United States Office of Water
Environmental 4503 F EPA 841-B-99-004
Protection Agency Washington DC 20460 October 1999
Protocol for Developing
Sediment TMDLs
First Edition
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Acknowledgments
The Protocol for Developing Sediment TMDLs was prepared under the direction of Donald Brady and Chris Zabawa
of EPA's Office of Wetlands, Oceans, and Watersheds, Assessment and Watershed Protection Division, and Mimi
Dannel, Office of Science and Technology, Standards and Applied Science Division. The document was developed
under EPA Contract 68-C7-0018. Th Protocol for Developing Sediment TMDLs was written by EPA's Sediment
Protocol TMDL Team, led by David W. Smith of EPA Region 9, with assistance from John Craig of Terra Tech, Inc.,
in Fairfax, Virginia. The authors gratefully acknowledge the many comments of reviewers from within EPA and stat
environmental agencies, as well as the detailed reviews conducted by Lee MacDonald of Colorado State University and
Thomas Lisle of USDA Forest Service, Redwood Sciences Laboratory.
This report should be cited as:
U.S. Environmental Protection Agency. 1999. Protocol for Developing Sediment TMDLs. EPA 841-B-99-004.
Office of Water (4503F), United States Environmental Protection Agency, Washington D.C. 132 pp.
To obtain a copy of the Protocol for Developing Sediment TMDLs/EPA 841-B-99-004 (1999) free of charge,
contact:
National Service Center for Environmental Publications (NSCEP)
Phone: 513-489-8190
Fax: 513-489-8695
This EPA report is available on the Internet at:
http://www.epa.gov/owow/tmdl/techsupp.html
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Protocol for Developing Sediment TMDLs
First Edition: October 1999
Watershed Branch
Assessment and Watershed Protection Division
Office of Wetlands, Oceans, and Watersheds
Office of Water
United States Environmental Protection Agency
Washington, DC 20460
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Foreword
Although many pollution sources have implemented the required levels of pollution control technology, there are still
waters in the nation that do not meet the Clean Water Act goal of "fishable, swimmable." Section 303(d) of the act
addresses these waters that are not "fishable, swimmable" by requiring states, territories, and authorized tribes to
identify and list impaired waters every two years and to develop total maximum daily loads (TMDLs) for pollutants in
these waters, with oversight from the U.S. Environmental Protection Agency. TMDLs establish the allowable pollutant
loadings, thereby providing the basis for states to establish water quality-based controls.
Historically, wasteload allocations have been developed for particular point sources discharging to a particular
waterbodyto set effluent limitations in the point source's National Pollutant Discharge Elimination System (NPDES)
discharge permit. This approach has produced significant improvements in water quality by establishing point sourc
controls for many chemical pollutants. But water quality impairments continue to exist in the nation's waters. Some
point sources need more controls, and many nonpoint source impacts (from agriculture, forestry, development activities,
urban runoff, and so forth) are causing or contributing to impairments in water quality. To address the combined,
cumulative impacts of both point and nonpoint sources, EPA has adopted a watershed approach, of which TMDLs ar
a part. This approach provides a means to integrate governmental programs and improve decision making by both
government and private parties. It enables a broad view of water resources that reflects the interrelationship of surfac
water, groundwater, chemical pollutants and nonchemical stressors, water quantity, and land management.
The Protocol for Developing Sediment TMDLs is a technical guidance document prepared to help state, interstate,
territorial, tribal, local, and federal agency staff involved in TMDL development, as well as watershed stakeholders and
private consultants. Comments and suggestions from readers are encouraged and will be used to help improve th
available guidance as EPA continues to build experience and understanding of TMDLs and watershed management.
Robert H. Wayland III, Director
Office of Wetlands, Oceans, and Watersheds
Office of Water
US Environmental Protection Agency
Washington, DC 20460
First Edition: October 1999 iii
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Preface
EPA has developed several protocols as programmatic and technical support guidance documents for those involved in
TMDL development. These guidance documents have been developed by an interdisciplinary team and provide an
overall framework for completing the technical and programmatic steps in the TMDL development process. Th
Protocol for Developing Sediment TMDLs is one of the three TMDL technical guidance documents prepared to date.
The process presented here will assist with the development of rational, science-based assessments and decisions and
ideally will lead to the assemblage of an understandable and justifiable sediment TMDL. It is important to note that
this guidance document presents a suggested approach, but not the only approach to TMDL development.
This document provides guidance to states, territories, and authorized tribes exercising their responsibility under section
303(d) of the Clean Water Act for the development of sediment TMDLs. The protocol is designed as programmatic
and technical support guidance to those involved in TMDL development. The protocol does not, however, substitut
for section 303(d) of the Clean Water Act or EPA's regulations; nor is it a regulation itself. It cannot impose legally
binding requirements on EPA, states, territories, authorized tribes, or the regulated community, and it might not apply
to a particular situation based on the circumstances. EPA and state, territorial, and tribal decision makers retain th
discretion to adopt approaches on a case-by-case basis that differ from this protocol where appropriate. EPA may
change this protocol in the future.
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Contents
Foreword Ill
Preface iv
Figures vi
Tables vi
Introduction Purpose of This Protocol 1-1
General Principles of Sediment Water Quality Analysis 2-1
Problem Identification 3-1
Identification of Water Quality Indicators and Target Values 4-1
Source Assessment 5-1
Between Water Quality Targets Sources 6-1
Allocations 7-1
Follow-up Monitoring Evaluation 8-1
the 9-1
Appendix: Case Studies
Deep Creek, Montana Appendix-1
Redwood Creek, California AppendIx-9
References References-1
Acronyms Acronyms-1
Glossary Glossary-1
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Figures
1-1 General of the water quality-based approach 1-4
1-2 General components of TMDL development 1-5
2-1 Sediment TMDL logical sequenc 2-2
2-2 Factors Influencing the level of detail for the TMDL 2-3
4-1 Factors for determining indicators endpoints 4-2
4-2 Guidelines for on watcrbody type several designated uses 4-14
5-1 Sedimentation process 5-2
Tables
2-1 Utility of watershed assessment frameworks and methods for sediment TMDL analysis 2-13
3-1 Examples of sediment impacts on or existing use categories 3-2
3-2 Advantages and disadvantages of different TMDL watershed analysis scales 3-5
3-3 Approaches for incorporating margins of safety into sediment TMDLs 3-7
4-1 Examples of multiple indicators for TMDL targets similar studies 4-4
4-2 Examples of appropriate single-indicator sediment TMDLs 4-4
4-3 Advantages and disadvantages of water column indicators 4-7
4-4 Advantages of sediment indicators 4-8
4-5 Advantages and disadvantages of other channel condition 4-10
4-6 Advantages and of biological assessment indicators 4-11
4-7 Examples of in-strcam and hillslope targets, allocations, and implementation measures 4-13
4-8 Advantages and of riparian hillslope indicators 4-13
4-9 Considerations in indicators) for large watersheds 4-15
4-10 Sensitivity of indicators to designated uses 4-16
4-11 Sensitivity of indicators to sediment sources 4-17
4-12 Comparison of sediment-related indicators for TMDL development 4-18
4-13 Utility of sediment-related indicators for different environmental settings 4-19
4-14 Methods for expressing numeric targets for TMDLs 4-23
4-15 Methods for comparing existing and target conditions for numeric targets 4-24
5-1 Advantages and of sediment source grouping methods 5-4
5-2 Advantages and disadvantages of source sensitivity estimation methods 5-10
5-3 Erosion process model comparisons 5-10
5-4 Advantages and disadvantages of hillslope source models 5-11
5-5 Advantages and of hillslope in-stream models 5-12
5-6 Advantages and disadvantages of direct measurement methods 5-13
5-7 Advantages and disadvantages of rating curves and statistical extrapolation methods 5-15
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Protocol for Developing Sediment TMDLs
Introduction and Purpose of This Protocol
Objective: This Total Maximum Daily Load (TMDL)
protocol was developed to provide EPA regions, states,
territories, and tribes with an organizational framework
for establishing TMDLs for sediment. The
recommendations and methods proposed in this protocol
focus on sediment as the pollutant; this protocol does
not address other contaminants that can be associated
with sediment. The process presented here will assist
with development of rational, science-based assessments
and decisions and ideally will lead to the establishment
of an understandable and justifiable TMDL.
Audience: The protocols are designed as tools for state
and tribal TMDL staff, EPA regional TMDL staff,
watershed stakeholders, and other agencies and private
consultants involved in TMDL development.
OVERVIEW
Section 303(d) of the Clean Water Act provides that
states, territories, and authorized tribes are to list waters
for which technology-based limits alone do not ensure
attainment of water quality standards. Beginning in
1992, states, territories and authorized tribes were to
submit their lists to the EPA every two years. Beginning
in 1994, lists were due to EPA on April 1 of each even
numbered year. States, territories, and authorized tribes
are to set priority rankings for the listed waters, taking
into account the severity of the pollution and the
intended uses of the waters.
EPA's regulations for implementing section 303(d) are
codified in the Water Quality Planning and Management
Regulations at 40 CFR Part 130, specifically at
sections!30.2, 130.7, and 130.10. The regulations
define terms used in section 303(d) and otherwise
interpret and expand upon the statutory requirements.
The purpose of the Protocol for Developing Sediment
TMDLs is to provide more detailed guidance on the
TMDL development process for waterbodies impaired
due to sediments.
On August 23, 1999, EPA published proposed changes
to the current TMDL rules at 40 CFR 130.2, 130.7, and
130.10. These changes would significantly strengthen
the Nation's ability to achieve clean water goals by
ensuring that the public has more and better information
about the health of their watersheds, States have clearer
direction and greater consistency as they identify
impaired waters and set priorities, and new tools are
used to make sure that TMDL implementation occurs.
