DEVELOPING WATER QUALITY CRITERIA FOR

SUSPENDED AND BEDDED SEDIMENTS (SABS)

Potential Approaches

A U.S. EPA Science Advisory Board Consultation

DRAFT DRAFT

US EPA

Office of Water

Office of Science and Technology

August 2003
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TABLE OF CONTENTS:

ACKNOWLEDGMENTS 4

GLOSSARY OF TERMS 5

WHAT IS THE PURPOSE OF THIS DOCUMENT? 8

BACKGROUND 8

– What Are Suspended and Bedded Sediments (SABS)? 8

– What Are the Impacts of SABS? 9

– What Are Water Quality Standards? 14

– What Are Water Quality Criteria? 14

WATER QUALITY CRITERIA FOR SABS– CURRENT STATUS 15

– What Has EPA Issued for Criteria in the Past? 15

– Other Recommended Values 16

– What Are States and Tribes Currently Doing? 16

– Turbidity 18

– Suspended Solids 20

– Biological and Other Criteria as Measures of SABS 20

– Narrative Criteria 21

--Recent Efforts by States to Develop New SABS Criteria 21

Idaho 21

New Mexico 23

– What Is Being Done Elsewhere in the World? 26

Canada 26
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Australia and New Zealand 27

European Union (EU) 28

POTENTIAL APPROACHES FOR IMPROVED SABS CRITERIA 29

1. Toxicological Dose-Response Approach 31

2. Relative Bed Stability and Sedimentation Approach 32

3. Conditional Probability Approach to Establishing Thresholds 36

4. State-by-State Reference Condition Criteria Derivation Approach 37

5. Fluvial Geomorphic Approach 42

6. Water Body Use Functional Approach 44

7. Use of New State/International Approaches 46

8. Combinations/Synthesis of Above Approaches 46

CONCLUSIONS 47

REFERENCES CITED 51

APPENDICES 57
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ACKNOWLEDGMENTS:

This paper has been compiled by William Swietlik of the Office of Water, Office of

Science and Technology (OST), Health and Ecological Criteria Division (HECD) at EPA

Headquarters with contributions and help from members of the workgroup listed below. All

inquiries about this paper should be directed to Mr. Swietlik by e-mail at

swietlik.william@epa.gov, or by phone at (202) 566-1129.

A group of EPA professionals has been assembled to work on Suspended and Bedded

Sediment Criteria. The group consists of the following individuals:

William Swietlik, HECD-OST-OW, HQ

Walter Berry, ORD-NHEERL, Narragansett

Thomas Gardner, SHPD-OST-OW, HQ

Brian Hill, ORD-NHEERL, Duluth

Mitra Jha, EPA Region 8, Denver

Phil Kaufmann, ORD-NHEERL, Corvallis

Brian Melzian, ORD-NHEERL, Narragansett

Douglas Norton, AWPD-OWOW-OW, HQ

John Paul, ORD-NHEERL, RTP

Norman Rubinstein, ORD-NHEERL, Narragansett

Robert Shippen, SHPD-OST-OW, HQ

Robert Spehar, ORD-NHEERL, Duluth

Acknowledgment goes to each of these individuals for the contributions they have made

to this discussion paper and to the better understanding of SABS and possible approaches to

developing water quality criteria.

Acknowledgment is also given to Michael Paul and Benjamin Jessup of Tetra Tech, Inc.,

Ownings Mills, Maryland, (one of EPA’s contractors) for their contributions.
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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 which moves along and is in contact with stream or river bottom.

Clean sediments- Suspended and bedded sediments that are not contaminated with toxic

chemicals.

Contaminated sediments- Deposited or accumulated sediments, typically on the bottom

of a water body, that contain contaminants. These may or may not be toxic as revealed

by a whole sediment toxicity test, or as predicted by equilibrium partitioning.

1Criteria- Under section 304(a) of the Clean Water Act, EPA publishes scientific

information regarding concentrations of specific chemicals or levels of parameters in

water that protect aquatic life and human health.

2Criteria- Levels of individual pollutants, or water quality characteristics, or

descriptions of conditions of a water body, 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 EPA under definition #1 above.

Designated Uses- those uses specified in State/Tribal water quality standards for each

water body or segment whether or not they are being attained. 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 amount of silt and sediment deposited in and around the larger

gravel, cobble and boulders in the bottom of a stream or river. 

Fines- fine particulate material such as silt and clay particles typically of less than .85

mm diameter.

Jackson turbidity units (JTU)- An alternative way (to NTU) to measure turbidity in

water based on the length of a light path through a suspension that causes the image of a

standard candle flame to disappear.

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.
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Reference Condition (Biological Integrity)- the condition that approximates natural,

un-impacted conditions (biological, chemical, physical, etc.) for a water body. Reference

condition (Biological Integrity) is best determined by collecting measurements at a

number of sites in a similar water body class or region under undisturbed or minimally

disturbed conditions (by human activity), if they exist. Since undisturbed or minimally

disturbed conditions may be difficult or impossible to find, least disturbed conditions,

combined with historical information, models or other methods may be used to

approximate reference condition as long as the departure from natural or ideal is

understood. Reference condition is used as a benchmark to determine how much other

water bodies depart from this condition due to human disturbance.

Minimally disturbed- the physical, chemical, and biological conditions of a

water body with very limited, or minimal, human disturbance in comparison to

others within the water body class or region. Minimally disturbed conditions can

change over time in response to natural processes.

Least Disturbed Condition- the best available existing conditions with regard to

physical, chemical, and biological characteristics or attributes of a water body

within a class or region. These waters have the least amount of human

disturbance in comparison to others within the water body class, region or basin. 

Least disturbed conditions can be readily found, but may depart significantly from

natural, undisturbed conditions or minimally disturbed conditions. Least

disturbed condition may change significantly over time as human disturbances

change.

Regional Reference Condition- description of the chemical, physical, or biological

condition based on an aggregation of data from reference sites that are representative of a

water body type in an ecoregion, subecoregion, watershed, or political unit.

Sediment- Fragmented material that originates from weathering and erosion of rocks or

unconsolidated deposits, and is transported by, suspended in, or deposited by water.

Sedimentation- The depositing of sediment.

Settleable Solids- Those solids that will settle to the bottom of a cone-shaped container,

an Imhoff cone, in a 60-minute period.

Silt – Noncohesive soil whole 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 water body becomes clogged with

sediment.

Suspended and bedded sediments- particulate organic and inorganic matter that
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suspend in or are carried by the water, and/or accumulate in a loose, unconsolidated form

on the bottom of natural water bodies.

Suspended load- Sediment which is derived from a river/streambed and is wholly or

intermittently supported in the water column by turbulence.

Suspended solids concentration (SSC)- The amount of organic and inorganic particles

suspended in water. SSC is determined by measuring the dry weight of all the sediment

from a known volume of a water-sediment mixture.

Total suspended solids (TSS)- The entire amount of organic and inorganic particles

dispersed in water. TSS is measured by several methods, most of which entail measuring

the dry weight of sediment from a known volume of a subsample of the original.

1Turbidity- 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.

2Turbidity- A principal characteristic of water and is an expression of the optical

property that causes light to be scattered and absorbed by particles and molecules rather

than be transmitted in straight lines through a water sample. It is caused by suspended

matter or impurities that interfere with the clarity of water. These impurities may include

clay, silt, finely divided inorganic and organic matter, soluble colored organic

compounds, and plankton and other microscopic organisms.

Washload- Sediments smaller than 63 microns which are not from the bed but could be

from bank erosion or upland sources.

Water Quality Standards- are provisions in State or Tribal law or regulations that

define the water quality goals of a water body, or segment thereof, by designating the use

or uses to be made of the water; setting criteria necessary to protect the uses; and

protecting existing water quality through anti-degradation policies and implementation

procedures.
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WHAT IS THE PURPOSE OF THIS DOCUMENT?

The Office of Water in EPA, with support from the Office of Research and Development,

is preparing to develop and issue improved water quality criteria (either recommended values or

methodologies) for use by the States to better manage Suspended and Bedded Sediments (SABS)

in water bodies across the country. Before undertaking this effort, the Office of Water is

undergoing a consultation with the EPA Science Advisory Board to gain their review and

recommendations on the best scientific approaches to accomplish this. This paper is being

prepared as the discussion paper for the Science Advisory Board to consider the key scientific

questions regarding methods and approaches for developing water quality criteria for SABS.

This paper provides an introduction to SABS and water quality criteria and discusses the

types and status of water quality criteria that have been or are currently being used by the States,

Canada and elsewhere. The paper also proposes several new approaches or methods for

developing SABS criteria for consideration by U.S. EPA Science Advisory Board. The

consultation with the EPA Science Advisory Board is scheduled to take place October 2, 2003 in

Washington, DC.

After the consultation, the Office of Water intends to prepare a comprehensive strategy

for developing and implementing new SABS criteria, or methods, to be used by the States and

Tribes in their water quality standards programs within the next few years as they adopt new and

revised criteria to protect their waters.

BACKGROUND:

– What are Suspended and Bedded Sediments (SABS)? 

Suspended and bedded sediments (SABS) are defined by EPA as particulate organic and

inorganic matter that suspend in or are carried by the water, and/or accumulate in a loose,

unconsolidated form on the bottom of natural water bodies. This includes the frequently used

terms of clean sediment, suspended sediment, total suspended solids, bedload, turbidity, or in

common terms, dirt, soils or eroded materials.

EPA’s definition of SABS also includes organic solids such as algal material, particulate

leaf detritus and other organic material. This initiative on SABS criteria intentionally does not

look at contamination in sediments, another significant environmental issue, rather, EPA has

dealt directly with the toxicity of chemicals in sediments through its work on Equilibrium

Partitioning-Derived Sediment Benchmarks. EPA does recognize however, that managing

SABS in the aquatic environment will have either direct or indirect consequences on the amount

of contaminated sediments and may need to further examine these relationships in future efforts. 

SABS can be further defined in regards to particle size which are related to the mode of

action in the aquatic environment. SABS can be broken into two fractions based on size – fine

sediment and coarse sediment. Fine sediment is typically considered to consist mostly of
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particles smaller than 0.85 mm and coarse sediment is defined as greater than 9.5 mm. Particles

less than 0.063 mm (silt and clay) remain suspended in flowing water and are largely the cause

of turbidity (IDEQ, 2003).

– What are the impacts of SABS?

SABS are a unique water quality problem when compared to 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 which 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 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 two major avenues of effect in aquatic systems; 1)

direct effects on biota, and 2) direct effects on physical habitat, which result in effects on biota. 

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. (An additional summary of the

effects of SABS can be found in Appendix 1 and a comprehensive review can be found in Jha,

2003. The following discussion is excerpted from Jha, 2003.)

In streams and rivers, fine inorganic sediments, especially silts and clays, affect the

habitat for macroinvertebrates and fish spawning, as well as fish rearing and feeding behavior.

Larger sands and gravels can scour diatoms and cause burying of invertebrates, whereas

suspended sediment affects the light available for photosynthesis by plants and visual capacity of

animals. A potential problem with suspended sediment in reservoirs, coastal wetlands, estuaries,

and near-shore 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. Increased sedimentation also may functionally shift the fish community from

generalist feeding and spawning guilds to more bottom-oriented, silt tolerant fishes.

Sediment starvation caused by structures such as dams and levees is also a problem in

some ecosystems, ranging from the loss of native fish species and native riparian ecosystem
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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).

Effects of excess suspended and bedded sediments on habitat structure include changes in

refugia for biota (e.g., changes in macrophyte communities), increased fines (and embeddedness)

and scouring in streams, aggradation and destabilization of stream channels, and filling in of

wetlands and other receiving waters, and for sediment starvation, scouring and removal of

riparian and pool habitat, and subsidence and disappearance of wetlands and lowering of the

water table. Increased turbidity and concomitant changes in light regime may be considered to

be aspects of altered habitat. Indirect effects on biota will occur as the fish, invertebrates, algae,

amphibians, and birds that rely upon aquatic habitat for reproduction, feeding, and cover are

adversely affected by habitat loss or degradation. 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. There 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.

