defensible criteria when different data 

sets and different types of associations support or corroborate one another. Examples of different 

types of evidence include: 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

• Plausible effects based on laboratory and field exposures 

• The interactions among gradient, flow, substrate, and other variables 

• The connectedness of abiotic and biotic components in ecosystems

• Characteristics of chronic and episodic exposures to SABS 

• Levels of SABS in upstream locations and how they relate to downstream resources 

with different tolerances to SABS. 

III.D.1. Measurements of SABS; Applicable in Step 3 of the Framework

Measurements are usually required for sources, exposures, and responses of SABS. The 

mechanistic pathways through which sediment can affect biological assemblages can be depicted 

in conceptual models. Associations between indicators that are close together in the conceptual 

model (only one arrow connecting) are easy to demonstrate because there are few unmeasured 

variables that will affect the interaction. Keep in mind that the measurements that are selected 

will need to be associated with a designated use so that an effect level can be demonstrated. 

Readily Available Measures

Some of the technical issues and considerations for selecting measurements of SABS were 

described as part of steps 2, 3, 4 and 5 and in Section III.C.2. Table 4 lists possible indicators 

sorted by their usefulness in measuring suspended or bedded sediment and their applicability to 

waterbody type. Naming conventions are listed in ASTM’s Terminology for Fluvial Sediment, D 

4410-98 (2005), which contains the widely accepted definitions for riverine and most other 

freshwater environments. Of the five fundamental sedimentation methods listed by ASTM D 

4410-98, erosion, transportation, and deposition are relevant to the SABS guidelines. 

Approaches are also reviewed and published by ASTM (2005), for example, turbidity (ASTM D 

1889-00) and suspended sediment concentration (ASTM D 3977-97). The USGS has been a 

leader in the development of reliable measures of the fluvial-sediment method and their Web site 

is a good place to find useful methods for measuring SABS 

(http://water.usgs.gov/osw/techniques/sediment.html). 

 III. Technical Elements 

The mechanistic pathways through which sediment can affect biological assemblages are 

depicted in several conceptual models (Appendix F). For suspended (Model 1) and bedded 

sediments (Model 2), boxes are highlighted in grey that directly measure characteristics of 

sediment that affect aquatic life. For instance, Secchi distance could be selected to measure light 

penetration. Substrate stability and substrate movement and scouring are more dynamic 

processes that can be inferred, measured, or modeled. Land cover/land use and in-stream factors 

that alter sediment supply are depicted in Model 3. Whichever SABS measurements are selected 

should be associated with a response variable so that an effect level can be estimated. 

Associations between indicators that are directly connected conceptual model are easier to 

confirm because there are fewer unmeasured variables that will affect the interaction. The 

following two sections describe two methods, sediment transport curves and Relative Bed 

Stability (RBS), that may be less well known than more commonly used measures of SABS. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Sediment Transport Curves

Sediment transport curves (STC) are graphics for displaying the relationship between measured 

sediment values (either bedload or suspended sediment load) and measured or expected flow or 

discharge. Departure of measured sediment values at a given flow from expected sediment loads 

may help indicate the type and magnitude of impairment and may help a resource manager 

identify targets for reestablishing more stable sediment conditions for the waterbody. 

Stream stability shifts are reflected in STCs, also termed sediment rating curves, where measured 

sediment values are regressed against measured discharge. The upward shift in the slope or 

intercept values of the STC are due to increased sediment supply resulting from a variety of 

sources. The upward shift in the STC exponentially increases the sediment yield for selected 

increments of stream-flow. Land uses that increase stream-flow magnitude and duration can be 

instrumental in accelerating "flow related" increases in sediment. Figure 5, below, provides an 

example of STCs for two rivers of different channel type, sediment budget, and stability. 

 III. Technical Elements 

Figure 5: Suspended sediment transport curves for South Fork, Forked Deer and Hatchie River 

(from Simon, 1989). 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Although understanding of STCs is limited, they may have some application potential related to 

criteria if reference relationships can be developed. Suspended sediment concentration, for 

example, is often correlated with flow rate, and the literature offers some evidence that sediment 

transport coefficients and flow are predictably interrelated within a given region (Hawkins 

2002). In an examination of STCs for suspended sediment and bedload of 160 Rocky Mountain 

rivers and streams, Troendle et al. (2001) were not able to show differences in dimensionless 

sediment transport attributable to geomorphic channel type, but the analysis did reliably detect 

departure of generally unstable stream types as a group from values expected of stable channels. 

Ongoing work in developing and testing reference STCs continues mainly in the Rocky 

Mountain States with some investigations in other regions of the United States and Great Britain. 

Preliminary findings suggest that channel type plus stability may reveal a stronger relationship 

than channel type alone. 

Relative Bed Stability

Relative bed stability (RBS) is a comparison of bed substrate size divided by the mobile diameter 

at bankfull flow, which is proportional to the 

estimated shear stress at bankfull flow. Although 

many human activities directly or indirectly alter

stream substrates, streambed particle sizes also 

vary naturally in streams with different sizes, 

slopes, and surficial geology (Leopold et al. 

1964; Morisawa 1968). The size composition of 

a streambed depends on the rates of supply of 

various sediment sizes to the stream and the rate 

at which the flow takes them downstream

(Mackin 1948). Topography, precipitation, and 

land cover influence sediment supply to streams, 

but the source of sediments is the basin soil and 

geology, and supplies are greater where these 

materials are inherently more erodible. 

Relative Bed Stability is an index of 

substrate mobility with respect to 

physical characteristics of the 

waterbody. Substrates are 

expected to move a calculable 

degree for each natural hydrologic 

and geomorphic condition. When 

observed substrate mobility is 

considerably greater or less than 

the predicted, human-induced 

SABS stresses are indicated. 

 III. Technical Elements 

Once sediments reach a channel and become part of the streambed, their transport is largely a 

function of channel slope and discharge during floods (in turn, discharge is largely dependent 

upon drainage area, precipitation, and runoff rates). For streams that have the same rate of 

sediment input from watershed erosion, steeper streams tend to have coarser substrates than 

those with lower gradient, and larger streams (because they tend to be deeper) have coarser 

substrates than small ones flowing at the same slope. However, this transport capability can be 

greatly altered by the presence of such features as large woody debris and complexities in 

channel shape (sinuosity, pools, width/depth ratio, etc.). 

The combination of these factors determines the depth and velocity of streamflow and the shear 

stress (erosive force) that it exerts on the streambed. By comparing the actual particle sizes 

observed in a stream with a calculation of the sizes of particles that can be mobilized by that 

stream, the streambed stability can be evaluated. Furthermore, the degree to which streambed 

instability is due to accumulation of fine sediments can be evaluated, and watershed data can be

42
Framework for Developing SABS Water Quality Criteria U.S. EPA 

examined to infer whether the sediment supply to the stream may be augmented by upslope 

erosion from human activities and natural disturbances. 

RBS is calculated as the ratio of observed bed substrate particle diameter divided by the 

calculated “critical” or mobile particle diameter (Dingman 1984; Gordon et al. 1992). RBS is the 

inverse of the substrate “fining” measure calculated by Buffington and Montgomery (1999a,b) 

The RBS is conceptually similar to the “Riffle Stability Index” of Kappesser (2002), the bed 

stability ratio discussed by Dietrich et al. (1989), and the ratio of critical near-bed water velocity 

to actual near-bed velocity defined by Jowett (1989). 

When evaluating the stability of whole streambeds (vs. individual bed particles), observed-bed 

substrate is typically represented by the average diameter of surface substrate particles (e.g., D50

or the geometric mean). The widely accepted procedures for measuring substrate particle size 

distribution in a stream channel typically employ a systematic “pebble count" as described by 

Wolman (1954). For calculating critical (mobile) substrate diameter in a natural stream, it is 

necessary to estimate average streambed tractive force, or shear stress, for some common 

reference flow conditions likely to mobilize the streambed. Bankfull discharge is typically 

chosen for this purpose although this is more appropriate for gravel-bed streams than for “livebed” streams such as naturally sand-bedded streams that transport bedload at lower flows. 

One method for estimating the critical substrate particle diameter in a stream is based on 

sediment transport theory (e.g., Simons and Senturk 1977), which allows an estimate of the 

average streambed shear stress or erosive tractive force on the bed during bankfull flow. When 

developing this method, EMAP researchers (Kaufmann et al. 1999; Kaufmann and Larsen 2006) 

used physical habitat measurements collected in synoptic surveys (Kaufmann and Robison 1998) 

to estimate the channel characteristics affecting bed shear stress at bankfull flows. These field 

measurements include bankfull channel dimensions, slope, channel complexity, and large woody 

debris. Using channel and substrate data as described above, EMAP researchers modified the 

Dingman (1984) critical diameter calculation to accommodate losses in shear stress resulting 

from large woody debris and channel complexity (Kaufmann et al. 1999). The reductions in 

shear stress and, therefore, critical diameter, caused by these roughness elements allow fine 

particles to be more stable in a stream of a given slope and depth. 

 III. Technical Elements 

RBS values in EMAP sample streams range from 0.0001 to 1000. A high positive value of RBS 

(e.g., 100-1000) indicates an extremely stable, immovable stream substrate like that in an 

armored canal, a tailwater reach below a dam, or other situations where the sediment supply is 

low, relative to the hydraulic competence of the stream to transport bedload sediments 

downstream (Dietrich et al. 1989). Very small RBS values (e.g., 0.0001-0.01) describe a channel 

composed of substrates that are frequently moved by even small floods. 

Scientists hypothesize that given a natural disturbance regime, sediment supply in watersheds not 

altered by human disturbances will be in approximate long-term dynamic equilibrium with 

transport. Kaufmann et al. (1999) argued that, on a regional scale, streams will adjust sediment 

transport over time to match supply from natural weathering and delivery mechanisms driven by 

the natural disturbance regime. Consequently, for streams with sediment transport limited by 

competence (critical shear stress) rather than total capacity (stream power), RBS in appropriately 

43
Framework for Developing SABS Water Quality Criteria U.S. EPA 

stratified regional reference sites should tend towards a range characteristic of the climate, 

lithology, and natural disturbance regime (Kaufmann and Hughes 2006). 

In support of this assertion, Stoddard et al. (2005) found that Log10 (RBS) in reference sites 

differed among aggregated ecoregions of the Western U.S.A., where, for example, the 25th

percentiles of reference sites in mountain ecoregions ranged from -0.6 to -1.1 compared with -1.7 

for plains ecoregions. RBS values considerably lower than 1.0 (Log10 RBS <<0} may be the 

norm in streams draining watersheds relatively undisturbed by humans if those streams are 

characterized by natural features (lithology, soils, topography, climate, and vegetation) that are 

conducive to high rates of sediment supply and transport. 

In particular, naturally fine-bedded streams with unstable beds (i.e., Log10RBS <<0), would be 

expected to drain relatively undisturbed watersheds where streambed textural responses are 

constrained by a lack of coarse particle sizes in sediment inputs from the drainage area. In 

addition, RBS in streams with minimal human disturbance might be expected to differ 

systematically across a geomorphic gradient from streams with transport dominated by bedload 

to those dominated by suspended load – generally this occurs in a downstream direction in the 

stream continuum. Log10 (RBS) values considerably lower than zero may be expected in these 

examples of naturally fine-bedded alluvial streams where transport is limited by average stream

power rather than bankfull shear stress. 

Alternate hypotheses concerning the expected values of RBS using synoptic data from EMAP 

surveys are being evaluated. As the EMAP approach for assessing excess streambed 

sedimentation in low-gradient, fine-bedded streams and rivers is refined, it may be necessary to 

modify the method (currently based on the competence of bankfull floods to move given sizes of 

particles). For these waters, it is useful to estimate bed stability in terms of the proportion of the 

year that the bed is in motion. 

 III. Technical Elements 

In watersheds where sediment supplies are augmented relative to a stream’s bedload transport 

competence, evidence will likely show an excess of fine sediments (Dietrich et al. 1989). Very 

small RBS values (e.g., 0.0001- 0.01) indicate excessive amounts of fine particles compared with 

expected values in most relatively undisturbed watersheds. Such evidence of excess fine 

sediments in the stream bed (RBS<<1) typically occurs when land use activities increase 

hillslope erosion (Lisle 1982; Dietrich et al. 1989; Lisle and Hilton 1992), especially when there 

is also damage to riparian vegetation. 

In streams draining basins of equal erodibility, RBS values should decrease in proportion to 

increases in sediment supply above that provided by the natural land disturbance regime. To the 

extent that human land use increases sediment supply by land erosion within regions of relatively 

uniform erodibility, RBS of streams in surveys should be inversely proportional to basin and 

riparian land use intensity and extent (Kaufmann et al. 1999; Kaufmann and Larsen 2006). 

Finally, as the basin lithology within a geoclimatic region becomes more erodible, the RBS 

steeply declines with progressive disturbance (Kaufmann and Hughes 2006). As demonstrated 

for streams in the Pacific coastal region by Kaufmann and Larsen (2006), this means that any 

given amount of land use disturbance is expected to augment sediment supplies to a greater 

degree in basins underlain by erodible rocks than by more resistant rock (Figure 6). 

44
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Figure 6. RBS in streams of the Coast Range ecoregion of Oregon and Washington as a function 

of a relative disturbance gradient in hard volcanic and soft sedimentary geologies (Kaufmann et 

al. 2004). 

 III. Technical Elements 

stimated 

lages

d

re

that

e low

tent

iting 

Figure 7. RBS in streams of the Coast Range 

ecoregion in relation to EPT taxa richness 

(Kaufmann et al. 2004). Data points represented 

with an “x” have 20% or more bedrock at the 

site. Circles are sites with less than 20% bedrock.

Once the degree of sedimentation is e

for sample sites, deviations from expected 

values can be examined in relation to key 

aquatic species, guilds, or biotic assemb

(algae, macroinvertebrates, fish, rooted 

aquatic plants). A relationship observe

between RBS and the biotic metric is positive

evidence that excessive fine sediments a

affecting aquatic life uses (Figure 7) and

the RBS indicator may be a reliable basis for 

establishing SABS criteria. Scatter at th

end of the plot may be due to poor biological 

conditions that are attributable to stressors 

other than RBS. These patterns are consis

with the hypothesis that sediment is lim

biota when the upper limits of the plot are

showing a response. In large, representative 

surveys of sites from across an ecoregion, the 

upper limits represent the best biological 

conditions that can be expected for the 

corresponding RBS values.

45
Framework for Developing SABS Water Quality Criteria U.S. EPA 

 III. Technical Elements 

II.D.2. Waterbody Classification: Applicable in Step 4 of the Framework

ediment is a natural component of aquatic ecosystems. Some ecosystems, by their very nature, 

 that 

fied

he natural sediment regime for a waterbody can be estimated based on geographical, 

nce

mpirical Classification

I

S

have evolved under conditions of extremely low sediment supply and others with a lot. Some

systems evolved with unstable substrates and others with stable substrates. Some experience a

steady supply of sediment and others have periods of sediment starvation and periods of 

sediment inundation. It doesn’t make sense to apply very low sediment criteria to a system

would naturally experience a heavier supply of sediment. Similarly, it would be inappropriate to

permit high levels of fine sediments in a system that is normally characterized by cobbles or 

bedrock substrate. Therefore, aquatic systems with similar sediment regimes need to be classi

and sorted into similar categories or arranged along a predictable continuum so that appropriate 

sediment criteria can be developed and applied. 

T

geomorphic, and climatic characteristics of waterbodies in a nearly natural state (refere

conditions). We refer to this method as the Empirical Classification Method. The Fluvial 

Geomorphology Method is based on model building and field observation and is useful for

selecting stable sites and avoiding those in successional states. 

E

fers to an investigation of SABS conditions that can be expected in 

e

al 

lassification techniques could be

s

it

ifferences. For this reason, the classification techniques are 

he first step in empirical classification is identifying wholly natural or minimally disturbed 

ved

Empirical classification re

systems that are functioning in pristine or minimally disturbed watersheds. The expectations ar

not uniform across all systems. Rather, they vary according to variations in underlying geology, 

soil characteristics, climate, vegetative types, and other natural determinants. At the heart of 

empirical classification is the identification of the natural determinants that are most influenti

to variations in SABS conditions. Once determinants are identified, they can be used to describe

distinct site classes or a continuum of classes. The SABS conditions observed in those sites with 

minimal landscape disturbance become the standard to which any other site within the class can 

be compared. 

C

used to identify degraded site classe

with respect to SABS. However, if the 

differences attributable to natural 

variation were not first identified,

would be difficult to distinguish true

degradation from acceptable natural d

best applied in sites with no known impacts or few impacts if non-impacted sites are nonexistent. 

Sites with few or no impacts are generally termed reference sites as these are the sites to which 

we refer when defining unaltered (or best observable) SABS conditions. 

At the heart of empirical classification is 

ential to 

the identification of the natural 

determinants that are most influ

variations in SABS conditions. 

T

reference sites. After removing sites with known impacts, it is assumed that any observed 

variation in SABS conditions is due to natural factors. The next step is to explain the obser

variation in SABS conditions in terms of natural determinants. The step described above 

regarding definition of reference SABS conditions and comparison to those conditions for

46
Framework for Developing SABS Water Quality Criteria U.S. EPA 

 III. Technical Elements 

6 of

dentifying Reference Sites. Sediment supply and hydrology respond to most landscape 

es.

al

er

treams in catchments that have experienced historic landscape disturbance by human activities 

odifications within the channel or waterbody are also important for defining sites with nearly 

. 1992).

diment 

n

deliberative process for identifying reference sites includes listing all conditions that should be 

ed. Persons

he following are examples of possible criteria for selecting reference streams based on 

be

determination of imbalances is really beyond the scope of the classification exercise but is 

addressed in subsequent sections. If analytical anomalies are discovered as indicated in step

the Framework, it may be necessary to return to this step and reclassify. 

I

modifications. Thus, contemporary land use data are important in identifying reference sit

Current land use data are available for most of the contiguous U.S. (e.g., LANDSAT), and the

technology is advancing rapidly so that more contemporary data are being made available 

rapidly. Historic land uses should also be considered when selecting sites with nearly natur

sediment regimes, especially for bedded sediments. The time required for stream channels to 

return to equilibrium after landscape alteration is on a scale of decades to centuries, if not long

(Trimble 1974; Schumm 1977; Brunsden and Thornes 1979; Trimble 1999). 

S

for an extended time or intensity may still be undergoing geomorphic readjustment. Unless this 

is an acceptable class in itself, these sites should be excluded from the reference data set. Other 

waterbody types may also require considerable time to reach equilibrium after disturbance in the

watershed. Historic land use data can often be reconstructed from tax data, historic photographs, 

and historic diaries. Techniques have been developed by fluvial geomorphologists to identify or 

infer past land use disturbance (e.g., dendrochronology, sediment profile dating, floodplain and 

terrace coring, etc.) (Knighton 1984). These can be used to investigate past impacts within a 

potential reference catchment though they may be prohibitive in terms of cost, time, and 

expertise. 

M

natural sediment regimes. The presence of dams, channelization, dredging, and diversions will 

all affect in-stream sediment dynamics. Dams alter the sediment supply and hydrology of rivers

and, therefore, have dramatic impacts on sediment dynamics, often for long distances 

downstream (Walker 1985; Reiser et al. 1989; Gregory and Madew 1982; Gordon et al

Channelization, dredging, and other channel modifications alter stream channel geometry 

because channel geometry is related to stream power and, therefore, sediment transport, se

and channel features can migrate downstream and upstream following channel impacts, causing 

long-term channel instability and altered sediment dynamics (Miller 1991; Simon and Hupp 

1992). Water diversions alter the hydrology of receiving streams and the resulting reduction i

flow can lead to channel destabilization by sediment accretion. 

A

met for a site to be designated as reference. Criteria should address measures that are 

independent of the SABS and response indicators for which criteria are being develop

familiar to the region are most knowledgeable about what factors might be used. 

T

information about land use/land cover and stream morphology. Obviously, criteria would

differently customized for other waterbody types and prevailing regional stressors. 

47
Framework for Developing SABS Water Quality Criteria U.S. EPA 

• Upwards of 95% of the watershed is in natural and undisturbed cover. 

• Historical land uses did not disturb more than 10% of the land in the last 50 years or more 

than 25% of the land in the last 100 years. 

• Activities in the portions of the watershed are not in natural cover or are not in sediment 

generating land uses, such as mining, clear-cut logging, or cultivation on steep slopes. 

• Roads cross the stream once per kilometer or less and do not dominate riparian areas. 

• The stream channel is not altered by dams, channelization, dredging, or diversions within 

10 miles upstream of the sampling location. 

• The stream channel was not altered in the last 50 years. 

• Stream channel is not in an erosive successional stage. 

Reference Site Identification in Oregon 

The Oregon Department of Environmental Quality (ODEQ) is in the process of establishing 

SABS criteria in wadeable streams. As a first step in the process, reference sites were 

identified using multiple types of quantitative and qualitative information (Drake 2004). To 

identify reference sites, ODEQ used GIS analysis and aerial photos or thematic mapping 

data, or both, to pre-screen areas and find watersheds with minimal human disturbance. 

Using best professional judgment (BPJ), resource specialists edited the list of potential sites 

within unimpaired areas. A Human Disturbance Index (HDI) was developed for the 

candidate reference reaches and watersheds based on reach level observations and 

watershed-scale geographic information. The HDI score was used to help select and rank 

reference sites in a basin or region. Verification of reference sites includes evaluating 

physical habitat and biological and water quality data. Outlying data may indicate problems

that would exclude sites from the reference set. After identifying reference sites, ODEQ 

went on to investigate differences in SABS indicators among potential site classes. The 

studies revealed that ecoregions are reasonable determinants of natural SABS variations. 

 III. Technical Elements 

Identify Potential Class Determinants. The naturally occurring factors that can potentially 

affect SABS supply make a lengthy list. Well established empirical and theoretical relationships 

describe the effects of landscape topography, climate, and geology (including soil properties) on 

sediment dynamics (examples in Knighton 1984 and Gordon et al. 1992). Classification 

determinants may include underlying geology, soil type, gradient, hydrology, climate, 

topography, and catchment geomorphology. Determinants that are substantially influenced by 

human activities, such as land use or vegetative cover, should be avoided because their use 

would introduce the risk of defining classes based on degrees of impact, not natural variation. 

48
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Since many state and federal biological monitoring programs (e.g., state biocriteria programs, 

EMAP, NAWQA) have identified reference sites and now have sizable reference databases, it 

may be possible to mine the existing regional reference data, augmented with basin-level data as 

necessary, to examine preliminary models. In some cases, EMAP and NAWQA have sufficient 

data, including extensive sediment, physical and hydrologic data, to develop good predictive 

models of reference sediment conditions. Many of the state programs, however, do not collect 

hydrologic or sediment data other than that necessary to conduct qualitative habitat assessments, 

and their reference sites may need to be revisited to collect the relevant data. 

Data on soils, including factors such as soil type, texture, erodibility, and porosity, would be 

ideal for determining classes. Soil maps containing such information are available for much of 

the U.S. and are maintained by the Natural Resources Conservation Service (NRCS). Climate 

data, including precipitation and hydrology are also desirable for building predictive models. 

Climate data are available for most of the U.S. through NOAA and state climate offices and are 

often accessible via the Internet. Hydrologic data are maintained by several agencies, including 

the USGS and state geological surveys. However, detailed hydrology is only available for 

gauged catchments and may have to be modeled for others. A variety of hydrologic models can 

be used as necessary (Gordon et al. 1992), those predicting base-flow and peak-flow perhaps 

being most useful. Catchment geomorphology is necessary, including data on topography and 

catchment size. These data are readily extracted from surface topographic maps using GIS 

software. 

 

If there is an absence of a robust data set for reference sites across the range of waterbodies in a 

region, then the suspended sediment regime may be modeled from theoretical principles that do 

not require detailed field data. Some validation would be necessary for acceptable uncertainty in 

the results. Theoretical models could be used to predict sediment characteristics for specific sites 

or site classes and then used to classify streams based on the modeled sediment regimes. 

Classification using existing stochastic or deterministic modeling does not require as many data 

points per class as classification methods based exclusively on field data. However, the cost (in 

terms of dollars and time) of initiating a new model development effort may be prohibitive. 

 III. Technical Elements 

Establish Meaningful Classes. The challenge of defining classes is to achieve a balance 

between accounting for the natural variation in SABS among individual waterbodies and finding 

some commonalities among waterbodies. If this is not done, each waterbody will have its own 

SABS criteria, which can become cumbersome and costly. Too many classes may make it 

difficult to know which criteria to apply in a particular case. These types and amounts of relevant 

data may limit classification analysis. There may not be enough sites to define multiple classes or

enough resources to collect additional data from the field. Five reference samples per discrete 

waterbody type is an absolute minimum reference data set; however, the small sample set will 

have low statistical power to detect differences. A data set of 30 samples per waterbody class is 

desirable but often unobtainable (Elliott 1977). 