The text box on 1-2 summarizes these proposed
changes.
EPA's regional offices are responsible for approving or
disapproving state, territorial, or tribal section 303(d)
lists and TMDLs, and for establishing lists and TMDLs
in cases of disapproval. Public participation is to be
provided for by states and tribes (or EPA regional
offices, in the case of disapproval) when they establish
lists or TMDLs.
In accordance with the priority ranking, states,
territories, and authorized tribes are to establish TMDLs
that will meet water quality standards for each listed
water, considering seasonal variations and a margin of
safety that accounts for uncertainty. States, territories,
and authorized tribes are to submit their lists and
A TMDL is the sum of the individual wasteload allocations for point=
sources and load allocations for nonpoint sources and natural^
background (40 CFR 130.2) with a margin of safety (CWA Section=
303(d)(1)(c)). The TMDL can be generically described by the=
following equation: =
TMDL = LC = £WLA +£LA + MOS =
where:= LC loading capacity,8 or the greatest loading a=
waterbody can receive without violating water=
quality standards;=
WLA wasteload allocation, or the portion of the=
TMDL allocated to existing or future point=
sources; =
LA = load allocation, orthe portion of theTMDL=
allocated to existing or future nonpoint sources^
and natural background; and =
MOS margin of safety, or an accounting of=
uncertainty about the relationship between^
pollutant loads and receiving water quality. =
The margin of safety can be provided implicitly^
through analytical assumptions or explicitly by=
reserving a portion of loading capacity.^
aTMDLs can be expressed in terms of mass per time, toxicity, or=
other appropriate measures. =
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Introduction and Purpose of This Protocol
Summary of Proposed Regulatory Requirements for Establishing TMDLs
A TMDL must be established for all waterbody and pollutant combinations on Part 1 of the list. TMDLs are not required for waterbodies on
Part 2, 3, or 4 of the list (§ 130.31 (a)).
A TMDL must be established according to the priority rankings and schedules (§ 130.31 (b)).
TMDLs must be established at a level necessary to attain and maintain water quality standards, as defined by 40 CFR 131.3(1), considering
reasonably foreseeable increases in pollutant loads (§ 130.33(b)(9)).
TMDLs must include the following minimum elements (§ 130.33(b)):
1. The name and geographic location, as required by §130.27(c), of the impaired or threatened waterbody for which the TMDL is being
established and the names and geographic locations of the waterbodies upstream of the impaired waterbody that contribute significant
amounts of the pollutant for which the TMDL is being established;
2. Identification of the pollutant for which the TMDL is being established and quantification of the pollutant load that may be present in the
waterbody and still ensure attainment and maintenance of water quality standards;
3. Identification of the amount or degree by which the current pollutant load in the waterbody deviates from the pollutant load needed to
attain or maintain water quality standards;
4. Identification of the source categories, source subcategories, or individual sources of the pollutant for which the wasteload allocations
and load allocations are being established consistent with §130,2(f) and §130.2(g);
5. Wasteload allocations to each industrial and municipal point source permitted under §402 of the Clean Water Act discharging the
pollutant for which the TMDL is being established ; wasteload allocations for storm water, combined sewer overflows, abandoned mines,
combined animal feeding operations, or any other discharges subject to a general permit may be allocated to categories of sources,
subcategories of sources or individual sources; pollutant loads that do not need to be allocated to attain or maintain water quality
standards may be included within a category of sources, subcategory of sources or considered as part of background loads; and
supporting technical analyses demonstrating that wasteload allocations when implemented, will attain and maintain water quality
standards;
6. Load allocations, ranging from reasonable accurate estimates to gross allotments, to nonpoint sources of a pollutant, including
atmospheric deposition or natural background sources; if possible, a separate load allocation must be allocated to each source of natural
background or atmospheric deposition; load allocations may be allocated to categories of sources, subcategories of sources or individual
sources; pollutant loads that do not need to be allocated may be included within a category of sources, subcategory of sources or
considered as part of background loads; and supporting technical analyses demonstrating that load allocations, when implemented, will
attain and maintain water quality standards;
7. A margin of safety expressed as unallocated assimilative capacity or conservative analytical assumptions used in establishing the
TMDL; e.g., derivation of numeric targets, modeling assumptions, or effectiveness of proposed management actions which ensures
attainment and maintenance of water quality standards for the allocated pollutant;
8. Consideration of seasonal variation such that water quality standards for the allocated pollutant will be met during all seasons of the
year;
9. An allowance for future growth which accounts for reasonably foreseeable increases in pollutant loads; and
10. An implementation plan
As appropriate to the characteristics of the waterbody and pollutant, the maximum allowable pollutant load may be expressed as daily,
monthly, seasonal or annual averages in one or more of the following ways (40 CFR 13Q.34(b)):
» The pollutant load that can be present in the waterbody and ensure that it attains and maintains water quality standards;
• The reduction from current pollutant loads required to attain and maintain water quality standards;
• The pollutant load or reduction of pollutant load required to attain and maintain riparian, biological, channel or geomorphological
measures so that water quality standards are attained and maintained; or
* The pollutant load or reduction of pollutant load that results from modifying a characteristic of the waterbody, e.g., riparian, biological,
channel, geomorphological, or chemical characteristics, so that water quality standards are attained and maintained.
The TMDL implementation plan must include the following (§ 130.33(b)(10)):
• A description of the control actions and/or management measures which will be implemented to achieve the wasteload allocations and
load allocations, and a demonstration that the control actions and/or management measures are expected to achieve the required
pollutant loads;
• A time line, including interim milestones, for implementing the control actions and/or management measures, including when source-
specific activities will be undertaken for categories and subcategories of individual sources and a schedule for revising NPDES permits;
• A discussion of your reasonable assurances, as defined at 40 CFR §130.2(p), that wasteload allocations and load allocations will be
Implemented;
» A description of the legal under which the control actions will be carried out;
• An estimate of the time required to attain and maintain water quality standards and discussion of the basis for that estimate;
• A monitoring and/or modeling plan designed to determine the effectiveness of the control actions and/or management measures and
whether allocations are being met;
« A description of measurable, incremental milestones for the pollutant for which the TMDL Is being established for determining whether
the control actions and/or management measures are being implemented and whether water quality standards are being attained; and
• A description of your process for revising TMDLs if the milestones are not being met and projected progress toward attaining water
quality standards is not demonstrated.
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Protocol for Developing Sediment TMDLs
TMDLs to EPA for approval and, once EPA approves
them, are to incorporate these items into their continuing
planning processes. If EPA disapproves a state,
territorial, or tribal list and/or TMDL, EPA must (within
30 days of disapproval and allowing for public
comment) establish the list and/or TMDL. The state,
territory, or tribe is then to incorporate EPA's action
into its continuing planning process.
A TMDL is a tool for implementing state water quality
standards. It is based on the relationship between
sources of pollutants and in-stream water quality
conditions. The TMDL establishes the allowable
loadings for specific pollutants that a waterbody can
receive without violating water quality standards,
thereby providing the basis for states to establish water
quality-based pollution controls.
For many chemical pollutants, guidance on developing
TMDLs is readily available. For some pollutants,
however, the development of TMDLs is complicated
because of the lack of adequate or proven tools or
information on the fate, transport, or impact of each
pollutant within the natural system. EPA is developing
TMDL protocols to provide guidance on TMDL
development. The protocols represent a suggested
approach, but not the only approach to TMDL
development. EPA will continue to review all TMDLs
submitted by states pursuant to Section 303(d) of the
Clean Water Act and Title 40 of the CFR, section 130.7.
The TMDL protocols focus on Step 3 (Development of
TMDLs) of the water quality-based approach, depicted
in Figure 1-1 (USEPA, 1991a, 1999). This specific step
is divided into seven components common to all
TMDLs, and each component is designed to yield a
product that is an element of a TMDL analytical
document.
COMPONENTS OF TMDL DEVELOPMENT
The following components of TMDL development may
be completed concurrently or iteratively depending on
the site-specific situation (Figure 1-2).
• Problem Identification
• Identification of Water Quality Indicators and
Target Values
• Source Assessment
• Linkage Between Water Quality Targets and
Sources
• Allocations
• Follow-up Monitoring and Evaluation Plan
• Assembling the TMDL
Note that these components are not necessarily
sequential steps, but are provided more as a guide and
framework for TMDL development. Although some of
the submittal components (e.g., TMDL calculation and
allocations) are part of the legally required TMDL
submittal and others are part of the administrative record
supporting the TMDL and providing the basis for
TMDL review and approval, this protocol considers
each component equally.
Problem Identification
The objective of problem identification is to identify for
a listed waterbody the key factors and background
information that describe the nature of the impairment
and the setting for the TMDL. Problem identification is
used to develop a plan for the remaining elements of the
TMDL process.
Identification of Water Quality Indicators and
Target Values
The purpose of this component is to identify numeric or
measurable indicators and pollutant values that can be
used to evaluate attainment of water quality standards in
the listed waterbody. Often the numeric target value for
the TMDL pollutant will be the numeric water quality
standard for the pollutant of concern. In some cases,
however, TMDLs must be developed for pollutants that
do not have numeric water quality standards. When
numeric water quality criteria do not exist, impairment
is determined on the basis of narrative water quality
criteria or identifiable degradation of designated or
existing uses (e.g., impaired fishery). The narrative
standard is then interpreted and used to develop
indicator(s) with quantifiable target(s) to measure
attainment or maintenance of the water quality
standards.