SABS also affect fish populations. Three major effects of SABS on fishes include: 1)

behavioral effects, such as inability to see prey or feed normally; 2) physiological effects, such

as gill clogging; and 3) effects due to sediment deposition, such as burial and suffocation of eggs

and larvae. Physiological effects of sedimentation 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, depending on other contaminants that may be adsorbed to the sediment. Some

other physiological changes include; release of stress hormones (i.e., cortisol and epinephrine), a

compensatory response to a 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. 

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. Some fishes are able to hunt better as SABS concentrations increase up to a

point because of increased contrast between the prey and the surrounding water. 

Many species of fish may relocate when sediment load is increased, because fish can

readily disperse. Other behavior responses include an increased frequency of the cough reflex

and temporary disruption of territoriality. The severity of the behavioral response is associated
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with the timing of disturbance, the level of stress, decreased energy reserves, phagocytes,

metabolic depletion, seasonal variation, and alteration of the habitat. 

Severity of effect caused by suspended sediments is a function of many factors, which, in

addition to sediment concentration, duration, particle size, and life history stage, may include

temperature, physical and chemical characteristics of the particles, associated toxicants,

acclimatization, other stressors, and interactions of these factors. Suspended sedimentation

effects have been scored on a qualitative scale as “severity of ill effect” (SEV), that 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). 

According to Griffiths and Walton (1978), the upper tolerance level for suspended sediment is

between 80-100 mg/l for fish, and as low as 10-15 mg/l for bottom invertebrates.

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 streambed and from

burial by settled particles. Thin coverings (a few mm) of fine particles are believed to disrupt the

normal exchange of gases and metabolic wastes between the egg and water. Sediment

deposition has caused a 94% 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. It can also cause reduced larval

survival because of armoring of the sediment surface, which traps the larvae. 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. For example, emergence success

of cutthroat trout was reduced from 76% to 4% when fine sediment was added to redds (Weaver

and Fraley, 1993).

There are also detrimental effects of SABS on aquatic invertebrates. SABSs impact the

density, diversity and structure of invertebrate communities. High and sustained levels of

sediment may cause permanent alterations in community structure including, diversity, density,

biomass, growth, rates of reproduction, and mortality. Direct 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. Indirect effects are primarily

from light attenuation leading to changes in feeding efficiency, behavior (i.e., drift and

avoidance), and alteration of habitat from changes in substrate composition, affecting the

distribution of infaunal and epibenthic species. 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
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substrate composition.

Sedimentation alters the structure of the invertebrate community by causing a shift in

proportions from one functional group to another. Sedimentation can lead to embeddedness,

which blocks critical macroinvertebrate habitat by filling in the interstices of the cobble and

other hard substrate on the stream bottom. As deposited sediment increases, changes in

invertebrate community structure and diversity occur. 

Invertebrate drift is directly affected by increased suspended sediment load in freshwater

streams. These changes generally involve a shift in dominance from ephemeroptera, plecoptera

and trichoptera (EPT) taxa to other less pollution-sensitive species that can cope with

sedimentation. 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). A significant correlation was observed

between aquatic ecology and normalized total suspended solids (TSS) data. 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.

SABS also have a negative affect on the survival of freshwater mussels. Increased levels

of SABS impair ingestion rates of freshwater mussels in laboratory studies. However, it has

been suggested 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.

Corals differ greatly in their ability to resist SABS, with most species being highly

intolerant of 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 they eventually reach the

point where they can no longer spare the energy to keep themselves clean, and the affected tissue

dies back. Excess SABS cause reduced growth rates, temporary bleaching, and complex food

web-associated effects with SABS killing not only corals but other reef dwelling organisms. 

Coral larvae will not settle and establish themselves in shifting sediments. Increases in
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sedimentation rates alter the distribution of corals and their associated reef constituents by

influencing the ability of coral larvae to settle and survive.

Changes in the supply rate of sediment causes 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, 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. 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. The periphyton communities are likely to be most susceptible to the

scouring action of suspended particles or burial by sediments. For example, large-scale declines

of submerged aquatic vegetation (SAV) in Chesapeake Bay is directly related to increasing

amounts of nutrients, and secondarily to sediments entering the Bay (Staver et. al., 1996). 

Indirect impacts of excess sediment on water quality can occur through its influence on

aquatic plant communities, organic exchange substrates, and microbial populations. In

environments with high concentrations of SABS, reductions in plant species density, biomass,

and diversity throughout a trophic level are translated into reductions in energy input to the next

trophic level. Decreases in plant populations may result in decreases in populations of

zooplankton, insect abundance and overall biomass which may initiate reductions in herbivore,

omnivore and predatory fish. SABS deposition may cover microbes, or organic matter needed

for microbial processes, or alter redox profiles important in the performance of water quality

processes.

For other uses of water bodies, excessive SABS can, among other things, affect water

clarity and the aesthetic quality of swimming waters, increase pre-filtration efforts and expenses

at drinking water purification facilities and lead to accelerated in-fill of dredged shipping

channels, harbors and marinas.

In summary, the current literature suggests SABS are significant contributors to declines

in populations of 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. 

– What Are Water Quality Standards?

Water quality standards consist of a designated use(s) for a water body, water quality

criteria to protect the designated use(s) and an antidegradation policy. States, and Tribes with
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authorization to conduct a water quality standards program, are required by section 303(c) of the

Clean Water Act (CWA) to adopt water quality standards. States and Tribes adopt water quality

standards 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 water

quality standards 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

the water”. Section 303(c) states that water quality standards should be established for water

bodies taking into consideration their use and value for public water supplies; propagation of fish

and wildlife, recreational, agricultural, industrial, navigation and other purposes.

– What Are Water Quality Criteria?

Water quality criteria are levels of individual pollutants, or water quality characteristics,

or descriptions of conditions of a water body that, if met, will generally protect the designated

use(s). EPA, under section 304(a) of the CWA, periodically publishes water quality criteria

recommendation for use by States, Tribes and territories in setting water quality standards. 

Water quality criteria published pursuant to Section 304(a) of the CWA are based solely on data

and scientific judgements on the relationship between (pollutant) concentrations and

environmental (and human health) effects and do not reflect consideration of economic impacts

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

When establishing numeric criteria, States and Tribes can 1) adopt EPA’s recommended

criteria into their water quality standards, or 2) adopt EPA’s recommended water quality criteria

modified to reflect site-specific conditions, or 3) adopt criteria derived using other scientifically

defensible methods. EPA’s 304(a) criteria recommendations have been critical tools for the

States, Tribes and territories for controlling many forms of pollution and improving water quality

across the Nation. 

There are also other types of designated uses of water bodies, other than aquatic life,

which need to be protected from excess SABS. These include recreation in and on the water,

shipping, drinking water sources, industrial water use, agricultural water use and others. Water

bodies may have multiple use designations, including aquatic life, as well as those other uses

listed above or may be limited to uses other than aquatic life if use attainability analyses have

been performed by the State, Tribe or territories. There are human health criteria, and other

criteria, that are most appropriate for these uses. 
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WATER QUALITY CRITERIA FOR SABS– CURRENT STATUS:

During recent discussions between the States and EPA while developing a water quality

standards and criteria strategy for the next decade (EPA 2003), the need for new/improved water

quality criteria for SABS, or for methodologies for deriving SABS criteria on a regional or sitespecific basis, was identified as one of the highest priorities for the EPA water quality criteria

program. As a result, the EPA Office of Water has committed to do so. 

At this time, EPA believes the biggest challenge will be to develop improved SABS

criteria to protect aquatic life. Most other designated uses of water bodies (possibly with the

exception of drinking water source uses) where aquatic life uses overlap, may be protected by

the potentially more stringent aquatic life criteria. Drinking water uses may need more stringent

criteria, but typically apply to few water bodies. Aquatic life uses typically apply to most all

waters. However, EPA also believes at this time that other forms of criteria for protecting uses

other than aquatic life may still be necessary, where aquatic life uses do not exist or where the

other uses are affected differently by SABS.

The section below provides a description of the current status of criteria related to SABS

in State and Tribal water quality standards, and elsewhere, primarily as background for

considering new criteria development methodologies. However, some of these examples of past,

current and future criteria approaches may hold promise as approaches that could be used on a

national scale by EPA.

– What Criteria Recommendations Has EPA Issued in the Past?

In 1976, EPA published a water quality criteria recommendation for solids and turbidity

that is based on light reduction. This criterion is summarized in the 1986 EPA Quality Criteria

for Water as:

“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.”

The criterion and a brief description of the rationale can be found at

http://www.epa.gov/waterscience/criteria/goldbook.pdf. This criteria has not been frequently

adopted or used by the States. However, in June 2003, Idaho DEQ proposed to use this criterion

value as one component of their newly revised sediment TMDL targets (See description of Idaho

below).

EPA also published a narrative “free from” aesthetic standard that States have since

adopted into their water quality standards. This narrative states:

“Aesthetic Qualities - All waters shall be free from substances attributable to wastewater
16

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; produce undesirable or nuisance aquatic life.” 

– Other Recommended Values:

Referenced in the 1986 EPA Quality Criteria for Water are two reports by the National

Academy of Sciences (NAS, 1972) and the National Technical Advisory Committee (NTAC,

1968) which were predecessor documents on water quality criteria. In these reports, criteria

recommendations related to drinking water and freshwater aquatic life were also provided. 

These are:

“Raw Drinking Water with Treatment - 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.” 

“Freshwater Aquatic Life - Combined effect of color and turbidity should not change the

compensation point more than 10 percent from its seasonally established norm, nor

should such a change take place in more than 10 percent of the biomass of

photosynthetic organisms below the compensation point.”

For other types of designated uses such as boating, fishing, swimming, wading, aesthetics

and hunting, a variety of factors contribute to the recreational quality of a water body

(Parametrix, 2003). Visual factors such as color and clarity are important along with perceived

changes in these factors. The ability to use water safely- to be able to see what is there- is also

important. The National Academy of Sciences (NAS/NAE, 1973) recommended that 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. The

National Technical Advisory Committee (NTAC) in 1968 recommended that 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 (Parametrix, 2003).

– What Are States and Tribes Currently Doing?

Most States currently have water quality criteria that can be applied to SABS. Two

unpublished summary tables – one of State sediment criteria and the other, State sediment

TMDLs, prepared by EPA in 2001, are provided in Appendices 3 and 4 for reference. A few

States are developing new criteria for SABS and examples are described below.
17

Another summary of the current regulatory guidelines for SABS is in the Technical

Appendix to the Ambient Water Quality Guidelines (Criteria) for Turbidity, Suspended and

Benthic Sediments (Caux et al. 1997), prepared for the British Columbia Ministry of

Environment, Land and Parks. Caux et al. (1997) built on an earlier review of available criteria

by Singleton (1985). A third review of sediment targets used for TMDLs is provided in Idaho

DEQ, 2003.

From these reviews it becomes clear there are a wide range of sediment criteria in current

use in the United States. Some States use numerical criteria, some use narrative criteria, some

use both, and some States have no criteria related to SABS at all. Many States have different

criteria for different stream channel substrate types. When they are differentiated, States

typically have more stringent criteria for streams with hard substrates (gravel, cobble, bedrock)

and less stringent criteria for streams with soft substrates (sand, silt, clay). Hawaii has a separate

criterion for reefs. Cold water fisheries typically have more rigorous criteria than do warm water

fisheries in states that differentiate between the two uses. A few States use biocriteria (e.g.,

biotic indices), and at least one uses soil loss as a criterion. Several States provide criteria for an

averaging period (e.g., 30 days) as well as an allowed daily maximum concentration. Some

States set an absolute value, some set a value over a background level.

Most States with numerical criteria use turbidity as a surrogate measure. Some use

exceedances over background (e.g., “Not greater than 50 NTU over background”, or “not more

than 10% above background” or “no more than 5 NTUs above background”), while some use

absolute values (e.g., “Not greater than 100 NTU”). Some States have established numeric

standards that are basin-specific while others vary with the presence of salmonids. In general,

most States are concerned with the effects of water clarity and light scattering on aquatic life. 