The impacts and behavior of suspended and settled particles have different modes of action and 

may require separate classification analyses. For that matter, each SABS indicator may require a 

separate analysis although multivariate analysis would allow consideration of multiple SABS 

signals in a single analysis. If discrete classes are to be defined (as opposed to a continuum), then 

49
Framework for Developing SABS Water Quality Criteria U.S. EPA 

the investigator should define the categorical parameters for each grouping of sites, based on one 

determinant or a combination of determinants. Exploration of potential groupings is difficult to 

automate, so a priori hypotheses of reasonable classes should be tested first, and further 

exploration should be guided by the preliminary results. 

The full range of conditions can be evaluated rather than categorically defining classes. For 

instance, basin size as a classification variable need not have arbitrarily sized bins to define 

distinct classes. Rather a continuous range of stream sizes can be modeled if there is sufficient 

power to predict SABS conditions relative to stream size. Often, several variables have more 

predictive power than a single variable, in which case multivariate analysis is required. 

If identifiable groups of sites are found to be different then a decision must be made whether to 

separate the groups or retain a single group. The example in Figure 8 illustrates that groups can 

appear different but closer examination suggests that they should remain a single classification. 

The magnitude of difference between groups, sample sizes, and uncertainty will affect the 

decision. Serious consideration should be given to the possibility that any statistical difference is 

due to difference in disturbance between the groups rather than different sediment supply and 

transport regimes. For example, reference streams with erodible soils and resistant soils may 

appear to be reasonable classes of streams; however, both groups have similar levels of turbidity 

under least disturbed conditions (Figure 8). This similarity could be misinterpreted if the criteria 

for reference sites are less stringent; thereby allowing a few disturbed sites into the “reference” 

group. 

 III. Technical Elements 

Figure 8. Turbidity in Oregon streams by reference status and erodibility (Rosetta 2005). 

50
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Empirical classification is based on appropriately applied statistical methods that test whether 

two or more groups are likely to be similar or different. The basic premise is that the sediment 

indicator of interest will behave similarly in similar systems and differently in different systems. 

Within sites of the same class, SABS indicators are expected to have similar natural levels. 

Therefore, a single criterion can be defined to illustrate the natural expectations within each 

distinct class. Characteristics of the reference indicator distribution such as central tendencies 

(mean, mode, median) and shape of the distribution (skewness and kurtosis) are compared 

among classes. Most statistical texts and statistical software packages are available that describe 

commonly used techniques. 

The selection of statistical methods will vary depending on the assumed underlying statistical 

distribution of the data, whether discrete or continuous relationships are analyzed, and whether 

single or multivariate comparisons are analyzed. Various statistical methods have been described 

for classification in developing biological criteria (Barbour et al. 1999; Hughes 1995). One rather 

simple visual is to construct box-and-whisker plots of the sediment indicator of interest and to 

compare overlapping confidence intervals. Another is to construct a series of cumulative 

distribution functions (CDFs) and compare differences using the Kolmorogorv-Smirnov Test. 

Fluvial Geomorphology 

Fluvial geomorphology involves the study of the primary physical processes in streams and 

rivers that erode, transport and deposit sediment, thereby influencing channel form, stability, and 

changes over time. Geomorphology is relevant to criteria development as a source of measurable 

parameters that can indicate departure from a sediment regime needed to support the designated 

uses of a given waterbody. Further, classification of different waterbody types based on 

geomorphic principles can be used to stratify waterbodies into more homogeneous clusters for 

which more specific and appropriate sediment criteria can be developed. 

 III. Technical Elements 

Numerous authors (Rosgen 1994, 1996; Montgomery and Buffington 1993; Meyers and 

Swanson 1992; Simon 1992) have observed the relationship between channel type classifications 

and differences in stability among channel types. This relationship has ramifications for selecting 

reference streams and for determining appropriate strategies for sediment management. Channel 

evolution theory, which generally contrasts the structural properties of stable and unstable (or 

transitional) channels and identifies common sets of steps that transitional channels pass through 

in evolving toward a more stable state, further suggests that it may be possible to predict the type 

of stable channel that will evolve from a given type of transitional, unstable channel. This could 

be valuable when setting waterbody-specific sediment criteria. 

Several decades ago, Pfankuch (1975) developed a system to rate channel stability. This rating 

system has been widely used by hydrologists to quantify stream erosion potential and by fish 

biologists to measure potential stresses to littoral habitat. Channel instability measures that are 

not sensitive to natural expectations for the channel type and evolution may give a false sense of 

impairment. Instability of a stream channel might be acceptable and, in some cases, might be 

considered a reference condition because for short time intervals, all self-adjusting (alluvial) 

channels, whether natural or altered, can be viewed as being unstable because the fluxes of water 

and sediment are always changing. Rosgen (1996) has proposed a channel stability rating scale 

that combines Pfankuch stability ratings and stream geomorphology. 

51
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Streamflow changes, sediment budget changes, and many other causes lead to channel change 

that result in stability shifts. These shifts and adjustments lead to stream channel morphological 

changes culminating in a stream type change. Stream type succession sequences were first 

described as stages of channel evolution by Schumm et al. (1984) and Simon and Hupp (1986). 

The nine successional sequences (Figure 9) show progressions through different stream classes 

from the Rosgen system and indicate a larger range of possible morphological shifts and their 

tendency toward a stable end-point (Rosgen 1999, 2001). The stream successional theory 

suggests that streams depicted in the first and last frames of Figure 9 are morphologically stable 

and would be appropriate reference sites. The intermediate stages are inappropriate reference 

conditions because sediment is either being eroded or deposited at unnatural rates. 

 

The channel type classes in the Rosgen 

classification system (Rosgen 1994) 

were developed and defined by 

recognizing consistent patterns in 

channel measurements from numerous 

reference reaches. Parameters 

commonly measured to document 

channel dimension, pattern and profile 

include bankfull width/depth ratio, 

channel slope, sinuosity, entrenchment 

ratio, and bedload particle size 

distribution. For a channel class that is 

typically stable, the physical traits of a 

reference reach would likely 

complement the biological traits 

documented in the same channel type’s 

bioassessment reference condition. 

 III. Technical Elements 

Likewise, typically unstable classes’ 

reference reach data may co-occur with 

and help explain sub-par 

bioassessments. The added value of 

structural reference reach data is their 

closer relationship to sediment supply 

and transport processes that play a part 

in determining stream disturbance by 

sediment. Figure 9: Various stream type succession 

scenarios (after Rosgen 2001). 

III.D.3. Associating Suspended and Bedded Sediments with Response 

Indicators Applicable in Step 6 of the Framework 

There are two general categories of methods for establishing quantitative associations between a 

relevant measure of SABS and a response measurement that are relevant to the designated use 

(see Section III.B step 4). The first method has the potential to reduce uncertainty regarding the 

52
Framework for Developing SABS Water Quality Criteria U.S. EPA 

cause of changes in the biological response by controlling experimental conditions. This is 

referred to as the Controlled Experiment method and may be performed in the laboratory or in 

field mesocosms. The second method embodies all the complexity of waterbodies as they occur 

in the region of interest and is based on field sampling but cannot control other variables in the 

same way as in controlled experiments. This is referred to as the Field Observational method. 

Using evidence from both controlled experiments and field observational analysis provides a 

powerful duo of experimental rigor and a characterization of actual SABS and biological 

conditions in a waterbody class. Furthermore, when both controlled experimental findings and 

associations derived from in-stream measurements result in similar values, there is greater 

confidence in setting the SABS criterion. 

The Chesapeake Bay Criteria (Batiuk et al. 2000) and the Draft Technical Basis for Revising 

Turbidity Criteria (Rosetta 2005) are excellent examples of criteria development programs that 

benefit from the combination of mechanistic knowledge, controlled experiments, and field 

observations for setting criteria for different designated uses. The Chesapeake Bay project is 

described as an example of integration of many types of evidence and the complexity of

biological endpoints that can be affected. The Draft Technical Basis for Revising Turbidity 

Criteria is concerned with water clarity and uses NTU as the measurement endpoint and 

considers NTU as a surrogate that is somewhat protective of sedimentation and loss of habitat. 

The U.S. EPA Science Advisory Board identified the conditional probability approach as 

particularly useful for evaluating field observation data, which assigns probabilities of 

impairments based on SABS measurements. Our example uses EMAP data from the midAtlantic Region. 

 III. Technical Elements 

Controlled Experiments 

Since the early 1980's, under Section 304(a) 

of the CWA, U.S. EPA has been developing 

WQC for toxic chemicals to protect aquatic 

life. The majority of U.S. EPA’s aquatic life 

criteria have been derived from two 

methods: (1) the 1980 Guidelines for

Deriving Water Quality Criteria for the 

Protection of Aquatic Life and Its Uses

(U.S. EPA 1980, Appendix B), and (2) the 

1985 Guidelines for Deriving Numerical 

National Aquatic Life Criteria for Protection of Aquatic Organisms and Their Uses (Stephan et 

al. 1985). The U.S. EPA is preparing a third revision that will incorporate the scientific and 

technological advancements of the last 20 years. Current chemical criteria incorporate 

magnitude, duration, and frequency endpoints. These are developed according to strict guidelines 

using a species sensitivity distribution method (Stephan et al. 1985). SABS criteria based on 

exposure-response data can be developed, in theory, much like chemical criteria. However, 

achieving this goal – development of SABS criteria using the exposure-response – will be a 

challenge because suitable methods, relevant data requirements, and accepted “endpoints” for 

SABS currently do not exist. 

The controlled experiment is one in 

which aquatic organisms are tested 

under controlled conditions for 

behavioral or physical responses to 

stressors. The stressors are varied 

during the experiments so that 

responses can be quantified with 

respect to the level of exposure.

53
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Thresholds for SABS can be developed using the exposure-response if exposure-response 

relationship(s) can be developed for selected groups of organisms. This method involves testing 

aquatic organisms for adverse effects using suspended sediment (e.g. water cloudiness) or 

bedded sediment (e.g., spatial extent) to quantify the character and severity of response as a 

function of level of exposure. Experiments can be conducted either in the laboratory or field and 

the results can be used in conjunction with other SABS measurements to determine impairment 

in a waterbody. Results can also be used to develop exposure-response models which may be 

useful at similar sites. 

Exposure-response models currently exist for some species in some habitats, and criteria have 

been developed for their protection (e.g., British Columbia Guidelines in Caux et al. (1997a), 

Chesapeake Bay Water Clarity Guidelines in U.S. EPA 2003c). The Chesapeake Bay Water 

Clarity Guidelines, for example, use a model that predicts the effect of reduced water clarity, due 

in part to suspended sediments, on submerged aquatic vegetation (U.S. EPA 2003c). 

Similar constructs are available in some commercially available modeling software packages as 

well as in the U.S. EPA-supported ecosystem model AQUATOX (freely available at 

http://www.epa.gov/ost/models/aquatox/). Currently, AQUATOX is able to simulate the impacts 

of suspended sediment on light penetration in the water column and associated impacts on 

primary productivity and ecosystem structure and function. It also can simulate the effects of the 

organic portion of the sediments on the nutrient dynamics of the system. Future versions of the 

model may include the ability to simulate other effects, including physical smothering of 

spawned fish eggs by deposited sediment. 

 III. Technical Elements 

Guidelines for water quality criteria presented in Stephan et al. (1985) promote an approach 

based on data from at least eight families from a diverse group of taxa. The diversity of tested 

species is intended to assure protection of various components of an aquatic ecosystem. A 

Criterion Maximum Concentration (CMC) is determined using average effects levels. Chronic 

toxicity test data (longer term survival, growth, or reproduction) should be available for at least 

three taxa to derive a Criterion Continuous Concentration (CCC). The chronic criterion can be 

set by determining an appropriate acute–chronic ratio (the ratio of acutely toxic concentrations to 

the chronically toxic concentrations) and applying that ratio to the criteria. When necessary, the 

criteria – acute or chronic or both – can be adjusted to protect locally important or sensitive 

species that were not considered during development of the criterion, or it can be adjusted based 

on local water chemistry.

Sediment criteria may be based on experimental studies for a few sensitive indicator species 

(e.g., salmonids, certain corals, certain mayfly, stonefly and caddisfly taxa, or bluegills). Each 

indicator species could represent certain types of beneficial uses, aquatic systems, or regions of 

the country. This is similar to a risk assessment approach. 

The main strength of the controlled experiment method is that it employs techniques that are 

used in standardized toxicity test methodologies and that are generally accepted by the scientific, 

regulatory and stakeholder communities. The method is explicitly causative; controlled

laboratory or field mesocosm analyses address a single SABS indicator in relation to one or a 

few response indicator(s). SABS criteria can be customized to the types of aquatic life present at 

54
Framework for Developing SABS Water Quality Criteria U.S. EPA 

each site and may be adjustable to account for field conditions that are not simulated in the 

laboratory. Moreover, it may be possible, using this method, to specify the amount of reduction 

in SABS needed to maintain desired aquatic resources. 

U.S. EPA has concluded that sound exposure-response, SABS data are lacking for most species, 

and standardized consensus-based test methods for determining SABS effects are generally 

unavailable. Therefore, it is unlikely that a list of acute and chronic values for SABS can be 

developed in the short-term and such an effort would require substantial resources. A second 

difficulty is that SABS can consist of many substances depending on the site. Therefore, much 

like other “conglomerate” substances such as oil and grease or dissolved solids, it will be 

difficult to identify appropriate criteria for SABS without first determining the specific type of 

SABS (organic vs. inorganic; silt vs. clay, fine vs. coarse, etc.). 

For bedded sediments, the substrate surrounding the fine sediments is an additional variable. The 

lack of standard endpoints for determining the effects of either suspended or bedded sediments 

on specific organisms and the need for the development of minimum data requirements are 

additional drawbacks. If thresholds could be developed through controlled experimentation, there 

would still be uncertainties due to interactions of the many other factors that influence SABS 

effects and that are not generally tested during controlled experiments. 

The controlled experiment method has two characteristics that result in uncertainty. Firstly, it is 

difficult to account for natural or background conditions and organisms’ acclimation to dynamic 

environmental changes in SABS. Secondly, SABS do not necessarily act on organisms in the 

environment in the same way as toxicants. The change point between a detrimental level of 

SABS and a beneficial one is a function of amount, duration, and distribution rather than of 

concentration and duration. In principle, these limitations could be addressed through certain 

U.S. EPA-approved mechanisms to modify national criteria on a site-specific basis. The 

Recalculation Procedure (U.S. EPA 1994), for example, could be used in lieu of national SABS 

criteria based on the types of species that could occur in the region or waterbody classification, 

and their natural sensitivity to SABS. However, use of such a procedure assumes the availability 

of fairly large acute toxicity database (>20 genera, at a minimum), which may not be feasible in 

the short-term.

 III. Technical Elements 

 

Field Observations 

As bioassessment and biocriteria have become common tools for assessing the status of aquatic 

life, rich data sets have been generated that include measures of physical, chemical, biological, 

and landscape characteristics. These data sets provide an opportunity to examine relationships 

between SABS and other variables. This Section focuses only on the relationship between SABS 

and biological indicators, but the analytical methods and study design concepts are also relevant 

to other physical and chemical attributes of aquatic systems and is essentially the basis of the 

Waterbody Use Functionality (Section III.D.3). The strength of using field observational 

methods is that they enable analysis of SABS and their potential effect on biota as they occur in a 

defined region or class of waterbody type. This strength is also its weakness because variability 

among field samples might reflect natural variability, or SABS, or some other stressor linked to 

human activity. Therefore, analysis must take into account that a lower than expected 

measurement of a biological indicator may be due to other causes besides the one of interest, in 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

this case SABS. Any analysis must consider these other sources of variation when developing 

stressor/response relationships using field sampling. 

Percentile Analysis (Including Reference Condition Methods). One method is to attempt to 

remove sites with known stressors from the data set that is analyzed. This is the basis for some

types of reference condition analyses more specifically termed here as Percentile Analysis. 

Percentile Analysis method for developing sediment criteria follows the example of the regional 

reference condition method for developing biological criteria (Barbour et al. 1999; Hughes 

1995). It is based on the a priori selection of a population of sites with a similar SABS regime

(Section III.D.2.). From the population of sites with similar sediment regimes, a subset of sites 

are selected that meet designated uses (e.g., supports cold water fishery), represent best attained 

conditions for a specific assessment endpoint (e.g., presence of threatened species) or represent 

nearly natural SABS conditions (as described in Section III.D.2). Some factors should be kept in

mind when using a Percentile Analysis method. 

(1) Using a population of sites that meets designated uses is defensible, but may put valued 

resources at risk if the sites do not protect downstream uses, if the designated uses are 

somewhat lax, or if waterbody sub-types were too broadly defined. 

(2) Best attained condition as an approach to select sites can demonstrate that the standards 

will be achievable but may underestimate impacts in classes of waterbodies that are 

generally highly altered. Even the best available conditions might not really meet the 

expectations of the CWA. However, using the best sites can point management in the 

right direction and clearly help to define highly degraded sites. 

 III. Technical Elements 

(3) Using sites with nearly natural SABS regimes is sensitive to errors in selecting criteria for 

defining natural sites. This does not directly demonstrate how SABS affects the response 

indicator or designated use. 

In all three cases, distributions of SABS for the population of sites is described, usually as a 

cumulative distribution function or box plot, a value from within that distribution is selected as 

the SABS criterion. More than one designated use can be defined for a class of streams. For 

instance, a different criterion might be selected for exceptional waterbodies and another selected 

criterion that enables streams to meet state water quality standards for aquatic life. Typically, the 

criterion is set at the 75th percentile of sites attaining their designated use or characterized as best 

attainable conditions. The selection of the percentile is also influenced by the desired level of 

protection, which is dependent on the designated use. Therefore, criteria for designated uses of 

“exceptional biodiversity” or “irrigation supply” may be based on different percentiles. 

Exposure and Effects Analysis. Another method assumes that SABS is a limiting stressor on 

biological communities and that the upper limit of biological measurements is an estimate of the 

best possible performance expected for a system given any point along a range of exposures. 

This assumption may be violated if the biological measurement is influenced in a positive 

direction by another stressor, for instance, moderate organic enrichment increasing fish biomass. 

There are a number of statistical methods that can be used to analyze these data sets. For 

continuous variables they include, but are not limited to, conditional probability analysis, 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

regression, quantile regression, maximum response curves, and several different multivariate 

statistical analyses. With quantile regression, the likely biological conditions in the absence of 

any other stressors are described by estimating changes in the response variable relative to a 

measurement of SABS near the upper range of the response distribution (i.e., 90th or 95th 

percentile; Figure 10). Regular regression models the median (i.e., 50th percentile) relationship. 

These same statistical methods can also be applied to data sets in which SABS is reduced as a 

part of mitigation. Specifically, if the response indicator is measured before and several times 

after intervention at a single site, the level of SABS that is present when the designated use is 

met represents a threshold, which may be considered when setting criteria. The combination of 

field observations and controlled experiments is illustrated in the Chesapeake Bay Case. 

% Fines

0 10 20 30 40 50 60 70 80 90 100

Intolerant taxa

Ecoregions 46, 47, 48, and 51

Ecoregions 50 and 52

0

5

10

15

20

 richness

 III. Technical Elements 

Figure 10. Quantile regression of the 90th percentile of intolerant invertebrate taxa over a full 

range of percent fines in Minnesota streams in two groups of ecoregions. The Northern Lakes 

and Forests and the Driftless Plains (Ecoregions 50 and 52) appear to support more intolerant 

taxa than streams with the same percentage of fines in the other ecoregions, Northern Glaciated 

Plains, Western Corn Belt Plains, Lake Agassiz Plain, and North Central Hardwoods 

(Ecoregions 46, 47, 48, and 51) (figure from Michael Griffith with U.S. EPA, unpublished data). 

57
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Synthesis of Controlled Experiments and Field Observations in the Chesapeake Bay

The Chesapeake Bay-specific water clarity criteria constitute one of the best examples of the use 

of exposure-response methods for development of SABS criteria. The criteria are based on a 

conceptual model of the effects of reduced light to the leaves of submerged aquatic vegetation 

(Figure 11). This model was developed using knowledge from both controlled experiments and 

field observations. 

The loss of underwater bay grasses from the shallow waters of the Chesapeake Bay is a 

widespread, well-documented problem caused by decreased light intensity. Also certain 

wavelengths of light may not be transmitted through the water. The loss of underwater bay grass 

beds is of particular concern because these plants create rich animal habitats that support the 

growth of diverse fish and invertebrate populations and provide food for waterfowl. The primary 

causes of losses are nutrient over-enrichment and increased suspended sediments in the water 

and the associated reduction 

of light. The key to 

restoring the bay grass beds 

is to provide the necessary

levels of light penetration in 

shallow waters to support 

their survival, growth, and 

reproduction. The 

Chesapeake Bay Water 

Clarity Guidelines employ a 

model to predict the effect 

of reduced water clarity, 

due in part to suspended 

sediments, on underwater 

bay grasses (U.S. EPA 

2003c). This model is based 

on associations derived 

from both controlled 

experiments and field 

observations that link 

changes in valued attributes 

of the Bay with different 

exposures to nutrient 

enrichment and suspended 

sediment. 

Figure 11. Availability of light for underwater grasses is influenced 

 III. Technical Elements 

by water column and at-the-leaf surface light attenuation. DIN = 

dissolved inorganic nitrogen, DIP = dissolved inorganic phosphorus. 

The Chesapeake Bay-specific water clarity criteria were derived in four stages: (1) water 

column-based light requirements for bay grass survival and growth were determined, (2) factors 

contributing to water-column light attenuation were quantified, (3) contributions from epiphytes 

to light attenuation at the leaf surface were factored into analyses for estimating total light 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

59

 III. Technical Elements 

Synthesis of Controlled Experiments and Field Observations in the Chesapeake Bay 

(continued)

attenuation and (4) a set of minimal requirements for light penetration through the water and at 

the leaf surface were determined to give the water clarity criteria values. 

The principal relationships between water quality conditions and light regimes for the growth of 

underwater bay grasses are illustrated in a conceptual diagram (Figure 11). Incident light is 

attenuated through the water column above the bay grasses by particulate matter (chlorophyll-a

and total suspended solids), by dissolved organic matter and by water itself. The water-column 

light attenuation coefficient (Kd) is dominated by contributions from chlorophyll-a and total 

suspended solids. Light that actually reaches the underwater bay grass leaves also is attenuated 

by the epiphytic material (i.e., algae, bacteria, detritus and sediment) that accumulates on the 

leaves. This epiphytic light attenuation coefficient (Ke) increases exponentially with epiphyte 

biomass. Dissolved inorganic nitrogen (DIN) and phosphorous (DIP) in the water column

stimulate the growth of epiphytic (and water-column) algae. Suspended solids also can settle 

onto bay grass leaves. Because epiphytic algae also require light to grow, water depth and watercolumn light attenuation constrain epiphyte accumulation on bay grass leaves, and light 

attenuation by epiphytic material depends on the mass of both algae and total suspended solids 

settling on the leaves. 

An algorithm was developed to estimate light attenuation at the leaf due to the biomass of 

epiphytic algae and other materials attached to bay grass leaves (Kemp et al. 2004; Batiuk et al. 

2000). The algorithm was verified by applying it to Chesapeake Bay water quality monitoring 

data. It uses monitoring data for the water-column light attenuation coefficient (or Secchi depth), 

total suspended solids, DIN and DIP concentrations to calculate the potential contribution of 

epiphytic materials to total light attenuation for bay grasses at a particular depth. Using a set of 

commonly monitored water quality parameters, attainment of the percent light-through-water 

(PLW) water clarity criteria and percent light-at-the-leaf (PLL) diagnostic parameter can be 

readily determined for any established restoration depth. 

To determine the Chesapeake Bay water clarity criteria necessary to ensure that sufficient light 

reaches bay grass leaves at a defined restoration depth, three lines of evidence were compared: 

• Application of bay grasses habitat requirement parameter values to the new algorithm

for calculating percent light-at-the-leaf. 

• Evaluation of results of light requirement studies in areas with few or no epiphytes. 

• Comparison of median field measurements of the amount of light reaching plants’ 

leaves (estimated through the percent light-at-the-leaf algorithm) along gradients of 

underwater bay grasses growth observed in the Chesapeake Bay and its tidal tributaries. 