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Introduction and Purpose of This Protocol
1. Identification of Water
Quality-Limited Waters
Review water quality standards
Evaluate monitoring data
Determine if adequate controls
are in place
5. Assessment of Water
Quality-Based Control Actions
» Monitor point/nonpoint sources
« Audit NFS controls for effectiveness
t Evaluate TMDL for attainment of
water quality standards
4. Implementation of
Control Actions
Update water quality management plan
Issue water quality-based permits
Implement nonpoint source controls
(section 319 management plans)
2. Priority Ranking
and Targeting
Integrate priority ranking with
other water quality planning and
management activities
Use priority ranking to target
waterbodies for TMDLs
3. Development of TiDLs
Apply geographic approach
where applicable
Establish schedule for phase
approach, if necessary
Complete TMDL development
Figure 1-1. General elements of the water quality-based approach (adapted from USEPA, 1991 a)
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Protocol for Developing Sediment TMDLs
Components in TMDL Development
Suggested TMDL Submitted Elements
Identify Problem >- Problem Statement
Develop Numeric
Targets
Select indicators) >~ Numeric Targets
Identify target values
Compare existing and
target conditions
1
Source Assessment
. identify sources .>, Source Assessment
* Estimate source
i loadings
*
Link Targets and Sources
linkages ^ Linkage Analysis
Estimate total loading capacity
Allocate Loads
Among Sources
Divide loads ^- Allocations
Develop Monitoring and ^ Monitoring/Evaluation Plan
Review Plan/Schedule (for phased approach)
Develop Implementation Plan >- Implementation Measures in
' State Water Quality
Management Plan
Figure 1-2. General components of TMDL development
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Introduction and Purpose of This Protocol
Source Assessment
During source assessment, the sources of loading for the
pollutant of concern for the waterbody are identified and
characterized by type, magnitude, and location.
Linkage Between Water Quality Targets and
Sources
For each TMDL, a linkage between the selected
indicator(s) and target(s) and the identified sources must
be defined. This linkage establishes the cause-and-
effect relationship between the pollutant sources and the
in-stream pollutant response and allows for an
estimation of the loading capacity. The loading capacity
is the maximum amount of pollutant loading (e.g.,
sediment) a waterbody can assimilate without violating
water quality standards. Seasonal variation in water
quality must be addressed when discussing the linkages.
Allocations
Based on the target/source linkage, pollutant loadings
that will not exceed the loading capacity can be
determined. These pollutant loadings are distributed or
"allocated" among the significant sources of the
pollutant. The allocations include wasteload allocations
for existing and future point sources and load allocations
for natural background and existing and future nonpoint
sources. A margin of safety must be included in the
allocations to account for uncertainty in the analysis.
The margin of safety may be provided implicitly through
the use of conservative assumptions in the TMDL
development process or explicitly by setting aside a
portion of the allowable loading.
Follow-up Monitoring and Evaluation
TMDL submittals often include a monitoring plan to
determine whether the TMDL has resulted in attainment
of water quality standards and to support any revisions
to the TMDL that might be required. Follow-up
monitoring is recommended for all TMDLs given the
uncertainties inherent in TMDL development (USEPA,
1991a, 1997a, 1999). Although the rigor of a monitoring
plan can be based on the confidence in the TMDL
analysis, a more rigorous monitoring plan should be
considered for TMDLs with high degree of uncertainty
and where the environmental and economic
consequences of the TMDL are great.
Assembling the TMDL
In this component, the elements of a TMDL submittal
package required by statute or regulation are clearly
identified and compiled. Supplemental information is
also provided to facilitate TMDL review.
For each component addressed in this protocol, the
following presentation format is used:
• Guidance on key questions or factors to consider.
• Brief discussions of analytical methods.
• Discussions of products to express the results of the
analysis.
• Examples of approaches.
• References on methods and additional guidance.
By addressing each of the TMDL components, analysts
can complete the technical aspects of TMDL
development. Although public participation is an
extremely important component of TMDL development,
it is largely outside the scope of this document. The
protocols also do not discuss issues associated with
TMDL implementation (note the line across Figure 1-1).
Methods of implementation such as National Pollutant
Discharge Elimination System (NPDES) permits, state
nonpoint source (NPS) management programs, and
public participation are discussed in Guidance for Water
Quality-based Decisions: The TMDL Process (USEPA,
1991a, 1999) and in the August 8, 1997, memorandum
"New Policies for Establishing and Implementing Total
Maximum Daily Loads (TMDLs)" (USEPA, 1997a).
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
USEPA. 1991 a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1995a. Watershed protection: A statewide
approach. EPA 841-R-95-001. U.S. Environmental
Protection Agency, Washington, DC.
1-6
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Protocol for Developing Sediment TMDLs
USEPA. 1995b. Watershed protection: A project focus.
EPA 841-R-95-003. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1997a. New policies for establishing and
implementing Total Maximum Daily Loads (TMDLs).
U.S. Environmental Protection Agency, Washington,
DC.
USEPA 1999. Draft guidance for water quality-based
decisions: The TMDL process (second edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
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Introduction and Purpose of This Protocol
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Protocol for Developing Sediment TMDLs
General Principles of Sediment Water Quality Analysis
Objective: To develop a sediment TMDL, it is important
to have a basic understanding of sediment processes in a
watershed and how excessive or insufficient sediment
can affect water quality and designated uses of water.
This section provides background information on
sediment impacts on designated uses, sediment sources
and transport, and potential control strategies. Naiman
and Bilby (1998) and Waters (1995) offer general
information discussing sediment water quality.
IMPACTS OF SEDIMENTS ON DESIGNATED USES
Unlike many chemical pollutants, sediment is a vital
natural component of waterbodies and the uses they
support. However, sediments can impair designated
uses in many ways, including those discussed here.
Aquatic life and fisheries
Excessive sediments deposited on stream and lake
bottoms can choke spawning gravels (reducing survival
and growth rates), impair fish food sources, fill in
rearing pools (reducing cover from prey and thermal
refugia), and reduce habitat complexity in stream
channels. Excessive suspended sediments can make it
more difficult for fish to find prey and at high levels can
cause direct physical harm, such as clogged gills. In
some waters, hydrologic modifications (e.g., dams) can
cause sediment deficits that result in stream channel
scour and destruction of habitat structure. For more
information, see Waters (1995).
Drinking water supply
Sediments can cause taste and odor problems, block
water supply intakes, foul treatment systems, and fill
reservoirs. Although most treatment systems can
remove most turbidity, very high sediment levels
sometimes require that water supply intakes be shut
down until turbidity clears or system maintenance (e.g.,
backflushing) is performed.
Recreational use
High levels of sediment can impair swimming and
boating by altering channel form, creating hazards due
to reductions in water clarity, and adversely affecting
aesthetics. Aquatic habitat impairment by sediments can
also interfere with fishing.
SEDIMENT SOURCES AND TRANSPORT
Sediment is created by the weathering of host rock and
delivered to stream channels through various erosional
processes, including sheetwash, gully and rill erosion,
wind, landslides, dry ravel, and human excavation. In
addition, sediments are often produced as a result of
stream channel and bank erosion and channel
disturbance. Movement of eroded sediments downslope
from their points of origin into stream channels and
through stream systems is influenced by multiple
interacting factors. Eroded sediments are often trapped
on hillslopes and stored in and alongside stream
channels. Sediment analyses conducted for TMDLs
often account for the influence of these sediment storage
and transport mechanisms on the magnitude, timing, and
location of sediment-related impairment of designated
uses. For more information on sediment sources and
transport processes, see Reid and Dunne (1996).
In some settings, land management changes cause
changes in runoff even if they do not result in increased
upslope erosion. Where this occurs, channel erosion or
sediment deposition may increase. It might be
appropriate to develop sediment TMDLs to address this
type of situation.
Because erosion is a natural process and some
sedimentation is needed to maintain healthy stream
systems, it is often necessary to evaluate the degree to
which sediment discharge in a particular watershed
exceeds natural rates or patterns. This analysis can be
complicated because sedimentation processes in many
systems are highly variable from year to year. This type
of analysis is particularly important in settings that are
vulnerable to high natural sediment production rates and
are particularly sensitive to land disturbance (e.g., the
Pacific Northwest and many areas of the desert
Southwest). Erosion rates under natural and disturbed
conditions can be compared through several approaches,
including comparative analysis with reference streams
and literature values for similar settings.
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General Principles of
SEDIMENT SOURCE CONTROLS
Several approaches are available to manage sediment-
related problems, but preventing erosion in the first
place is usually the most cost-effective. A variety of
management practices have been applied effectively to
prevent or reduce erosion from the source. Extensive
guidance on sediment best management practices
(BMPs) is available from the Natural Resources
Conservation Service (NRCS), USDA Forest Service
(USFS), and the Bureau of Land Management (BLM),
transportation departments, conservation districts, and
many state water quality and forest management
agencies. In some cases, it is possible to reduce or
prevent delivery of eroded sediments to streams by
developing or maintaining buffer strips, vegetated
swales, or sediment detention basins, some of which
also provide collateral benefits in the form of wildlife
habitat, nutrient trapping, and stream shading.
Sometimes sediment impacts can be managed at
relatively high cost after sediments reach waterbodies of
concern. Control options include channel and bank
restoration and dredging to remove sediments from some
types of waterbodies, although dredging can sometimes
cause more harm than benefit.
ISSUES IN SEDIMENT WATER QUALITY ANALYSIS
Sediment water quality analysis is less straightforward
than analysis of many other pollutants because clean
sediment is rarely discharged intentionally to
waterbodies. (Dredge and fill operations are an
exception.) Rather, adverse sediment discharges usually
occur as a result of changes in processes that influence
erosion and the capacity of watersheds to store sediment
and transport it through the system.