The majority of States use EPA method 180.1 to measure turbidity and method 160.2 to measure

total suspended solids (TSS). Most States use optical backscatter or optical transmission

technology for turbidity either by measuring in situ or in the lab after collecting grab or singlepoint samples. Very few, if any States, attempt to correlate turbidity with TSS or biological

impacts, and only a few States measure suspended solids concentration (SSC). Very few States

measure particle size distribution and no States measure bedload. 

Only a few States use suspended solids as a criterion. Suspended solids criterion values

vary from 30 mg/L up to 158 mg/L. At least one State uses transparency (> 90% of background)

as a standard. A number of States have criteria based on sediment deposited over a time period,

or during a storm event. Values are typically 5 mm during an individual event (e.g., during the

24 hours following a heavy rainstorm) for streams with hard substrates bottoms and 10 mm for

streams with soft bottoms. Hawaii's reef criterion is 2 mm deposited sediment after an event.

The Chesapeake Bay Program (a multi-state effort) has a criterion based on clarity,

including a measurement of the percent light through water (PLW) and secchi disk clarity. The

criteria are stratified by depth and salinity regime and are adjusted by season. Water clarity

criteria are used in the Chesapeake Bay because it is assumed that they will result in achievement

of clarity/solids levels that would not impair other habitats and organisms (with the exception
18

that the water clarity criteria may not fully protect smothering of soft or hard bottom habitats

with large sized sediment particles from sources that by-pass (don’t influence) shallow water

habitats), since submerged aquatic vegetation represents one of the components of the

Chesapeake Bay ecosystem that is most sensitive to increases in SABS. A detailed explanation

of the derivation of the Chesapeake Bay water clarity criteria can be found in Appendix 1.

Many States have narrative criteria for SABS in addition to, or instead of, numerical

criteria. These criteria most frequently pertain to turbidity or appearance of the water (e.g.,

“Free of substances that change color or turbidity”). Others refer to undesirable biological

effects (e.g., “No adverse effects” or “No actions which will impair or alter the communities”). 

States that employ narrative sediment standards, typically also use a translator -- a numeric or

quantifiable target for regulatory purposes (TMDLs, WLAs and permit limits). 

Information from the EPA survey conducted in 2001 (Appendix 4) indicates that numeric

sediment criteria of some type were identified in 32 of the 53 States. Narrative criteria were

identified in13 of the States with no numeric criteria (and in 23 of the States with numeric

criteria as well), leaving 8 States where no sediment criteria (either numeric or narrative) were

identified. Of these 8 States without criteria, 5 listed an alternative method or guide for

establishing sediment criteria such as effluent controls or regional criteria. 

Of the 32 States with numeric criteria, 29 were for turbidity and 5 were for suspended

solids, including three States listing criteria for both turbidity and suspended solids. Illinois

listed criteria for upland erosion, using the soil loss statistic “T”. Alaska and Hawaii are the only

States that list numeric criteria for bedded sediments. The narrative criteria are broader than the

numeric criteria, covering a large range of objectionable conditions that could affect aquatic life

or other designated uses. Those related to sediments include water color (turbidity), floating and

settleable solids, harmful deposits, and channel habitat measures. 

In addition, biological and habitat measures are used to indicate suspended and bedded

sediment conditions. Florida is the only State with a numeric criterion for benthic

macroinvertebrates as an indicator of sediment conditions. In other States, biological and habitat

criteria are narrative or nonexistent.

– Turbidity Criteria:

Turbidity criteria were variable among the States and can be categorized into three

variations. 

(1) Either thresholds in excess of background turbidity or absolute thresholds

(independent of background) were established. The majority of States (15) set thresholds

in comparison to background, 12 used absolute thresholds, and 2 used a combination of

absolute thresholds and those based on a comparison to background (Figure 1). 
19

no numeric standard for

turbidity (34)

compare to background

or natural conditions (15)

absolute threshold (12)

combination of absolute

and comparison (2)

Figure 1. Comparison of numeric criteria for turbidity, showing

types of thresholds, among states.

no numeric standard for turbidity

(34)

statew ide numeric standard, not

variable (11)

numeric standard variable by

w aterbody class, designated

use, or fishery type (14)

numeric standard variable by

w aterbody, NV, LA (2)

numeric standard variable by

region, AR (1)

numeric standard variable by

season (w et/dry), HI (1)

Figure 2. Comparison of the application of turbidity thresholds by Statewide, water body or class, region and season among States.

(2) Another variation regarded

the frequency of exceedances -

daily or monthly averages,

percentage of readings above a

threshold, or instantaneous

readings. Instantaneous

exceedances of absolute

thresholds might be expected to

result from rainfall events,

though accounting for natural and

periodic high turbidity was

lacking in most of the criteria. 

Few States specified sampling

during low flow only and Hawaii

defined two criteria - one for the wet season and a lower threshold for the dry season.

(3) Within 17 States, thresholds vary based on designated uses, stream classes, fishery types,

regions, or rivers (Figure 2). The other twelve of the 29 States with turbidity criteria have a

single threshold that applies throughout the State. Most (14) of the States with varying

thresholds have stricter

criteria for streams that

support cool water aquatic

communities (trout) or are

sources of potable water. 

These streams are identified

by their designated use,

stream class, or fishery type. 

Nevada and Louisiana

describe criteria for specific

water bodies. Criteria in

Arkansas vary by region,

probably based on underlying

geologies.

The strictest criteria

for turbidity for all States are

for highly protected streams

in New Hampshire and in the dry season in Hawaii. These criteria require turbidity no greater

than background (NH) and a mean value of 2 nephelometric turbidity units (NTU) in Hawaii. 

Mountainous States with stable geology generally have stricter criteria than those in

coastal or low gradient regions with sedimentary geology. The strictest thresholds within a State

appear to be driven by aquatic life uses, whereas the more relaxed thresholds are driven by

agricultural and non-aquatic life uses. In other words, where States have varying criteria, the

strictest criteria are generally in trout streams or highly protected waters. The highest numeric
20

NTUs above NTU NTUs above NTU

background # states threshold # states background # states threshold # states

0 1 2 1 10 4 20 1

5 4 5 1 10% 3 25 2

10 4 10 6 15 2 50 5

10% 3 15 1 20% 1 75 1

25 1 20 1 25 1 150 2

29 1 50 2 29 1 qualitative 1

50 2 50 4

Strictest of state's criteria Most relaxed of state's criteria

Table 1. Numeric turbidity criteria. The strictest criteria within each State may only apply to highly

protected waterbodies and the most relaxed criteria may only apply to naturally turbid waterbodies. If

States have uniform statewide criteria, they are tabulated in both sides of the table (as both strictest and

most relaxed). Criteria are either NTUs above background levels or absolute thresholds.

thresholds (most relaxed criteria) are for large rivers in Louisiana and instantaneous readings in

Maryland, both at 150 NTUs. The variability of turbidity criteria can be ascertained from Table

1, which enumerates the States by their strictest and most relaxed criteria. The most common

criterion is an absolute threshold of 10 NTUs, which is among the stricter criteria. 

– Suspended Solids Criteria:

Four States have criteria for total suspended solids (TSS), of which two also have

turbidity criteria. However, it is not clear how these criteria are used in concert with each other. 

Hawaii has the strictest TSS criteria, which apply in their dry season, with a geometric mean of

readings not to exceed 10 mg/L, less than 10% of readings to exceed 30 mg/L, and less than 2%

of readings to exceed 55 mg/L. Utah, North Dakota, and South Dakota have similar criteria for

their cold water streams; 35 mg/L, 30 mg/L, and 30 mg/L as a 30 day average or 58 mg/L daily

maximum, respectively. Utah and South Dakota have higher thresholds for their warm water

streams; 90 mg/L and 150 mg/L as a 30 day average or 263 mg/L daily maximum, respectively. 

– Biological and Other Criteria as Measures of SABS:

Florida’s biological criterion related to suspended sediments requires that the ShannonWeaver index be reduced no more than 75% of a suitable background condition. New Mexico’s

matrix of aquatic life use attainment for sediment (NMED, 2002) uses three measures in

comparison to reference conditions. Embeddedness and percent pebble-count fines are evaluated

as percent increases above reference conditions. A biological index is evaluated as percent

decrease below reference conditions. Final assessments of support are then based on the

combination of physical and biological assessments. Other criteria based on biological

community metrics are narrative (see below). 

In Hawaii, criteria are described for episodic sediment deposits in hard-bottomed and

soft-bottomed streams following storm events, allowing no more than 5 to 10 mm, respectively,
21

of episodic deposition. In addition, criteria for oxidation-reduction potential and grain size

distribution in pools are defined. In Alaska, the percent accumulation of fine sediment in

spawning gravel may not be increased more than 5% by weight above natural conditions and in

no case may the fine sediment in those gravel beds exceed a maximum of 30% by weight. 

Florida has a criterion for transparency, not to be reduced by more than 10%.

– Narrative Criteria:

Narrative criteria are general statements regarding protection of aquatic life or designated

uses. They are mostly of the form: “Surface waters shall be free from pollutants in amounts that

cause objectionable conditions or impairment of designated uses (including aquatic life uses)”. 

Some specify the resources that should be protected and the pollutants that should be controlled,

while others are general. Of the 36 States with narrative criteria, 32 specifically advocate control

of suspended solids or turbidity and 23 specifically advocate control of bottom deposits or

settleable solids (bedded sediments). While many narrative criteria have protection of aquatic

life as a goal, only 8 recommend that the effects of sediments be determined by direct

measurement of biological community integrity as evidenced by changes in community

composition or reduction in diversity. 

--Recent Efforts by States to Develop New SABS Criteria:

Idaho:

In Idaho, excessive fine sediment is the most common pollutant in impaired

streams. Total Maximum Daily Load (TMDL) plans prepared by the State to address

excessive fine sediment must comply with the existing narrative water quality standard

for sediment, which states “Sediment shall not exceed quantities ... which impair

beneficial uses” (IDAPA 58.01.02.200.08). While for the State, this aptly described a

goal, it did not describe quantifiable objectives for TMDL plans and stream restorations. 

Because of this, the Idaho Department of Environmental Quality recently prepared a

study suggesting appropriate water column and streambed measures for gauging

attainment of the narrative sediment goal.

One of the important beneficial uses of Idaho streams is production of trout and

salmon for ecological and recreational purposes. The effects of excessive fine sediment

on the embryo, fry, juvenile, and adult life stages of salmonids are well studied by Idaho

and others. Characteristics of the stream that change with increasing fine sediments and

are known to affect salmonids and other aquatic biota are the best measures of sedimentcaused impairment of beneficial uses. These characteristics, and the threshold values that

describe minimal degradation, are the targets that are being contemplated for use by the

State.

Water column and instream measures were determined to be the best indicators of

sediment related impacts including decreased light penetration; increased turbidity, total
22

suspended solids and sediments; increased embeddedness, increased extent of streambed

coverage by surface fines and percent subsurface fines in potential spawning gravels,

decreased riffle stability, and reduced intergravel dissolved oxygen. The relationships

between these measures and the aquatic biota were considered by the State, with special

attention given to growth, survival, reproductive success, and habitat suitability of

salmonids. Target levels for most measures are recommended based on generalized

relationships found in the scientific literature and specific background conditions that

exist in Idaho streams. The targets for turbidity and intergravel dissolved oxygen were

established based on existing Idaho Water Quality Standards. Where data to describe

sediment-biota relationships were lacking or highly variable or background conditions

are highly variable, statewide numeric thresholds were found to be inappropriate. For

total suspended solids and sediments, embeddedness, and surface sediments, target levels

could also be established for each individual stream based on local reference sediment

conditions. To provide a regional perspective of the recommended SABS target levels,

Idaho made comparisons to standards adopted in neighboring states and provinces. A

table of these are included in the Idaho report (Idaho, 2003). The targets developed by

Idaho were derived from literature values for studies primarily in the northwest U.S.