Based on a thorough review of controlled shading experiments and model findings published in 

the scientific literature, a PLW value of greater than 20 percent is needed for the minimum light 

requirement of Chesapeake Bay mesohaline and polyhaline species (Batiuk et al. 2000). 
Framework for Developing SABS Water Quality Criteria U.S. EPA 

60

 III. Technical Elements 

Synthesis of Controlled Experiments and Field Observations in the Chesapeake Bay 

(continued)

Consistent with the literature-derived value, the PLW requirement of 22 percent was determined 

for mesohaline and polyhaline regions of the Chesapeake Bay and its tidal tributaries using the 

algorithm for calculating percent light-at-the-leaf. This PLW requirement was confirmed by 

almost two decades of field observations in the Potomac and York Rivers (Batiuk et al. 1992, 

2000; Moore 1996; Moore et al. 2001). 

Based on published model findings reviewed in Batiuk et al. (2000) and confirmed by a review 

of recent tidal Potomac and Patuxent River research and monitoring studies, a PLW requirement 

of 13 percent was determined to apply to Chesapeake Bay tidal-fresh and oligohaline species. 

This light requirement was calculated using the algorithm for calculating percent light-at-the-leaf

and the appropriate SAV habitat requirements for Kd. The PLW requirement is consistent with 

the 13.5 percent value published by Dennison et al. (1993). The PLW requirements in both 

salinity regimes were validated through an ecoepidemiological analysis of 14 years (1985-1998) 

of Chesapeake Bay water quality monitoring data.

The Chesapeake Bay water clarity criteria are summarized in Table 5 as PLW and Secchi depth 

equivalents over a range of application depths. They reflect a set of minimum light requirements 

to protect underwater bay grass species. The Secchi depth criteria vary across salinity regimes 

and through the seasons because of differing light requirements, growth potential, and 

reproductive strategies. 

Table 5. Summary of Chesapeake Bay water clarity criteria for application to shallow-water bay 

grass designated use habitats (U.S. EPA 2003c).* 

Water Clarity Criteria as Secchi Depth 

Water Clarity Criteria Application Depths

0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.0 Salinity 

Regime

Criteria as 

Percent 

Light 

Through 

Water Secchi Depth (meters) 

for above Criteria Application Depth 

Temporal 

Application 

Tidal-fresh 13% 0.2 0.4 0.5 0.7 0.9 1.1 1.2 1.4 Apr 1 - Oct 31 

Oligohaline 13% 0.2 0.4 0.5 0.7 0.9 1.1 1.2 1.4 Apr 1 - Oct 31 

Mesohaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 Apr 1 - Oct 31 

Polyhaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 Mar 1 - May 31 

Sep 1 - Nov 30

*Based on application of the equation, PLW = 100exp(-Kd*Z). The appropriate PLW criterion value and 

the selected application depth (Z) are inserted and the equation is solved for the light attenuation 

coefficient (Kd). The generated Kd value is then converted to Secchi depth (in meters) using the 

conversion factor Kd = 1.45/Secchi depth.
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Conditional Probability Analysis. This detailed section is devoted to the Conditional 

Probability Analysis (CPA) method because the Science Advisory Board found this to be one of 

the more useful methods for showing the relationships between the SABS indicator and the 

desired condition of the waterbodies, conveying the impacts of selecting different SABS criteria 

and ability to inherently incorporate uncertainty into the analyses. The CPA method is illustrated 

in the mid-Atlantic stream case. This case also introduces some methods for evaluating changepoints (thresholds or transition points) that may be helpful for identifying reasonable criteria 

values. Refer to Paul and McDonald (2005) for details of the CPA method and the application to 

mid-Atlantic streams. 

The application of the CPA method for criteria development describes the association between 

the SABS indicator and the designated use indicator as a probability of observing impairment (or 

not observing impairment) when a particular level of SABS indicator is exceeded. The CPA 

method communicates the outcome in terms that are relatively easy to understand. A 

hypothetical outcome might include sites with more than 60% fines, where there is a 90% 

probability that the biota will be impaired. The analysis provides the user with the ability to 

evaluate the probability of impact across the full range of observed SABS levels. 

The following are recommended for application 

for criteria development to take advantage of the 

full capability of CPA: (1) monitoring data should 

be acquired using a probability-based sampling 

design, (2) some metric must quantify SABS 

levels, (3) a response metric must be sufficiently 

sensitive to respond to the extant levels of the 

SABS metric, (4) independent studies should 

identify the characteristics of an impacted 

response metric; and (5) the SABS metric must be 

capable of exerting a strong effect on the response 

metric. 

 III. Technical Elements 

Probability-based design data can provide 

estimates of the probability of occurrence for a 

sampled variable in the statistical population. The 

statistical population is the desired resource for which various statistical parameters will be

estimated and from which samples will be drawn for data acquisition. For example, consider the 

statistical population of all stream segments in a state. If 75% of the stream segments sampled 

exhibit impacted benthic communities, then the probability of observing benthic impairment in 

any of the stream segments in the state was 0.75 during the sampling period. When data are 

collected from a targeted set of sites and are not probability-based, then the bias introduced by 

site selection factors must be accounted for if the results are to have any reasonable meaning 

beyond the locations actually sampled. 

Conditional probability 

analysis quantifies the 

likelihood that biotic impacts 

will occur when a given level 

of SABS exposure is 

exceeded. Probabilities are 

based on the likelihood of 

observing an undesirable 

response indicator. Judgments 

as to acceptable SABS 

indicator levels can be made 

based on desired probability of 

impact. 

The probability of observing a certain event, y, is denoted as P (y). A conditional probability 

is the probability of an event y occurring given that some other event x also has occurred. It is 

denoted P (y | x). The vertical line means “conditioned on,” not “divided by.” Thus, a conditional 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

probability describes the likelihood of observing an event of interest in a subset of samples 

drawn from the original statistical population. These subsets are defined by conditions when x 

has occurred, in addition to those used to define the entire statistical population. Conditional 

probability can be calculated as the ratio of the joint probability that y and x occur 

simultaneously in a given sample (P (y, x)) from the original statistical population, to the 

probability of x in the original population 

P (y | x) = P (y, x) / P (x) (1)

This is considered a definition of conditional probability (Hogg and Ledolter, 1992). An example 

of a conditional probability statement would be the probability of benthic community impact if

total copper levels in the sediments exceed 10 ppm. The events y and x are considered

statistically independent if, and only if, their conditional probabilities (of one another) are equal 

to their (unconditional) probabilities in the original statistical population. Conditional 

probabilities differ from joint probabilities, which are often used in risk assessment (e.g., 

Verdonck et al. 2003). Joint probability, when the two variables are statistically independent, is 

calculated simply as the product of P (y) and P (x). So, P (y, x) = P (y) * P (x). If two variables 

are statistically independent, then the conditional probability is equal to the unconditional 

probability (see Paul and McDonald (2005) for additional information). 

Application of Conditional Probability Analysis for Criteria Development. Our application 

of the CPA method for criteria development starts with a two-step procedure to calculate the 

conditional probabilities (Paul and McDonald 2005). We let y represent the dichotomous 

response variable (1 for impaired conditions, 0 for good conditions) and assume it to be a 

random variable. We let x be the SABS indicator, which is also a random variable. We let xC be 

the conditioning value for the SABS indicator. In the first step, we identify subsets of the 

sampled resource (e.g., stream segments) for which x ≽ xC (i.e., we order the samples based on 

the value of SABS indicator). In the second step, we determine which of the SABS indicator 

values also have impaired response indicator values. This allows us to determine, for example, 

the fraction of the stream miles in which SABS indicator values are greater than or equal to a 

specific value (xC) and also had impaired biological response. This two-step procedure is applied 

over the range of observed SABS indicator values. This produces an empirical curve for the 

conditional probability, the probability of expecting an impaired biological response when 

observed SABS indicator values are greater than or equal to xC. 

 III. Technical Elements 

This empirical curve provides the probability of impairment of the ecological system (e.g., 

benthic community structure degradation) for an exposure to high levels of SABS indicator. 

Confidence intervals (CIs) for this empirical curve are estimated for each value of xC by 

assuming that the individual values that go into determining P(y = 1 | x < xC) can be treated as a 

simple random sample when at least two individual values are available. 

Identifying Thresholds of Impact. Threshold levels for pollutants or pollution, such as SABS, 

that elicit different levels of biological impact in waterbody elements of a region need to be 

identified for eventual use in developing criteria. A threshold of impact is identified as a 

changepoint separating the empirical conditional probability curve into two parts: the part of the 

curve above the changepoint and the part below it. For those samples that are above the 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

changepoint, the probability of impact is different than what one would expect for the entire 

geographic area. A confounding factor in the identification of a changepoint is that these two 

groups created by the changepoint are not independent (i.e., the numbers used to create the points 

above the changepoint are a subset of the numbers used to create the points below the 

changepoint). Thus, a traditional t-test cannot be used in the determination of the changepoint 

since the data are not independent (Venables and Ripley 1997). Using a weight-of-evidence 

approach with different techniques will identify the change point. Three examples of these 

techniques are (1) non-overlapping confidence intervals, (2) change in curvature of fitted curve, 

and (3) nonparametric deviance reduction. Other possible techniques could be used to identify a 

changepoint. In this demonstration, specific values for factors and confidence intervals were 

selected only as examples. Values used in an actual application of this approach would depend 

on the particular management requirements and objectives. 

The use of non-overlapping confidence intervals (CI) to determine a changepoint involves 

determining when the lower CI of the empirical curve no longer overlaps the upper CI of the 

unconditional value (Cherry 1996, 1998; Austin and Hux 2002; Rahlfs 1997). This procedure is a 

conservative estimate for significant difference since the CIs could overlap when the values are 

significantly different (Austin and Hux 2002). The bootstrap percentile confidence intervals, 

based on a bootstrap distribution of 1000 samples, were used for this evaluation. The "-level for 

the non-overlapping confidence interval must be adjusted to account for the one-sided nature of 

this test, whereas the "-level for developing the confidence intervals for the curves was based on 

a two-sided test (i.e., a factor of 2 in the "-level).

The second technique used for selecting a threshold of impact through changepoint identification 

is to fit an equation to the empirical curve for conditional probability. The following constraints 

are used: the conditional probability approaches the unconditional value, P (y = 1) as x goes to 

the minimum x-value; the conditional probability approaches 1 as x goes to the maximum value; 

and there is a curvature change at the inflection point of the curve. The following functional form 

satisfies these constraints:

 III. Technical Elements 

 

(2) ( )

( ) P(y 1|x x ) = > C = + − + − >

+ − + − ≤

⎧

⎨

⎪

⎩

⎪

1 D 1 1 exp B x x for x x

1 D 1 1 exp B x x for x x

0 0 C 0

0 1 C 0

( ) / ( ( )) ,

( ) / ( ( )) ,

C 0

C 0

where: 

exp is the exponential function to base e, 

D0 is unconditional probability value P(y = 1 ), 

x0 is the changepoint where curvature changes, 

B0 is curvature for values of xC > x0, and 

B1 is curvature for values of xC < x0. 

The parameters x0, B0, and B1 are determined from a nonlinear least squares regression

(Venables and Ripley 1997). Uncertainty in the parameters is estimated from the standard errors 

generated by the regression software and, where possible, by computing asymmetric confidence 

intervals (Venables and Ripley 1997). The residuals from the regression are checked for 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

normality. While it may be generally possible to fit equation (4) to the empirical curve, the 

curvature values (B0 and B1) may not be significantly different, and a threshold would not be 

identified with this technique. 

The third technique uses nonparametric deviance reduction to determine the changepoint. This 

determines the dividing point for splitting the data into two groups resulting in the largest 

reduction in the deviance in the data (Qian et al. 2003). The deviance is defined as 

∑ (3) =

= −

N

i

D Pi P

1

2 ( *)

where: 

D is the deviance, 

N is the sample size, 

Pi is the conditional probability P (y = 1 | x > xi), and 

P* is the mean of Pi based on a sample size of N. 

When the data are divided into two groups, the sum of the deviance for the two subgroups is 

always less than or equal to the deviance for the entire data set. When the split in the data 

minimizes the deviance, the threshold is identified. This has been used to detect ecological 

changes along an environmental gradient (Qian et al. 2003). Qian et al. (2003) compared results 

of deviance reduction with a Bayesian hierarchical modeling and found that the nonparametric 

provides similar results with the Bayesian analysis. 

 III. Technical Elements 

The deviance reduction point generally can be determined, but it may or may not be of biological 

significance. Uncertainty in the deviance reduction changepoint (90% and 95% confidence 

intervals) is estimated from the empirical percentiles for the bootstrap distribution from 

resampling 1000 times (Manly 1997). An approximate χ2

 test was used to determine the 

significance of the changepoint. The test assumes that the deviance reduction divided by the 

scale parameter is approximately χ2

 distributed with 1 degree of freedom (Venables and Ripley 

1997). A large deviance reduction will result in a small p-value, and the consequent rejection of 

the null hypothesis (H0: no changepoint). 

Biological Importance of Identified Thresholds. For use in criteria development, some level of 

biological importance needs to be associated with the threshold of impact value that is identified. 

The changepoint value determined by each technique must separate the samples so that the 

probability of impact for samples above the threshold would be different than what one would 

expect for the entire geographic area. As an example, a summary of literature values on the 

response of fish and benthic invertebrates at low reported levels of percent fines in the substrate 

(Newcombe and Jensen 1996; Berry et al. 2003; Bash et al. 2001) was used to identify biological 

importance for the mid-Atlantic streams case. 

Statistical Analysis of Data. Several statistical analyses are useful in addition to the conditional 

probability determination. The cumulative distribution function (CDF), the conditional 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

cumulative distribution function (CCDF), and their reverses were used to complement the 

conditional probability calculation. The CDF gives probability that x is less than or equal to xC: 

∑

≤

≤ ≈ =

i c x x

c c i i P(x x ) F(x ) f (x ) (4)

The reverse CDF is the probability that x is greater than xC, which is the complement of equation 

(5) or, 

∑ ∑

≤ >

> ≈ − = − =

i c i c x x

i i

x x

c c i i P(x x ) 1 F(x ) 1 f (x ) f (x ) (5) 

The conditional cumulative distribution function (CCDF) is the distribution for a subset of the 

total data, conditioned on a second variable [F(y | x)]. The reverse CCDF uses 1-F(y | x). The 

reverse functions are consistent with the CPA results, which are expressed as a threshold (i.e., 

exceeding some value xC). 

Application of Conditional Probability Analysis to Mid-Atlantic Wadeable Streams

CPA was used to establish realistic thresholds for impacts to stream biotic condition from nonpoint source pollution in the mid-Atlantic region of the U.S. (Paul and McDonald 2005). The 

mid-Atlantic was selected because of the extensive amount of research and monitoring of 

streams that has been done in this region (see example in Boward et al. 1999; U.S. EPA 2000b), 

which provided the information base needed to satisfy conditions for application of CPA. 

 III. Technical Elements 

These data were collected from mid-Atlantic streams in 1993 and 1994 and include 102 stream

segments in 1st to 3rd (Strahler) order wadeable streams as part of EMAP (Herlihy et al. 2000) 

(Figure 12). These segments were selected 

for sampling using a spatially balanced 

probability design. Inclusion probabilities 

for each sampled stream segment were 

determined using the sample sizes for each 

Strahler order and the total length of

streams within each order in the region. 

Sampling locations within stream

segments were chosen randomly. 

Quantitative data for stream

macroinvertebrates, habitat, and water 

quality were collected at each site. 

Sampling took place during a yearly, twomonth sampling window from April 

through mid-June. 

38 o N

40 o N

42 o N

82 o W 75 o W

Figure 12. Mid-Atlantic region of the U.S. with 

EMAP wadeable stream sampling sites. 

65
Framework for Developing SABS Water Quality Criteria U.S. EPA 

66

 III. Technical Elements 

Application of Conditional Probability Analysis to Mid-Atlantic Wadeable Streams (continued) 

Stream benthic macroinvertebrates are a robust measure of stream condition, integrating 

temporal pollutant exposure. They are responsive to in-stream changes to sediment levels. 

Benthic stream community taxa in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies), 

and Trichoptera (caddisflies) (collectively known as EPT) are considered reasonably sensitive 

indicator organisms since they exhibit a decrease in taxa richness with increased degradation of 

stream conditions. EPT taxa were used to identify SABS-related impacts in stream segments in 

the mid-Atlantic. When EPT taxa were < 9 in these stream segments, the streams were 

considered impaired (Davis and Scott 2000). 

For the purpose of this study, percent fines in the substrate were used as a surrogate indicator for 

sedimentation in streams. Percent fines (silt/clay fraction, < 0.06 mm) represent a direct measure 

of the smallest class of sediments. Percent fines are strongly correlated with sediment 

embeddedness, a source of the most-likely-to-be resuspended sediment, and an indirect measure 

of suspended sediment levels in the water column. Streams containing a larger fraction of fine 

sediment would be expected to have a benthic community at greater risk for impact. 

The reverse cumulative distribution function (CDF) and reverse conditional CDFs for percent 

fines in the substrate are expressed as proportion of stream miles (Figure 13). The sampled 

stream segment values are weighted by inclusion probabilities to convert to stream miles. The 

distribution for impacted benthic communities is displaced to the right of the distribution for 

benthic communities in good condition as should be expected. The distribution for reference 

conditions (the best conditions) is shifted to the left (towards lower percent fines) of that for 

unimpacted streams. 

0 2 0 4 0 6 0 8 0 1 0 0

P e r c e n t Fi n e s i n S ubs t r a t e

im pac t e d b ent h i c c ond it ions

a l l

u n im pac t ed bent h ic c o ndit ions

r e f e r enc e c ond it ions

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 . 0

Proportion of Stream Miles with Condition > x

p e r c e n t f in e s = 14. 8

0 . 7 4

0 . 4 7

0 . 2 1

0 . 0 6

Figure 13. Reverse cumulative distribution function (CDF) for percent fines in the substrate 

(silt/clay fraction, < 0.06 mm) for stream miles across entire area (all), and reverse conditional 

CDFs of stream miles for impacted benthic conditions (EPT taxa richness < 9), unimpacted 

benthic conditions (EPT taxa richness > 9) and reference conditions. Vertical line is where the 

threshold of 15 percent fines intersects the curves. 
Framework for Developing SABS Water Quality Criteria U.S. EPA 

67

 III. Technical Elements 

Application of Conditional Probability Analysis to Mid-Atlantic Wadeable Streams (continued) 

The outcome of the CPA application suggests that when percent fines in the substrate is greater 

than 49%, there is a 100% probability that the benthic communities are impacted (Figure 14). All 

sites with percent fines in the substrate in excess of 49% had EPT taxa richness less than 9. As 

the percent fines approach zero, there is a background level of impact on EPT taxa richness from

all sources of stress in the region (mean = 42%, 95% confidence interval of 30-56%). Thus, 

irrespective of the level of percent fines in the substrate, approximately 42% of the stream-miles 

in the region will likely exhibit an impact on EPT taxa richness, Therefore, to detect a significant 

signal due to percent fines in the substrate affecting the U.S. EPA taxa richness, the upper 

confidence limit on our estimate of the background impairment (e.g., 56%, Figure 14) must not 

overlap with the lower confidence limit on the probability of benthic impact. This occurs when 

the percent fines in the substrate is 15%. It could be argued that this is the initial threshold of

impact that is distinguishable from background within this geographic area. The mean 

probability of observing impacted EPT taxa richness associated with this threshold is 67%. 

Probability of EPT

Taxa Richness 9 when Exceeding x value

Probability of EPT

Taxa Richness < 9 when Exceed ni g x-va

0 20 40 60 80 100

Percent Fines in Substrate

0 0. 0 2. 0 4. 0 6. 0 8. 1 0.

0.67

0.56

percent fines = 49

percent fines = 14.8

Figure 14. Probability of observing EPT taxa richness < 9 (benthic impact) in mid-Atlantic 

streams (open circles) if specified value of percent fines in the substrate (silt/clay fraction, < 0.06 

mm) is exceeded. Solid line is fit to data using equation (2). 

The CPA method identified a threshold of 15% fines (from non-overlapping confidence 

intervals) would translate into approximately 47% of the total stream miles in the geographic 

area exceeding the threshold (from Figure 13). Similarly, only a small percentage of streams with 

reference condition characteristics (6%) or good benthic conditions (21%) would exceed the 15% 

fines threshold, but a much larger percentage of streams where impacts are occurring (74%) 

would exceed it. These values provide an estimate of the number of "false positives" for this 

value of a threshold for percent fines as the indicator of sedimentation. Because multiple 

stressors often impact stream communities, we cannot estimate the "false negatives." A 

community not stressed by the stressor of interest might be stressed in some other way.
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Waterbody Use Functionality 

The waterbody use functionality method is proposed for developing SABS criteria for designated 

uses other than aquatic life. This method examines the existing literature and focuses criteria on 

non-aquatic life uses such as recreational (swimming, boating, etc.), industrial, navigational, 

drinking water, and agricultural uses, among others. Although not emphasized in the CWA, 

economic impacts from poor stewardship of sediment supply can also have costly repercussions. 

Some impaired functional uses related to sediment management include flooding, bank erosion 

with collapsing infrastructure, and loss of coastal wetlands and protection from storm surges 

among others. As costs continue to rise, these functions can no longer be overlooked. 

Functional-based benchmarks for protecting uses other 

than aquatic life apply primarily to waterbodies where 

aquatic life uses do not exist (historically, not present or 

removed through a Use Attainability Analysis (UAA), or 

where multiple designated uses have been assigned to a 

waterbody (such as a large river system) and SABS 

levels fluctuate substantially throughout the extent of the 

system. However, where multiple designated uses (such 

as aquatic life and irrigation) overlap in a waterbody or 

on a specific segment or portion of the waterbody, 

SABS criteria established to protect the aquatic life use 

most likely will be stringent enough to protect all other 

uses except perhaps drinking water uses. In such cases, 

additional functional criteria may not be necessary. This 

is a presumption that needs further investigation. 

The waterbody use 

functionality approach 

focuses the process of 

SABS criteria development 

on the desired outcome: 

attainment of all the 

designated uses of the 

waterbody. This approach 

is proposed in cases where 

uses other than aquatic life 

uses must be attained. 

 III. Technical Elements 

Benchmarks protective of the functional use would be based on data and information from the 

literature, field observations, and state experiences. For example, if shipping and navigational 

uses were the primary use of a waterbody, criteria would be established to prevent or minimize 

the depositional rates of sediments that would prevent accelerated filling of shipping channels 

thereby preventing frequent dredging to maintain those channels. 

For agricultural water usage, including irrigation and livestock watering, benchmarks could be 

established based on data that illustrate the level of sediment that causes problems to pumps and 

piping or increases the need and expense for filtering. Similarly, benchmarks could be set to 

protect levels of clarity for swimming, sources of drinking water and other functional uses where 

the literature indicates potential thresholds for protecting these non-aquatic life uses. Exposureresponse relationships for aquatic biota would not be a critical basis for these criteria. 

Examples where functional benchmarks have already been suggested or applied include National 

Academy of Sciences (NAS)/National Academy of Engineering (NAE) (1973), National 

Technical Advisory Committee (NTAC) (1968), Australian and New Zealand Environment and 

Conservation Council (ANZECC 2000; Parametrix 2003). Some narrative and numeric examples 

include: 

68
Framework for Developing SABS Water Quality Criteria U.S. EPA 

• Waters used for bathing and swimming should have sufficient clarity to allow for the 

detection of subsurface hazards or submerged objects and for locating swimmers in 

danger of drowning. 

• Clarity should be such that a Secchi disk is visible at minimum depth of four feet given

its conclusion that clarity in recreational waters is highly desirable from the standpoint of 

visual appeal, recreational opportunity, enjoyment, and safety. 

• The visual clarity guidelines are based on the objective that to protect visual clarity of 

waters used for swimming, the horizontal sighting of a 200mm diameter black disc 

should exceed 1.6 m.

• Turbidity in water should be readily removable by coagulation, sedimentation, and 

filtration; it should not be present to an extent that will overload the water treatment plant 

facilities, and should not cause unreasonable treatment costs. In addition, turbidity should 

not frequently change or vary in characteristics to the extent that such changes cause 

upsets in water treatment processes. 

• No more than 15 NTUs over background will generally protect the visual aesthetic 

quality of a clear water stream. 

Advantages and Disadvantages of the Methods

The U.S. EPA Science Advisory Board recommended that the distinct advantages and 

disadvantages of each method should be considered when deciding how to apply them in specific 

criteria development situations. Table 6 summarizes this information. 