To evaluate potential impacts of land management
activities on designated uses, the analyses must assess
the influence of land management activities on factors
such as changes in erosion processes, water discharge
amounts and timing, and channel form. This assessment
requires evaluation of the extent to which existing
conditions diverge from natural conditions and how
existing conditions will respond to planned land
management activities. Ideally, the analysis will
reconstruct past conditions, accurately describe present
conditions, and identify desired future conditions. The
condition of the water resource as it relates to erosional
processes must be evaluated, and the relationship
between erosion processes and impacts must be
understood (Figure 2-1).
Key Question
How do land management
activities affect sediment
production?
How is the sediment routed into
the stream?
How is an increased sediment
load routed through the stream
system?
How does the change in sediment
affect channel structure and
stability?
How do changes in sediment
loading and channel morphology
affect designated uses of
concern?
TMDL Element(s)
Source
Assessment/Allocation
Source Assessment
Source
Assessment/Linkage
Targets/Linkage
Targets
Figure 2-1. Sediment TMDL logical sequence
The general goal of sediment TMDL analyses is to
protect designated uses by characterizing existing and
desired watershed condition, evaluating the degree of
impairment to the existing (and future) conditions, and
identifying land management and restoration actions
needed to attain desired conditions.
Although this guidance focuses on sediment as the water
quality stressor of concern, analysts should consider the
combined effects of multiple pollutants on the designated
uses of water resources. For example, streams impaired
by the effects of high temperature are typically impaired
only during low flow. Assessments that consider
multiple pollutants might need to incorporate more
analytical work than that necessary to complete a
sediment TMDL, but the additional effort would result in
development of TMDLs for multiple pollutants.
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Protocol for Developing Sediment TMDLs
SEDIMENT TMDLS
TMDL development is pollutant- and site-specific. This
protocol provides descriptions of the main elements of
TMDLs established for sediments. It also includes case
studies from past and ongoing TMDL efforts, as well as
hypothetical examples, to illustrate the major points in
the process. The protocol emphasizes the use of
rational, science-based methods and tools for TMDL
development. The availability of data influences the
types of methods analysts can use. Ideally, extensive
monitoring data are available to establish baseline water
quality conditions, pollutant source loadings, and
waterbody system dynamics. If long-term monitoring
data are lacking, however, the analyst will have to use a
combination of monitoring, analytical tools (including
models), and qualitative assessments to collect
information, assess system processes and responses, and
make decisions. Although some aspects of TMDLs
must be quantified (e.g., numeric targets, loading
capacity, and allocations), qualitative assessments are
acceptable as long as they are supported by sound
scientific justification or result from rigorous modeling
techniques. A goal of this document is to assist analysts
in using a rational TMDL development process that
incorporates the required elements of a TMDL.
References and recommended reading lists are provided
for readers interested in obtaining more detailed
background information. The protocols are written with
the assumption that analysts have a general background
in the technical aspects of water quality management
and are familiar with the statutory and regulatory basis
for the TMDL program.
Range of Viable Sediment TMDL Approaches
Analysts should be resourceful and creative in selecting
TMDL approaches and should learn from the results of
similar analytical efforts. The degree of analysis
required for each of the components of TMDL
development can range from simple, screening-level
approaches based on limited data to detailed
investigations that might take several months or even
years to complete. A variety of interrelated factors
affect the degree of analysis in each of these analytical
elements. The factors include the type of impairment
(e.g., violation of a numeric criterion versus designated
or existing use impairment); the physical, biological, and
chemical processes occurring in the waterbody and its
watershed; the size of the watershed; the number of
sources; the data and resources available; and the types
and costs of actions needed to implement the TMDL (see
Figure 2-2).
Standard I tep
VJ Ol eft! 0 n 1 =::::::::
Sou ice
1 linUpieS | ^=::::::::
Few Data ' =::=
Resources
::::; ) Imnpirmpnt
Souices
= ] Reseai ch
= 1 More Data
Resources
^-
Increasing Level of Detail
Figure 2-2. Factors influencing the level of detail for the
TMDL analysis
Decisions regarding the extent of the analysis must
always be made on a site-specific basis as part of a
comprehensive problem-solving approach. TMDLs are
essentially a problem-solving process to which no
"cookbook" approach can be applied. Not only will
analyses for different TMDLs studies vary in complexity,
but the degree of complexity in the methods used within
individual TMDLs might also vary substantially.
Screening-level approaches afford cost and time savings,
can be applied by a wide range of personnel, and are
generally easier to understand than more detailed
analyses.
The trade-offs associated with using simple approaches
include a potential decrease in predictive accuracy and
often an inability to make predictions at fine geographic
and time scales (e.g., watershed-scale source predictions
versus parcel-by-parcel predictions, and annual estimates
versus seasonal estimates). When using simple
approaches, these two shortcomings should be considered
when determining an appropriate margin of safety.
The advantages of more detailed approaches are
presumably an increase in predictive accuracy and greater
spatial and temporal resolution. These advantages can
translate into greater stakeholder "buy-in" and smaller
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General Principles of
margins of safety, which usually reduce source
management costs. Detailed approaches might be
necessary when the screening-level approaches have
been tried and have proven ineffective or when it is
especially important to "get it right the first time" (e.g.,
where protection of aquatic life habitat is a TMDL
issue). In addition, more detailed approaches might be
warranted when there is significant uncertainty
regarding whether sediment discharges are attributable
to human or to natural sources and the anticipated cost
of controls is especially high. However, more detailed
approaches are likely to cost more, require more data,
and take more time to complete.
Using Sediment Loads Versus Alternative
Approaches for Sediment TMDLs
The traditional approach to TMDL formulation is to
identify the total capacity of a waterbody for loading of
a specific pollutant while meeting water quality
standards. This loading capacity is not to be exceeded
by the sum of pollutant loads allocated to individual
point sources, nonpoint sources, and natural background.
Therefore, TMDLs have often been expressed in terms
of maximum allowable mass load per unit of time.
However, alternative approaches to sediment TMDL
analysis might also be appropriate. In many cases, it is
difficult or impossible to relate sediment mass loading
levels to designated or existing use impacts or to source
contributions. These analytical connections can be
difficult to draw for several reasons, including the
following:
• Sediment yields vary radically at different spatial
and temporal scales, not only within a watershed,
but across the country, making it difficult to derive
meaningful "average" sediment conditions.
• Sediments are a natural part of all waterbody
environments, and it can be difficult to determine
whether too much or too little mass loading is
expected to occur in the future and how sediment
loads compare to natural or background conditions.
• A significant level of uncertainty is associated with
sediment delivery, storage, and transport estimates.
Fortunately, it is acceptable for TMDLs to be expressed
through appropriate measures other than mass loads per
time (40 CFR 130.2). It is important to note, however,
that some of the limitations associated with mass load
approaches, such as high temporal variability, are also
present in the alternative approaches and the
consequences of these limitations should be assessed and
acknowledged. The alternative measures for sediment
TMDLs can take several forms, including the following:
• Expression of numeric targets in terms of substrate or
channel condition, aquatic biological indicators, or
hillslope indicators such as road stream crossings
with diversion potential or road culvert sizing. The
hillslope indicators and targets should complement
in-stream indicators and targets.
• Expression of numeric targets and source allocations
in terms of time steps different from daily loadings
and as functions of other watershed processes such as
precipitation or runoff.
• Expression of allocations in terms other than loads or
load reductions (e.g., specific actions shown to be
adequate to result in attainment of TMDL numeric
targets and water quality standards).
This protocol discusses a range of pollutant load-based
and alternative measures that can be used for sediment
TMDLs. In general, the load-based approach to sediment
TMDL development is recommended. In cases where
this approach is used, numeric targets can be stated in
terms that express desired environmental conditions (e.g.,
suspended sediment concentration or substrate size
distribution) while the TMDL itself is expressed in mass-
based units. Where alternative approaches are used,
analysts should carefully document the basis for the
alternative method and explain why a conventional load-
based approach is not appropriate.
Sediment TMDL Examples That Illustrate the Range
of Appropriate Approaches
Brief summaries of four approved and two hypothetical
sediment TMDLs show that a range of viable methods
are appropriate for TMDL development and that
individual TMDLs often combine relatively complex
analysis for some elements with simple analysis for
others. In addition, they illustrate several factors that can
be important for effective TMDL development, including
(1) focusing on implementation of the TMDL, (2) using
existing information and adaptive management, and (3)
using expert judgment. More detailed case studies are
provided in the Appendix.
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Protocol for Developing Sediment TMDLs
Sycamore Creek, Michigan
Sycamore Creek is designated for the support of warm
water fish, other indigenous aquatic life, and wildlife;
total body contact recreation and navigation; and as an
industrial and agricultural water supply (USEPA,
1992a). Elevated sediment loadings from agricultural
land practices caused significant impacts on aquatic life
and habitats in Sycamore Creek and contributed to low
dissolved oxygen levels. Modeling results indicated that
sediment oxygen demand was the most significant
oxygen sink during drought periods. Placement of
Sycamore Creek on the state's 303(d) list was supported
by in-stream monitoring conducted by the Michigan
Department of Natural Resources (MDNR) that revealed
multiple violations of water quality standards at seven of
eight sampling stations.
MDNR used a quasi-steady-state dissolved oxygen (DO)
model to predict DO concentrations in the creek during
critical low-flow drought conditions (USEPA, 1992a).
Modeling revealed that sediment oxygen demand (SOD)
was the most significant DO sink during critical low-
flow periods and that respiration by aquatic plants
significantly contributed to the oxygen deficit at some
locations in the creek (USEPA, 1992a). MDNR
determined that nutrients bound to suspended sediment
particles were a major source driving the growth of
aquatic plants and the subsequent elevated respiration
rates in aquatic plants (USEPA, 1992a). Based on these
results, MDNR believed that reducing suspended solids
loadings to the creek would increase DO concentrations,
improve aquatic habitats, and restore the designated uses
of the stream (USEPA, 1992a).