In Idaho, biological assessments and criteria are not used directly to manage

sediments. Macroinvertebrate and fish community integrity is measured using the

Stream Macroinvertebrate Index (SMI) and the Stream Fish Index (SFI), respectively. 

Reference conditions have been described for macroinvertebrates and fish after

recognizing variability in natural stream types in Idaho. Departure from reference

conditions indicates that the community is exposed to a stressor(s). Neither the Idaho

SMI nor the SFI are specifically calibrated to sediments as a stressor, rather they are

sensitive to a range of stressors, including sediments. 

 Idaho also considered other options for targets for SABS than those summarized

in Table 2 below. These included measurements of channel and watershed

characteristics. Channel characteristics considered included: width/depth ratio, sediment

rating curves, pool frequency and quality, bank stability, and changes in peak flow. 

Watershed characteristics that were considered included: land area disturbed (especially

in unstable areas), road crossings, length and hydrologic connectivity, or condition. 

Idaho concluded that numeric targets would be difficult to establish for channel and

watershed characteristics and suggested that narrative targets or criteria would be more

appropriate.
23

Table 2: Idaho DEQ recommended instream sediment parameters and associated target levels.

Instream Sediment

Parameter

Recommended Target Levels

Turbidity Not greater than 50 NTU instantaneous or 25 NTU for more than 10

consecutive days above baseline background, per existing Idaho

water quality standard. Chronic levels not to exceed 10 NTU at

summer base flow

Light Penetration Not to reduce the depth of the compensation point for

photosynthetic activity by more than 10% from the seasonally

established norm for aquatic life

Total Suspended Solids and

Suspended Sediment

No specific recommendation, establish site specific reference

Embeddedness No specific recommendation, establish site specific reference

Surface Sediment No specific recommendation, establish site specific reference

Subsurface Sediment in

Riffles

For those streams with subsurface sediment less than 27% - do not

exceed the existing fine sediment volume level. For streams that

exceed the 27% threshold - reduce subsurface sediment to a 5-year

mean not to exceed 27% with no individual year to exceed 29%. 

Percentage of subsurface sediment < 0.85 mm should not exceed

10%

Riffle Stability Not to exceed a Riffle Stability Index of 70

Intergravel Dissolved

Oxygen

Not less than 5.0 mg/L for a 1-day minimum or not less than 6.0

mg/L for a 7-day average mean, per existing Idaho water quality

standard

New Mexico:

New Mexico recently developed a draft protocol to support an interpretation of

their State Water Quality Standards narrative standard for stream bottom deposits

(NMED, 2002). The current standard for the deposition of material on the bottom of a

stream channel is listed in the State Of New Mexico Standards for Interstate and

Intrastate Surface Waters, Section 1105.A General Standards: and states:

“Bottom Deposits:

 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.” 

The State’s draft protocol for making use attainment decisions 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
24

instream habitat by measuring either of two stream bottom substrate parameters or

indicators, namely 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.

New Mexico’s step-by-step procedures are described below.

1. Select study site(s) along with a comparable reference site.

2. Perform a bioassessment on the benthic macroinvertebrate community at each

reference in which a pebble count and/or embeddedness procedure is to be performed.

3. Do a pebble count and/or embeddedness evaluation at the reference sites. Pebble

counts should be done in the same habitat unit(s) where the macroinvertebrates were

collected. When doing pebble count evaluations, it is important to determine the

necessary sample size (see page7) needed at each study site based on the evaluated

sample size and determined percent fines at each reference site. This calculation should

preferably be done streamside at the reference site using the pebble count analyzer

software so that sufficient data can be collected with one visit. However, it is acceptable

to do the calculations in the office, but realize that an additional visit to the stream may

be required if the sample size is inadequate.

4. Perform a bioassessment of the benthic macroinvertebrate community at each study

site, accompanied by collection of either pebble count and/or embeddedness data of

sufficient size to be statistically significant.

5. Compare the physical and biological data between the study and reference sites by

dividing the results obtained at the study site by that of the reference site to obtain

percent “comparability.”

6. Using the final assessment matrix (Table 4 below), locate the proper support cells for

both the physical and biological percentages calculated in step 5, and determine the final

degree of support for the aquatic life use that is affected by sediment.
25

Table 4: New Mexico Final Assessment Matrix for Aquatic Life Use Attainment:

 Biological

Physical

Severely Impaired

0-17%

Moderately

Impaired

21-50%

Slightly Impaired

54-79%

Non-impaired

84-100%

Non-Support

Fines or

Embeddedness

>40% increase

Non-Support Partial Support Full Support,

Impacts Observed

Full Support,

Impacts Observed

Partial Support

Fines or

Embeddedness

28-40%increase

Non-Support Partial Support Full Support,

Impacts Observed

Full Support,

Impacts Observed

Supporting

Fines or

Embeddedness

11-27% increase

Non-Support1 Partial support1 Full Support,

Impacts Observed

Full Support

Full Support

Fines or

embeddedness

<10% increase2

Non-Support1 Partial Support1 Full Support,

Impacts Observed

Full Support

1 Reduction in the relative support level for the aquatic life use in this particular matrix cell is probably not due to

sediment. It is most likely the result of some other impairment (temperature, D.O., pH, toxicity, etc.), alone or in

combination with sediment.

2 Raw percent values of =20% fines (pebble counts) and = 33% embeddedness at a study site should be evaluated as

fully supporting regardless of the percent attained at the reference site.

The complete New Mexico stream bottom assessment protocol can be found at

http://www.nmenv.state.nm.us/swqb/protocols/StreamBottomProtocol.pdf. 
26

– What Is Being Done Elsewhere in the World?

Canada:

Environment Canada has narrative guidelines for deposited bedload sediment,

streambed substrate, suspended sediment, and turbidity for aquatic life uses. The British

Columbia Ministry of Water, Land and Air Protection released the Ambient Water

Quality Guidelines (Criteria) for Turbidity, Suspended and Benthic Sediments which

contains numeric thresholds in support of the national narrative guidelines. The BC

guidelines are broken down by 5 water uses, 3 sediment parameters, and 2 flow

conditions. The water use categories include untreated drinking water, treated drinking

water, recreation and aesthetics, aquatic life, and the final catch-all, terrestrial life,

irrigation, and industrial uses. Of the 3 sediment parameters, i.e., turbidity, suspended

sediments, and streambed substrate composition, turbidity guidelines are defined for all

water uses. 

The strictest criterion is for untreated drinking water, allowing a turbidity increase

of only 1 NTU above background. The most relaxed criterion is for terrestrial life,

irrigation, and industrial uses, allowing 10 NTUs or 20% above background (whichever

is greatest). Suspended sediments guidelines are defined for aquatic life, and terrestrial

life, irrigation, and industrial uses. Streambed substrate composition guidelines are only

defined for aquatic life uses and are only applied in actual and potential salmonid

spawning areas. The criteria for aquatic life address all three parameters, with turbidity

and suspended sediments thresholds varying for clear flow and turbid flow conditions. 

The thresholds for aquatic life uses are detailed below. 

Turbidity: 

Clear flow: Induced turbidity should not exceed background levels by more than

8 NTU during any 24-hour period (hourly sampling preferred). For sediment inputs that

last between 24 hours and 30 days the mean turbidity should not exceed background by

more than 2 NTU (daily sampling preferred).

Turbid flow: Induced turbidity should not exceed background levels by more than

8 NTU at any time when background turbidity is between 8 and 80 NTU. When

background exceeds 80 NTU, turbidity should not be increased by more than 10% of the

measured background level at any one time.

Suspended Sediments:

Clear flow: Induced suspended sediment concentrations should not exceed

background levels by more than 25 mg/L during any 24-hour period (hourly sampling

preferred). For sediment inputs that last between 24 hours and 30 days, the average
27

suspended sediment concentration should not exceed background by more than 5 mg/L

(daily sampling preferred).

Turbid Flow: Induced suspended sediment concentrations should not exceed

background levels by more than 25 mg/L at any time when background levels are

between 25 and 250 mg/L. When background exceeds 250 mg/L, suspended sediments

should not be increased by more than 10% of the measured background level at any one

time. 

Stream substrate composition: These guidelines apply to actual and potential

spawning sites in streams throughout the province. The composition of fine sediment in

streambed substrates should not exceed 10% having a diameter of less than 2.00 mm,

19% having a diameter of less than 3.00 mm, and 25% having a diameter of less than

6.35 mm at potential salmonid spawning sites. The geometric mean diameter and Fredle

number of streambed substrates should not be less than 12.0 mm and 5.0, respectively. 

The minimum and 30-day average guideline for intra-gravel dissolved oxygen levels are

6.0 and 8.0 mg/L, respectively. The British Columbia, Canada water quality standards

for turbidity, suspended and benthic sediments are highlighted in Appendix 2.

A Summary of Existing Canadian Environmental Quality Guidelines is available

at: www.ccme.ca/assets/pdf/e1_06.pdf. The British Columbia Ambient Water Quality

Guidelines (Criteria) for Turbidity, Suspended and Benthic Sediments are available at:

wlapwww.gov.bc.ca/wat/wq/BCguidelines/turbidity.html. A guideline on sampling for

turbidity and suspended and benthic sediments can be found at

http://wlapwww.gov.bc.ca/wat/wq/BCguidelines/sampstrat.html. As mentioned earlier, a

detailed technical appendix to their criteria guidelines was prepared by Caux et. al., 1997

and is available at http://wlapwww.gov.bc.ca/wat/wq/BCguidelines/turbiditytech.pdf. 

Australia and New Zealand:

In Australia and New Zealand, guidelines have been developed for recreational

water quality and aesthetics (ANZECC, 2000). Turbidity is not addressed. 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%.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality

(ANZECC, 2000) define an approach for defining trigger values which, when exceeded,

indicate that a problem may be present due to the stressor of concern. To determine

low-risk trigger values, measure the statistical distribution of water quality indicators

either at a specific site (preferred), or an appropriate reference system, and also study the

ecological and biological effects of physical and chemical stressors. Then define the

trigger value 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.
28

To apply the guidelines where an appropriate reference system is available and

there are sufficient resources to collect the necessary information for the reference

system, the low-risk trigger concentrations for suspended particulate matter (suspended

solids) or turbidity should be determined as the 80 percentile of the reference system

distribution. Where possible the trigger values should be obtained for high flow

conditions for rivers and streams and during inflow periods for other ecosystems, when

most suspended particulate matter will be transported.

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. Ranges of lowrisk default trigger values for turbidity indicative of slightly disturbed ecosystems in

south-east Australia are as follows; upland rivers: 2-25 NTUs, lowland rivers: 6-50

NTUs, lakes and reservoirs: 1-20 NTUs, and estuaries and marine systems: 0.5-10 NTUs. 

For moderately or highly disturbed systems, more intensive study is recommended and

trigger values may be established using some appropriate percentile of the reference

distribution less than the 80th percentile.

The Australian and New Zealand guidelines are available at:

www.mfe.govt.nz/publications/water/anzecc-water-quality-guide-02/anzecc-water-qualit

y-guide-02-pdfs.html

European Union (EU):

The European Water Framework Directive (WFD) directs the member states to

establish goals, basin plans, and monitoring of ecological quality. Assessment of

ecological quality is based on a reference condition approach. Annex II of the Directive

specifies methods for establishment of type-specific reference conditions for surface

water body types. 

For each water body type, type-specific hydromorphological, physicochemical

and biological conditions shall be established representing the parameter values for that

surface water body type at high ecological status. In applying the reference condition

methods in heavily modified or artificial water bodies, high ecological status shall be

construed as maximum ecological potential. The values for maximum ecological

potential for a water body shall be reviewed every six years.