 III. Technical Elements 

III.E. Hypothetical Examples of the Synthesis of Methods Within the 

Framework

The following hypothetical examples illustrate the process for developing SABS criteria in 

representative waterbody types. The first scenario describes the sequence of SABS criteria 

development steps for a statewide set of high gradient, 2nd to 3rd order headwater streams. This 

hypothetical scenario includes (1) the decision process for the selection of measurements for 

SABS and response variables that are appropriate to the waterbody type and designated uses; (2) 

the possible rationales for selecting analytical methods for linking SABS to impacts; and (3) the 

importance of using a logical and transparent decision analysis to select SABS criteria. Fewer 

detailed example scenarios are also provided for several other waterbody types, including large 

rivers, regulated rivers, wetlands, lakes, ponds and reservoirs, estuaries, estuarine wetlands, and 

coastal waters. Different designated uses and types of criteria are also mentioned to give the 

reader a sense of the range of situations in which SABS criteria development might occur. Actual 

data analysis is not included in these hypothetical cases. Efforts are ongoing to prepare one or 

more case studies based on actual data sets. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Table 6. Advantages and disadvantages of methods used in SABS criteria development. 

Advantages Disadvantages

Measurement of SABS 

Readily 

Available 

Measures 

(e.g., SSC, 

Percent fines, 

Secchi 

distance) 

• Published methods with known 

performance 

• Often measured by state, tribal, 

territorial, and federal monitoring 

programs 

• Good body of published literature 

linking direct measures to 

biological effects and to land 

cover/land use 

• Often not easily tracked to sources 

Sediment 

Transport 

Curves 

• Can reveal channel stability’s 

effects on within-channel sediment 

loads, and explain past, present, 

and predicted erosional and 

depositional processes that may

affect restoration 

• Applies only in flowing waters (though 

similar systems may be developed for slow 

and still waterbody types) 

• Requires extensive field sampling under 

specific field conditions. 

• Not vetted for all waterbody types. 

Relative Bed 

Stability 

• Accounts for local environmental 

conditions (standardized to the 

reference condition) 

• Measures both excessive and 

deficient sediments 

• Not as effective in sand bedded rivers and 

streams where fine sediments are 

transported frequently and where SABS 

impairment is not closely related to 

sediment transport competence 

• Current formulation only useful for 

flowing waterbodies though analogous 

methods may be developed to evaluate 

stability of sediments in lakes and coastal 

waters as influenced by wave action. 

Classification

Empirical 

Classification 

• Many states are familiar with this 

method, having used it in

biological assessment programs 

• May be cost effective because the 

framework is in place in many

states 

• Reference site selection can be subjective. 

• Large data sets are preferred and not 

always available for all classes that should 

be compared. 

Fluvial 

Geomorphology

• Good for stratification before 

assessment or for diagnostics after 

identifying impairment 

• Can reveal channel stability’s 

effects on within-channel sediment 

loads and explain past, present, 

and predicted erosional and 

depositional processes that may

affect restoration 

• May be more indicative of sediment effects 

some distance from the observed 

geomorphology rather that at the location 

• Measurements are local rather than based 

on landscape scale parameters, and 

therefore, require field sampling. 

• Not verified for all waterbody types. 

• Inferring mechanisms from form has not 

been demonstrated to be technically

supportable 

 III. Technical Elements 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Table 6. (continued)

 III. Technical Elements 

Advantages Disadvantages

Associating SABS to Response Indicators

Controlled 

Experiments

• Cause and effect relationships 

supported 

• Familiar derivation and application 

• Criteria can be tailored to biotic 

types in the system

• Thresholds can be identified for 

individual species 

• Standard development is 

independent of setting so that 

states could adopt standards after 

development in any region (more 

cost effective to states)

• Data are lacking for many species and 

development of criteria would take time 

and money (if only sensitive species were 

addressed, investment could be reduced) 

• Sediment criteria may not be specific to 

site conditions (because sediment character 

and site context are variable) 

• SABS do not act in the environment as do

toxicants 

• Difficult to factor in background levels

Field 

Observations: 

Percentile of a 

Distribution of 

Exposures 

and 

Full Range of

Exposures and 

Effects 

• Familiar derivation and application 

• Criteria can be tailored to biotic 

types in the system

• Thresholds can be identified for 

individual species 

• Field conditions and background 

levels are taken into account 

• Many states are familiar with this , 

having used it in biological

assessment programs 

• May be cost effective because the 

framework is in place in many

states

• Other stressors confound the association. 

• When least disturbed sites are compared, 

there is an assumption that these will meet 

designated uses and that may not be true 

• The reference condition may represent an 

unattainable condition 

Field 

Observations: 

 

Conditional 

Probability of a 

Selected Effect 

• Provides likelihood of impact for 

exceeding pollutant or pollution 

level 

• Incorporates statements of 

uncertainty

• Use of probability-based survey

data permits an unbiased 

extrapolation of results to the 

statistical population from which 

the sample was drawn 

• Other stressors confound the association. 

• Traditionally, a single-factor (although it 

could be modified to include multiple 

factors) 

Waterbody Use 

Functionality 

• Applies in waterbodies where 

aquatic life is not a primary 

concern 

• Explicit stratification by

designated use 

• Does not protect ecological integrity in 

waterbodies that are not designated as 

having an aquatic life use 

71
Framework for Developing SABS Water Quality Criteria U.S. EPA 

The detailed scenario and other examples illustrate how some of the proposed methods might be 

used together to establish SABS criteria (Table 7). Each of these cases is based on activities and 

steps within the process that is described in Section III.B of this Framework: 

1. Review current designated uses and criteria for a set of waterbodies 

2. Describe SABS effects on the waterbodies’ designated uses 

3. Select specific SABS and response indicators 

4. Define potential ranges in value of the SABS and response indicators 

5. Identify a response indicator value that protects the designated use 

6. Analyze and characterize SABS - response associations 

7. Explain decisions that justify criteria selection 

Table 7. Specific applications of the methods used in the hypothetical model for criteria 

development and application. 

 III. Technical Elements 

Application/Use

To characterize range of biological, physical, or 

Empirical Classification chemical conditions 

To verify stream type classification 

Fluvial Geomorphology To classify waterbodies with similar sediment 

dynamics 

Relative Bed Stability To evaluate observed against expected stream bed 

particle size characteristics 

To evaluate threshold of impact Controlled Experiments 

Field Observations To confirm a plausible effect given the exposure 

frequency, duration and magnitude 

Conditional Probability Analysis To establish thresholds and criteria 

Possibly to classify waterbodies Waterbody Use Functionality To establish thresholds and criteria 

The examples below illustrate how several methods are used together to develop independent 

response ranges and identify criteria based on thresholds of effects. That is, a combination of 

classification, controlled laboratory findings, departure from reference condition, and 

associations derived from in-stream measurements all play a part. When different quantitative 

methods result in values that are similar, there is greater confidence the criteria will be protective 

of the designated use. Different methods are italicized and bolded at each appearance to 

emphasize the roles they play individually and together in the development process. Note that all 

numbers are hypothetical and are included, not to recommend criteria values but rather to more 

clearly demonstrate the decision process. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

III.E.1. Example: Northeastern Headwater Streams 

In this scenario, we assume that a resource manager is developing criteria for a statewide set of 

2nd or 3rd order, high gradient headwater streams. These streams had been grouped by similarity 

in form and function during a statewide classification of all waterbodies, based on a fluvial 

geomorphology method. The headwaters class contained high gradient systems that move 

substrates of widely varying sizes during storm events. These were small streams with mostly 

cobble/gravel bed materials and sediment transport that were limited by competence (critical 

shear stress). Despite the high gradient of the streams and the predominantly coarse bed 

materials and natural tendency to export rather than accumulate sediment, substantial sources of 

fine sediment may exist in the watershed, banks and bed. Moreover, in- and near-channel 

disturbances combined with 'flashy' high-flow patterns were capable of mobilizing excessive fine

sediment loads thereby causing channel alterations, bank instability, and subsequent biotic 

impairments in these streams. 

Step 1. Review current designated uses and criteria for a set of waterbodies: 

The major designated use of these streams is a cold-water fishery. No specific criteria existed for 

SABS indicators. The designated use was stated in very general terms and the resource manager 

decided to refine it as 'support of spawning populations of native brook trout' to distinguish it 

from 'seasonal survival of stocked trout'. Continuing to meet this designated use is dependent on 

many attributes of stream condition, such as sufficient depth, flow, clarity, and oxygenation; 

clean gravels for spawning; sufficient habitat and cover for invertebrates and small fish, as well 

as the trout themselves; an appropriate water temperature regime; and the absence of other 

conflicting or incompatible uses. Excessive sediment loads can affect several of these attributes 

at sensitive life stages. 

 III. Technical Elements 

Step 2. Describe SABS effects on the waterbodies’ designated uses: 

To begin the process, the resource manager considered the potential ways that excess sediment 

could adversely affect the brook trout fishery. The resource manager identified several 

mechanisms that could reduce trout survival: (1) physical abrasion by suspended particles, (2) 

decreased visibility reducing successful sight-feeding, (3) reduced prey capture due to low 

abundance of prey from the lack of suitable habitat for invertebrates, ( 4) poor 

reproduction/recruitment through the loss of spawning habitat or damage to the eggs or sac fry, 

(5) increased width/depth ratio, lower pool frequency and depth due to sediment deposition, 

reducing the abundance and quality of territory for adult and juvenile trout; and (6) increased 

maximum water temperatures associated with the deposition-driven increased width/depth ratio, 

causing decreased DO and lethal or sub-lethal effects (e.g., disease, crowding at cool seeps) on 

adult fish. These mechanisms were depicted in a conceptual model, which was useful for 

illustrating the relationships among the SABS, designated uses, and potential measurements to 

quantify the associations (Figure 15). The resource manager conducted a literature review to 

support the linkages described in the conceptual model and discovered a variety of observed sublethal effects for brook trout including inhibition of prey capture, growth, and egg survival. A 

review of available data sets revealed that these exact measurements were not monitored in the 

state’s own studies though reasonable surrogates were noted. As a result, our hypothetical 

resource manager considered what types of data were available to use or what could reasonably 

be developed in the context of a variety of possible methods for criteria development. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

 III. Technical Elements 

Figure 15. Conceptual model for the northeastern headwater stream example. 

Decreased survival 

and growth 

S. Cormier 20050205 

Increased 

Deposition

NTU: water 

clarity Increased 

Suspended Fine 

Particles 

Increased settled 

particles 

Decreased 

light 

penetration 

Reduced 

visibility

Increased 

physical 

abrasion 

Reduced prey

abundance 

Reduced prey

capture 

Loss of suitable 

habitat for prey 

maintenance and 

reproduction 

Loss of suitable

holding lies for 

adults and 

juveniles 

SABS and 

Response 

Indicators 

Exposure and 

Response 

Relationships

KEY

Decreased

brook trout 

Loss of 

spawning 

habitat 

Increased 

width/depth ratio, 

lower pool depth 

and frequency

Increased 

temperature and 

decreased 

dissolved oxygen

Reduced 

reproduction 

Swim-up 

success 

Number of 

EPT taxa 

Presence of 

brook trout 

% fines: 

embeddedness

74
Framework for Developing SABS Water Quality Criteria U.S. EPA 

Step 3. Select specific SABS and response indicators: 

In this step the resource manager selected measurements that defined the impairment as well as 

the suspended or bedded sediment measurements. The resource manager knew that selection 

could be based either on previously established designated use criteria or could be independently 

established. The resource manager recognized that the absence of brook trout would be the most 

definitive threshold, but significantly reduced populations could also be documented and 

defended as impairments. 

In this hypothetical case, the conceptual model illustrates that three response indicators were 

identified: (1) the presence of brook trout, (2) reproductive success, and (3) available prey. The 

resource manager needed to select appropriate measurements for these response indicators. The 

resource manager selected density of adult brook trout as a direct measure of the designated use. 

For assessing reproductive success, the resource manager chose the percent survival to swim-up 

stage because this addresses a life stage of the brook trout that is sensitive to SABS and is 

feasible to measure. For prey availability, the number of Ephemeroptera, Trichoptera, and 

Plecoptera (EPT) insect taxa was considered a reasonable surrogate although some of these 

species are not normally brook trout prey and the number of species may not necessarily 

represent either abundance or availability as prey for trout. These uncertainties were noted in the 

decision record. 

Likewise, data for prey capture and abundance may be unavailable or too costly to measure, and 

we assume that this is the case for our hypothetical case. Inspection of the conceptual model 

suggested that, at a minimum, there should be one SABS indicator for suspended sediments as 

well as an indicator for bedded sediments. The resource manager selected turbidity (NTU) for 

water clarity and percent fines for settled particles, based on the availability of data in the region 

and based on reported mechanistic and exposure/response associations between turbidity and 

percent fines and effects to salmonids and invertebrates. The resource manager documented two 

reasons for his decision to use these SABS indicators: (1) based on the literature, low levels of

turbidity and percent fines were linked with trout spawning success and macroinvertebrate prey 

productivity, and (2) data for analysis regarding turbidity, percent fines, density of trout and the 

macroinvertebrate assemblage were readily available from both state studies and EMAP. 

 III. Technical Elements 

Step 4. Define potential ranges in value of the SABS and response indicators

In our case, we will assume that the EMAP data set had more than 100 sample locations in cold, 

headwater streams where fish surveys were conducted along with benthic macroinvertebrate 

sampling, water quality analysis, and characterization of physical habitat. To determine the range 

of indicator values that are possible for the waterbody class, the empirical classification method 

was used. First, non-SABS parameters were 

selected to identify high quality reference streams. 

The resource manager used both land cover (high 

percent natural) and water quality (low 

conductivity and metals concentrations) criteria. 

Through GIS analysis and database queries, the 

resource manager identified 25 sites with more 

than 95% natural land cover, specific conductance 

less than 100 μS/cm, and no exceedances of U.S. 

All numbers used in these 

examples are hypothetical and 

are included not to recommend 

criteria values but rather to 

more clearly demonstrate the 

decision process. 

75
Framework for Developing SABS Water Quality Criteria U.S. EPA 

EPA hardness adjusted metals criteria. These 25 sites were considered to be minimally impacted 

and were representative of as nearly natural conditions as was available. Additional parameters 

were examined in the reference sites to confirm the classification and to minimize the influence 

of other potential stressor sources. The resource manager sought evidence of cold water 

temperatures throughout the year, suitable hydrologic conditions, the absence of point sources or 

development, excellent water quality including low levels of contaminants, high concentrations 

of dissolved oxygen, and a forested riparian zone. No further classification was deemed 

necessary after examining the reference data. 

Natural indicator ranges were plotted for these 25 sites and were compared to ranges of the same

indicators in the 75+ remaining sites. For most of the indicators plotted, the reference distribution 

overlapped partially with the non-reference distribution, with the ranges of non-reference values 

showing a greater percentage of sites with “worse” SABS and biological conditions. These 

findings suggested that some sites had conditions that were closer to the natural potential than 

others and that the tested indicators may be reasonable measurements for assessing SABS and 

biological conditions. There were consistently three to four reference sites that had poorer 

indicator values than the remaining data and the resource managers decided to use the 75th 

percentile of SABS data and the 25th percentile of biological data to describe reasonable 

expectations for the natural potential. The few sites with poorer indicator values could not be 

associated with a consistent source of variability.

Step 5. Identify a response indicator value that protects the designated use

Three biological measures were selected as response indicators: (1) The 25th percentiles of the 

distributions were 4.3 adult brook trout per 100 square meters, (2) 15 EPT taxa, and (3) percent 

survival to swim-up stage. In this hypothetical example, percent survival to swim-up stage was 

not measured in the field because it would require destructive sampling. For this response 

indicator, literature suggested that 86% survival was adequate for sustained reproduction. 

Additional literature review supported the state’s findings regarding adult trout densities, with a 

mean value of 6.2 fish/100 square meters in productive trout streams averaged over three studies. 

The EPT richness values in reference sites were found to be similar in cold water streams of 

neighboring states. 

 III. Technical Elements 

These numbers are for illustration purposes only and are not meant to represent actual targets. 

The 25th percentile of reference values were therefore established as response indicator 

transition points between attainment and non-attainment of the designated use (i.e., support of 

spawning populations of native brook trout). Below, the completion of the hypothetical case 

using the multi-step process is discussed separately for suspended sediments and for bedded 

sediments, with reference to the individual methods used to develop the criteria for each. 

Suspended Sediment Criterion Development

In this case, two exposure-response techniques (controlled experiments and field observations) 

are used in combination to complete the development of a criterion for suspended sediment. 

Step 6. Analyze and characterize SABS - response associations 

To use the controlled experiment method to define the association between SABS indicators and 

biological responses, the resource manager carefully reviewed the scientific literature for 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

independent reviews, reports, and peer-reviewed publications linking specific levels of turbidity 

and suspended solids to adverse responses of salmonids including brook trout. In the tradition of 

criteria-setting based on controlled laboratory tests of chemicals, the most sensitive life stage of

the brook trout was selected as the specific response measurement whenever possible. 

Fortunately for our resource manager, studies that extended from fertilization to the swim-up 

stage for brook trout were available. The resource manager identified three high quality studies 

that were based on (1) high percentage of survival in controls, (2) appropriate statistical analysis, 

and (3) clear documentation. Since the thresholds for significant effects for 86% survival from

the three studies were within the same order of magnitude, the geometric mean was calculated 

and, for illustrative purposes, it was assumed to be 8 NTU. In addition, physiological condition 

studies were examined and assumed effects were reported between 3 and 10 NTUs. Although 

this might be sufficient to set a suspended sediment criterion and thereby define impairment, 

additional evidence would strengthen the confidence in the decision. Thus, in our hypothetical 

case, the resource manager decided to use another analytical method to confirm the 

exposure/response analysis. 

There are several ways that the field observational methods can be used to partially characterize 

SABS-response indicator associations. For the sake of brevity, we only illustrate one here, the 

conditional probability analysis (CPA) method. The analysis depended on multiple fieldcollected samples that should include a measure of SABS and a measurement of the designated 

use. In our hypothetical case, the resource manager wanted to determine the turbidity level at 

which adult brook trout density is reduced below 4.3 fish/100m2

, the transition point identified in 

step 5. So, the resource manager plotted turbidity on the x-axis and brook trout density on the yaxis, performed a quantile regression analysis, and recorded the maximal trout abundance given 

an observed level of turbidity. 

 III. Technical Elements 

For our hypothetical case using the data set of more than 100 sample locations in headwater 

streams, the analysis indicated that during low flow conditions adult brook trout only occurred in 

streams with less than 20 NTUs. Furthermore, a strong association between turbidity and brook 

trout density was found using the state’s own data with a reduction to 4.3 fish/100m2

 occurring 

between 12 and 15 NTUs. The greatest densities were observed between 3 and 10 NTU. These 

turbidity levels were compared with results of the controlled experiment method described 

previously. 

An additional method was applied based on a separate data set: creel surveys of fly fishermen. 

The survey showed that most fishing on popular trout streams occurred only when stream

turbidity was less than 5 NTU. Results from the questionnaire of fly fisherman revealed that their 

decision to fish or not to fish was based on perceived fishing success attributed to the visibility of

their trout flies to the brook trout. 

Step 7. Explain decisions that justify criteria selection

In this hypothetical case, two response indicators were evaluated, survival to swim-up stage from

controlled experiments reported in the scientific literature and density of brook trout based on 

exposure/response analysis of field observations. Based on these two different types of 

information presented in the scenario, our hypothetical resource manager drafted his decision as 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

well as the rationale for that decision. A decision table (Table 8) is valuable for illustrating the 

benefits and drawbacks of alternative criteria levels. The turbidity levels associated with the 

transition points of the response indicators were 8 NTU for 86% survival of swim-up fry and 12-

15 NTU for adult densities of 4.3 fish/100 square meters. The resource manager decided that 15 

NTU was not sufficiently protective since adverse effects appeared to have occurred in streams 

in the state at or near that level. The resource manager might also consider that although 5 NTU 

may have an economic benefit on recreational fisheries, this level of water clarity may be 

difficult to achieve and was lower than necessary to protect the fishery because the state’s own 

data clearly showed that brook trout could thrive in waters as high as 10 NTU. Since the duration 

and frequency of the exposures in the field was uncertain, the resource manager decided to adopt 

8 NTU as a reasonably protective criterion based on controlled laboratory studies on the most 

sensitive life stage and because this value was within the range in which high quality trout 

fisheries were reported for the state. Additional site specific testing for extent and duration would 

be addressed on a site-by-site basis. 

Table 8. Decision rationale for selecting a suspended sediment criterion. 

 III. Technical Elements 

Potential 

criterion (NTU) Advantages Disadvantages

15

Value was not sufficiently protective 

since adverse effects occurred at or 

near that level in the state’s streams. 

10 

Brook trout were present at this 

value based on the state’s 

monitoring data. 

8 

Value is the geometric mean 

threshold in controlled laboratory 

exposures. 

5 Value may have an economic 

benefit. 

Value may be lower than necessary 

to protect the fishery. Value may be 

difficult to achieve. 

This hypothetical scenario illustrates the approach and reasoning for indicator selection, data 

analysis and suspended sediment criterion selection. Another alternative might be to use species 

sensitivity distribution curves to derive a criterion that is protective of 95% of species; and there 

are still other alternatives. What is essential is that the scientific analysis be sound and the 

rationale for decision-making transparent, logical, and defensible. Remember that this is a 

hypothetical example and values are not based an actual analysis of the literature or data sets. 

Bedded Sediment Criterion Development 

In this case, the conditional probability analysis (CPA), fluvial geomorphology, and relative 

bed stability (RBS) methods were used to complete the development of a criterion for bedded 

sediment. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

Step 6. Analyze and characterize SABS - response associations 

The resource manager used the CPA method to determine the probability of observing reduction 

below acceptable levels of EPT taxa (15 taxa). Percent fines was selected as the SABS 

measurement for bedded sediment (Step 3). The resource manager could confidently apply the 

CPA method because data were available from an EMAP study where sampling locations were 

randomly selected. Results from the CPA indicated an 80% chance for the presence of fewer 

than 15 species of EPT when the percentage of fine sediments (<0.06mm) exceeded 20%. There 

was a 60% chance of fewer than 15 species of EPT when the percentage of sediments exceeded 

10% fines. In a similar analysis using density of brook trout, there was an 80% chance of less 

than 4.3 fish/m2

 in cold water streams with less than 25% fine sediments and a 60% chance at 

12% fine sediments. 

The resource manager also knew that in a neighboring state restoration efforts were already 

underway in two streams that had originally only supported stocked brook trout. The resource 

manager of the study had used the fluvial geomorphology method to evaluate SABS in the two 

streams and designed controls including stabilization of stream banks consistent with the ongoing adjustment of the channel toward a more stable form and the creation of in-stream

complexity by adding large boulders to the stream. Before implementing the controls, SABS and 

biological response indicators were measured. After implementation, sampling continued at 

regular intervals. Year-old trout were observed in one stream two years after intervention; the 

percent fines had declined to 5%. 

No recovery was seen in the second stream where percent fines were reduced but were measured 

at 12%. The resource manager was unsure of the reason(s) why the second stream had not 

recovered. Stressor(s) could include insufficient recovery to permit areas of down-welling and 

up-welling, which are necessary for spawning, or insufficient recovery time to reduce the levels 

of percent fines. Although this was not enough information to use in development of alternative 

criteria, the resource manager recognized its value in providing some quantitative response data 

consistent with the results from other methods, providing SABS measures that were more closely 

related to problematic SABS source locations (e.g., the unstable banks) and thereby helping him

target restoration actions more effectively, and providing valuable post-project monitoring 

information. 

 III. Technical Elements 

The resource manager also recognized that he could apply the RBS method because fluvial 

geomorphology data were also collected by a state agency and by EMAP. These measures 

included ongoing channel adjustment, bank instability, and dominant bed particle size along with 

channel gradient and other measures to help classify the waterbody type. The channel 

morphology data provide an opportunity to characterize a range of values for headwaters streams 

for percent fines and RBS measures. In particular, the RBS data set provided him with 

information on the abiotic sediment regime in its characterization of expected bed composition 

and particle sizes, and a range of departures from reference exemplified by the observed bed 

composition. 

As a comparison with the other methods that analyze associations with percent fines, the 

resource manager determined whether thresholds occurred at a relatively consistent RBS ratio 

value. The resource manager also noted that results from such an analysis might demonstrate 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

suitability of a selected RBS value associated with an effects threshold as an alternative criterion 

for percent fines. Further, the resource manager planned to look for associations among the RBS

values, embeddedness, and geomorphic indicators of ongoing channel instability and adjustment, 

in the possibility that these can either cross-validate or provide additional criteria alternatives in 

the future. 