Development of a sediment TMDL for Sycamore Creek
began with an assessment of the existing sediment
loadings to the stream. Rates of average annual sediment
loading from nonpoint sources were examined. Primary
nonpoint sources of sediment within the watershed
included urban runoff, streambank erosion, agricultural
fields, and septic tank systems. Site-specific monitoring
data, load estimation equations, and nonpoint source
loading models were used to estimate suspended solid
loads from the most significant sources—agricultural
areas, eroding banks, and urban areas (USEPA, 1992a).
Modeling efforts established the relationship between in-
stream DO levels and SOD. To determine the needed
load reductions, it was necessary to link SOD to
suspended solid loads. In the absence of models to
reliably predict the effects of reducing suspended solids
on habitat, aquatic life, or SOD, MDNR assumed a
proportional response by SOD rates to reductions in
suspended solids loads. Based on this assumption,
loading analysis results indicated that a 52 percent
reduction in the overall suspended solids loading was
necessary to restore the designated uses of the stream
(USEPA, 1992a). MDNR has not yet finalized a load
allocation scheme for achieving the suspended solids
reduction goals. A proposed allocation plan includes
reducing agricultural erosion by 56 percent, streambank
erosion in organic soils by 100 percent, and loading from
urban runoff by 30 percent (USEPA, 1992a).
To determine whether the TMDL will improve conditions
to support designated uses and maintain water quality
standards, MDNR is monitoring throughout three
agricultural subwatersheds that drain to Sycamore Creek.
Sycamore Creek
Level of Analysis
Simple Complex
Problem
Definition
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Loads
Monitoring
1
|
1
1
|
Water Quality
Targets
• TSS and DO/SOD
relationships
• total annual
sediment loads
TMDL/
Allocations
• % reductions by
source category
as long-term
average
Water Quality
Controls
• cropland BMPs
• bank stabilization
Source Analysis: monitoring data, regression model, urban loading
model
Link to Indicators: modeled linkage of suspended sediments and
sediment oxygen demand
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General Principles of
Data collected from this monitoring program will be
used to model storm runoff from agricultural fields, the
major land use in the watershed, using the Agricultural
Nonpoint Source Model (AGNPS). Future monitoring
data collected from these subwatersheds will be used to
refine the AGNPS model (USEPA, 1992a).
South Fork Salmon River, Idaho
The South Fork Salmon River (SFSR) supports valuable
game fish populations of trout, char, and salmon. In
recent years, however, fish spawning in the SFSR has
sharply declined. Monitoring data collected since the
1960s show that excessive levels of fine sediments
entering the river adversely affect salmonid spawning
and rearing habitats (USEPA, 1992b). The waters of the
SFSR were found to be impaired in a 1988 Idaho Water
Quality Report and Nonpoint Source Assessment, which
listed three stream segments of the SFSR as impaired
due to elevated fine sediment loadings from forestry
activities in the basin (USEPA, 1992b). As a result of
these findings and public support to restore the
beneficial uses, the state of Idaho targeted the waterbody
as a high priority for TMDL development.
The TMDL development process for the SFSR included
the formation of a consensus team consisting of
members from the USFS and USEPA and state
representatives. Based on results of the site-specific
sediment loading model BOISED, fisheries results, and
professional experience in the region, the team
developed the following numeric targets for the SFSR:
(1) a 5-year mean of 27 percent depth fines by weight,
with no single year over 29 percent; (2) a 5-year mean of
32 percent cobble embeddedness, with no single year
over 37 percent; or (3) acceptable improving trends in
monitored water quality parameters that reestablish the
beneficial uses of the SFSR (USEPA, 1992b).
In addition to extensive amounts of monitoring data and
the BOISED model, the team also used sediment loading
analysis procedures developed during detailed research
on erosion and sediment delivery from roads in a
watershed in the Boise National Forest to evaluate
current conditions in the SFSR watershed. These
procedures were used to estimate loads originating from
roads, while all other sediment loading estimates were
generated using BOISED.
The watershed was divided into units of similar
landform, geologic, soil, and vegetative characteristics.
Then dominant erosion processes, including surface and
mass erosion, were evaluated for each land unit to
estimate the sediment yield. Where erosion and sediment
yield data were missing, available research data were
extrapolated to areas of similar characteristics to predict
the effects of various watershed disturbances. The model
estimated average annual sediment yields for undisturbed
conditions, past activities, and proposed future activities.
Although the model results were not regarded as highly
reliable in predicting absolute quantities of sediment
delivered to the river at a specific time, they were
appropriate for comparing alternative management
scenarios within the watershed.
South Fork Salmon River
Problem
Definition
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Monitoring
Level of Analysis
Simple Complex
1
|
|
1
1
|
Water Quality
Targets
• % fine sediments in
spawning gravels
• cobble
embeddedness
• 5-yr mean and
annual maximum
TMDL/
Allocations
• 25% overall
long-term
reduction
• specific load
reduction
estimates for
each project
Water Quality
Controls
• road improvement
projects
• slide restoration
projects
Source Analysis: BOISED sediment loading model and road erosion
estimation method
Link to Indicators: best professional judgment of team
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Protocol for Developing Sediment TMDLs
The BOISED model was used in combination with best
professional judgment and experience in the area to
develop a sediment reduction scheme to meet the
numeric criteria developed by the consensus group.
Based on these results, a TMDL was established to
reduce sediment inputs from anthropogenic activities by
25 percent (USEPA, 1992b). Because of the phased
approach of the TMDL, an implementation and
monitoring plan was developed to establish reasonable
assurances that designated uses would be restored. By
2001, if monitoring determines that salmon spawning
has increased to acceptable levels, no change in the
program will be needed. If, however, monitoring
indicates that designated uses are not being restored,
additional recovery projects and methods for designated
use attainment will be considered.
Ninemile Creek, Montana
The Ninemile Creek TMDL illustrates the development
of a TMDL based on simple analytical methods to
determine numeric targets, sources, and allocations,
while focusing available resources on identification of
specific source management and restoration practices.
Sediment loading from rangeland, bank erosion, and
possibly upstream silvicultural activities was believed to
be causing impairment of trout spawning. A nonpoint
source management project was initiated to select and
implement sediment BMPs, and a TMDL was derived
based on planning work done for this project.
Monitoring data were available for total suspended
solids (TSS), streamflow, and redd counts per mile. The
numeric targets were based on comparison of spawning
redd counts above and below the impacted area and
were expressed in terms of redds per mile. The most
significant source area for the sediment loadings was
determined by evaluating TSS and flow data for a 1-year
period at several sampling sites around the study area.
Sediment load reduction targets were determined through
data evaluation and the best professional judgment of a
multiagency team. A detailed set of range management
BMPs and bank stabilization actions was identified in
concert with landowners, the USFS, and the NRCS. The
numeric target and source analysis methods were
adequate to guide the development and implementation
of a specific set of BMPs and restoration practices, and
follow-up monitoring of total sediment loading (using
automatic samplers) and annual redd count changes was
planned.
Upper Birch Creek, Alaska
The Upper Birch Creek TMDL is an example of a
sediment TMDL involving both point and nonpoint
sources that is based primarily on relatively simple
analysis of available turbidity and TSS monitoring data
for the creek and loading sources. The water quality of
Upper Birch Creek is affected by discharges from active
mines, bank erosion, resuspension of deposited
sediments, and runoff from abandoned mine sites.
Source water for drinking water, recreation, and aquatic
life are affected by these discharges. Monitoring data for
suspended and bottom sediments, flow, and biological
parameters were collected for more than 20 years.
Designated uses were believed to be affected by
suspended sediment (turbidity) and by sediment
deposition, which affected stream morphology and bed
structure. To develop TMDL targets and a source
analysis based on sediment loading, the relationship
between turbidity and TSS was determined through
Definition
Select
Source
Analysis
Link Source
to Impact
Allocate
Monitoring
N
Level of Analysis
Simple Complex
1
|
1
1
1
inemile C
Ireek
Water Quality
Targets
• 130 redds/mile
TMDL/
Allocations
• 80% reduction in
annual sediment
loads
Water Quality
Controls
• rangeland BMPs
• streambank
stabilization
Source Analysis: sediment and flow monitoring data above and below
study area
Link to Indicators: BPJ and reference site comparisons
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General Principles of
regression analysis. As a result, it was possible to
establish numeric targets and TMDL allocations in
terms of allowable sediment loading per day.
A careful analysis of critical flow and loading conditions
was conducted. After determining the total assimilative
capacity, existing nonpoint source contributions were
estimated based on comparisons of mined areas with
unmined areas. An explicit 10 percent MOS was also
provided. It was determined that Upper Birch Creek
could meet the turbidity standard in the absence of point
source discharges; therefore, needed load reductions
would be obtained by curbing discharges from active
mines. Wasteload allocations were established in the
form of maximum pounds of suspended solids per day
per mine.
Although the TMDL is focused primarily on attainment
of the turbidity standard, channel condition and
associated spawning habitat are expected to improve
dramatically as well. The follow-up monitoring plan
focuses on stream channel sediment parameters as well
as suspended sediment indicators. In addition, the
TMDL plan includes a discussion of control actions and
schedules, which assists in assessing implementation of
controls.