Type-specific reference conditions may be either spatially based or based on

modeling, or may be derived using a combination of these methods. Where it is not

possible to use these methods, expert judgement may be used to establish such

conditions. A reference network for each water body type should be developed using a

large enough reference data set to provide a sufficient level of confidence about the

parameter values for the reference conditions, given the variability in the values and the

modeling techniques. Type-specific biological reference conditions based on modeling

may be derived using either predictive models or hindcasting methods. The methods

should use historical, palaeological and other available data.
29

The Annex goes on to state that Member States should collect and maintain

information on the type and magnitude of the significant anthropogenic pressures. The

significant pressures include:

--Significant morphological alterations to water bodies.

--Other significant anthropogenic impacts on the status of surface waters.

--Land use patterns, including the main urban, industrial and agricultural areas

and, where relevant, fisheries and forests.

In Annex VIII, a set of “main pollutants” are listed, among which is “Materials in

suspension”, but no specific references are made to sediments. The WFD is available at:

europa.eu.int/comm/environment/water/water-framework/index_en.html

POTENTIAL APPROACHES FOR IMPROVED SABS CRITERIA:

When developing improved SABS criteria, EPA anticipates that the biggest challenge

will be developing improved criteria to protect aquatic life. Other designated uses of water

bodies where aquatic life uses overlap, most likely will be protected by the potentially more

protective aquatic life criteria (with the exception possibly of some drinking water uses such as

untreated water source). However, EPA anticipates that other forms of criteria for protecting

uses other than aquatic life will still be necessary, where aquatic life uses do not exist or where

the other uses are affected differently by the SABS. Therefore, the primary focus of this section

is on new and improved SABS criteria methods aimed primarily at aquatic life protection.

Regardless, EPA expects that establishing appropriate criteria for SABS will follow

much the same process used for establishing other water quality criteria. EPA, however, does

not anticipate that issuance of a singular national recommended SABS criteria that would apply

to all water bodies will be possible. Because water bodies vary from region to region with

respect to natural SABS regime, it is anticipated that States and Tribes will need adaptable

methodologies for deriving SABS on a water body-category basis or using a regional

classification scheme. 

Initially, EPA plans to produce a SABS criteria development strategy that outlines a

general process that States and Tribes may follow when developing and adopting SABS criteria. 

As a part of this overall strategy, EPA anticipates laying out major goals and expectations, with

key milestones and approximate time frames for each activity. EPA plans to prepare a series of

technical and programmatic memoranda to assist the States and Tribes during each critical step. 

EPA anticipates it will ask States, territories and authorized Tribes to develop plans for

implementing new and improved SABS criteria in phases. The first phase, will likely include the

development of individual State/Tribal/Territorial SABS adoption plans. The second phase will

likely include the adoption of improved narrative standards for SABS, with implementation

procedures where States do not currently have effective narrative standards. The third, and final

phase, will likely be to adopt regional or water body-category numeric criteria using one or more

EPA recommended procedures or methodologies, or scientifically defensible alternatives. 
30

EPA also anticipates developing supporting technical information for the recommended

procedures or methods. Potential methodologies that could be used by the States, Tribes and

territories are described in this section and are the specific subject of the consultation with the

EPA Science Advisory Board. While there may be several ways to develop SABS criteria for

aquatic life protection, and each method has strengths and limitations, EPA’s current thinking is

the best approaches should be based on a correlation of SABS with effects on biota or aquatic

life uses.

In general terms, an initial step in the process of developing aquatic life criteria for SABS

is deciding which species, communities or designated aquatic life use to protect. The simplest

approach is to protect everything, that is, to set the criteria at a level protective of the most

sensitive aquatic organisms. This is roughly equivalent to making sure that SABS do not exceed

the natural background levels for a particular region or class of water bodies. 

Another approach is to protect most everything, as is done for the toxic chemical criteria,

which attempt to be protective of 95% of the genera tested (Stephan et al, 1985) as a surrogate

for the entire population or community. An alternative approach is to choose the most sensitive,

or important of the biota and protect it.

Any approach, however, will be difficult because SABS are a natural component of the

environment, and vary considerably within and among various habitats and regions. Biota in

various habitats has evolved to tolerate or even require various levels of SABS.

The following generic steps may be useful to consider when developing a method for

setting SABS criteria: 

1) Develop a conceptual model outlining the ecological processes effected by SABS for a

particular water body;

2) Choose the ecological processes, species or groups of species, and beneficial uses

deemed desirable for protection; and

3) Develop numerical targets for protecting the ecological processes, species or groups of

species, and beneficial uses deemed desirable for protection based on the correlations

between SABS and the biota.

At this time, EPA is examining eight potential approaches to developing water quality

criteria for SABS that need to be evaluated and then explained more thoroughly before any one

is recommended for use by the States, Tribes or territories. These eight preliminary approaches

include; 1) the Toxicological Dose-Response Approach, 2) the Relative Bed Stability and

Sedimentation Approach, 3) the Conditional Probability Approach to Establishing Thresholds, 4) 

State-by-State Reference Condition Approach, 5) the Fluvial Geomorphic Approach, 6) the

Water Body Use Functional Approach, 7) successful new State approaches and, 8) combinations

of 1-7 or a synthesis of components of each. The first 5 approaches focus on aquatic life. These

approaches are described in more detail below.
31

Potential Options:

1. Toxicological Dose-Response Approach:

Since the early 1980's, EPA has developed water quality criteria for specific

pollutants to protect aquatic life under Section 304(a) of the Clean Water Act. The

criteria provide recommendations to States and Tribes for adopting water quality

standards which are the basis for water quality-based National Pollutant Discharge

Elimination System (NPDES) permit limits for controlling point source discharges and

for establishing total maximum daily loads (TMDLs) for water bodies. The majority of

EPA’s aquatic life criteria have been derived from two methodologies: the 1980

Guidelines for Deriving Water Quality Criteria for the Protection of Aquatic Life and Its

Uses, and the 1985 Guidelines for Deriving Numerical National Aquatic Life Criteria for

Protection of Aquatic Organisms and Their Uses. A third revision is currently underway

at EPA to incorporate the science and technology advancements of the last 20 years.

When considering approaches for SABS criteria, it is useful to have an

understanding of how the Guidelines are ordinarily applied. Under the Guidelines

approach, acute toxicity test data must be available for species from a minimum of eight

families with a minimum required taxonomic diversity. The diversity of tested species is

intended to assure protection of various components of an aquatic ecosystem. The final

acute value (FAV) is an estimate of the fifth percentile of a sensitivity distribution

represented by the average LC50/EC50s of the tested genera. The Criterion Maximum

Concentration (CMC) is set to one-half of the FAV to correspond to a lower level of

effect than the LC50s/EC50s used to derive the FAV. Chronic toxicity test data (longer

term survival, growth, or reproduction) must be available for at least three taxa to derive

a final chronic value (FCV). A Criterion Continuous Concentration (CCC) can be

established from a FCV calculated similarly to an FAV, if chronic toxicity data are

available for eight genera with a minimum required taxonomic diversity; or most often

the chronic criterion is 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 FAV. When necessary, the acute and/or chronic criterion may be adjusted to

protect locally important or sensitive species not considered during development of the

criterion, or can be adjusted based on local water chemistry. Once developed, the CMC

and CCC incorporate exposure duration and frequency factors, i.e; the CMC one-hour

average should not be exceeded more than once in three years on average, or the CCC

four-day average should not be exceeded more than once in three years.

SABS criteria based on toxicological and/or behavioral effects can be developed,

in theory, much like other EPA toxic chemical criteria. However, EPA has concluded

that sound data are lacking for most species, and standardized consensus-based test

methods for determining sediment effects are generally unavailable. Therefore, it is

unlikely that a list of genus mean acute and chronic values for sediment can be developed

in the short-term and such an effort would require substantial resources. A second

difficulty is that sediment can consist of many things 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 sediments without first determining the

specific type of sediment (organic vs. inorganic; silt vs. clay, fine vs. coarse, etc.).
32

However, toxicological or behavioral-based criteria for SABS have the advantage

of specifying appropriate management levels depending on the types of aquatic life

present. Furthermore, this approach is explicitly causative; controlled laboratory or field

analyses are used to determine threshold effect concentrations. In addition, it could be

possible to specify the amount of reduction in suspended sediment or sedimentation

needed to maintain desired aquatic resources using this approach. One modified way in

which sediment thresholds can be reasonably implemented is through sediment criteria

based on a few sensitive target indicator species for which some sediment effect levels

are known (e.g., trout, certain corals, certain EPT taxa, or bluegills). Each indicator

would represent certain types of beneficial uses, aquatic systems or regions of the U.S. 

This is similar to a risk assessment approach. If such thresholds could be developed,

however, there would still be uncertainties due to synergistic interaction of the many

other factors that influence sedimentation effects.

SABS have many impacts in aquatic ecosystems, and effects on the biota vary

considerably among habitats. However, there are dose-response models for some species

in some habitats, and criteria have been developed for their protection (e.g., British

Columbia Guidelines in Caux et al., 1997, Chesapeake Bay Water Clarity Guidelines in

U.S.EPA, 2000b). Using these approaches at a national level needs further investigation..

In summary, if the necessary data were available in the literature, the main

strength of pursing a toxicological approach is that it employs a standardized

methodology which has general acceptance by the scientific, regulatory and stakeholder

communities. In addition, this approach would be more cost-effective and less

burdensome on the States, as nationally recommended criteria values could be readily

adopted without extensive data collection, analysis or water body-specific adjustments. 

This approach, however, would suffer from two additional key limitations. First is the

absence of natural or background concentrations and organism acclimation being

factored into the methodology. The second is the presumption applied to toxic chemicals

that there is an absolute value above which effects are likely to occur for certain sensitive

species, and below which they do not. SABS do not necessarily act on organisms in the

environment in the same way as do toxicants. Also how would duration and frequency

be defined for SABS, if at all? In principle, these limitations could be addressed through

certain EPA-approved mechanisms to modify national criteria on a site-specific basis. 

The Recalculation Procedure (USEPA 1994), for example, could be used to refine the

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.

2. Relative Bed Stability and Sedimentation Approach:

Stream bed characteristics are often cited as major controls on the species

composition of macroinvertebrate, periphyton, and fish assemblages in streams (e.g.,

Hynes, 1972; Cummins, 1974; Platts et al., 1983). Along with bedform (e.g., riffles and

pools), substrate size influences the hydraulic roughness and consequently the range of

water velocities in a stream channel. It also influences the size range of interstices that

provide living space and cover for macroinvertebrates, salamanders, sculpins, and

darters. Accumulations of fine substrate particles fill the interstices of coarser bed
33

materials, reducing habitat space and its availability for benthic fish and

macroinvertebrates (Platts et al. 1983; Hawkins et al., 1983; Rinne 1988). In addition,

these fine particles impede circulation of oxygenated water into hyporheic habitats. 

Substrate characteristics are often sensitive indicators of the effects of human activities

on streams (MacDonald et al., 1991). Decreases in the mean substrate size and increases

in stream bed fine sediments can destabilize stream channels (Wilcock 1998) and may

indicate increases in the rates of upland erosion and sediment supply (Lisle, 1982

Dietrich et al., 1989).

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). Sediment supply to

streams is influenced by topography, precipitation, and land cover, but the source of

sediments is the basin soil and geology, and supplies are greater where these materials

are inherently more erodible. Once sediments reach a channel and become part of the

stream bed, 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 stream bed

stability can be evaluated. Furthermore, it can be evaluated whether low values of bed

stability are due to accumulation of fine sediments (“excess fining”), and may examine

watershed data to infer whether the sediment supply to the stream may be augmented by

upslope erosion from anthropogenic and natural disturbances.

Quantifying Relative Bed Stability and Sedimentation

Relative Bed Stability (RBS) is calculated as the ratio of observed substrate diameter

divided by the calculated “critical” or mobile diameter (Dingman, 1984). RBS is the

inverse of the substrate “fining” measure calculated by Buffington and Montgomery

(1999a, b), and is conceptually similar to the “Riffle Stability Index” of Kappesser (1995)

and the bed stability ratio discussed by Dietrich et al., (1989).