Step 7. Explain decisions that justify criteria selection 

The resource manager knew from the adjacent state’s experience that a reduction to 5% fines 

could restore a fishery, but the exact threshold was still very uncertain and based on only one 

stream that had recovered and one that did not. The resource manager also knew that the choice 

of a probable effect level was critical to a decision. A decision table (Table 9) is valuable for 

illustrating the benefits and drawbacks of alternative criteria levels. If the resource manager 

chose the 80% level (20 – 25% fines) he/she would have a high probability of losing the trout 

fishery. The resource manager believed that he/she could demonstrate to the water director the 

economic and political efficacy of setting the threshold at a 60% effect level (10-12% fines), 

which would be more protective. Percent fines at this level still posed some risk to the fishery, so 

the resource manager recommended that the lower end of the range (10%) be selected as a 

provisional criterion and that the criterion should be revisited after data were collected from

several streams in his state that he/she knew would require TMDLs and restoration. The resource 

manager recommended careful monitoring of streams during the provisional period and after the 

criterion was implemented. The 10% fine sediment provisional criterion was selected as a 

reasonably protective level for the support of brook trout. 

Table 9. Decision rationale for selecting a bedded sediments criterion 

 III. Technical Elements 

Potential 

Criterion 

(percent fines) 

Advantages Disadvantages

20-25% 

80% chance of loss invertebrate food 

base and reduced fishery, may require 

costly stocking due to lack of survival 

of early life stages 

10-12%

60% chance of loss of fishery. No 

recovery in similar fishery at 12% 

fines. 

10% More likely to be protective More difficult to achieve than a more 

relaxed criterion. 

5% 

Unstocked, juvenile trout 

observed in similar fishery after 

5% fines were achieved 

More difficult to achieve than a more 

relaxed criterion. 

Scenario Summary

In this hypothetical scenario, the SABS criteria established for headwater streams were 

developed and confirmed using statewide and regional data sets. We could imagine that a limited 

statewide analysis validated the regional study and that the criteria of 8 NTUs for suspended 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

sediments and 10% fines for bedded sediments were adopted as standards for headwater streams 

with the native cold-water fisheries designation throughout the state. 

This scenario illustrated a variety of applications of the methods discussed throughout this 

Framework but these do not constitute all the roles each might potentially play. For more 

detailed examples of applications of the individual methods, see Section III.D. 

III.E.2. Abbreviated Examples 

SABS criteria can be developed using the multi-step process and these same general methods for 

any waterbody type. To avoid redundancy, other waterbody types are presented in a much 

shorter format than for headwater streams. 

Large Rivers

Large rivers (e.g., fifth order or greater) collect and transport SABS in ways inherently different 

than the smaller headwater streams. Sediments may reach the larger and lower gradient 

watercourses through upstream sources as well as erosion from the intensive land uses 

(agriculture and urban development) that are prevalent in wide, gently sloping valleys. The 

predominant bed material would be composed of gravel and smaller size particles that could be 

suspended or moved with small flow increases. Deep pools and large quantities of water allow 

for designated uses such as drinking water supply and primary contact recreation (swimming and 

boating). Aquatic life uses shift to warm water species (e.g., bass fisheries) and the benthic 

macroinvertebrate community is fundamentally different compared to upstream. 

 III. Technical Elements 

Resource managers will be faced with a separate SABS criteria development effort for the large 

river waterbody type or class to address unique designated uses and different expectations for 

SABS indicators and the biotic assemblages. This separate effort will follow the same multiple 

steps described in Section III.B of this Framework. SABS indicators and criteria development 

approaches for large rivers may differ from the scenario above. Indicators pertaining to 

suspended sediments (TSS, turbidity, clarity) may be more universally applicable than measures 

of bedded sediments. However, some large rivers may have a certain degree of cobble and larger 

substrates that should be preserved or restored as important habitat. All the previously described 

methods for SABS criteria development could be applied to large rivers, including the waterbody 

use functionality method, which has limited applicability in headwater streams. Waterbody use 

functionality drives criteria development efforts for the uses not pertaining to aquatic life (e.g., 

navigation, drinking water source, and recreation). Turbidity/suspended sediments should be low 

enough to allow efficient water filtration for drinking water, and water clarity must allow 

visibility that is safe for swimmers and boaters. 

Regulated Rivers

Dams that disrupt river flow to create reservoirs also block the flow of sediments. Cobble, heavy 

gravel, and sands can build up behind dams, causing channel armoring and a deficiency of 

sediments below dams. While these changes can result in alterations to water quality, the major 

impacts are on habitat for fish and benthic macroinvertebrates as measured by the composition of 

the substrate. The RBS method can yield effective indicators of substrate changes below dams. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

After examining RBS values in areas unaffected by dams (empirical classification) as well as 

scientific literature regarding sediment alterations caused by dams, a SABS criterion based on 

RBS could be established, above which altered sediment supplies and channel armoring would 

be indicated. 

Wetlands

Riparian wetlands in side channels and floodplains are critical habitat for fish spawning and for 

amphibians that lay egg masses on stable substrates. Because wetlands are natural deposition 

zones for sediments, bedded sediment criteria for stream channels would not be appropriate for 

the adjacent wetlands. Instead, the Sediment Risk Index (SRI, U.S. EPA 2002) could be used as 

an indicator. The indicator, based on predicted soil erosion and delivery from agricultural lands, 

could be correlated with metrics from amphibian surveys. A criterion could be established based 

on field observation methods that demonstrate associations between the SRI and the presence of 

sensitive frog species. Turbidity criteria that might be applied in the main channel would not be 

applicable in the wetlands because water turnover rates are generally slower and fine clays can 

remain in suspension for longer periods. 

Lakes, Ponds, and Reservoirs

Natural lakes and ponds would likely be designated for aquatic life use such that naturally 

occurring species could survive and reproduce, providing opportunities for recreational fisheries 

and wildlife observations. These waterbodies would vary considerably in SABS conditions and 

might require classification based on size and substrate type. 

 

For aesthetic purposes related to aquatic life and recreational uses, Secchi depth was selected as 

an indicator of water clarity. This measure is easy to understand from an aesthetic perspective; it 

is a visual estimate of the depth of water through which a black and white disk can be seen. A 

criterion was established such that the Secchi disk must be visible at a minimum depth of four 

feet. This allows sufficient clarity in recreational waters to provide visual appeal, recreational 

opportunity, enjoyment, and safety (Smith and Davies-Colley 1992). Secchi depth also indicates 

planktonic density. This aspect of the measure needs consideration when management options 

are recommended because both excess sediment supply and high nutrient concentrations can 

cause shallower Secchi depth readings. 

 III. Technical Elements 

 

Many lakes and ponds are actually reservoirs created to provide hydropower, drinking water 

supply, and agricultural water supply. Secondary uses include non-contact recreational use. Low 

turbidity is required for efficient operation of pumps, turbines, filters, and treatments; and water 

clarity can be desirable for aesthetic reasons. Therefore, the waterbody use functionality method 

can be used for setting criteria for these designated uses. Criteria for bedded sediments may not 

be required if reservoir capacities are not threatened by excessive sedimentation and lakebeds are 

naturally composed of fine materials. 

 

Estuaries

Bass fisheries, shellfish, and submerged aquatic vegetation (SAV) beds that provide critical

habitat are valued resources in estuaries. SAVs represent one of the components of the estuarine 

ecosystem that is most sensitive to increases in SABS. A criterion based on water clarity would 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

(if attained) provide conditions for optimal growth and reproduction of SAVs and would not 

impair other habitats and organisms. 

 

Criteria could be developed using the field observations method. In an example from the 

Potomac estuary and the Chesapeake Bay, existing studies were compiled in a worldwide 

literature synthesis. The criteria derived from the literature were evaluated with site-specific field 

studies, model simulation, and diagnostic tools (see example in Section III.D.3). The criteria 

were stratified by depth and salinity regime and adjusted by season. The final criteria used 

percent light through water (PLW) as the indicator and had a range of 13-22 PLW.

 

Estuarine Wetlands

Emergent wetlands that line estuaries and bays may also be subject to excessive SABS effects. 

Water clarity may not be an issue in these generally shallow waterbodies, but sediment 

accumulation as it affects anadromous fish spawning may require establishment of criteria for 

bedded sediments. If the majority of sediments settling in the wetlands come from upland 

sources, as opposed to suspended sources flowing in from the deeper estuary, then an indicator 

of sediment supply (such as the Sediment Risk Index) may be appropriate for the estuarine 

wetlands as it was for the wetlands in the upper parts of the watershed. 

 

Coastal Waters

Natural marine sediment supplies as well as discharge from the estuary and other smaller rivers 

and streams heavily influence SABS conditions at the mouth of the estuaries and in other coastal 

waters. Criteria established in the contributing waterbodies may be considered sufficient for 

protecting designated uses for coastal waters and beaches. Some states may have sensitive 

aquatic life (corals), ecologically significant coastal wetlands, and economically important 

recreational uses (beaches) that merit protection that is not provided through criteria applied to 

the contributing waterbodies. Classification could be guided using the Classical Framework for 

Coastal Systems (U.S. EPA 2004). This framework includes conceptual models of SABS 

impacts in coastal areas that would be a good starting point for criteria development. 

 III. Technical Elements 

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Appendix A 

Glossary of Terms

Aquatic Life Use- A use designation in state/tribal water quality standards that generally 

provides for survival and reproduction of desirable fish, shellfish, and other aquatic organisms; 

classifications specified in state water quality standards relating to the level of protection 

afforded to the resident biological community. 

 

Bedload- Sediment that moves along and is in contact with the stream or river bottom.

Clean sediments- Suspended and bedded sediments that are not contaminated with toxicants. 

Contaminated sediments- Deposited or accumulated sediments, typically on the bottom of a 

waterbody, that contain contaminants. These may or may not be toxic as revealed by a whole 

sediment toxicity test or as predicted by equilibrium partitioning. 

Controlled experiment- An experiment in which replicate experimental units (e.g., organisms, 

sediment microbial communities, or colonized rock baskets) are randomly assigned to treatment 

groups that receive controlled levels of exposure to an agent and responses of interest are 

observed. 

1

Criteria- Under section 304(a) of the Clean Water Act, U.S. EPA publishes scientific 

information regarding concentrations of specific chemicals or levels of variables in water that 

protect aquatic life and human health. 

 

2

Criteria- Levels of individual pollutants, water quality characteristics, or descriptions of 

conditions of a waterbody, adopted into state water quality standards that, if met, will generally 

protect the designated use of the water. In many cases, states make use of the criteria developed 

by U.S. EPA as described in the first definition of criteria. 

Designated Uses- Those uses specified in state/tribal water quality standards for each waterbody 

or segment, whether or not they are being attained. The term is sometimes referred to as 

Beneficial Uses, (i.e., desirable uses that water quality should support). Examples are drinking 

water supply, primary contact recreation (such as swimming), and aquatic life support. 

Embeddedness- The degree to which larger substrate particles (gravel, cobble and boulders) in 

the bottom of a stream or river are surrounded by deposited sediment. 

Erodibility- A soils sensitivity to the effects of wind and water on the soil structure. 

Fines- Fine particulate material such as silt and clay particles typically of less than 0.85 mm

diameter though other diameters can be specified. 

Fluvial Geomorphology- The study of the influence of flowing surface water on the Earth’s 

surficial sediments through the processes of erosion and deposition. 

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Kurtosis- Kurtosis is the degree of peakedness of a distribution.

Nephelometric Turbidity Units (NTU)- The units of measurement for turbidity in water as 

determined by the degree light is scattered at right angles when compared to a standard reference 

solution.

Reference Condition- The condition that approximates a natural, unimpacted condition 

(biological, chemical, physical, etc.) for a waterbody. Reference condition is best determined by 

collecting measurements at a number of sites in a similar waterbody class or region under 

undisturbed or minimally disturbed conditions (by human activity), if they exist. 

Secchi disk- A black and white quadrant disk, typically 20cm in diameter, used to determine 

water clarity by measuring the distance through the water column at which the disk disappears 

and appears. 

Sediment- Fragmented material that originates from weathering and erosion of rocks or 

unconsolidated deposits, including organic material, and is transported by, suspended in, or 

deposited by water. 

Sedimentation- The deposition of sediment. 

Settleable solids- Solids that will settle to the bottom of a cone-shaped container in a standard 

time interval (e.g., an Imhoff cone in a 60-minute period). 

Silt- Non-cohesive inorganic particles. Individual particles are not visible to the unaided human 

eye (0.002 to 0.05 mm). Silt will crumble when rolled into a ball. 

Siltation- The process by which a river, lake, or other waterbody becomes clogged with 

sediment. 

Suspended and Bedded Sediments (SABS)- Organic and inorganic particles that are suspended 

in, are carried by, or accumulate in waterbodies. SABS are natural parts of aquatic systems and 

cannot be considered as pollutants until they are out of balance, in excess or deficient.

 

Suspended load- Sediment that is derived from a river/streambed and is wholly or intermittently 

supported in the water column by turbulence. 

Suspended sediment- Very fine soil particles that remain in suspension in water for a 

considerable period of time without contact with the bottom. Such material remains in 

suspension due to the upward components of turbulence and currents and/or by colloidal 

suspension. 

Suspended-sediment concentration (SSC)- The dry weight of sediment from a know volume of 

water-sediment mixture, typically expressed in milligrams per liter. Primarily fine inorganic clay, 

silt, and sand, but also includes the well-decomposed organic matter typically found in soils. 

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Total Suspended Solids (TSS)- Suspended organic and inorganic solids that are not in solution

and can be removed by filtration. Suspended solids usually contribute directly to turbidity. 

Turbidity- The scattering of light by fine, suspended particles which causes water to have a 

cloudy appearance. Turbidity is an optical property of water. More specifically, turbidity is the 

intensity of light scattered at one or more angles to an incident beam of light as measured by a 

turbidity meter or nephelometer. 

Washload- Sediments smaller than 63 microns that are not from the bed but could be from bank 

erosion or upland sources. 

Water Quality Standards- Are provisions in state, tribal, or territorial law or regulations that 

define the water quality goals of a waterbody, or segment thereof by (1) designating the use or 

uses to be made of the water, (2) setting criteria necessary to protect the uses, and (3) protecting 

existing water quality through anti-degradation policies and implementation procedures. 

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Appendix B 

Impacts of Suspended and Bedded Sediments (SABS) 

SABS are a unique water quality problem when compared to most toxic chemicals, in that 

suspended solids and bedded sediments (including the organic fraction) occur naturally in water 

bodies in natural or background amounts and are essential to the ecological function of a water 

body. Suspended solids and sediments transport nutrients, detritus, and other organic matter in 

natural amounts that are critical to the health of a water body. Suspended solids and sediment in 

natural quantities also replenish sediment bedloads and create valuable micro-habitats, such as 

pools and sand bars. Therefore, a basic premise for managing suspended and bedded sediments 

in water bodies to protect aquatic life uses may be the need to maintain natural or background 

levels of SABS in water bodies. 

However, SABS in excessive amounts constitute a major ecosystem stressor. According to the 

U.S. EPA National Water Quality Inventory - 2000 Report, excessive sediment was the leading 

cause of impairment of the Nation’s waters. The highest frequency of impairment was reported 

for rivers and streams, followed by lakes, reservoirs, ponds, and estuaries. In 1998, 

approximately 40% of assessed river miles in the U.S. were impaired or threatened from

excessive SABS. 

Suspended and bedded sediments have three major avenues of effect in aquatic systems: (1) 

direct effects on aquatic life, (2) direct effects on physical habitat, which result in indirect effects 

on aquatic life, and 3) effects on uses other than aquatic life, such as recreation or drinking water. 

SABS can be broken down into suspended sediments and bedded sediments. In considering 

impacts, suspended sediment is the portion of SABS that exert a negative impact via suspension 

in the water column, such as shading of submerged macrophytes. Bedded sediments are those 

sediments that have a negative impact when they settle out on the bottom of the water body and 

smother spawning beds and other habitats. In discussions within the Framework, thresholds of 

effects on biota are omitted because of high variability found in the literature, specificity of 

application that cannot be explained in brief, and intentions to avoid bias in future criteria 

development exercises. The following discussion is excerpted from Jha (2003). Comprehensive 

reviews of the effects of SABS can be found in the scientific literature (e.g., Jha 2003; Berry et 

al. 2003;Wilber and Clarke 2001; Waters 1995; Chapman 1988; Wood and Armitage 1997; 

Newcombe and Jensen 1996; Nalepa and Quigley 1980). 

Suspended sediments

-Direct effects on aquatic life 

Suspended sediments can directly affect many components of the biota, including algae and 

macrophytes, invertebrates, and fish. The increased turbidity associated with suspended 

sediments can reduce primary productivity of algae as well as the growth and reproduction of 

submerged vegetation. In some systems, increased sediment can lead to a shift from macrophytedominated productivity to algal-dominated productivity. 

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The direct effects of suspended sediments on invertebrates and fish are complex, ranging from

behavioral to physiological to toxicological. The severity of effect caused by suspended 

sediments is a function of many factors, including sediment concentration, duration, organism

life history stage, temperature, physical and chemical characteristics of the particles, associated 

toxicants, acclimatization, other stressors, and interactions of these factors. Suspended sediment 

effects have been scored on a qualitative scale as severity of ill effect (SEV), and they include 

everything from no behavioral effects (lowest on the scale) to behavioral effects (low on the 

scale), to sublethal effects (higher on the scale), to lethal effects (highest on the scale) 

(Newcombe and Jensen 1996). 

Invertebrates may show behavioral, physiological, or toxicological responses to excess 

suspended sediment. For example, invertebrate drift is a behavior that is directly affected by 

increased suspended sediment load in freshwater streams. These changes may be associated with 

a shift in dominance from Ephemeroptera, Plecoptera, and Trichoptera (EPT) insect taxa to other 

less sediment-sensitive taxa of the benthic assemblage. 

Suspended sediments also have a negative affect on the survival of freshwater mussels. Increased 

levels of SABS impair ingestion rates of freshwater mussels. Laboratory studies have shown 

that survival may be species-specific. Mussels compensate for increased levels of suspended 

sediment by increasing filtration rates, increasing the proportion of filtered material that is 

rejected, and increasing the selection efficiency for organic matter. Species-specific responses to 

SABS are adaptations to sediment levels in the local environment, such that species inhabiting 

turbid environments are better able to select between organic and inorganic particles. Many of 

the endangered freshwater mussel species have evolved in fast flowing streams with historically 

low levels of suspended sediment. Such species may not be able to actively select between 

organic and inorganic particles in the water column. Therefore, even low levels of sediment may 

reduce feeding and, in turn, reduce growth and reproduction. 

Suspended sediments also affect fish populations. Two major effects of SABS on fish include (1) 

behavioral effects, such as inability to see prey or feed normally and (2) physiological effects, 

such as gill clogging. Certain fish populations may be severely impacted in their ability to feed 

by even small increases in SABS concentrations because of increased turbidity. Fish that need to 

see their prey to feed suffer from reduced visibility in turbid water and may be restricted from

otherwise satisfactory habitat. 

Many species of fish may relocate when sediment load is increased because fish can readily 

disperse. Other behavioral responses include an increased frequency of the cough reflex and 

temporary disruption of territoriality. The severity of the behavioral response is associated with 

the timing of disturbance, the level of stress, decreased energy reserves, phagocytes, metabolic 

depletion, seasonal variation, and alteration of the habitat. 

Physiological effects of gill clogging can result in impaired growth, histological changes to gill 

tissue, alterations in blood chemistry, and an overall decrease in health and resistance to 

parasitism and disease. Lower doses or shorter duration of SABS will have transitory effects, 

while higher doses for longer periods can result in more lasting and severe effects. Fish can also 

swallow large quantities of sediment, causing illness, reduced growth and eventual death, 

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depending on other contaminants that may be adsorbed to the sediment. Some other 

physiological changes include release of stress hormones (e.g., cortisol and epinephrine), 

compensatory response to decrease in gill function, and clogging gill mucus causing 

asphyxiation and traumatization of gill tissue. The severity of damage appears to be related to the 

dose of exposure as well as the size and angularity of the particles involved. 

-Indirect effects on aquatic life 

A potential problem with suspended sediment in reservoirs, coastal wetlands, estuaries, and nearshore zones is decreased light penetration, which often causes aquatic macrophytes to be 

replaced with algal communities, with resulting changes in both the invertebrate and fish 

communities. A loss of macrophytes can represent a loss of habitat for certain species that use 

them as protective refugia. Reduced light availability can also limit the feeding efficiency of

macroinvertebrates and fish. Invertebrates and fish may avoid areas of high turbidity or low light, 

affecting community structure and dynamics. 

-Effects on other designated uses 

Excessive suspended sediments can affect designated uses other than aquatic life. Recreation can 

be impacted if swimmers prefer clear water to turbid water, or if highly turbid water makes 

swimming hazardous by hiding submerged objects. Anglers may be less able to see fish in turbid 

water. Finally, excess sediments in waterbodies used for drinking water necessitate the use of 

expensive filtration systems to make the water suitable for human consumption. 

Bedded sediments

-Direct effects on aquatic life

Excessive bedded sediment can affect aquatic life in several ways. The effects of reduced 

primary production on aquatic invertebrates and fishes at higher trophic levels are compounded 

when SABS settles on remaining macrophytes. The macrophyte quality also is reduced as a food 

source. Sea grasses and other submerged aquatic vegetation (SAV) are considered “keystone” 

species in temperate and tropical estuaries and coastal areas. These flora have a variety of 

beneficial attributes including providing food and shelter for many aquatic and terrestrial species. 

For example, large-scale declines of submerged aquatic vegetation (SAV) in Chesapeake Bay are 

directly related to increasing amounts of nutrients, and secondarily to sediments entering the Bay 

(Staver et al. 1996). There also has been a worldwide decline in sea grasses including dramatic 

regional losses in the Gulf of Mexico. When studied in detail, seagrass declines have always 

been linked to nutrient enrichment as the most important cause, but suspended sediment remains 

a suspected secondary cause in several cases. 

Many species of fish and macroinvertebrates use the interstitial spaces at the bottom of streams 

to lay their eggs. Reproductive success is severely affected by sediment deposition particularly in 

benthic spawning fishes. The primary mechanisms of action are through increased egg mortality, 

reduced egg hatch and a reduction in the successful emergence of larvae. The cause of egg 

survival rates and egg death are due to reduced permeability of the streambed and to burial by 

settled particles. Thin coverings (a few millimeters) of fine particles are believed to disrupt the 

normal exchange of gases and metabolic wastes between the egg and water. 

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Sediment deposition has caused significant reduction in numbers and standing crop biomass in 

large game fish because of increased vulnerability of their eggs to predation in gravel and small 

rubble, reduction in oxygen supply to eggs, and increased embryo mortality. Differences in 

sensitivity, egg mortality effects, early life stages (i.e., eggs, larvae) and magnitude of impact 

upon fish population are associated with amount of elevated sediment loads, size of the sediment 

particles involved, seasonal variation, and rates of sediment deposition. Even if intergravel flow 

is adequate for embryo development, sand that plugs the interstitial areas near the surface of the 

stream bed can prevent alevins from emerging from the gravel. 

High and sustained levels of bedded sediment may cause permanent alterations in 

macroinvertebrate community structure, including diversity, density, biomass, growth, rates of 

reproduction, and mortality. Three major relationships between benthic invertebrate communities 

and sediment deposition in streams have been reported, including correlation between abundance 

of micro-invertebrates and substrate particle size, embeddedness of substrate and loss of 

interstitial space, and change in species composition with change in substrate composition. 

Specific effects on invertebrates include abrasion, clogging of filtration mechanisms, thereby 

interfering with ingestion and respiration and, in extreme cases, smothering and burial resulting 

in mortality.

In marine environments, corals differ greatly in their ability to resist SABS, with most species 

being highly sensitive to even small amounts while a minority are able to tolerate extremely 

embedded sediment conditions and a few are even able to live directly in sedimented bottoms. 

Excessive sedimentation can adversely affect the structure and function of the coral reef 

ecosystem by altering physical and biological processes through a variety of mechanisms. These

all require expenditure of metabolic energy and when sedimentation is excessive, organisms 

eventually reach the point where they can no longer spare the energy to keep themselves clean, 

and the affected tissues die back. Excess SABS cause reduced growth rates, temporary 

bleaching, and complex food web-associated effects to reef dwelling organisms other than corals. 

Coral larvae will not settle and establish themselves in shifting sediments. Increases in

sedimentation rates alter the distribution of corals and their associated reef constituents by 

influencing the ability of coral larvae to settle and survive.

-Indirect effects on aquatic life 

Some of the indirect effects of bedded sediments stem from the feeding mechanisms of aquatic 

animals. Increases in sediment deposition that affect the growth, abundance, or species 

composition of the periphytic (attached) algal community will also have an effect on the 

macroinvertebrate grazers that feed predominantly on periphyton. For example in the Chattooga 

River watershed, accelerated sedimentation was identified as the leading cause of habitat loss 

and reduction in bed form diversity (Pruitt et al. 2001). Effects on aquatic individuals,

populations, and communities are expressed through alterations in local food webs and habitat. 