Chris Creek (hypothetical)
The "Chris Creek" example is a hypothetical TMDL
based on three TMDLs currently under development in
northern California. This example illustrates a variety
of creative approaches to TMDL interpretation and
analysis where watersheds are dominated by infrequent,
high-magnitude runoff events and where sediment
impacts, sources, and control needs are difficult to
characterize. Chris Creek is a steep forested watershed in
which hillslopes are unstable and erosion-prone. Chris
Creek provides spawning and rearing habitat for several
threatened salmonid species, but habitat quality is
degraded due to excessive sedimentation of spawning
gravels and rearing pools. Historical land use activities
and periodic extreme storms and associated sediment
erosion effects are responsible for much of the current in-
stream sedimentation problem. Silviculture and livestock
grazing are the predominant land uses in the watershed
and are believed to be contributing additional sediment to
the stream. The TMDL is being developed concurrently
with development offish habitat protection and
watershed-scale timber production plans by fisheries and
land management agencies. In addition, the TMDL is
addressing temperature-related habitat impairment.
Extensive data are not available for Chris Creek, but
limited sampling of substrate sediment composition and
fish counts has been completed. More extensive land use
and management information is available (e.g., road
inventories, timber harvest records and plans, and
landslide mapping). Extensive analysis offish habitat
conditions, sediment sources, and sediment management
actions has been conducted in neighboring watersheds.
In addition, extensive research on salmonid habitat
requirements has been published. The analysts decided
that multiple environmental indicators and associated
Upper Birch Creek
Level of Analysis
Simple Complex
Problem
Definition
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Loads
Monitoring
1
1
Water Quality
Targets
1 . total suspended
solids load per
day
TMDL/
Allocations
2. maximum TSS
load per day per
mine (PS)
3. TSS load per day
total (NPS)
4. explicit 10%
margin of safety
Water Quality
Controls
• NPDES permit
limits
Source Analysis: regression analysis of ambient and discharger
monitoring data
Link to Indicators: analysis of monitoring data regression analysis of
TSS-turbidity relationship
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Protocol for Developing Sediment TMDLs
targets would be needed for Chris Creek because no
single indicator was believed to provide a reliable basis
for measuring stream response to changes in
management activity and restoration actions (Reiser and
Bradley, 1992; Young etal., 1991). Numeric targets for
Chris Creek include both "core" and "secondary"
indicators. The core indicators are to provide the
primary indicators for measuring TMDL effectiveness;
the secondary indicators are intended to complement the
core indicators and provide additional information for
reevaluating the TMDL in the future. The core
indicators and associated targets were selected based on
how closely they fit the sediment-habitat issues of
concern for Chris Creek and how well they are
supported by research literature and local "on the
ground" experience.
Both in-stream and hillslope indicators were selected.
In-stream indicators were determined to be necessary to
be able to establish relationships between stream
sediment levels and habitat functions. Hillslope
indicators were selected to provide a means of directly
measuring reductions in hillslope erosion, which in-
stream indicators might not be able to identify
effectively. The core in-stream indicators included
residual pool volume occupied by fine sediments (V*),
median sediment size (D50), and invertebrate counts
(Lisle and Hilton, 1992; Peterson et al., 1992; Reiser and
Bjorn, 1979). Core hillslope indicators include miles of
unimproved roads per square mile and road-related
landslides. Target values for each indicator were
selected by consensus of an expert team based on data
from reference watersheds, and literature reviews.
Secondary indicators included width-depth ratios,
volume of large woody debris per stream mile, and
salmonid counts.
Because Chris Creek is fairly large (200 square miles),
remote analysis methods supplemented by field
verification were used to develop rough absolute and
relative estimates of sediment source contributions to
Chris Creek. A screening-level analysis of sequential air
photo coverages was used to identify erosion features
and channel changes over time. An initial sediment
source inventory was conducted by stratifying the
watershed into areas of similar geology, slope, and
vegetation cover. Simple erosion estimates were
developed for each major source category in each
stratified land area using literature-based relationships.
Field verification was conducted to assess whether these
simple "remote" estimates were reasonable and to ensure
accounting of all major sediment sources. Particular
attention was paid to evaluating erosion potential
associated with road-related erosion because roads were
believed to be one of the main erosion sources. Field
evaluations of road erosion hazards and estimates of
erosion potential were made for a subset of roads in the
watersheds. The results were extrapolated for the entire
watershed based on the distribution of road types
determined through air photo analysis. The erosion
estimates from roads and other sources were summed.
Finally, it was assumed that all eroded sediment would
reach the stream. This conservative assumption was
adopted for three reasons:
• Lack of site-specific information on sediment
delivery.
• Because roads are a major source and literature
sediment delivery values are typically very high.
• To include an implicit margin of safety in the source
loading estimate.
TMDL allocations were developed in two steps. First,
sediment reduction needs were estimated by comparing
existing values for core indicators with target values
established by the team. Based on this comparison, the
team established an overall percentage reduction target.
Based largely on the team's best professional judgment,
allocations were established by source category. The
allocations considered the relative sediment contributions
from each source, the proximity of these sources to the
stream, and the feasibility and cost of reducing erosion
from different sources. The allocation
section of the TMDL was complemented by the
development of a detailed set of implementation
recommendations for consideration by involved
landowners and land management agencies. Finally, a
detailed monitoring plan was developed to track each of
the core and secondary indicators. An adaptive
management schedule for reviewing project results was
established, with reviews scheduled every 5 years. In the
second phase of the project, the developers will consider
whether more detailed geomorphic analysis and stream
restoration planning are needed. If fish habitat quality
begins to recover in response to continuing reductions in
sediment inputs, more intensive analysis and restoration
might not be needed.
First Edition: October 1999
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General Principles of
"Chris Creek"
Simple
Level of Analysis
Problem
Definition
Select
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Loads
Monitoring
Complex
Water Quality Targets
• median sediment size
• V* (pool sediment
indicator)
• road-related landslides
• road density
TMDL/
Allocations
• % reductions
by category in
long-term annual
averages
Water Quality
Controls
• forestry BMPs
• road
improvements
Source Analysis: rapid sediment budget, measurement of erosion
potential from roads
Link to Indicators: set erosion reduction need (percentage) in
proportion to degree existing targets exceed target levels
Wendell Creek (hypothetical)
The "Wendell Creek" TMDL example is based on
several watershed analysis and restoration planning
efforts conducted in the western United States that
incorporated relatively complex geomorphic analysis
and sediment budgeting methods to develop numeric
targets, estimate source contributions, and allocate
loads. Wendell Creek drains a 150-square-mile
watershed in which livestock grazing is the predominant
land use. Aquatic habitat in Wendell Creek is impaired
by high-magnitude sediment loading associated with
infrequent flood events and landslides. As a result of
these sedimentation and flooding events, the stream
channel has changed from a relatively deep, meandering
channel that provided plentiful spawning gravels and
deep rearing pools to a broad, shallow, braided channel
with poor gravels and few pools. These changes in
stream channel structure were documented through
comparative analysis of sequential air photo coverages
and intensive monitoring of stream channel structure,
including the following:
• Width-depth ratios
• Channel cross sections
• Longitudinal profiles
• Meander pattern and sinuosity
• Particle size distributions
• Pool frequency and depth
• Streambank recession rates in key erosion areas
In addition, flow measurements were taken along with
suspended and bedload sediment samples at five
locations in the watershed during times of high,
moderate, and low flow. The sample sites were below
junctions with major tributaries and at the mouth of the
creek. Numeric targets were developed by comparing
geomorphic indicator values for Wendell Creek with
values obtained in neighboring Little Deer Creek, which
supports good fisheries and is believed to be relatively
unimpaired. A sediment budget was prepared based on
several types of analyses. First, sediment rating curves
were developed for each of the sample stations and used
to estimate total annual sediment loads at each station.
Annual loads for each station were compared to gain an
understanding of relative contributions from each
tributary and from streambank erosion. The annual load
estimates were also used to derive an initial estimate of
in-channel sediment storage between stations and net
outflow from the watershed. A sediment budget was also
developed for neighboring Little Deer Creek for purposes
of identifying relatively natural sediment discharge
conditions. The analysts obtained a more detailed
understanding of key sediment sources by developing
independent estimates of erosion quantities from three
major sediment sources of concern identified during
initial stream surveys. Sheet and rill erosion from
rangeland was estimated through the application of a
model based on the Revised Universal Soil Loss
Equation (RUSLE). Expected future erosion from five
active landslide areas was estimated based on direct
measurement of slide volumes and was assumed to
eventually enter the stream system in response to high-
magnitude runoff events. Finally, erosion from road
surfaces was estimated by identifying drainage crossings
prone to failure and estimating volumes of sediment that
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Protocol for Developing Sediment TMDLs
would be discharged if these crossings failed during
high-magnitude storms. Because land use, landslide,
and road networks were mapped for Wendell Creek
watershed, the analysts stratified the results of the
rangeland, landslide, and road erosion estimates by
watershed and used the results as an independent check
on the tributary-based sediment budgets developed
through the rating curve approach. The comparison
indicated that the source estimates by watershed were
accurate within a factor of 2. The in-stream targets were
linked with the source analysis in two ways. First, the
analysis team estimated the degree of annual sediment
reduction needed based on a comparison of annual tons
of sediment yield per acre-foot of discharge for Wendell
Creek and Little Deer Creek. Second, existing
geomorphic indicator values for Wendell Creek were
compared with geomorphic conditions in Little Deer
Creek.
Based on the professional judgment of the team, it was
determined that reduction of sediment loads to Wendell
Creek to the levels present in Little Deer Creek was
infeasible and that such reductions would not be
adequate to restore aquatic life uses in Wendell Creek.
Therefore, the team devised plans that called for
substantial sediment source reductions to be carried out
through implementation of rangeland BMPs,
stabilization of two key landslides near the channel, and
road network upgrades (principally upgrades of stream
crossings that were vulnerable to failure). In addition,
the team recommended several streambank stabilization
projects in the areas most affected by bank erosion.