Bed Substrate Size: When evaluating the stability of whole streambeds (vs. individual

bed particles), observed substrate is typically represented by the average diameter of

surface substrate particles (e.g., D50 or the geometric mean). To characterize the actual

substrate particle size distribution in a stream channel, EMAP follows widely accepted

procedures. The EMAP field protocols (Kaufmann and Robison, 1998) like those of

most practitioners (e.g., Platts et al., 1983; Bauer and Burton, 1993) employ a systematic

“pebble count," as described by Wolman (1954), to quantify the substrate size

distribution.
34

Critical Substrate Size: 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, though it is more appropriate for gravelbed streams than for “live-bed” streams such as naturally sand-bedded streams that

transport bedload at lower flows. The EMAP approach 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. Stream channels can be very

complex, exhibiting a wide range in local bed shear stress due to small-scale spatial

variation in slope, depth, and roughness within a channel reach (Lyle et al., 2000). When

developing this approach, EMAP researchers (Kaufmann et al., 1999; Kaufmann and

Larsen, in prep.) 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 the channel and substrate data

described in the two preceding paragraphs, EMAP researchers modified the Dingman

(1984) RBS 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.

RBS Range: 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., .01-.0001) describe a channel composed of substrates that are frequently moved by

even small floods.

RBS Expectations in Unaltered Streams: It is hypothesized 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. For streams with

sediment transport limited by competence (critical shear stress), rather than total capacity

(stream power), the mean of RBS values in these relatively unaltered streams should

approximate 1.0 (range from 0.3 to 3), and may have slight surface coarsening due to low

hillslope erosion rates (Dietrich et al., 1989). Alternatively, RBS for streams draining

watersheds relatively undisturbed by humans should tend towards values other than 1.0

that are characteristic of the region or specific classes of streams within a region,

depending upon their natural lithology, soils, topography, climate, and vegetation. 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. RBS values considerably lower than 1.0 may be

expected in 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, finebedded streams and rivers, is refined, it may be necessary to modify the approach
35

(currently based on the competence of bankfull floods to move given sizes of particles). 

For these waters, it may be useful to estimate bed stability in terms of the proportion of

the year that the bed is in motion.

Excess Sediment: In watersheds where sediment supplies are augmented relative to a

stream’s bedload transport competence, it is expected there will be evidence of excess

fine sediments, or “textural fining” (Dietrich et al., 1989). Very small RBS values (e.g.,

.01-.0001) describe a channel composed of substrates that are frequently moved by even

small floods, indicating excessive amounts of fine particles compared with expected

values in most relatively undisturbed watersheds. Such evidence of textural fining of the

stream bed (RBS<<1) typically occurs when land use activities increase hillslope erosion 

(Lisle, 1982; Dietrich et al., 1989; Lisle and Hilton 1992). It is further expected that, for

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. This association of lower

RBS with land use disturbances in several regions has been demonstrated (Kaufmann et

al, 1999, Kaufmann and Larsen, in prep.) Finally, the more erodible the basin lithology

within a geoclimatic region, the steeper the decline in RBS with progressive disturbance

is expected. As demonstrated for streams in the Pacific Coastal region by Kaufmann and

Larsen (in prep.), 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. 

Evaluating Effects of Sediment on Biota

Once the degree of sedimentation is estimated for sample sites, associations between

biotic assemblages (algae, macroinvertebrates, fish, rooted aquatic plants), and/or key

aquatic species or guilds, and deviations of sediment from expected values will be

examined. In most cases, the data sets will include sites affected by multiple stressors

besides sediment that could potentially act upon these aquatic biota. In such cases, a

regional plot of sediment concentration versus some biotic assemblage characteristic

(e.g., %EPT macroinvertebrates), will appear as a wedge-shaped pattern of points, where

progressively higher fine sediment concentrations are sufficient to limit %EPT numbers,

but low concentrations do not guarantee abundant EPT because of other habitat or

chemical limitations. These patterns are consistent with a hypothesis that sediment is

limiting biota. After demonstration of a plausible causal mechanism (from detailed

experimental studies) and elimination of other plausible explanations for these

observations, these kinds of associational data in a weight-of-evidence approach to

support modeling of the effects of bedded sediments on aquatic biota will be used.

For suspended sediments in streams and rivers, the effort will focus initially on chronic

levels of suspended sediments in streams and rivers, rather than those resulting from

episodic events such as those accompanying storms. Expected natural levels of chronic

suspended solids will be set on the basis of data from flowing waters in basins relatively

undisturbed by human land uses and (in rivers) historic water clarity data to the extent

possible. Regional reference areas could serve this purpose. Where no relatively

undisturbed waters exist, as for large rivers, historic data or reconstructions of fish and/or
36

macroinvertebrate assemblage composition will be used to infer (from published

tolerance information) pre-disturbance suspended sediment characteristics. In an

approach similar to that for bedded sediments, associations between biotic and/or key

aquatic species or guilds and deviations of sediment from expected values in appropriate

regional settings will be examined. As for bedded sediments, patterns will be sought that 

are consistent with biotic limitation by suspended sediment in a weight-of-evidence

approach to support modeling the effects of bedded sediments on aquatic biota,

supporting this information with controlled experimentation or literature reference to

establish the suspended sediment levels that cause substantial impacts on assemblages,

sensitive guilds, or key species.

3. Conditional Probability Approach to Establishing Thresholds:

 

A conditional probability approach using survey data is a third proposal for

developing SABS criteria. This approach is consistent with the expression of numeric

water quality criteria as likelihood of impacts when exceeding a value of a pollution

metric. The approach uses survey data (sites selected with a probabilistic design) and

determines the likelihood of impaired biology for varying levels of a stressor (in this

case, some form of sediment). The use of probability-based survey data permits an

unbiased extrapolation of results to the statistical population from which the probability

sample was drawn (e.g., the results would be applicable to all of the wadeable streams in

a state if the sample was drawn from a sampling frame of all wadable streams in the

state).

For application to numeric water quality criteria, a conditional probability

statement provides the likelihood (probability) of impacts, if the value of the pollution

metric is exceeded. The conditional probability is the probability of an event when it is

known that some other event has occurred, and is denoted P( Y | X* ), where X* is the

other event that has occurred. For criterion development, X* is replaced with X > XC,

where XC is the specific threshold that is exceeded. Therefore, the conditional

probability statement is P ( Y | X > XC). This approach is similar to the apparent effects

threshold approach developed by Long and Morgan (1991) and MacDonald and Ingersoll

(2002) to derive sediment quality guidelines.

Data on benthic communities in Mid-Atlantic wadable streams were collected by

USEPA’s Environmental Monitoring and Assessment Program (EMAP) in 1993-94 and

are used to test and evaluate the approach. These data were part of a suite of indicators

collected at sites selected with a probability-based design, and have been reported in the

Mid-Atlantic Highlands Assessment State-of-the-Streams report (EPA-903-R-00-015). 

A stream sedimentation threshold of impacts was determined for a channel sedimentation

index (CSI). The CSI expresses the deviation in the actual amount of substrate fines from

that which would be normally expected to occur. EMAP stream benthic invertebrate

survey data were used to determine the likelihood of impaired benthic community (EPT

taxa < 9) as a function of the CSI.

This approach is implemented as a two-step process: first, subset the surveyed

stream segments into those that exceed a specific CSI value, and second, determine the

fraction of the subset with impaired biology. Since the sites were selected with a

probabilistic design, the fraction of the stream segments that is impaired is the probability
37

of observing impaired streams if a specific CSI value is exceeded. This process is then

repeated for the entire range of observed CSI values. The result is an empirical curve for

probability of impact for streams exceeding CSI values. Different analytical procedures

are used to illustrate how thresholds of impact can be identified from this empirical

curve. 

To implement this approach, the following must be assumed or provided:

1. Some metric, X, that quantifies the pollution parameter for which criteria will be

developed. In the example, the CSI is used.

2. It is not necessary that X be the only stressor affecting the aquatic community, but it

must be a strong stressor, that is, aquatic community condition Y is clearly related to the

stressor X for higher values of X. Thus, if the value of Xcis exceeded, it is likely an

impact of the biological resource will be present, over and above what occurs naturally

and from other stressors.

3. Some independent measure for determining biological impact must be available. In

the example, EPT taxa < 9 defined biological impact.

4. Data from a probabilistic design must be available in order to establish the likelihood

for impact across an entire geographic area. This is currently the only scientifically

defensible means of extrapolation from sites with data to all the sites across an entire

region.

Perhaps the biggest limitation of this approach is that it is correlative and not

causative. If other factors (including unmeasured ones) are actually responsible for

biological impact and not SABS at a given site, the model inaccurately represents SABS

effects, and inappropriate SABS criteria may result. This may be sufficient for screening

but is inappropriate for regulatory actions.

4. State-by-State Reference Condition Criteria Derivation Approach:

The reference condition approach for developing sediment criteria is derived from

the regional reference approach for developing biocriteria (EPA 1996; 1998, 2000;

Barbour et al. 1999). Analytical approaches 2 and 3 above (relative bed stability and

conditional probability), and 5 below (fluvial geomorphological approach) are also

compatible with examining and identifying reference conditions, and many of the same

measurements would be used in all three approaches. In fact, the derivation of

expectations for relative bed stability (RBS) in unaltered streams (Approach 2 above) is a

specific reference condition predictive model. Described below is a more generic

approach to deriving sediment criteria from reference site information.

There are well-established empirical and theoretical relationships describing the

effects of landscape topography, climate, and geology (including soil properties) on

channel morphology and sediment dynamics of streams (see Fig. 3 and examples in

Knighton 1984 and Gordon et al. 1992). It seems reasonable, therefore, that empirical

modeling of sediment characteristics based on these known relationships would be an

appropriate method of developing criteria for SABS. The most defensible expectations
38

would be built using relationships derived from non- or minimally disturbed streams (the

desired condition).
39

 

Figure 3 – Three major determinants of sediment characteristics in streams are catchment soil type,

topography, and climate. The reference approach builds empirical models of sediment characteristics from

minimally disturbed sites using factors related to these major landscape determinants.

The reference approach to developing biocriteria uses minimally disturbed

reference streams to build predictive models of stream condition based on measurable

characteristics (e.g. topography, geographic region, site and basin physical

characteristics). Similar models can be constructed and confirmed to predict reference

conditions with respect to sediment. They can then be used to predict acceptable ranges

for specific streams based on the physical catchment characteristics of the stream. From

this, a variety of criteria could be developed. For example, a certain deviation from

prediction can be used (e.g. no more than 20 percent of predicted suspended solids) or

models for different stream classes can be averaged to come up with class-specific

criteria (e.g., the 75th percentile for Piedmont streams with a watershed size less than 50

km2). In addition, gradients or increases above reference condition associated with

increasing levels of human disturbance can both be explored and related to human

disturbance levels much as suggested for biological condition responses. In either case,

the reference condition represents one point along the gradient. The approach also

applies to both suspended and bedded sediment characteristics and should be applicable

to other water body types other than streams and rivers, with some modification.

Although the models are empirical in that they require data analysis to develop

them, the hypothesized relationships between climate, topography, soils, etc. are firmly

based in theory and experiment from the body of hydrological knowledge. These models

do not merely attempt to find the best statistical predictors, but the best measurable

predictors that fit well in hydrological knowledge.

Defining Reference

An important step in the reference approach is selecting those streams that will

make up the reference database (i.e., to build the model). Reference, in this sense, does

not mean pristine; rather, it represents the desired stream state or what is “referred” to

when evaluating the condition of any stream. Reference catchments are usually selected

using a set of a priori designated reference criteria. In the case of model building for

predicting sediment, it is important to include criteria that screen for minimally disturbed

catchments. Since sediment supply and hydrology respond to most landscape

modifications, the first reference criteria are derived from contemporary land use/land

cover data and catchments with predominantly natural vegetation cover. A unique

consideration for selecting sediment reference sites is also historic land use. The
40

response time of stream channel equilibrium to landscape alteration is on the decades to

centuries time scale, if not longer (Trimble 1974, Schumm 1977, Brunsden and Thornes

1979, Trimble 1999). Therefore, it is important to consider historic catchment land use

when evaluating potential reference catchments. Those that have experienced historic

anthropogenic landscape disturbance may likely still be undergoing geomorphic

readjustment. Unless this is an acceptable “reference”, these sites should be excluded

from the reference database. 