When sedimentation exceeds certain thresholds, ensuing effects will likely involve decline of the 

existing aquatic invertebrate community and subsequent colonization by pioneer species. 

Increased sedimentation also may functionally shift the fish community from generalist feeding 

and spawning guilds to more bottom-oriented, sediment tolerant fishes. 

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-Effects on other designated uses 

The build-up of deposited sediment can interfere with other designated uses besides aquatic life. 

Sedimentation can interfere with habitat quality in all waterbody types, but particularly in 

wetlands, where the water filtering capabilities may be affected. Over time, the deposition of 

sediment can alter water tables and channel depths, affecting drinking water, agriculture, and 

recreational and commercial boating and navigation. The removal of deposited sediments via 

dredging is costly and may cause detrimental re-suspension of sediments. 

Other SABS Effects

Effects of SABS on waterbodies result not only from excess SABS but also from SABS 

starvation and changes in supply. Sediment starvation caused by structures such as dams and 

levees is a problem in some ecosystems, ranging from the loss of native fish species and native 

riparian ecosystem structure in many dammed western rivers (e.g., Colorado River, Platte River, 

Missouri River) to the subsidence and loss of wetlands (e.g., Mississippi Delta in Louisiana). 

Changes in the supply rate of sediment can cause drastic changes in aquatic, wetland, and 

riparian vegetation. Undesirable changes in vegetation can be induced by both decreases and 

increases in SABS from natural levels. 

For example, in the Platte and Missouri Rivers, decreases in both sediment supply and scouring 

flows have resulted in the growth of stable riparian forests (including many exotic eastern tree 

species) and the loss of sandbar habitat for several wildlife species (e.g., cranes and piping 

plovers) (Johnson 1994). In the Colorado River, decreased sediment supply (but continuing 

scouring flow) has resulted in the loss of riparian wetland habitat dependent on sandbars 

(Stevens 1995). The magnitude and timing of sedimentation may influence structure and 

recolonization of aquatic plant communities. 

In summary, the current literature suggests that imbalanced SABS contribute significantly to 

detrimental effects on North American aquatic life and can impact other uses of waters. 

Improved SABS criteria are needed to properly manage the level of SABS in aquatic ecosystems 

to minimize or avoid these effects. 

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Appendix C 

State Needs Survey 

Conducted in 2004 

In September, 2004, a survey was conducted to solicit input from states on the status of SABS 

related impairment and monitoring in their state, as well as technical, budgetary, and other needs 

for developing numeric SABS criteria. One state was randomly chosen from each of the 10 U.S. 

EPA regions. States initially contacted included New Hampshire (NH), New York (NY), 

Delaware (DE), Louisiana (LA), North Carolina (NC), Michigan (MI), Kansas (KS), Wyoming 

(WY), Oregon (OR), and California (CA). In each state, a person working with water quality 

standards was contacted and sent the survey, which was often completed with the aid of people 

working directly with water quality monitoring. In one case (Kansas), two state employees 

responded with similar answers. The staff in Louisiana chose not to respond to the survey per se, 

but provided written responses that were modified into survey answers. The responses 

summarized below are from the following states: NH, NY, DE, NC, MI, KS, WY, OR. 

California did not respond. 

STATE NEEDS SURVEY 

Name

Telephone Number 

Job position 

Date 

The U.S. EPA intends to publish a draft Framework for Developing Suspended and Bedded 

Sediment (SABS) Water Quality Criteria. This survey is being conducted to summarize issues 

regarding SABS criteria development that are important to the states. Please answer to the best of

your knowledge. If you cannot answer confidently, provide a reference to another state employee 

that would be more qualified to answer. Though some questions are categorical, additional 

comments are invited. 

1. How would you characterize suspended and bedded sediment (SABS) related 

water body impairment in your state? 

(5) Major problem

(3) Minor problem

(0) Not a problem at all 

2. What is the current status of criteria/standards for SABS in your state? Are they

fully implemented or under development? 

Existing Under Development 

 (1) (0) No criteria or standards 

 (1) (0) Narrative criteria 

 (1) (1) Numeric criteria 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

 (5) (0) Standards with narrative criteria 

 (3) (0) Standards with numeric criteria 

3. Are you applying SABS criteria now? In what capacity or which programs (e.g., 

requirements of the Clean Water Act, TMDLs, upstream/downstream 

monitoring for discharges)? 

KS: Kansas 305(b) reports and 303(d) lists have long recognized SABS-related impairments 

in streams and reservoirs, but the extent of the problem has not been accurately reflected 

in these documents. Most of the reported problems in streams have been identified 

through biological monitoring efforts rather than through the state’s more extensive 

stream chemistry monitoring program. An expansion of the state’s biological monitoring 

program would undoubtedly paint a bleaker picture. (Historically, a TSS criterion of 100 

mg/L was applied to streams in Kansas for diagnostic and 305(b) reporting purposes. 

This BPJ-based criterion was ultimately abandoned owing to a general lack of supporting 

scientific evidence.) 

MI: Yes, Michigan is currently applying SAB type criteria under the NPDES program and the 

surface water monitoring program. 

NH: Not for benthic deposits. Streams: Photo documentation or BPJ for assessing impairment. 

Yes, for turbidity. Primarily for episodic events related to construction. Ad hoc. 

NC: Yes- CWA requirements, TMDL (turbidity –TSS); monitoring (NPDES and ambient)- 

Lakes and Streams; Storm water 

DE: No

NY: Yes, we are applying narrative sediment standards currently. 

OR: We have done TMDLs for sediment. We require turbidity monitoring for some sources. 

WY: Turbidity limits and monitoring are routinely required when appropriate on construction 

sites. Limits for suspended solids (TSS) are also place on various industrial and 

municipal discharge permits e.g., (coal mines, municipalities). 

4. Do you feel there is a need for improving your water quality criteria for SABS? 

KS: Definitely 

MI: The current approach is working, however other options would be considered. 

NH: I guess so for benthic deposits, no further development for turbidity 

NC: Yes 

DE: Not sure 

NY: Numeric standards are preferable to narrative, but development of numeric standards is 

not a high priority for NYS. We believe that our assessments done for aquatic life use are 

appropriate and adequate. To protect the aesthetic quality of the waters, and recreation 

and other best uses, the standards might be useful, but there are other higher priorities for 

standards development in the state. 

OR: Yes 

WY: There is always a need for improving WQ standards. 

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5. If you have SABS criteria/standards, what is/are your indicator(s) for: 

a. Suspended sediments: (6) turbidity 

 (5) total suspended solids 

 (1) light penetration 

 (1) other- secchi depth 

b. Bedded sediments: (1) Wolman pebble counts 

(3) embeddedness 

 ( ) percent fines by volume

 (2) percent fines by area 

 ( ) silt depth 

 (1) substrate stability 

 ( ) residual pool volume 

(2) other – best personal judgement & 

photos; intergravel dissolved oxygen 

c. Biology (7) benthic macroinvertebrates 

 (4) fish

 (3) periphyton 

 (1) other - mussels 

6. What designated uses other than aquatic life uses do you feel are vulnerable to 

SABS impairment in your state? 

(3) Fish consumption 

(5) Primary contact recreation 

(3) Secondary contact recreation 

(7) Drinking water supply 

(0) Agriculture use 

(2) Industrial use 

(1) Navigation 

7. Do you foresee specific technical/scientific problems with development or 

application of SABS criteria in your state? If yes, please explain. 

(5) Yes 

(0) No 

(3) Not sure 

KS: Money and other resource issues may pose a far greater concern. 

In agricultural regions, political opposition may pose an even greater 

challenge (technical and scientific difficulties may seem minor by 

comparison). U.S. EPA will need to convince the states that it is serious 

about tackling this issue. 

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NH: No expert on staff, what parameters, bedload, rate of erosion, deposition, embeddedness 

tough to hang your hat on, for streams: rock baskets – if impaired – then pursue 

sedimentation measure. 

NC: Analytical techniques, background issues 

NY: For bedded sediments, there will some difficulties 

OR: Yes how to deal with natural variability; which are the best measures; what levels are 

needed to protect threatened and endangered species, particularly salmonids 

WY: The largest problem with sediment in Wyoming is clean sediment rather than 

contaminated sediment and its effects on habitat. The issue is keeping sediment transport 

in balance which is different for each stream system. This makes every decision sitespecific and usually requires more data than we can get to do it right. 

8. The following elements/resources are potentially part of the draft Framework 

for Developing SABS Criteria that is being considered. Please rate their utility 

for your criteria development process as: very useful, somewhat useful, 

unknown, not very useful, not at all useful. 

Elements 

Very 

useful 

Somewhat 

useful 

Unknown 

Not very 

useful 

Not at all 

useful 

a. Personnel/expertise 8

b. Money/grants 6 1 1

c. Existing criteria/standards 3 5

d. Technical documentation/manuals 3 5

e. Access to data on SABS effects from scientific 

literature 

6 2

f. SABS data for your State 5 2 1 

g. Analytical methods for converting narrative to 

numeric criteria 

4 3 1

h. Example case studies 1 5 1 1 

i. Web-based communication with U.S. EPA and 

others in criteria development process 

2 3 1 2

j. Data management tools 1 4 1 2 

9. What other information, in addition to what is listed in the above table, would 

you find useful for improving or deriving better numeric SABS criteria? 

KS: In the assessment of aquatic life support, we would benefit from a 

clearer knowledge of the sensitivity of different taxa and assemblages 

to SABS exposure, that is, from the application of more widely 

accepted biological indicators 

MI: U.S. EPA derived SAB criteria and standards that included state 

involvement. 

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NH: Workshops 

NC: Data specific to bedded sediments 

OR: Clarity about what uses we’re trying to protect at what level and which measures/criteria 

are best suited to each purpose. A way to do this with as few criteria/measures as possible 

and as simply as possible. Something that is implementable technically and from a 

resource perspective. Assistance with how to deal with uncertainty and sublethal impacts. 

How to deal with systems that are dynamic and with natural disturbance. 

WY: I don’t know. 

Survey Respondents:

Delaware: Hassan Mirsajadi, Environmental Engineer, Watershed assessment, Department of 

Natural Resource and Environmental Control 

Kansas: Robert T. Angelo, Chief, Technical Services Section, Bureau of Environmental Field 

Services, Kansas Department of Health and Environment; and Bret Holman, Kansas Water 

Quality Standards Coordinator, Kansas Department of Health and Environment 

Louisiana: Kristine Pintado, Environmental Scientist, Office of Environmental Assessment, 

Department of Environmental Quality 

Michigan: Sylvia Heaton, Senior Aquatic Biologist, Water Quality Standards Coordinator, 

Department of Environmental Quality 

New Hampshire: David Neils, Biologist, Department of Environmental Services 

New York: Margaret Novak, Chief, Statewide Waters Monitoring Section, Department of 

Environmental Conservation 

North Carolina: Dianne Reid, Environmental Biologist, Supervisor, Intensive Survey Unit, 

Department of Environment and Natural Resources; and Connie Brower, Environmental 

Chemist, Classifications and Standards Unit, Department of Environment and Natural Resources 

Oregon: Debra Studevant, Water quality standards coordinator, Department of Environmental 

Quality 

Wyoming: Bill DiRienzo, Watershed Program Supervisor, Department of Environmental 

Quality 

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Appendix D 

SABS-Related Criteria for Surface Water Quality 

D.1 Examples of Approaches Currently in Use or Under Development in States and 

Internationally 

Idaho:

In Idaho, as in many states, new numeric criteria must comply with existing narrative WQS, such 

as: “Sediment shall not exceed quantities ... which impair beneficial uses” (IDAPA 

58.01.02.200.08). One of the important beneficial uses of Idaho streams is production of trout 

and salmon for ecological and recreational purposes. Although macroinvertebrate and fish 

community integrity are measured in Idaho (using the Stream Macroinvertebrate Index and the 

Stream Fish Index), these measures are not currently used as indicators of SABS impairment. 

Rather, the state considers as indicators water column and instream measures that change with 

increasing fine sediments and are known to affect growth, survival, reproductive success, and 

habitat suitability of salmonids and other aquatic. These include decreases in light penetration, 

riffle stability, and intergravel dissolved oxygen, and increases in turbidity, total suspended 

solids, embeddedness, extent of streambed covered by surface fines, and percent subsurface fines 

in potential spawning gravels. Target levels for these measures are based on relationships in the 

scientific literature (primarily from studies in the Northwestern U.S.), background conditions in 

Idaho streams, and existing Idaho WQS (Idaho DEQ 2003). 

New Mexico:

New Mexico recently developed a draft protocol to support an interpretation of their state WQS 

stream bottom deposits narrative standard (New Mexico Environment Department 2002), which 

states: 

Surface waters of the State shall be free of water contaminants from other than natural 

causes that will settle and damage or impair the normal growth, function, or 

reproduction of aquatic life or significantly alter the physical or chemical properties of 

the bottom. 

Unlike Idaho, New Mexico’s draft protocol calls for making use attainment decisions based on 

both biological and non-biological indicators. The approach is based on reference condition sites. 

Specifically, the protocol is a quantitative, three-step assessment procedure for determining 

whether the above narrative standard is being attained in a particular stream reach or segment by 

(1) comparing changes or differences, if any, between the site of concern and a reference site, (2) 

directly evaluating instream habitat by measuring either substrate size (mainly fines, 2 mm or 

less) abundance or cobble embeddedness, and (3) verifying or confirming results obtained in step 

2 by assessing and comparing benthic macroinvertebrate communities (or fish) at the same sites.

British Columbia, Canada:

Environment Canada has narrative guidelines for deposited bedload sediment, streambed 

substrate, suspended sediment, and turbidity for aquatic life uses. The British Columbia (BC) 

Ministry of Water, Land and Air Protection released the Ambient Water Quality Guidelines

(Criteria) for Turbidity and Suspended and Benthic Sediments that contain numeric thresholds 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

112

compliant with the national narrative guidelines (Singleton 2001, technical appendices; Caux et 

al. 1997a,b). 

The BC guidelines are broken down by five water uses (untreated drinking water, treated 

drinking water, recreation and aesthetics, aquatic life, and the final catch-all, terrestrial life, 

irrigation, and industrial uses), three sediment indicators (turbidity, suspended sediments, and 

stream substrate composition), and two flow conditions (clear flow and turbid flow). Numeric 

criteria, based on background conditions, exist for each indicator and flow condition for aquatic 

life use. 

Australia and New Zealand:

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC 

2000) define criteria for visual clarity and aesthetics, and outline an approach for defining trigger 

values which, when exceeded, indicate that a problem may be present due to the stressor of 

concern. The visual clarity guidelines are based on the objective that to protect visual clarity of 

waters used for swimming, the horizontal sighting of a 200mm diameter black disc should 

exceed 1.6 m. For protecting the aesthetic quality of recreational waters the natural visual clarity 

should not be reduced by more than 20 percent, the natural hue of water should not be changed 

by more than 10 points on the Munsell Scale and the natural reflectance of the water should not 

be changed by more than 50 percent. 

The trigger values approach mirrors the reference condition method using biological or 

ecological indicators. The trigger value is defined as the level of key physical or chemical 

stressors below which ecologically or biologically meaningful changes do not occur, i.e. the 

acceptable level of change. Regarding sediments as pollutants, the guidelines address turbidity 

and suspended particulate matter, and the 80th percentile of the reference system distribution is 

chosen. Default trigger values are provided for use where either an appropriate reference system 

is not available, or the scale of operation makes it difficult to justify the allocation of resources to 

collect the necessary information on a reference system. 

European Union (EU):

The European Water Framework Directive (WFD) directs the member states to establish goals, 

basin plans, and monitoring of ecological quality (The European Parliament and the Council of 

the European Union 2000). Assessment of ecological quality is based on a reference condition 

method. Annex II of the Directive specifies methods for establishing type-specific reference 

conditions for surface waterbody types. Reference conditions may be based on field data, 

modeling, or professional judgment. Member states are also directed to collect and maintain 

information on the type and magnitude of significant anthropogenic pressures such as urban 

development, forestry, and fisheries. 
Framework for Developing SABS Water Quality Criteria 

Table D.1. Suspended and Bedded Sediments (SABS)-Related Criteria for Surface Water Quality by state (U.S. 

State Numeric Narrative

Alabama 

TURBIDITY:Public Water Supply: There shall be no turbidity of other than natural originthat will cause substantial visible contrast with the natural appearance of waters or interfere with any beneficial uses they serve. Furthermore, in no case shall turbidity exceed 50 Nephelometric units above background. Background will be interpreted as the natural condition of the receiving waters, without the influence of man-made or man-induced causes. Turbidity levels caused bynatural runoff will be included in establishing background levels. The following uses require the same turbidity criteria as described above: swimming and other whole body water-contact sports; shellfish harvesting; fishand wildlife; agricultural and industrial water supply; industrial operations; and navigation.

Alaska 

FRESH WATER USES: Drinking Water Supply and Culinary Food Processing, Contact Recreation: Nephelometric turbidity units (NTU) may not exceed 5 

Nephelometric units above natural conditions when the natural turbidity is 50NTU or less, and may not have more than 10% increase in turbidity when the natural turbidity is more than 50, not to exceed a maximum increase of 25NTU. No measurable increase in concentration of settleable solids abovenatural conditions, measured by the volumetric Imhoff cone. Secondary Contact Recreation: Shall not exceed 5 NTU above natural conditions when natural turbidity is 50 NTU or less, and not have more than20% increase in turbidity when the natural condition is more than 50 NTU, not to exceed a maximum increase of 50 NTU. For all lake waters, shall not exceed 5 NTU over natural conditions. Aquaculture: May not exceed 25 NTU above natural conditions. For all lakewaters, may not exceed 5 NTU above natural conditions. 

Water Supply: aquaculture, industrial: Ninterfere with established water supply treAgriculture: may not cause detrimental eIn other surface waters: no sediment loadeposited) that may cause adverse effects plant life, their reproduction, or habitat ma

113
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Alaska (cont.)

Growth and Propagation of Fish, Shellfish, and Other Aquatic Life: The 

percent accumulation of fine sediment in the range of 0.1 mm to 4.0 mm in the gravel bed of waters used by anadromous or resident fish for spawning may notbe increased more than 5% by weight above natural conditions (as shown fromgrain size accumulation graph). In no case may the 0.1 mm to 4.0 mm finesediment range in those gravel beds exceed a maximum of 30% by weight (as shown from grain size accumulation graph).Water Supply Agriculture, including Irrigation and Stock Watering: For sprinkler irrigation, water must be free of particles of 0.074 mm or coarser. Forirrigation or water spreading, may not exceed 200 mg/l for an extended periodof time. 

Arizona

Designated uses of a surface water may include full body contact, partial bodycontact, domestic water source, fish consumption, aquatic and wildlife (coldwater fishery), aquatic and wildlife (warm water fishery), aquatic and wildlife (ephemeral), aquatic and wildlife (effluent dependent water), agricultural irrigation, and agricultural livestock watering. The following water quality standards for turbidity, expressed as a maximum

concentration in Nephelometric Turbidity Units (NTU), shall not be exceeded: Full body contact and incidental human contact: Not to exceed 50 NTU in streams, or 25 NTU in lakes. Aquatic and Wildlife (cold water fishery): Not to exceed 10 NTU in rivers, streams, other flowing waters, lakes, reservoirs, tanks and ponds. Aquatic and Wildlife (warm water fishery): Not to exceed 50 NTU in rivers, streams, and other flowing waters. Not to exceed 25 NTU in lakes, reservoirs, tanks and ponds. 

A surface water shall be free from pollutacombinations that: 

1. Settle to form bottom deposits th

habitation, growth, or propagatioimpair recreational uses. 

2. Cause objectionable odor in the a

water is located. 

3. Cause off-taste or odor in drinkin4. Cause off-flavor in aquatic organ5. Are toxic to humans, animals, pl6. Cause the growth of algae or aqu

prohibit the habitation, growth, oaquatic life or that impair recreat

7. Cause or contribute to a violation 

quality standard. 

8. Change the color of the surface w

background levels of color.

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Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Arkansas

In establishing these standards, the Commission has taken into consideration the use and value of the streams for public water supplies, commercial, industrial and agricultural uses, aesthetics, recreational purposes, propagationof fish and wildlife, other beneficial uses, and views expressed at publichearings.There shall be no distinctly visible increase in turbidity of receiving waters attributable to municipal, industrial, agricultural, other waste discharges orinstream activities. 

Water bodies/Streams Limit (NTU) 

Ozark Highlands 10 Boston Mountains 10Arkansas River Valley 21 Ouachita Mountains 10Springwater-influenced Gulf Coastal 21Typical Gulf Coastal 45Channel-Altered Delta 75Arkansas River 50 Mississippi River 50 Red River 50 St. Francis River 75 Trout 10Lakes and Reservoirs 25 

Significant physical alterations of the habresource waters, ecologically sensitive wascenic waterways are not allowed. 

CaliforniaNone listed in state regulations. U.S. EPA provides some (from California Water Quality Standards by River Basins, Ca. 1975). 

115
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Colorado

Provide some numeric standards by major river systems, although no turbidity or other sediment-related criteria are specified. 

The Commission recognizes that excessivsolids levels can be detrimental to the watThe Commission has established salinity sColorado River Basin ("Water Quality Staincluding Numeric Criteria and Plan of ImControl", Commission Regulation No. 39or assigned other standards for salinity or practices to be developed through 208 plaagricultural agencies, and further studies o

ConnecticutCould not identify any sediment-related criteria for non-point source (U.S. EPA document lists upper turbidity limits for streams classed)

DelawareFor all Fresh Waters: Turbidity shall not exceed natural levels by more than 10 Nephelometric or Formazin Turbidity Units. For mixing zones, there is a limit of 10 NTU above natural background.Florida

Turbidity: Shall not exceed 29 NTUs above natural background conditions. Biological Integrity: No more than a 75% reduction of benthic macroinvertebrates using the Shannon-Weaver Index relative to established background levels measured using organisms retained by a U.S. Standard No. 30 sieve collected and composited from a minimum of three natural miniDendy type artificial substrate samples of 0.1 to 0.15 m2, incubated for 4 

weeks. Transparency: Shall not be reduced by more than 10%.

116
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Georgia

All waters shall be free from turbidity which results in a substantial visual contrast in a water body due to a man-made activity. The upstream appearance of a body of water shall be as observed at a point immediately upstream of a turbidity-causing man-made activity. That upstream appearance shall becompared to a point which is located sufficiently downstream from the activity so as to provide an appropriate mixing zone. 

All waters shall be free from material relaindustrial or other discharges which produor other objectionable conditions which inwater uses. 

Hawaii 

Streams: Not to exceed the given value: 

More Than:

Parameter Geometric Mean 10% of the 

Time

2% of the Time

Suspended Solids (mg/L) 

10.0** 30.0** 55.0**

Turbidity (N.T.U)

5.0* 15.0* 25.0*

2.0** 5.5** 10.0**

 *Wet Season- November 1 through April 30

**Dry Season- May 1 through October 31

Bottom criteria for streams:

(A) Episodic deposits of flood-borne soil sediment shall not occur in

quantities exceeding an equivalent thickness of five millimeters (0.20inch) over hard bottoms twenty-four hours after a heavy rainstorm.

(B) Episodic deposits of flood-borne soil sediment shall not occur in

quantities exceeding an equivalent thickness of ten millimeters (0.40inch) over soft bottoms twenty-four hours after a heavy rainstorm.

(C) In soft bottom material in pool sections of streams, oxidation-reduction

potential (EH) in the top ten centimeters (four inches) shall not be less than +100 millivolts. 

(D) In soft bottom material in pool sections of streams, no more than fifty

per cent of the grain size distribution of sediment shall be smaller than 0.125 millimeter (0.005 inch) in diameter. 

All waters shall be free of substances attriindustrial, or other controllable sources of 

(1) Materials that will settle to form 

bottom deposits. 

(2) Floating debris, oil, grease, scum

materials.

(3) Substances in amounts sufficient 

water or detectable off-flavor in tamounts sufficient to produce obturbidity or other conditions in th

(4) High or low temperatures; biocid

organisms; toxic, radioactive, cordeleterious substances at levels osufficient to be toxic or harmful tor aquatic life, or in amounts sufany beneficial use of the water. 

(5) Substances or conditions or comb

concentrations which produce un

(6) Soil particles resulting from eros

earthwork, such as the constructihighways; subdivisions; recreatioindustrial developments; or the cmanagement of agricultural land

117
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Hawaii (cont.)