TMDL allocations were expressed in terms of average
annual loads from each tributary and from bank erosion
in key reaches of the main stem of Wendell Creek (based
on 5-year rolling averages). In addition, key loading
sources needing attention in each tributary were
identified by location, although quantitative load
allocations were not established for each source location.
In addition to identifying specific bank stabilization
projects needed, the implementation plan developed
concurrent with the TMDL identified general types of
rangeland BMPs that should be considered and
established a process for BMP installation through
cooperative efforts of landowners, NRCS, and BLM.
Finally, a monitoring program was established to ensure
that progress is being made to implement needed BMPs
and restoration projects.
Conclusions
These six case study examples illustrate that a range of
viable methods are available for developing sediment
TMDLs. In addition, they illustrate several factors that
can be important for effective TMDL development,
including focusing on implementation, using existing
information and adaptive management, and using expert
judgment.
"Wendell Creek"
Problem
Definition
Indicator
Source
Analysis
Link Source
to Impact
Allocate
Loads
Monitoring
Level of Analysis
Simple Complex
1
1
1
1
1
1
Water Quality
Targets
• width:depth ratios
• longitudinal profile
(deviation)
• geometric mean
particle size
TMDL/
Allocations
• average
annual loads
by tributary
(5-year
average)
Water Quality
Controls
• rangeland BMPs
• bank stabilization
• slide stabilization
• road
improvements
Source Analysis: sediment rating curves, sediment budget,
RUSLE, direct volume measurement
Link to Indicators: comparison to reference site sediment
budget, geomorphic factors, and best professional judgment
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General Principles of
Focusing on implementation
Projects that focus on implementation planning (and for
which TMDLs are a by-product) can often use less
complex TMDL methods because specific
implementation actions can be identified, agreed to, and
implemented without controversy (e.g., Ninemile Creek,
Montana). Projects where implementation actions are
unclear, controversial, or expensive benefit from more
detailed TMDL analysis.
Using existing information and adaptive management
Each of these projects made use of existing information
and did not assume that extensive new data were
necessary. The wide range of methods for establishing
sediment TMDLs allows screening-level analyses that
provide the framework for targeting implementation
actions while collecting more data for any future TMDL
evaluations or revisions.
Using expert judgment
In many cases, sediment TMDL elements can be
completed through the use of expert interpretation of
available information. Since "off the shelf models and
methods are not usually available for sediment TMDLs,
sound judgment is critical to project success. Many
projects make productive use of expert teams from
different disciplines, including fisheries biologists,
geologists, hydrologists, geomorphologists, engineers,
and land management professionals. This approach
works well for TMDLs in controversial settings and
often benefits greatly from the inclusion of a
professional facilitator.
UTILITY OF ALTERNATIVE SEDIMENT ANALYSIS
FRAMEWORKS AND METHODS FOR TMDL
DEVELOPMENT
Several frameworks and methods have been used by
agencies, landowners, and resource professionals to
evaluate sediment processes and associated impacts on
designated uses. Commonly used examples include
Federal Watershed Analysis (Regional Ecosystem
Office, 1995), Washington State's Timber, Fish and
Wildlife (TFW) process (Washington Forest Practices
Board, 1994) and BLM's Proper Functioning Condition
process (USDOI-BLM, 1993/1995). Many of these
methods can be used to facilitate TMDL development. In
particular, these approaches can often be used to
• Characterize existing conditions and assist in
problem definition and cumulative impact analysis.
• Assist in defining acceptable levels of sediment
loading (numeric targets).
• Focus the source analysis on critical locations and
categories of sediment sources.
• Highlight areas with similar conditions.
• Assist in defining cause-and-effect relationships
among watershed processes (for target development,
source analysis, and linkage).
• Identify conflicting concerns that could limit the
effectiveness of proposed solutions.
Commonly used and recently developed frameworks and
methods do not always address the full range of TMDL
elements or cannot always generate results precise
enough for TMDL purposes. (See Reid [1997] analysis
of the Federal Watershed Analysis and the Washington
State TFW process.) Table 2-1 provides a summary
analysis of several frameworks and methods, indicating
the TMDL elements addressed and the main advantages
and disadvantages for TMDL application. Analysts are
encouraged to make use of other available sediment
analysis frameworks and methods and completed projects
to reduce the time and cost associated with TMDL
development as well as to increase opportunities for
integration of TMDLs with other assessment and
sediment management programs. However, the analyst
should carefully consider whether and under what
circumstances each approach will yield results
appropriate for individual TMDL elements.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of this document.)
Dunne, T., and L.B. Leopold. 1978. Water in
Environmental Planning. W.H. Freeman and Co., San
Francisco, CA.
Waters, T.F. 1995. Sediment in streams—Sources,
biological effects, and control. American Fisheries
Society Monograph 7. American Fisheries Society,
Bethesda, MD.
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Protocol for Developing Sediment TMDLs
Table 2-1. Utility of watershed assessment frameworks and methods for sediment TMDL analysis.
Framework/
Method (Source)
Useful In
Developing:
O)
Advantages
Disadvantages
Washington State
Timber, Fish & Wildlife
(TFW) (Washington
Forest Practices Board,
1994)
Holistic view of past cumulative effects
of watershed processes
Detailed protocol uses expert input in
structured approach
Helps plan forest BMPs
Does not evaluate future cumulative
effects
Analysis techniques not fully tested
Quantitative results may not be usable
for TMDL elements
Rapid Sediment
Budgeting
(Reid and Dunne,
1996)
Flexible framework for evaluating
different sediment sources with
different methods at watershed scale
Yields quantitative results
Relatively fast and inexpensive
Not highly data-intensive
As general methods guidance, does not
provide specific "recipe"
Provides no clear linkages to designated
or existing use analysis or development
of sediment management practices
Ecosystem Analysis at
the Watershed Scale
(Regional Ecosystem
Office, 1995)
Flexible enough to be tailored to
specific settings/watershed issues
Evaluates upland and aquatic resource
issues along with economic, cultural,
and social issues
Many watershed assessments (WAs)
have been completed
Actual WA approaches vary
Aquatics analysis often cursory
Different components are poorly
synthesized in individual WAs
Often provide inadequate basis for
specific source management
Watershed Hydrologic
Conditional
Assessment (USDA
Forest Service, 1996)
Specific method to assess physical
processes affecting water quality
Yields quantitative evaluations of
condition and recovery potential
New method, not yet widely used
Basis for connections between process
analysis and recovery potential analysis
unclear
Stream Typing Hydro-
Geomorphic Analysis
(Rosgen, 1996)
Organization by stream types provides
framework for assessing stream
behavior under stress
Helps assess recovery potential and
need for restoration action
Data-intensive
Ability to predict stream behavior or
habitat quality based on existing stream
type unvalidated
Does not address all sources
Proper Functioning
Condition (USDOI-
BLM, 1993/1995)
Rapid method for assessing stream
condition, identifying nearby sediment
sources, and setting priorities for
further analysis
Widely used
Does not yield rigorous quantitative
inputs for TMDL
Unvalidated as predictive tool
Often does not view entire watershed;
focuses on a few reaches
• Sometimes
* Usually
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General Principles of
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Protocol for Developing Sediment TMDLs
Problem Identification
Objective: Identify background information and
establish a strategy for specific 303(d) listed waters that
will guide the overall TMDL development process.
Summarize the sediment-related impairment(s),
geographic setting and scale, pollutant sources of
concern, and other information needed to guide the
overall TMDL development process and provide a
preliminary assessment of the complexity of the TMDL
(what approaches are justified and where resources
should be focused).
Procedure: Inventory and collect data and information
needed to develop the TMDL. Information collected
should include an identification of the degree and type
of water quality standards impairment and preliminary
identification of sources, numeric targets, proposed
analytical methods, data needs, resources required, and
possible management and control techniques. Interview
watershed stakeholders and local, state, tribal, and
federal agency staff to identify information relevant to
the waterbody and its watershed. Establish plans for
incorporating public involvement into the development
of the TMDL. Revise the problem definition as new
information is obtained during TMDL development.
OVERVIEW
To develop a TMDL, it is necessary to formulate a
strategy that addresses the causes and potential sources
of the water quality impairment and available
management options. The characterization of the causes
and sources should be an extension of the process
originally used to place the waterbody on the 303(d) list.
Typically, the impairment that caused the listing is
related to water quality standards that are being
violated—either pollutant concentrations that exceed
numeric criteria or waterbody conditions that do not
match those specified by narrative criteria or do not
support the designated use. Most sediment-related
303(d) listings are based on exceedances of narrative
water quality standards that state that waters should be
free from suspended or deposited sediments at levels
detrimental to designated uses, including aquatic life,
water supply, and recreation. In many cases, the
problem itself will be self-evident and its identification
will be relatively straightforward. In other cases, the
complexity of the system might make it more difficult to
definitively state the relationship between the sediment
sources and the impairment.
Key Questions to Consider for Linkage of Water Quality
Targets and Sources
1. What are the designated uses and associated impairments?
2. What data are readily available?
3. What is the geographic setting of the TMDL?
4. What temporal considerations affect the TMDL?
5. What are the sediment sources and how do they affect water
quality?
6. What margin of safety and uncertainty issues must be
considered? What level of accuracy is needed?
7. What are potential control options?
8. What is the problem?
9. What changes does the proposed rule speak to?
The following key questions should be addressed during
this initial strategy-forming stage. Answering these
questions results in defining the approach for developing
the TMDL. A problem statement based on this problem
identification analysis is an important part of the TMDL
document because it relates the TMDL to the 303(d)
listing and describes the context of the TMDL, thereby
making the TMDL more understandable and useful for
implementation planning.
KEY QUESTIONS TO CONSIDER FOR PROBLEM
IDENTIFICATION
1. What are the designated uses and associated
impairments?