In addition to land use/land cover, instream modifications are also important. The

presence of dams, channelization, dredging, and diversions will all affect instream

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.

1992). Channelization, dredging, and other channel modifications alter stream channel

geometry. Because channel geometry is related to stream power and, therefore, sediment

transport, readjustments such as knickpoint migrations occur following these channel

impacts. These impacts often migrate downstream and upstream through a catchment

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 in flow can lead to channel destablization by sediment accretion. 

Therefore, it is important to identify present or historic instream modifications within the

catchment when developing a reference database.

A list of criteria would be prepared such that all conditions must be met for a site

to be designated as reference (Hughes 1995). The following list is an example of

possible criteria for selecting reference sites for characterizing sediment benchmarks or

natural background. 

• 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 that are not in natural cover are not in

sediment generating land uses such as mining, logging or cultivation on steep

slopes, etc.

• Roads do not cross the stream more than once per mile. Road maintenance does

not include excessive sanding.

• 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. 

 These criteria might be considered too lenient in regions with extensive

undisturbed land (e.g. Rocky Mountains) or too restrictive in regions with high

population densities and few remote areas (e.g. Northeastern Coastal Plain). When

application of a set of criteria result in too many or too few many reference sites, the

criteria can be adjusted and re-applied until appropriate sample sizes are obtained. Five

reference samples per discrete stream type is an absolute minimum reference data set. 

Thirty samples per stream type are desirable but often unobtainable (Elliott 1977). When

reference stream types are not defined discretely a priori, then care must be taken to not

exclude important unique natural stream conditions. Criteria may vary from one region
41

to the next, or from one discrete stream class to the next (e.g. mountain streams or plains

streams). By varying the criteria to allow for natural variation in sediment loads or

ubiquitous land use patterns, all possible reference conditions are represented and models

built upon the reference data will be applicable in all types of streams in the region.

Data Requirements

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 reference data,

augmented with basin-level data as necessary to examine preliminary models. It is

highly likely that 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 beyond RBP habitat assessment, and their reference sites may need to be

revisited to collect the relevant data.

Once reference sites are identified, empirical models of suspended and bed

sediment characteristics of those reference streams can be constructed. The models are

built to predict the sediment characteristics of particular streams based on their soil,

topographic, and climatic setting – the assumption is that these primary factors control

the supply and transport of suspended and bed sediment. Several important sources of

data are required to identify reference sites and build the models: land use, soil data,

climate and hydrology, catchment geomorphology, and sediment data.

Current and historic land use data are necessary for reference site selection to

estimate land use/land cover and the presence of any instream modifications. Current

land use data are available for most of the contiguous US (e.g., LANDSAT), and the

technology is advancing rapidly so that more current data are being made available

rapidly. However, historic land use data are often harder to access due to the only

relatively recent development of GIS technology (e.g., ArcView, ArcInfo, ArcGIS). 

Fortunately, historic land use information can often be reconstructed from tax data,

historic photographs, historic diaries, etc. In addition, several techniques have been

developed by fluvial geomorphologists to identify and/or infer past land use disturbance

(e.g., dendrochronology, sediment profile dating, floodplain and terrace coring, etc., see

Knighton 1984). These methods can be used to investigate past impacts within a

potential reference catchment. 

To build predictive models, data on soils, including factors such as soil type,

texture, erodibility, porosity will be necessary. Fortunately, detailed soil maps are

available for much of the US and are maintained by the Natural Resources Conservation

Service (NRCS). Climate data, including precipitation and hydrology are also necessary

for building these 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, and are, likewise, often accessible via the internet. However, hydrology is often

only available for gauged catchments and may have to be modeled for others. A variety

of hydrologic models exist and can be used as necessary (Gordon et al. 1992). 

Catchment geomorphology is also necessary, including data on topography, catchment
42

size, etc. These data are readily extracted from surface topographic maps using a GIS. 

Ideally, the purpose of the models will be to predict reference sediment characteristics

measurable in single “snapshot” data collections during routine stream monitoring. 

Nevertheless, it will probably be necessary to begin with models and data sets that

include dynamics, including peak flows, stream power, sediment transport, etc. Initial

modeling efforts should focus on accurately and reliably predicting the critical dynamic

measures from catchment characteristics.

Lastly, and most importantly, suspended and bed sediment data for specified

study reaches are necessary. The same measures and derived quantities relevant to

approaches 2, 3, and 5 are also relevant here, e.g., relative bed stability (RBS), bed

substrate size, critical substrate size, RBS range, channel sedimentation index (CSI),

Rosgen class, etc. Total suspended sediment (TSS) data are ideal. Turbidity data using

nephelometric turbidity units (NTU) can be converted in some cases, depending on the

sediment composition, but the relationship between TSS and NTU is not always linear

and can be difficult to convert. Bed transport data are less often collected due to the lack

of robust methods, but bed texture data are often available from pebble count or core

data.

Analytical Approaches

Once data have been assembled for a region, a number of analytical approaches

can be used to build models to predict sediment characteristics for a stream. Empirical

models are those built from the existing data. Continuous predictive empirical models

predict the sediment characteristics for a specific stream reach based on its particular

topography, soil type, and hydrology. The derivation of RBS expectations in unaltered

streams described in (2) above is an example of a continuous predictive model for

reference conditions. Much like the River Invertebrate Prediction and Classification

System (RIVPACS)-type models (Wright et al. 1984, Hawkins et al. 2000, Wright 2000)

build site-specific predictions of invertebrate communities based on reference site

invertebrate data for biological assessment and biocriteria development, continuous

predictive empirical sediment models would build a site-specific model for sediment

characteristics at a particular site based on data from similar reference sites in the region. 

This can be done using a combination of multivariate and multiple regression techniques. 

Discrete predictive empirical models could also be used. Instead of building a sitespecific model, these models predict sediment characteristics for discrete classes of

streams. Streams would be explicitly classified from the outset, and then statistical

models of sediment characteristics used to identify the expected sediment characteristics

for each stream class. This has been the approach commonly used for building

multimetric-type biological assessment models (e.g., IBI). The Fluvial geomorphological

approach (option 5 below) is an example of a discrete classification.

In the absence of robust data for reference sites across the range of streams in a

region, which is often the case, theoretical models are also an option. Theoretical models

are built from theoretical principles and do not require field data. Theoretical models

could be used to predict sediment characteristics for specific sites (continuous) or site

classes (discrete). A combination of empirical and theoretical models could also be

developed that uses theoretical estimates of predictor variables that can then be used in

concert with empirical data to build predictive models. Likely, combined models will be
43

most often used, since large spatial and temporal data gaps will exist for certain regions

or for certain types of data.

Once the models are built and confirmed using validation datasets, criteria can be

developed based on statistical properties of the predicted sediment values. For site

specific predictions, deviations of the predicted values from observed values for

reference sites can be used to construct an acceptable level of deviation based on natural

reference site variability. For example, in RIVPACS models, the standard deviation of

observed/expected scores at reference sites is used as an indicator of methodological and

natural variability among reference sites. Any ratio outside that deviation is considered

impaired. In a similar way, the predicted sediment to actual sediment value ratio from

specific model building reference sites can be used as an indicator of acceptable

variability and a ratio outside that range (e.g., 20% greater than expected) would be

considered impaired. The criteria in that case would be a standard deviation or percentile

above 1.0, where the expected value equals the observed value.

For discrete models, a percentile of the reference site values can be used as the

criterion. In IBI models, the 25th percentile of IBI values for a specific class of streams is

often used as the criterion for defining impairment where an IBI score below that is

considered impaired. Similarly, the 75th percentile of reference site sediment values for a

specific class of streams could be used as the impairment criterion. A TSS value above

the 75th percentile for that class of streams would be considered impaired.

Values from either of these approaches can also be interpreted along disturbance

gradients. Either predicted to actual sediment scores or the sediment values themselves

can be related to human disturbance gradients. In either case, the reference condition

would be placed along the gradient and other values interpreted appropriately.

5. Fluvial Geomorphic Approach:

Analytical methods that address within-channel and hillslope sediment sources

and transport processes as well as sediment loads may be applicable to sediment criteria

development and relevant to management actions that address impairments at the source. 

Fluvial geomorphology as a discipline offers theory, classification systems, and field

measurement tools indicative of river or stream stability and changes relative to current

and predicted sediment supply. A geomorphic approach to criteria development would

likely have less measurement of effects on biota, but more emphasis on measuring

erosional and depositional processes and rates that may affect a variety of designated

uses. 

An ongoing, EPA-funded study conducted by David L. Rosgen is developing a

sediment assessment framework, called Watershed Assessment of River Stability and

Sediment Supply (WARSSS), that is based on geomorphic analysis of the current

sedimentary state of watersheds and stream systems. Although this study is directed

more toward assessment to guide sediment management actions than to detect thresholds

of adverse impact, as criteria do, the WARSSS framework merits examination for

elements potentially useful to sediment criteria development.

The analysis separately considers hillslope and channel processes responsible for
44

changes in erosion/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 sub-watersheds/river

systems to be subjected to a more detailed prediction assessment for process-specific

mitigation; and 2) a process-based, quantitative prediction of potential sediment source

and magnitude, 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 methods

will provide for validation of the assessment methodology and track 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 that are better suited to the region or water

body type being assessed.

Numerous authors (Rosgen 1994 and 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 determining appropriate strategies for sediment management. For

example, an individual who hasn’t considered channel type or stability could spend a

great amount of time and effort running bedload transport equations and doing factor of

safety analysis on streambanks, when the potential for instability and/or disproportionate

sediment supply problems may be minimal. The channel type/stability relationship also

may have value in determining appropriate differences in criteria among stable and

unstable stream types. 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 take into account the likely stable endpoint of

unstable channels when setting waterbody-specific sediment criteria. 

Moreover, a variation of the concept of reference condition discussed previously

is applied by geomorphologists and hydrologists to characterize “reference reaches” of

stable channel types. 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 of reference condition. 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.

Another element addressed in the WARSSS study that can be evaluated for

application to sediment criteria involves sediment rating curves (SRCs) that plot, for a

given channel, either suspended sediment or bedload against flow. Although general

understanding of SRCs is limited, they may have some application potential related to
45

criteria if reference relationships can be developed. Suspended sediment concentration,

for example, is often found to be correlated with flow rate, and the literature does offer

some evidence that sediment rating coefficients and flow are predictably interrelated

within a given region (Hawkins 2002). In an examination of SRCs 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

stream type, but the analysis did reliably detect departure of generally unstable stream

types as a group from values expected of stable channels. Ongoing work toward

developing and testing reference SRCs 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.

In conclusion, evaluating applicability of geomorphic approaches to EPA’s

sediment criteria development process should consider:

• What geomorphic measures associated with channel stability and instability

would make suitable numeric criteria?

• Can water-column or bedload sediment measurements be paired with channel

type classification, by developing different instream numeric criteria for different

channel types?

• How can measures of hillslope, land use-related sediment loads best be integrated

with measures of channel-derived sediment loads?

• What would be the cost and effort implications for state monitoring programs of

using various geomorphic measurements to assess sediment impacts?

• Will other regions be able to develop and apply sediment rating curve

relationships that are being developed in some regions of the US?

• Would integrating biotic with geomorphic reference data reduce variability in

biotic measures within a given channel type and make biocriteria for sediment

assessment consistent?

• As geomorphic measures are more closely related to sediment sources and

sediment transport processes than are measures of water column effects or

biological effects, would they be more useful for guiding sediment control and

remediation activities implemented as a result of criteria non-attainment?

• Can this approach be used to develop classification schemes for use with other

approaches?