Biological criteria for streams:The director shall prescribe the appropriate parameters, measures, and criteria for monitoring stream bottom biological communities including their habitat, which may be affected by proposed actions. Permanent benchmark stationsmay be required where necessary for monitoring purposes. The water quality criteria for this subsection shall be deemed to be met if time series surveys ofbenchmark stations indicate no relative changes in the relevant biologicalcommunities, as noted by biological community indicators or by indicator organisms which may be applicable to the specific site. Coastal and Marine Turbidity (NTU) not to exceed the given value: 

More Than

Location Geometric Mean 10% of the Time 2% of the TimeAll Estuaries 1.5 3.0 5.0Pearl Harbor 4.0 8.0 15.0 Embayments 0.4 1.0 1.5Open Coastal Waters 

0.5* 

0.02**

1.25* 

0.05**

2.0* 

1.0** 

Oceanic Waters 0.03 0.1 0.2 Marine 0.1

* Wet season - November 1 through April 30. ** Dry season - May 1 through October 31. Marine Bottom Types:Sand beaches: No more than fifty per cent of the grain size distribution ofsediment shall be smaller than 0.125 millimeters in diameter. Lava rock shorelines: Episodic deposits of flood-borne sediment shall not occur in quantities exceeding an equivalent thickness of five millimeters (0.20 inch) for longer than twenty-four hours after a heavy rainstorm.Marine pools and protected coves: No more than fifty per cent of the grainsize distribution of the sediment shall be smaller than 0.125 millimeters indiameter. Hard bottoms: No thicker than an equivalent of five millimeters (0.2 inch). Soft bottoms: No thicker than an equivalent of ten millimeters (0.4 inch). 

The water quality standards (for most subto be met if time series surveys of benchmrelative changes in the relevant biological by biological community indicators or by which may be applicable to the specific siSpecific criteria to be applied to all reef flNo action shall be undertaken which wouldamage, impairment, or alteration of the bof the areas named herein."Soft bottom communities" means poorly communities, mostly of burrowing organidepths between two to forty meters (approhundred thirty feet). The particle size of slevel, and degree of water movement and turnover dictate the composition of animabottom with burrows, trails, tracks, rippledepressions. 

118
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Hawaii (cont.) Reef Flats and Reef Communities: No more than fifty per cent of the grain size distribution of sand patches shall

be smaller than 0.125 millimeters in diameter; Episodic deposits of floodborne soil sediment shall not occur in quantities exceeding equivalent thicknesses for longer than twenty-four hours after a heavy rainstorm as follows: Living coral surfaces: No thicker than an equivalent of two millimeters (0.08inch). 

Idaho

Aquatic Habitat Parameters: These parameters may include, but are not limited to, stream width, stream depth, stream shade, measurements ofsediment impacts, bank stability, water flows, and other physical characteristics of the stream that affect habitat for fish, macroinvertebrates or other aquatic life; and (3-20-97). Biological Parameters: These parameters may include, but are not limited to, evaluation of aquatic macroinvertebrates including Ephemeroptera, Plecoptera and Trichoptera (EPT), Hilsenhoff Biotic Index, measures of functional feeding groups, and the variety and number of fish or other aquatic life to determine biological community diversity and functionality. 

In determining whether a water body fully existing beneficial uses, the Department sall of the applicable water quality standardincluding any criteria developed pursuant whether a healthy, balanced biological comDepartment shall utilize biological and aqlisted below and in the current version of Assessment Guidance", as published by thEnvironmental Quality, as a guide to assisbeneficial use status. These parameters are treated as individual water quality criteria or applied as water quality standards. 

Illinois

Soil Loss: Effective January 1, 1994 to January 1, 2000, all land greater than5% slope subject to this program shall be considered in compliance with the state program if the long term annual soil losses are kept at or below one andone-half "T" value. Effective January 1, 2000, and thereafter, all land subject tothe Act shall meet "T" value. The soil loss tolerance as established by the Soil Conservation Service and as published in the Soil Conservation Service Technical Guide (United States Department of Agriculture, Soil Conservation Service, Field Offices in Illinois) are adopted as the official "T" values for soils of Illinois.

Studies have not yet been able to accuratethe stream sediment load is attributable to what part comes from non-point sources oDepartment will encourage all conservatioto minimize stream bank erosion, more rebefore the feasibility of and the responsibistream bank erosion can be determined. 

119
Framework for Developing SABS Water Quality Criteria 

Table D.1. cont. 

State Numeric Narrative

Indiana

No sediment-related criteria identified. (1) All waters at all times and at all places

zone, shall meet the minimum conditions substances, materials, floating debris, oil, municipal, industrial, agricultural, and othother discharges that:

(A) Will settle to form putrescent or oth

deposits. 

(B) Are in amounts sufficient to be uns(C) Produce color, visible oil sheen, od

such degree as to create a nuisance

(D) Are in amounts sufficient to be acu

otherwise severely injure or kill aquplants, or humans. 

Iowa

Criteria applicable to all surface waters including general use and designated use waters, at all places and at all times to protect livestock and wildlife

watering, aquatic life, noncontact recreation, crop irrigation, and industrial, domestic, agricultural and other incidental water withdrawal uses not protectedby the specific numerical criteria. Turbidity: The turbidity of the receiving water shall not be increased by more 

than 25 Nephelometric Turbidity Units (N.T.U.) by any point source discharge. 

Physical and biological integrity: The wquality resource waters will receive protecthrough maintaining water quality levels nexisting uses or improve water quality to lthe designated use criterion. This involves features of the water body as channel aligncharacteristics, water velocity, aquatic habdistribution and abundance of existing aqu

Kansas

Surface waters shall be free, at all times, fof substances that originate from artificial that produce any public health hazard, nuiimpairment of a designated use. Suspended solids added to surface waters not interfere with the behavior, reproductiother factors related to the survival and prsemi-aquatic life or terrestrial wildlife. 

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Kentucky

AQUATIC LIFE:Warm water aquatic habitat: The following parameters and associated criteria shall apply for the protection of productive warm water aquatic communities, fowl, animal wildlife, arboreous growth, agricultural, andindustrial uses: Total suspended solids: Total suspended solids shall not be changed to theextent that the indigenous aquatic community is adversely affected. 

Settleable solids: The addition of settleable solids that may alter the stream

bottom so as to adversely affect productive aquatic communities is prohibited.

 Surface waters shall not be aesthetically osubstances that: 

(a) Settle to form objectionable deposi(b) Float as debris, scum, oil, or other m

nuisance. 

(c) Produce objectionable color, odor, (d) Injure, are chronically or acutely to

physiological or behavioral responsfish and other aquatic life. 

(e) Produce undesirable aquatic life or 

of nuisance species. 

(f) Cause fish flesh tainting. The conce

compounds which cause fish flesh five (5) :g/L as an instream value. 

Louisiana 

Turbidity other than that of natural origin shall not cause substantial visualcontrast with the natural appearance of the waters of the state or impair anydesignated water use. Turbidity shall not significantly exceed background; background is defined as the natural condition of the water. Determination ofbackground will be on a case-by-case basis. As a guideline, maximum turbidity levels, expressed as Nephelometric Turbidity Units (NTU), are established and shall apply for the following namedwaterbodies and major aquatic habitat types of the state: i. Red, Mermentau, Atchafalaya, Mississippi, and Vermilion Rivers and Bayou Teche-150 NTU; ii. estuarine lakes, bays, bayous, and canals-50 NTU; iii. Amite, Pearl, Ouachita, Sabine, Calcasieu, Tangipahoa, Tickfaw, and Tchefuncte Rivers—50 NTU; iv. freshwater lakes, reservoirs, and oxbows-25 NTU; v. designated scenic streams and outstanding natural resource waters notspecifically listed in Subsection B.9.b.i-iv of this Section—25 NTU; and vi. other state waters and waterbody segments where natural background turbidity exceeds the values specified in these clauses, turbidity in NTU caused by any discharges shall be restricted to the appropriate background value plus 10percent. This shall not apply to designated intermittent streams. 

All waters shall be free from such concentattributable to wastewater or other dischar

a. Settle to form objectionable depob. Float as debris, scum, oil, or othe

nuisances or to negatively impac

c. Result in objectionable color, od

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Louisiana (cont.)

Biological and Aquatic Community Integrity: The biological and communitystructure and function in state waters shall be maintained, protected, and restored except where not attainable and feasible as defined in LAC 33:IX.1109.B.3. This is the ideal condition of the aquatic community inhabitingthe unimpaired water bodies of a specified habitat and region as measured by community structure and function. The biological integrity will be guided bythe fish and wildlife propagation use designated for that particular water body. Fish and wildlife propagation uses are defined in LAC 33:IX.1111.C. Thecondition of these aquatic communities shall be determined from the measures of physical, chemical, and biological characteristics of each surface water body type, according to its designated use (LAC 33:IX.1123). Reference site conditions will represent naturally attainable conditions. These sites should bethe least impacted and most representative of water body types. Such reference sites or segments of water bodies shall be those observed tosupport the greatest variety and abundance of aquatic life in the region as is expected to be or has been recorded during past surveys in natural settingsessentially undisturbed by human impacts, development, or discharges. Thiscondition shall be determined by consistent sampling and reliable measures of selected, indicative communities of animals and/or invertebrates as establishedby the department and may be used in conjunction with acceptable chemical, physical, and microbial water quality measurements and records as deemed for this purpose. 

MaineNo sediment-related criteria identified. MarylandTurbidity (All streams): Turbidity in the surface water resulting from any discharge may not exceed 150 units at any time or 50 units as a monthly average. Units shall be measured in NTU. Turbidity may not exceed level detrimenta

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State Numeric Narrative

Massachusetts

Water Body ClassificationClass A - These waters are designated as a source of public water supply. Class B - These waters are designated as a habitat for fish, other aquatic life, and wildlife, and for primary and secondary contact recreation. (c) Class C - These waters are designated as a habitat for fish, other aquatic life and wildlife, and for secondary contact recreation. Class SA - These waters are designated as an excellent habitat for fish, other aquatic life and wildlife and for primary and secondary contact recreation. In approved areas they shall be suitable for shellfish harvesting without depuration (Open Shellfish Areas). These waters shall have excellent aesthetic value.Class SB - These waters are designated as a habitat for fish, other aquatic life and wildlife and for primary and secondary contact recreation. In approvedareas they shall be suitable for shellfish harvesting with depuration (Restricted Shellfish Areas). These waters shall have consistently good aesthetic value. No sediment-related numeric criteria are specified.

CLASS A, B, C, SA, SB Solids: These waters shall be free from flosettleable solids in concentrations or combimpair any use assigned to this class, that objectionable conditions, or that would imdegrade the chemical composition of the bColor and Turbidity: These waters shall turbidity in concentrations or combinationobjectionable or would impair any use ass

MichiganUses an effluent limitation system. No numeric criteria were identified.Minnesota

Turbidity:Domestic consumption 

 Class A–5  Class B–5 

 Class C–24 

Fisheries and recreation 

 Class A–10 

 Class B–25  Class C–25 

Industrial consumption 

 Class A–5 

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State Numeric Narrative

MississippiThe turbidity outside the limits of a 750-foot mixing zone shall not exceed the background turbidity at the time of discharge by more than 50 NTU. Waters shall be free from materials attribu

industrial, agricultural or other discharges taste, total suspended solids, or other condto create a nuisance, render the waters injurecreation or to aquatic life and wildlife or palatability of fish, aesthetic quality, or imdesignated uses. 

Missouri

Turbidity and Color: Water contaminantcontribute to turbidity or color that will cacontrast with the natural appearance of the interfere with beneficial uses. Solids: Water contaminants shall not causin excess of a level that will interfere with stream or lake bottom shall be free of matadversely alter the composition of the benspawning of fish or development of their ethe physical or chemical nature of the bottBiocriteria: The biological integrity of wlists or numeric diversity indices of benthialgae or other appropriate biological indicsignificantly different from reference watecompared with reference waters of similar ecoregion. Reference water locations are l

Montana

TurbidityB-1 Streams: The maximum allowable increase above naturally occurring turbidity is 5 NTU. B-2 and B-3 Streams: The maximum allowable increase above naturallyoccurring turbidity is 10 NTU. C-1 Streams: The maximum allowable increase above naturally occurring turbidity is 5 NTU. C-2 Streams: The maximum allowable increase above naturally occurring turbidity is 10 NTU. 

B1 B2 B-3 C-1 C-2 water bodies No increases are allowed above naturally of sediment, settleable solids, oils, or floatare likely to create a nuisance or render thdetrimental, or injurious to public health, welfare, livestock, wild animals, birds, fis

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State Numeric Narrative

NebraskaNo sediment-related criteria identified. Nevada

Class A waters include waters or portions of waters located in areas of little human habitation, no industrial development or intensive agriculture and wherethe watershed is relatively undisturbed by man's activity: Settleable solids: Only amounts attributable to man’s activities which will not make the waters unsafe or unsuitable as a drinking water source or which will not be detrimental to aquatic life or for any other beneficial use established for this class. Specific turbidity (NTU) and suspended solids (mg/l) values are given for

specific rivers in the state. Aquatic life: The water must be suitable as a habitat for fish and other aquaticlife existing in a body of water. This does not preclude the reestablishment of other fish or aquatic life. 

For some waters (not all), turbidity is inclstatement: Waters must be free from high temperaturpathogenic to human beings, toxic, corrossubstances attributable to domestic or inducontrollable sources at levels or combinatto human, animal, plant or aquatic life or iinterfere with any beneficial use of the waprovisions of this subsection may be deterwith methods of testing prescribed by the indicator, survival of test organisms must in test water than in control water. 

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State Numeric Narrative

New Hampshire

Deposits

(a) Class A waters shall contain no benthic deposits, unless naturally 

occurring. 

(b) Class B waters shall contain no benthic deposits that have a detrimental 

impact on the benthic community, unless naturally occurring.

Turbidity

(a) Class A waters shall contain no turbidity, unless naturally occurring.

(b) Class B waters shall not exceed naturally occurring conditioning by

more than 10 NTUs. 

(c) Waters identified in RSA 485-A:8, III shall contain no turbidity of

unreasonable kind or quality. 

(d) Class C is the same as class B. 

Aquatic Life

(a) The surface waters shall support and maintain a balanced, integrated, 

and adaptive community of organisms having a species composition, diversity, and functional organizational comparable to that of similar natural habitats of a region. 

(b) Differences from naturally occurring conditions shall be limited to nondetrimental differences in community structure and function. 

(1) All surface waters shall be free from squantity that: 

a. Settle to form harmful deposits. b. Float as foam, debris, scum or otc. Produce odor, color, taste or turb

naturally occurring and 

d. Would render it unsuitable for its e. Result in the dominance of nuisaf. Interfere with recreational activit

New Jersey

SOLIDS, SUSPENDED 25.0 (mg/L) Turbidity: Fresh waters that are not designated as FW1(those fresh waters, as designated in N.J.A.C. 7:9B-1.15(h) Table 6, that are to be maintained in their natural state of quality (set aside for posterity) and not subjected to any manmade wastewater discharges or increases in runoff from anthropogenic activities) or Pinelands Waters: Maximum 30-day average of 15 NTU, a maximum of 50 NTU at any time.Coastal saline waters: Levels shall not exceed 10.0 NTU.

Saline Estuaries: Maximum 30-day average of 10 NTU, a maximum of 30

NTU at any time. 

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State Numeric Narrative

New Mexico

Turbidity: Turbidity attributable to other not reduce light transmission to the point function, or reproduction of aquatic life is cause substantial visible contrast with the water. Bottom Deposits: Surface waters of the scontaminants from other than natural causdamage or impair the normal growth, funcaquatic life or significantly alter the physiproperties of the bottom.

New York

TURBIDITYWater Body Types AA, A, B, C, D, SA, SB, SC, SD, I: No increase except from natural sources that will cause a substantial visible contrast to natural conditions. In water body type GA, turbidity shall not exceed 5 NTU. 

Suspended, Colloidal and Settleable SolAA, A, B, C, D, SA, SB, SC, I, SD, A-SpNone from sewage, industrial colloidal anthat will cause deposition or impair the wa

North Carolina 

Turbidity: the turbidity in the receiving water shall not exceed: 50 Nephelometric Turbidity Units (NTU) in streams not designated as troutwaters. 10 NTU in streams, lakes or reservoirs designated as trout waters. 25 NTU for lakes and reservoirs not designated as trout waters. If turbidity exceeds these levels compared to natural background conditions, the existing turbidity level cannot be increased. Compliance with this turbidity standard can be met when land managementactivities that employ Best Management Practices (BMPs) [as defined by Rule .0202(6) of this Section] recommended by the Designated Nonpoint Source Agency [as defined by Rule .0202 of this Section]. BMPs must be in fullcompliance with all specifications governing the proper design, installation,operation and maintenance of such BMPs. 

Water Body ClassificationClass C: freshwaters protected for secondand aquatic life including propagation and All freshwaters shall be classified to proteminimum.Class B: freshwaters protected for primarincludes swimming on a frequent or organC uses. 

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State Numeric Narrative

North Carolina (cont.)

Nonpoint Source and Storm water Pollution Control Criteria For Entire WatershedWS-II Waters (i) Nonpoint Source and Storm water Pollution Control Criteria For Entire 

Watershed: (A) Low Density Option: Development density must be limited to either 

no more than one dwelling unit per acre of single family detached residential development (or 40,000 square foot lot excluding roadway right-of-way) or12 percent built-upon area for all other residential and non-residential development in the watershed outside of the critical area; Storm water runofffrom the development shall be transported by vegetated conveyances to the maximum extent practicable. 

(B) High Density Option: If new development exceeds the low density 

option requirements as stated in Sub-Item (3)(b)(i)(A) of this Rule, thenengineered storm water controls must be used to control runoff from the firstinch of rainfall; new residential and non-residential development shall not exceed 30 percent built-upon area. 

(C) Land within the watershed shall be deemed compliant with the density 

requirements if the following condition is met: The density of all existingdevelopment at the time of reclassification does not exceed the density requirement when densities are averaged throughout the entire watershed area at the time of classification. 

(D) Cluster development is allowed on a project-by-project basis. 

(E) Minimum 100 foot vegetative buffer is required for all new 

development activities that exceed the low density option requirements as specified in Sub-Items (3)(b)(i)(A) and Sub-Item (3)(b)(ii)(A) of this Rule; otherwise a minimum 30 foot vegetative buffer for development activities is required along all perennial waters indicated on the most recent versions ofU.S.G.S. 1:24,000 (7.5 minute) scale topographic maps or as determined bylocal government studies; nothing in this Section shall stand as a bar todesirable artificial stream bank or shoreline stabilization. 

Class WS: waters protected as water suppcategories depending on degree of developThe following are supplemental classifica

(A) Trout waters (Tr): freshwaters pro

propagation and survival of stocked 

(B) Swamp waters (Sw): waters which 

other natural characteristics which adjacent streams. 

(C) Nutrient Sensitive Waters (NSW

growths of microscopic or macrosclimitations on nutrient inputs. 

(D) Outstanding Resource Waters (O

waters of exceptional state or natioecological significance that require maintain existing uses. 

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State Numeric Narrative

North Carolina (cont.) 

(F) No new development is allowed in the buffer; water dependent

structures, or other structures such as flag poles, signs and security lights, which result in only diminimus increases in impervious area and public projects such as road crossings and greenways may be allowed where nopracticable alternative exists; these activities shall minimize built-uponsurface area, direct runoff away from the surface waters and maximize the utilization of BMPs. 

Other water classes have similar BMP type rules with some of the numbers changed slightly. Critical Area Nonpoint Source and Storm water Pollution Control Criteria: Total dissolved solids not greater than 500 mg/l.

NDorth

akotaClass I streams: Suspended solids- Thirty milligrams per liter consecutive 

thirty-day average. Class II: none

OhioWater quality standards are specified as deviation from biotic indices for each

ecoregion. Values of the index are specified in detail by waterbody orecoregion [not reproduced here]. 

Oklahoma 

Classification: The narrative and numerical criteria in this section are designated to promote fish and wildlife propagation for the fishery classifications of Habitat LimitedAquatic Community, Warm Water Aquatic Community, Cool Water Aquatic Community (Excluding Lake Waters), and Trout Fishery (Put and Take). (c) Cool Water Aquatic Community subcategory. Cool Water Aquatic Community means a subcategory of the beneficial use category "Fish and Wildlife Propagation" where the water quality, water temperature, and habitat are adequate to support warm water intolerant climax fish communities andincludes an environment suitable for the full range of cool water benthos. Typical species may include smallmouth bass, certain darters and stoneflies. 

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State Numeric Narrative

Oklahoma (cont.)

Turbidity from other than natural sources shall be restricted to not exceed the following numerical limits: Cool Water Aquatic Community/Trout Fisheries: 10 NTU. Lakes: 25 NTU Other surface waters: 50 NTU. In waters where background turbidity exceeds these values, turbidity from point sources shall be restricted to not exceed ambient levels. Numerical criteria listed above apply only to normal stream flow conditions. Elevated turbidity levels may be expected during, and for several days after, a runoff event. Biological CriteriaAquatic life in all waterbodies designated Fish and Wildlife Propagation(excluding waters designated "Trout, put-and-take") shall not exhibit degradedconditions as indicated by one or both of the following:(i) comparative regional reference data from a station of reasonably similar watershed size or flow, habitat type and Fish and Wildlife beneficial use subcategory designation or (ii) by comparison with historical data from the waterbody being evaluated. 

Oregon

Turbidity (Nephelometric Turbidity Units, NTU): No more than a ten percent cumulative increase in natural stream turbidities shall be allowed, as measuredrelative to a control point immediately upstream of the turbidity causingactivity. However, limited duration activities necessary to address an emergency or to accommodate essential dredging, construction or otherlegitimate activities and which cause the standard to be exceeded may beauthorized provided all practicable turbidity control techniques have been applied and one of the following has been granted.The formation of appreciable bottom or sludge deposits or the formation of anyorganic or inorganic deposits deleterious to fish or other aquatic life orinjurious to public health, recreation, or industry shall not be allowed [some modifications to standards for specific rivers].

Notwithstanding the water quality standarhighest and best practicable treatment andactivities, and flows shall in every case be maintain dissolved oxygen and overall wapossible levels and water temperatures, coconcentrations, dissolved chemical substaradioactivity, turbidities, color, odor, and at the lowest possible levels. 

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State Numeric Narrative

Pennsylvania

No statewide criteria. The following turbidity criteria are specific to waters in the Neshaminy Creek Basin where indicated, based on special studies: Potable water supply, warm water fishes, migratory fish: Not more than 100NTU.Potable water supply and Cold Water Fishes (Maintenance or propagation, or both, of fish species including the family Salmonidae and additional flora and faunawhich are indigenous to a cold water habitat.): For the period May 15—September 15 of any year, not more than 40 NTU. Warm Water Fish, Migratory fish: for the period September 16—May 14 ofany year, not more than 100 NTU. 

(a) Water may not contain substances 

nonpoint source discharges in concsufficient to be inimical or harmful protected or to human, animal, plan

(b) In addition to other substances liste

this chapter, specific substances to are not limited to, floating materialsubstances which produce color, tasettle to form deposits. 

Rhode IslandClass A (Potable water supply highest use): Turbidity not to exceed 5 NTU over background. Class B and C (fish and wildlife habitat and primary and secondary contact recreational activities. They shall be suitable for compatible industrial processes and cooling, hydropower, aquacultural uses, navigation, and irrigation and other agricultural uses:

Turbidity not to exceed 10 NTU over background. 

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State Numeric Narrative

South Carolina

Biological assessment methods may be employed in appropriate situations todetermine abnormal nutrient enrichment, median tolerance limits (TLm), concentration of toxic substances, acceptable instream concentrations, or acceptable effluent concentrations for maintenance of a balanced indigenous aquatic community. Put, Grow, and Take (TPGT) are freshwaters suitable for supporting growth ofstocked trout populations and a balanced indigenous aquatic community of fauna and flora. Suitable also for uses listed in Freshwaters. For this class: Turbidity: Not to exceed 10% above natural conditions, provided existing uses are maintained. Other water classes do not have specific criteria for turbidity. 

4. All ground waters and surface waters otimes, regardless of flow, be free from:

a. Sewage, industrial waste, or oth

to form sludge deposits that are odorous to such degree as to creinterfere with classified water uuses. 

b. Floating debris, oil, grease, scum

material attributable to sewage, waste in amounts sufficient to bdegree as to create a nuisance owater uses or existing water use

c. Sewage, industrial, or other was

odor or change the existing coloor biological conditions in the raquifers to such a degree as to cinterfere with classified water uuses within mixing zones as desor existing water uses. 

d. High temperature, toxic, corrosi

substances attributable to sewagother waste in concentrations or interfere with classified water. 

b. uses (except classified uses withi

described in this regulation), exisare harmful to human, animal, pl

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State Numeric Narrative

South Dakota

Coldwater permanent fish life propagation waters: Total suspended solids(TSS) less than 30 mg/L as a 30 day average and 53 mg/L as a daily maximum.Coldwater semi-permanent fish life propagation waters: TSS less than 90mg/L as a 30 day average and 158 mg/L as a daily maximum.Warm water permanent and semi-permanent fish life propagation waters: 

TSS less than 90 mg/L as a 30 day average and 158 mg/L as a daily maximum.Warm water marginal fish life propagation waters: TSS less than 150 mg/L as a 30 day average and 263 mg/L as a daily maximum.Effluent Criteria: Effluents discharged from water pollution control facilities into waters classified for the beneficial use of coldwater permanent fish life propagation and coldwater marginal fish life propagation must be of highquality. In order to protect these uses, the effluent may not exceed 10 mg/L of suspended solids and 10 mg/L of 5-day biochemical oxygen demand. 

Raw or treated sewage, garbage, rubble, umunicipal wastes, industrial wastes, or agrproduce floating solids, scum, oil slicks, mvisible gassing, sludge deposits, sedimentfungus growths, or other offensive effects or caused to be discharged into surface waAll waters of the state must be free from sattributable to human-induced point sourcsource activities, in concentrations or comadversely impact the structure and functiointentionally introduced aquatic communi

Tennessee Turbidity or Color - There shall be no turbidity or color in amounts or characteristics that cannot be reduced to acceptable concentrations by conventional water treatment processes. For all beneficial uses: Solids, Floating Materials and Deposits - 

distinctly visible solids, scum, foam, oily slimes, bottom deposits or sludge banks omay impair the usefulness of the water as water supply.

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State Numeric Narrative

Texas

Five subcategories of aquatic life use are established. They include limited,intermediate, high, and exceptional aquatic life and oyster waters. No specific criteria for a sediment-related number. 

Surface water shall be essentially free of fsuspended solids that are conducive to prresponses in aquatic organisms or putrescsediment layers which adversely affect beuses. Surface waters shall be essentially free of conducive to changes in flow characteristithe untimely filling of surface water in the shall not cause substantial and persistent cconditions of turbidity or color. Waste dissubstantial and persistent changes from amturbidity or color.Aquatic life uses. Vegetative and physicaaquatic environment will be maintained or aquatic life uses. 

Utah

Turbidity Increase: 10 NTU for coldwater and warm water game fish and other cold water aquatic life, including the necessary aquatic organisms in their food chain: 15 NTU for non-game fish and waterfowl, shore birds and other water-oriented wildlife. Total Suspended Solids: 35 mg/L for coldwater game fish and other coldwater aquatic life, including the necessary aquatic organisms in their foodchain; 90 mg/L for warm water game and non-game fish. 

It shall be unlawful, and a violation of theperson to discharge or place any waste or way as will be or may become offensive sdeposits, floating debris, oil, scum or otheodor or taste; or cause conditions which paquatic life or which produce objectionaborganisms; or result in concentrations or csubstances which produce undesirable phydesirable resident fish, or other desirable aundesirable human health effects, as deterother tests performed in accordance with s

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State Numeric Narrative

Vermont 

The following water quality criteria shall be achieved in all Class A(1)ecological waters. Turbidity - Not to exceed 10 NTU (Nepholometric Turbidity Units). Aquatic Biota, Wildlife, and Aquatic Habitat - Change from the naturalcondition is limited to minimal impacts from human activity. Measures ofbiological integrity for aquatic macroinvertebrates and fish assemblages are within the range of the natural condition. Uses related to either the physical, chemical, or biological integrity of the aquatic habitat or the composition or life cycle functions of aquatic biota or wildlife are fully supported. All life cycle functions, including over wintering and reproductive requirements are maintained and protected. Water Quality Criteria for Class B waters for Turbidity - The followingcriteria shall be achieved: a. In Cold Water Fish Habitat waters - Not to exceed 10 NTU. b. In Warm Water Fish Habitat waters - Not to exceed 25 NTU. In addition, the Secretary may determine whether there is full support of aquatic biota and aquatic habitat uses through other appropriate methods ofevaluation, including habitat assessments. 

Aquatic Biota, Wildlife and Aquatic Habitat - No change from the reference 

condition that would prevent the full support of aquatic biota, wildlife, oraquatic habitat uses. Biological integrity is maintained and all expectedfunctional groups are present in a high quality habitat. All life-cycle functions, including over wintering and reproductive requirements are maintained and protected. In addition, the following criteria shall be achieved:Water Management Type One waters - change from the reference condition for aquatic macroinvertebrate and fish assemblages shall be limited to minor changes in the relative proportions of taxonomic and functional components;relative proportions of tolerant and intolerant components are within the rangeof the reference condition. Changes in the aquatic habitat shall be limited tominimal differences from the reference condition consistent with the full support of all aquatic biota and wildlife uses. 

Settleable solids, floating solids, oil, greassuspended solids: None in such concentthat would prevent the full support of usesIn addition to other applicable provisions appropriate methods of evaluation, the Seapply numeric biological indices to determsupport of aquatic biota and aquatic habitabiological indices shall be derived from mintegrity of the reference condition for difIn establishing numeric biological indicesestablish procedures that employ standard methods to characterize the biological intereference condition. Characteristic measurinclude but are not limited to community as: species richness, diversity, relative abuintolerant species, density, and functional 

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Vermont (cont.) 

Water Management Type Two waters - change from the reference condition for aquatic macroinvertebrate and fish assemblages shall be limited to moderatechanges in the relative proportions of tolerant, intolerant, taxonomic, andfunctional components. Changes in the aquatic habitat shall be limited to minordifferences from the reference condition consistent with the full support of all aquatic biota and wildlife uses. Water Management Type Three waters - change from the reference condition for aquatic macroinvertebrate and fish assemblages shall be limited to moderate changes in the relative proportions of tolerant, intolerant, taxonomic, andfunctional components. Changes in the aquatic habitat shall be limited tomoderate differences from the reference condition consistent with the full support of all aquatic biota and wildlife uses. When such habitat changes are a result of hydrological modification or water level fluctuation, compliance maybe determined on the basis of aquatic habitat studies. 

Virginia

None identified for standards.Turbidity and suspended solid criteria provided as effluent limits on specific water bodies. 

All state waters, including wetlands, shall attributable to sewage, industrial waste, or concentrations, amounts, or combinations established standards or interfere directly designated uses of such water or which arhuman, animal, plant, or aquatic life.  Specific substances to be controlled inclufloating debris, oil, scum, and other floatinsubstances (including those which bioaccuproduce color, tastes, turbidity, odors, or sdeposits; and substances which nourish unaquatic plant life. Effluents which tend to the receiving water will also be controlled

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State Numeric Narrative

Washington

Class AA (Extraordinary), Class A (Excellent):Turbidity shall not exceed 5 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 10 percent increase in turbidity when the background turbidity is more than 50 NTU. Class B (Good) and C (Fair)Turbidity shall not exceed 10 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 20 percent increase in turbidity when the background turbidity is more than 50 NTU. Lake Class: Turbidity shall not exceed 5 NTU over background conditions. 

West Virginia

Categories A, B, and C: No point or non-point source to West Virginia's waters shall contribute a net load of suspended matter such that the turbidity exceeds 10 NTU's over background turbidity when the background is 50 NTU or less, or have morethan a 10% increase in turbidity (plus 10 NTU minimum) when the backgroundturbidity is more than 50 NTUs. This limitation shall apply to all earth disturbance activities and shall be determined by measuring stream quality directly above and below the area where drainage from such activity enters the affected stream. Any earth disturbing activity continuously or intermittentlycarried on by the same or associated persons on the same stream or tributary segment shall be allowed a single net loading increase. 

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Wisconsin

Practices attributable to municipal, industrdomestic, agricultural, land development ocontrolled so that all waters including the effluent channel meet the following condiunder all flow conditions: (a) Substances that will cause objectiona

or in the bed of a body of water shall amounts as to interfere with public rig

(b) Floating or submerged debris, oil, scu

not be present in such amounts as to irights in waters of the state. 

(c) Materials producing color, odor, taste 

not be present in such amounts as to irights in waters of the state. 

(d) Substances in concentrations or comb

or harmful to humans shall not be prebe of public health significance, nor spresent in amounts which are acutely or aquatic life. 

Wyoming

(a) In all Class 1 and 2 waters which are cold-water fisheries, the discharge

of substances attributable to or influenced by the activities of man shall not be present in quantities which would result in a turbidity increase of more than 10 Nephelometric Turbidity Units (NTUs). 

(b) In all Class 3 waters and in Class 1 and 2 waters which are warm-water 

fisheries, the discharge of substances attributable to or influenced by the activities of man shall not be present in quantities which would result ina turbidity increase of more than 15 NTUs. 

In all Wyoming surface waters, substanceinfluenced by the activities of man that wibank or bottom deposits shall not be presecould result in significant aesthetic degraddegradation of habitat for aquatic life or awater supplies, agricultural or industrial wwildlife. In all Wyoming surface waters, floating aattributable to or influenced by the activitipresent in quantities which could result in degradation, significant degradation of haadversely affect public water supplies, agrwater use, plant life or wildlife. 

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State Numeric Narrative

District of Columbia

No turbidity increase over 20 NTU for waterbody classes A, B, and C. The surface waters of the District shall be 

attributable to point or nonpoint sources ddo any one of the following: 

(a) Settle to form objectionable deposi(b) Float as debris, scum, oil or other m(c) Produce objectionable odor, color, (d) Cause injury to, are toxic to or prod

physiological or behavioral changeanimals. 

(e) Produce undesirable aquatic life or 

of nuisance species. 

(f) Impair the biological community w

the waters or depends on the waters propagation. 

Puerto Rico

Coastal waters and estuarine waters of high quality and/or exceptional ecological or recreational value whose existing characteristics shall not be altered, except bynatural causes, in order to preserve the existing natural phenomena. Coastal waters and estuarine waters intended for use in primary and secondary contact recreation, and for propagation and preservation of desirable species Turbidity shall not exceed 10 NTU, except by natural causes. Surface waters intended for use as a raw source of public water supply, propagation and preservation of desirable species as well as primary and secondary contact recreation: Turbidity shall not exceed 50 (NTU, except whendue to natural phenomena. 

The waters of Puerto Rico shall not contaiand other floating materials attributable to sufficient to be unsightly or deleterious to designated uses of the waterbody. The waters of Puerto Rico shall be free froturbidity attributable to discharges in such nuisance to the enjoyment of the existing waterbody. 

Virgin 

IslandsNone 
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Appendix E 

Summary of the October 2, 2003 

Consultation with the Science Advisory Board 

The Ecological Processes and Effects Committee (EPEC) of the Science Advisory Board met 

October 2, 2003 in an informal consultation to review and discuss potential approaches to 

developing water quality criteria for suspended and bedded sediments as described in a 

discussion paper prepared and presented by U.S. EPA staff. The following summary includes 

additional information that was not detailed in Section I.D of the Framework. This summary 

does not represent Committee consensus or majority opinions since votes were not taken and no 

attempt was made to reach consensus under the consultation process. 

EPEC Science Advisory Board Members 

Chair: Dr. Virginia Dale 

Panel Members: Dr. Gregory Biddinger 

 Dr. Ivan Fernandez 

 Dr. Cynthia Gilmour 

 Dr. Charles Hawkins 

 Dr. Lawrence Master 

 Dr. Judy Meyer 

 Dr. Michael Newman 

 Dr. Charles Pettinger 

Consultants: Dr. Brian Bledsoe 

 Mr. Charles Rabeni 

 Mr. Timothy Thompson 

SAB Staff: Dr. L. Joseph Bachman 

 Dr. Vanessa Vu 

Need to Focus on Both Flowing Waters as Well as Slow Waters

A couple of Committee members indicated that the focus of the U.S. EPA discussion

paper and the U.S. EPA staff presentations was primarily on running water habitats. 

Some of the Committee members wanted to emphasize that slow or still water habitats 

(large rivers, lakes, estuaries, and oceans) were as important. Members suggested that 

Idaho, California, Washington, and British Columbia have criteria/guidelines that would 

be a good starting point for developing criteria for running water habitats. The 

Chesapeake Bay methods may be a good starting point for large rivers and estuaries, 

especially where water column conditions are less variable in space and time. 

Some members of the Committee felt that because the two types of habitats are so 

different (running water and slow or still water), there may be a need to stratify using this 

division, use different biological endpoints in the two types, and develop different 

criteria. Some members suggested that bedded sediment criteria may be more appropriate 

for running water habitats and suspended measures would be more appropriate for slow 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

or still water habitats. Pelagic target organisms may be important in slow water habitats, 

whereas benthic organisms may be critical in running waters.

Too Little Sediment is a Problem

The focus of the discussion was on excess sediments, but some members of the 

Committee also pointed out that lack of sediments is sometimes a problem in regulated 

rivers and in bedrock channels. There was feedback that both extremes of sediment 

conditions should and could be addressed using some of the methods under discussion. 

Appropriate Focus of Criteria

There were different opinions voiced regarding the starting point of any assessment or 

criteria. Some thought that the criterion should reflect a water body’s ecological potential 

given the intended use of the water body, focusing on the question of “How should we 

manage given what’s here?” as opposed to “How does this compare to reference 

condition?” This would preclude any stratification based on natural waterbody types, 

using the intended use as the stratifying factor. This would also simplify the modeling 

processes; the endpoints would be selected to work within management models, and there 

would be no need to define reference conditions (which are sometimes difficult to 

identify). 

An opposing view was that reference condition is important to define, even if it is not 

attainable. Society should know what it is giving up in terms of natural waterbodies. 

When reference conditions are not attainable or can not be identified, then the natural 

conditions can be estimated and a Use Attainability Analysis can be performed. It was 

also suggested that designated uses of a waterbody may overlap and be in conflict with 

each other. Also, the intent is to protect aquatic life; by focusing only on designated uses, 

some systems may be written off as not being biologically valuable. 

Reference conditions were differentiated from background conditions, as being natural 

conditions found in unimpacted settings similar to the assessed water body, whereas 

background conditions are detected upstream of a suspected inducement of sediment 

pollution. Some Committee members were concerned about finding sufficient reference 

conditions, especially for large rivers. Expectations for reference conditions should not be 

set using estimates of pre-colonial conditions. It was not clear that any Committee 

member was advocating the use of background conditions.

Build In Uncertainty in Methods/Approaches 

Some Committee members stated more than once that uncertainty is an important 

component of any assessment and it should be inherent to any methods developed for 

setting or applying sediment criteria. Criteria could be set while recognizing and 

accounting for uncertainty before triggering management action. The Conditional 

Probability was attractive because it is inherently based on uncertainty. Variability also

needs to be addressed in terms of flow because suspended sediment measures are 

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associated with flow conditions. The time when a measurement is taken may be as 

important as how it is taken; base flow may be best for comparison with biological 

conditions. 

Work Towards National Consistency 

The Committee discussed maintaining consistency of sediment assessments among states. 

Obvious differences in sediment assessments across state borders should be eliminated. 

How this is to be done was not spelled out though coordination at the watershed or 

regional level was implied. The State-by-State Reference Condition Method implies that 

each state would be autonomous in setting criteria and that the state border issue could be 

a problem unless the U.S. EPA has some hand in maintaining consistency. 

Reaction to the Staff’s Criteria Development Methods 

Pros and cons of each criteria development approach were discussed by the Committee first in 

isolation, then as a synthesis of methods. The Committee concluded that there was no one single 

method that could do everything, but features of each one were valuable and should be combined 

into a synthesized framework. 

Toxicological Method 

The first method discussed was the Toxicological Method. It was thought to be very 

different from the other method with some merits and some detractions. One advantage is 

that it can identify thresholds for specific species. Also, the laboratory experiments may 

help define the nature of the response curve for single species and provide a basis for 

dose-response experiments in the field. Some Committee members thought that the 

Toxicological Method could complement another method, at least as an additional line of 

evidence, but that it was not a valid stand-alone method primarily because impacts are 

context dependent and are not reproducible in the laboratory. 

A concern that came up in relation to the toxicological method, but that is of general 

concern regardless of method, is that the endpoint of the experiments must be translatable 

into loads for management purposes. Managers may typically model in terms of turbidity 

or TSS and they are not accustomed to using LD50 concentrations, other explicitly 

toxicological measures, or other measures associated with other methods. For 

management purposes, the criteria must be in units that can be modeled. Other 

Committee members commented that methods must be “doable,” that is, able to be 

implemented. 

Conditional Probability Analysis (CPA) Method

The CPA method was attractive to some Committee members because it inherently 

includes statements of uncertainty (variability) and because it could lead to powerful 

causal analysis. When the question came up about whether this method is essentially 

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single factor ecology, it was suggested that multiple conditions could be used in the 

models, but that it would be data intensive to do so. 

Relative Bed Stability (RBS) Method

The RBS method was viewed as best for use in running water habitats and seemed, to 

some Committee members, as difficult to use in fine bedded systems such as large rivers. 

In large rivers, sediment analysis may require sieving techniques and assessment of 

stream power as opposed to stream competence. The limited applicability in slow or still 

waters was a detractor for the method. On the positive side, some members said the 

method showed promise if it used a classification scheme that truly adjusts expectations 

for natural erosional inputs. The comparison of observed conditions to expected 

conditions automatically puts the RBS value on a relative scale, which could be 

standardized across state lines and would be easier to interpret than a table of different 

criteria for different water body classes. There was considerable technical discussion 

regarding this method. 

One concern expressed by some members with the method was that the biological 

response to the RBS parameter did not seem to be linear; responses were only obvious 

with the very worst conditions. This was explained as evidence of a possible threshold. 

Members suggested that any method needs to show a strong link between the 

measurement and biological conditions. 

Reference Condition Method 

Many Committee members seemed to express that the Reference Condition Method was 

a good method but not a stand-alone approach. It was noted that many states have already 

invested in this method during biological assessments, and additional costs for 

developing sediment criteria would, therefore, be marginal. There was some concern 

about using single number thresholds, and some solutions included using 

observed/expected ratios, using sediment rating curves to incorporate variable flow 

conditions, and the Conditional Probability Analysis as part of the Reference Condition 

Method. 

Fluvial Geomorphological Method 

Some Committee members considered the Fluvial Geomorphological Method a good 

screening level method because sediment budgeting already uses such a method. 

Committee members noted that natural sediment regimes characteristic of particular 

stream types show some consistency, and channel evolution theory explains the changes 

of unstable channels in ways that may help clarify thresholds of impairment and aid 

efforts to restore impaired streams. Sediment Rating Curves were recognized as 

potentially useful but not sufficiently developed, and they are difficult to apply. Some

committee members called channel type classification useful to some degree but advised 

that U.S. EPA be aware of and consider the different schools of thought about classifying 

based on different channel parameters. 

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The Committee indicated that the Fluvial Geomorphological Method focused on the 

sediment sources and exposure without considering biotic effects which were considered 

essential for criteria development. Despite this point, one member did state that abiotic, 

in-channel measurements would be useful as a component of ecological condition. Some

members viewed Hydrogeomorphic classification as a good method for stratification after 

identifying impairment and before assessment and diagnosis. 

Synthesis of Methods 

Some members proposed a synthesis of methods that would take advantage of the 

strengths of several methods. The Reference Condition and Conditional Probability 

Approach methods were suggested as central to a framework that could be supported 

with elements from all of the other methods. In terms of the process that was presented 

by staff in the briefing materials, it was suggested that selection of indicators might not 

be the first step, but should come later. The Committee considered this a work in progress 

and suggested continued work on the synthesis of methods using real data. 

Key Feedback by the Committee on the Methods:

• A synthesis of the methods for setting sediment criteria would be optimal. 

• The Toxicological Method would be best used to support other methods, but should not 

be pursued as a primary method. 

• The CPA Method has merit because it inherently included measures of uncertainty. 

• The RBS Method has merit in running water systems. 

• The Reference Condition Method has merit and could be used as the core or backbone of 

a synthesized process. 

• The Fluvial Geomorphological Method would be best used for classification or 

diagnosis/causal assessment but not for effects assessment because it is not closely 

related to biological integrity. 

Key Differences of Opinion

The Committee was divided on the definition and use of reference conditions. Some

advocated description of reference conditions and classification by natural types, 

estimating reference conditions in cases where appropriate unimpaired systems could not 

be identified and sampled. Other members suggested that management objectives (water 

body function and designated uses) should be the primary classification scheme, 

especially for systems with no pristine reference examples (e.g., large rivers). 

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Appendix F 

Conceptual Models of SABS Sources and Effects 

The following conceptual model depicts relationships from sources of increased erosion of 

sediments from terrestrial environments to their effects on benthic invertebrates. The model can 

be viewed as three subunits (1) Increased suspended sediment supply through various 

mechanisms to their effect on the biota, (2) Increased deposited sediments and their effects on 

biota, and (3) Terrestrial environments to increased transport of sediment. Both suspended and 

deposited sediment can affect aquatic biota, and these effects have been examined in numerous 

review documents (e.g., Waters 1995; Wood and Armitage 1997). Models were prepared by 

Kate Schoffield, U.S. EPA, NCEA. 
Framework for Developing SABS Water Quality Criteria U.S. EPA 

↓ seston

quality

source

proximate

stressor response

KEY

additional step in

causal pathway

↓ visibility

↑ suspended sediment ↑ deposi

↑ physical abra

by sedimen

↑ filter

clogging

↓ biofilm

↓ light in

water column

↓ clingers

↓ visual feeders

↓ filterers

↓ scrapers 

biological impairment

↑ dislodge

↓ surface

gatherers

Model 1.Suspended Sediments

↓ seston

quality

↓ seston

quality

source

proximate

stressor response

KEY

additional step in

causal pathway

source

proximate

stressor response

KEY

additional step in

causal pathway

additional step in

causal pathway

↓ visibility

↑ suspended sediment ↑ deposi

↑ physical abra

by sedimen

↑ physical abra

by sedimen

↑ filter

clogging

↑ filter

clogging

↓ biofilm

↓ light in

water column

↓ clingers

↓ visual feeders

↓ filterers

↓ scrapers 

biological impairment

↑ dislodge

↓ surface

gatherers

↓ surface

gatherers

Model 1.Suspended Sediments

Model 1. Suspended sediments. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

↑ suspended sediment ↑ deposited sediment

↓ organic

matter

↓ substrate

stability

↓ substrate 

diversity

↓ substrate size ↓ interstitial spaces ↑ cove

↓ detritivores

↓ riffle species

↑ burrow

↑ 

↓ interstitial

flow

↓ DO

↑ NH3

↑ fine s

hab

↑ sediment movement

and scouring

↓ biof ↑ burial ilm

↓ scrapers

↑ dislodgement

↓ surface

gatherers

↓ interstitial

habitat

↓ aerophiles

biological impairment

Model 2.

↑ suspended sediment ↑ deposited sediment Deposited Sed

↓ organic

matter

↓ substrate

stability

↓ substrate 

diversity

↓ substrate size ↓ interstitial spaces ↑ cove

↓ detritivores

↓ riffle species

↑ burrow

↑ 

↓ interstitial

flow

↓ interstitial

flow

↓ DO

↑ NH3

↑ fine s

hab

↑ sediment movement

and scouring

↓ biof ↑ burial ilm

↓ scrapers

↑ dislodgement

↓ surface

gatherers

↓ surface

gatherers

↓ interstitial

habitat

↓ interstitial

habitat

↓ aerophiles

biological impairment

Model 2.Deposited Sed

Model 2. Deposited sediments. 

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Framework for Developing SABS Water Quality Criteria U.S. EPA 

150

↑ input of fine sediment

↑ bank erosion

poin

in

↑ sediment

content of water

channel

modification

riparian 

devegetation

livestock impoundment

(upstream)

road

sanding

gravel

mining

watershed

devegetation

↑ channel erosion

↓ bank stability

↑ terrestrial erosion

↑ water velocity 

or discharge ↑ surface runoff

↓ sediment

content of water

↑ trampling

↑ input of fine sediment

↑ bank erosion

poin

in

↑ sediment

content of water

channel

modification

riparian 

devegetation

livestock impoundment

(upstream)

road

sanding

gravel

mining

watershed

devegetation

↑ channel erosion

↓ bank stability

↑ terrestrial erosion

↑ water velocity 

or discharge ↑ surface runoff

↓ sediment

content of water

↑ trampling

↑ bank erosion

poin

in

poin

in

↑ sediment

content of water

↑ sediment

content of water

channel

modification

channel

modification

riparian 

devegetation

riparian 

devegetation

livestock impoundment

(upstream)

impoundment

(upstream)

road

sanding

road

sanding

gravel

mining

gravel

mining

watershed

devegetation

watershed

devegetation

↑ channel erosion

↓ bank stability

↑ terrestrial erosion

↑ water velocity 

or discharge

↑ water velocity 

or discharge ↑ surface runoff

↓ sediment

content of water

↓ sediment

content of water

↑ trampling

Model 3. Sources and processes.
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