6. Water Body Use Functional Approach:

The waterbody functional approach is proposed for developing SABS criteria for

designated uses other than aquatic life. This is not necessarily a new method or

approach, but is one that would examine the existing literature and focus criteria on non-
46

aquatic life uses. This approach would primarily apply to recreational (swimming,

boating, etc.), industrial, navigational, drinking water and agricultural uses, etc. Under

this approach there would not be a need to determine toxic or harmful levels of SABS to

aquatic life. Rather, benchmarks would be set based on data and information from the

literature and State experiences, that would be protective of the functional use. For

example, if shipping and navigational uses were the primary use of a water body, criteria

would be established to prevent or minimize the depositional rates of sedimentation that

would prevent accelerated filling of shipping channels thereby preventing frequent

dredging to maintain those channels.

Likewise, for agricultural water usage, including irrigation and livestock

watering, etc., benchmarks could be set based on data that illustrates 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,

drinking water and other functional uses where the literature indicates potential

thresholds for protecting these non-aquatic life uses. Dose-response relationships for

aquatic biota would not be a critical basis for these criteria.

Functional-based benchmarks for protecting uses other than aquatic life would

apply primarily to waterbodies where aquatic life uses do not exist (historically not

present, removed through a Use Attainability Analysis (UAA)), or where multiple

designated uses have been assigned to a water body (such as a extensive river system)

and SABS levels fluctuate substantially throughout the length of the system.

However, where multiple designated uses such as aquatic life and irrigation

overlap in a water body or on a specific segment or portion of the water body, SABS

criteria set to protect the aquatic life use most likely will be stringent enough to protect

all other uses and additional functional criteria may not be necessary. This is a

presumption that needs further investigation to confirm its validity.

Examples where “functional benchmarks” that have already been suggested or

applied include NAS 1972, NAS/NAE 1993, NTAC 1968, ANZECC 2000, Parametrix

2003. Both narrative and numeric examples include: 

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 form

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
47

extent that such changes cause upsets in water treatment processes. 

No more than 15 NTUs over background will protect the visual aesthetic quality

of a clear water stream. 

7. Use of successful new State/International approaches:

As summarized above, States under the pressure to develop and issue total

maximum daily loads (TMDLs) for SABS impaired water bodies, are moving forward on

their own to develop new and improved SABS criteria from which to implement these

regulatory actions. In many cases, these efforts are being initiated under the pressure of

legal actions and court ordered deadlines. EPA believes it is valuable to examine what

States have done in the past, are currently doing, and are planning to do in the future for

SABS criteria, to look for approaches and methods that may be useful, either directly, or

with adaptation, to the entire nation. EPA also believes this same consideration should

be given to the SABS criteria efforts of other countries. Where approaches and methods

of States and other countries appear promising, EPA intends to carefully review these

approaches and consider them for application nationwide. At this time, the efforts of

Idaho, New Mexico and the province of British Columbia, Canada appear to be

approaches that warrant further consideration. 

8. Combinations, or a synthesis of portions, of the above approaches.

This option is suggested as a separate approach primarily for the purpose of

stimulating consideration of a combination of the approaches described above, or a

synthesis of components of the approaches. It may be possible that the best approach to

developing SABS criteria would be the application of key concepts or components of all

or some of the approaches above. 

For example many possible synthesis approaches could be formulated from the following

outline:

I. Select Indicators That Should be Measured:

--Suspended sediment: suspended sediment concentration, turbidity, clarity (use

rating curves in flowing waters).

--Bedded sediment: systematic particle size tally (“Wolman pebble count”),

embeddedness.

--Biota that indicate sediment problems: biological assemblage composition,

“indicator taxa,” anomalies, etc.

II. Establish Expectations for Particular Water Bodies:

A. Scale measurements by dominant local controlling factors:

1. Rating curves (scaling by discharge: suspended sediment, turbidity,

clarity in streams and rivers).

2. Scale by bankfull shear stress (bedded sediments in streams and rivers). 

(Relative Bed Stability and Sedimentation Approach)

3. Scale by water depth and wave action (bedded sediment in lakes and

estuaries.

4. Scale fish assemblage measures by stream or lake size.
48

5. Scale macrobenthos measures by stream or river shear stress.

B. Stratify waterbodies by type and landscape setting:

1. Waterbody type, size.

2. Ecoregion.

3. Further geomorphic classification- for lakes and wetlands (Fluvial

Geomorphic Classification Approach), Rosgen classification for streams

and rivers, Montgomery-Buffington classification for streams and rivers.

C. Identify minimally-disturbed reference sites: where measurements shall be

made. (State-by-State Reference Condition Approach)

III. Link Sediment Measures with Biotic Response:

A. Use published literature: on tolerance and occurrence of biota.

B. Associational analysis: conduct an analysis on survey data where biota and

sediment have been measured (Evaluating Effects of Sediment on Biota --

Relative Bed Stability and Excess Sedimentation Approach).

C. Experimental dose-response relationships: Establish supplemental

relationships where needed. (Toxicological Approach).

D. Link relative risk: link sediment measures with biotic impacts that is

independently defined. (Toxicological Approach).

IV. Define Impacts:

A. Rule-based quantification of impacts: TSS value above the 75th percentile of

reference site, or 20% greater than expected, or more than 3 standard deviations

above mean (State-by-State Reference Condition Approach) .

B. Link relative risk: link biologically-defined impacts with sediment levels.

(Toxicological Approach).

C. Link impacts to uses other than aquatic life: (Water-Body Use Functional

Approach). 

CONCLUSIONS:

Developing and implementing improved water quality criteria for SABS will be a

significant challenge for EPA, the States, Tribes and territories. The biggest challenge lies in

improving criteria that are protective of aquatic life. The development of criteria for SABS may

be complicated because of the need to be site-specific. Different water bodies have different

processes involving SABS, and different tolerance levels depending on the species and the

habitat. The amount of suspended sediment tolerated in a mountain stream is obviously much

different from that tolerated in the Mississippi River. Even within habitats there may be great

variation in the effect of SABS, thus EPA concludes there is a need for habitat classification in

order to develop criteria.

EPA has examined the current status of SABS criteria throughout the country, and in

specific locations across the globe, to identify existing or new approaches that may be useful. 

EPA has also proposed four new possible approaches to SABS criteria development (the

Relative Bed Stability and Sedimentation Approach, the Conditional Probability Approach to

Establishing Thresholds, the State-by-State Reference Condition Approach and the Fluvial

Geomorphic Approach). 

During preparation of this discussion paper, some common conclusions or concepts 
49

emerged that could be relevant to any criteria development methodology. A brief discussion of

these concepts is presented below and are raised for consideration by the Science Advisory

Board.

Common Elements?

Two basic forms of criteria- The States and Tribes need to protect all designated uses

from the detrimental effects of suspended and bedded sediments. This includes aquatic life uses,

human health related uses, industrial, agricultural and others. It appears however, that criteria to

accomplish this will need to focus in two main areas; 1) criteria to protect aquatic life uses, and

2) criteria to protect other uses. The basic methods for deriving criteria in these two areas are

fundamentally different.

Aquatic Life Criteria - Most Stringent- It appears that SABS criteria established for

aquatic life would be the most protective or stringent of criteria for any other potential

designated use (excluding some drinking water uses). By setting aquatic life criteria for water

bodies with multiple uses in addition to aquatic life, most other uses (recreation, irrigation,

navigation, industrial, etc.) would most likely be protected. Only where aquatic life uses do not

exist, or in other special circumstances, such as untreated drinking water source uses, would

other forms of criteria be needed.

Natural or Background Levels- Criteria methods for aquatic life should factor in

background concentrations or possibly even natural levels of turbidity, suspended solids and

embedded materials as these are valuable and natural components of aquatic ecosystems when in

proper concentration and levels for the ecosystem. Although natural levels and background

levels could be considered the same, it may provide more flexibility to develop these as two

different concepts.

Lotic vs. Lentic (lacustrine)- Most likely, SABS criteria for aquatic life will need to be

developed or stratified by water body type especially flowing versus pooled. Streams and small

rivers have very different SABS background levels or natural regimes than do lakes, large rivers,

estuaries, wetlands, coral reefs and other water bodies.

Modes of action- The effects of SABS on aquatic organisms are due primarily to impacts

that can be grouped into two categories; 1) the effects of light scattering, in the case of excessive

turbidity, and 2) the effects of particles, in the case of suspended solids, settleable solids and bed

deposits.

Lack of data- There is inadequate data in the literature from which to develop

toxicological-based thresholds for protecting all aquatic life from the effects of suspended and

bedded sediments.

Classification- When developing SABS criteria using a reference condition approach, a

conditional probability approach, or a habitat stability approach, the classification of water

bodies into their natural groupings is critical and will be difficult, data-intensive, and time

consuming. 

Programmatic needs of SABS criteria- Once criteria are developed (whatever format

they take) there are a number of programmatic considerations for the successful use of the
50

criteria. They should relate to, and protect, designated uses. They need to be readily measurable

and easily monitored by States and Tribes. They need to be readily implemented by EPA, the

States and Tribes into their different water programs. They need to be a number(s), or

quantifiable in some way, so they can be translated into TMDL targets, wasteload allocations

and permit limits. They need to be able to indicate program effectiveness/success and they need

to apply to all water body types, including streams, rivers, lakes, reservoirs, estuaries, wetlands,

etc. 

EPA is seeking advice on the information and conclusions/concepts raised in this paper

and on the scientific viability of the proposed new approaches, a combination or synthesis of

these approaches, or other approaches from it’s Science Advisory Board as stated in the Charge

and Specific Questions listed below.

Overall Charge:

While many questions and much research remain, EPA seeks the opportunity for

a consultation with the Science Advisory Board to gain advice and recommendations on

the best potential approaches to developing water quality criteria for suspended and

bedded sediments as is described in this discussion paper. The Office of Water is also

seeking recommendations on additional criteria development approaches for different

types of water body uses, other than aquatic life, and is also seeking advice on any other

scientifically defensible criteria derivation methodology not included in this paper.

More Specific Consultation Questions:

1. Is it a scientifically valid premise that SABS in natural amounts (or at background

levels) are beneficial to ecosystems and therefore water quality criteria should

attempt to simulate natural regimes or background levels? If so, how should

natural levels or background be determined?

2. Can SABS criteria be stratified by water body type or by some other scheme? If

by water body-type, by what level of classification? Lotic and lacustrine? 

Rivers and streams, wetlands, lakes/reservoirs and estuaries/coastal areas? 

Others? If some other classification scheme is necessary, what type and how

much resolution must it have?

3. What indicators or components should a water quality criterion for SABS includeturbidity, suspended solids, and deposited solids? Others?

4. Can biological assessments and biocriteria play a role in SABS criteria? If so,

what role? 

5. Should EPA reconsider the inclusion of organic particulate material in its

definition of suspended and bedded sediments?

6. Which of the EPA proposed criteria methods do you believe have the greatest

potential? Why? Which ones should EPA not pursue further?

7. Can aspects of the different approaches described in the discussion paper be
51

combined into a synthesis approach?

8. Do any of the recent efforts of the States or other countries offer possibilities for a

national criteria approach?

9. Does the Chesapeake Bay approach to light penetration (clarity) hold promise for

a national scheme?

10. If SABS criteria are established to protect aquatic life in water bodies, is it

reasonable to assume that these criteria will be stringent enough to also protect

other uses of the water body (recreation, industrial water intake, drinking water

source, etc.)?

With the feedback and recommendations from the EPA Science Advisory Board, the

Office of Water anticipates proceeding forward to develop a strategy to be issued by the end of

2004 suggesting the best approaches, processes and schedules for EPA, States, Tribes and

territories to pursue for developing and adopting improved SABS criteria.
52

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APPENDICES:

Appendix 1: Literature review on SABS– Berry et al., 2003.

Appendix 2: British Columbia, Canada, Ambient Water Quality Guidelines (Criteria) for

Turbidity, Suspended and Bedded Sediments.

Appendix 3: EPA Summary Table of Current State Standards.

Appendix 4: EPA Summary Table of Sediment TMDLs.

Appendix 5: Idaho DEQ, Guide to Selection of Sediment Targets for Use in Idaho TMDLs. 

June 2003.