The goal of developing and implementing a TMDL is to
attain and maintain state water quality standards. With
that in mind, analysts should stay focused on addressing
the sediment-related problem interfering with the
designated uses. Some examples of how sediment
impairs designated or existing uses are listed in
Table 3-1. Identification of the designated uses being
impaired should include answers to the following:
• Are water quality standards for sediment expressed
as narrative or numeric criteria?
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Problem Identification
What water quality standards violation caused the
listing? What data or qualitative analyses were used
to support this decision?
• Where in the waterbody are designated uses
supported and where are they impaired?
• What are the critical conditions, in terms of flow
and season of the year, during which designated
uses are not supported?
• How do sediments affect the designated uses of
concern? (For example, do bottom sediments clog
spawning gravels? Does cloudy water create a
swimming hazard?)
• How are quantifiable targets determined to interpret
narrative water quality criteria?
2. What data are readily available?
To the greatest extent possible, the problem
identification should be prepared based on currently
available information, including water quality
monitoring data, watershed analyses, best professional
judgment, information from the public, and any previous
studies of the waterbody (e.g., state and federal agency
reports, university-sponsored studies, environmental
organizations). Ideally, these data will provide insight
into the nature of the impairment, potential sediment
sources, and the pathways by which sediments enter the
waterbody. Compilation of data necessary for TMDL
development should begin during the problem
identification stage. These data are likely to include the
following:
• Water quality measurements (e.g., TSS, turbidity,
bedload composition).
• Waterbody size and shape information (e.g.,
volume, depth, area, length, channel structure,
stream type).
• Biological information (e.g., fish, invertebrate, and
riparian vegetation information).
Table 3-1. Examples of sediment impacts on designated or existing use categories
Type
Aquatic Life
Fish
Invertebrates
Amphibians
Drinking Water
Recreation/Aesthetics
Agriculture
Industrial
Navigation
Resource Problem
Adult migration
Spawning
Fry emergence
Juvenile rearing
Escapement
Winter rearing habitat
Reduced or hidden food supply
Reduced diversity, population density
Larval development
Reduced reservoir capacity
Poor taste/appearance
Intakes clogged
Impaired treatment
Cloudy water
Channel modification impairs fishing, swimming,
rafting
Fouled pumps
Livestock watering
Loss of reservoir capacity
Process water
Cooling water
Navigation channel changes
Sediment Issue
Passage barriers
Cobble/gravel burial or scour
Turbidity/suspended sediment
Aggradation/scour
Changed channel form
Loss of riparian vegetation
Reduced interstitial dissolved oxygen due to filling of
substrate with fines
Filling of substrate with fines
Loss of riparian vegetation
Filling of substrate with fines
Sediment deposition
Turbidity
Total suspended solids
Aggradation or scour (disturbs intakes)
Turbidity
Channel modification
Pool filling
Suspended sediment
Turbidity too high to drink water
Sediment mass loads
Suspended sediment fouls equipment
TSS too high to treat water
Sediment deposition
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Protocol for Developing Sediment TMDLs
• Waterbody flow and runoff information, including
irrigation return flows.
• Watershed land uses, land use issues, and history.
• Processes of concern (e.g., surface erosion and
runoff, bank erosion, landslide features).
• Temperature and precipitation data.
• Soil surveys and geologic information.
• Topographic information.
• Information on local contacts.
• Past studies/surveys.
Maps of the watershed will also be invaluable. Maps
can be hard copies, such as USGS quad maps, or (if
available) electronic files for geographic information
systems (GIS). If possible, point sources, known
nonpoint sources, land uses, areas of geologic
instability, and road networks should be identified on
these maps to provide an overview of the watershed and
to identify priority areas for sediment loading caused by
human activities.
Photographs, both aerial and landscape, are also very
useful for evaluating sediment sources, sediment
deposition, and changes in geomorphic/channel features
overtime. If possible, analysts should obtain multiple
air photography sets for the watershed as far back as
photo records are available to facilitate time-series
comparisons. Photographs from the ground, although
less useful, can sometimes provide a qualitative
assessment of channel changes overtime.
Information on related assessment and planning efforts
in the study area should also be collected. Coordinating
TMDL development with similar efforts often reduces
TMDL analysis costs, increases stakeholder
participation and support, and improves the outlook for
timely implementation of needed sediment control or
restoration actions. Examples of related efforts that
should be identified include the following:
• State, local, or landowner-developed watershed
management plans.
• NRCS conservation plans, EQUIP projects, and
Public Law 83-566 small watershed plans.
• Land management agency assessment or land use
plans (e.g., Federal Ecosystem Management Team
[FEMAT] watershed analyses or BLM proper
functioning condition assessments).
• Nonpoint source management projects developed
with Clean Water Act (CWA) section 319 grants.
• Clean Lakes program projects developed with CWA
section 314 grants.
• Storm water management plans and permits.
• Habitat conservation plans developed under the
Endangered Species Act.
• Comprehensive monitoring efforts (e.g., National
Water Quality Assessment [NAWQA] and
Environmental Monitoring and Assessment Program
[EMAP] projects).
Missing the Mark With Problem Definition
A recent analysis of sediment water quality issues in a western river system illustrates the importance ot caretul problem detinition.
In that analysis, an assumption was made that the key limiting factor potentially impairing anadromous fish habitat quality was the
adverse effect of fine sediments in spawning gravels on egg survival and fry emergence. The analyst evaluated data on mean
sediment particle sizes in river gravels in relationship to graphs developed by fisheries biologists, which related mean particle size
to fish fry survival to emergence. The analysis showed that given the existing mean particle size conditions, over 80 percent
survival to emergence was expected. The analysis concluded that fish habitat was in good condition. A different analysis of
sediment conditions in the same river system had different results. That analysis found a bivariate particle size distribution, with
large amounts of very fine sand and very large rocks present in the system. The habitat problem found in the second analysis was
not too many fine sediments, but rather insufficient gravels suitable for spawning redds (egg pockets). Because fish could not find
adequate gravels of appropriate size, spawning success rates were very low. The initial analysis had misdefined the primary
problem as egg survival and fry emergence, missing the key problem of spawning impairment.
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Problem Identification
3. What is the geographic setting of the TMDL?
TMDLs can be developed to address a variety of
geographic scales, including specific stream reaches or
watersheds ranging from several square miles in size to
well over 1,000 square miles. The geographic scale of
the TMDL will primarily be a function of the
impairment that prompted the waterbody listing, the
type of waterbody impaired, the spatial distribution of
use impairments, sediment source locations, and the
scale of similar assessment and planning efforts under
way for the waterbody.
Where large watersheds or long stream segments have
been targeted for TMDL development, it might be
appropriate to divide the watershed into smaller
analytical units. For example, although the entire
Sycamore Creek, Michigan, watershed (106 mi2) was
targeted for TMDLs, one phase of the project focused
on the 37-mi2 subwatershed of greatest concern. Within
this smaller subwatershed, the study area was further
stratified by source category (e.g., agricultural, urban,
bank erosion) to apply different erosion estimation
methods for each source category. Sediment TMDLs
can be developed at virtually any scale that is
hydrologically meaningful (e.g., whole drainage units or
reaches) and analytically tractable (methods are
available to develop reasonably accurate TMDLs).
The selection of TMDL scale may involve trade-offs
between comprehensiveness in addressing all designated
use and source issues of concern and accuracy in the
analysis (Bisson et al., 1997; MacDonald, 1992). Table
3-2 summarizes the advantages and disadvantages of
developing TMDLs for larger (greater than 50 mi2) and
smaller (less than 50 mi2) watersheds.
Where relatively large watersheds are selected for
TMDL analysis, sediment transport and in-channel
storage may become more important to the analysis as
compared to smaller watersheds where sediment sources
and in-stream areas of impact are closer together.
Analysis of sediment fate and transport is often needed
to determine what happens to sediments once delivered
to streams and rivers. For example, fate and transport
analysis helps to determine how quickly sediments move
through the system, how much sediment remains behind,
and under what hydrological conditions sediments are
deposited at channel locations of concern. By
accounting for sediment transport out of the system, it
might be possible to allow larger sediment loadings and
still protect designated uses of concern.
Although extensive experience in sediment fate and
transport analysis has been gained in many parts of the
country, available methods are relatively time- and
resource-intensive. Analysts who are considering
incorporating more sophisticated analysis of sediment
fate and transport into a TMDL are advised to consult
with a qualified hydrologist or geomorphologist. It is
beyond the scope of this protocol to fully explore
sediment transport analysis methods, but several
published sources provide useful guidance in the
selection of sediment transport analysis methods (e.g.,
Gomez and Church, 1989; Reid and Dunne, 1996;
Vanoni, 1975; White etal., 1978).
Recommendations: Where the designated use
impairments are located at the bottom of a watershed
(e.g., in a lake, estuary, or lower main stem river), it is
often more effective to address the entire watershed at
once through the use of less intensive, screening-level
assessment methods. To evaluate sediment sources
effectively, large study areas can be stratified into
smaller analysis units to generate sediment loading
estimates and results can then be aggregated at the larger
study unit scale (Reid and Dunne, 1996). The TMDL
for a large study unit will often need to be developed
using the phased approach so that follow-up monitoring
can be used to assess the effectiveness of the source
reductions and to evaluate the accuracy of the TMDL
linkages between sediment sources and impacts. If
necessary, more in-depth analysis can be targeted to
specific "hot spots" within the watershed that have local
problems.
Where impairments occur throughout a watershed, it is
recommended that the analysis be conducted for smaller,
more homogenous analytical units (subwatersheds). For
example, specific impaired river reaches might require
detailed TMDLs to address individual sources. If this
subwatershed approach is chosen, care should be taken
to apply consistent methodologies within a basin from
one subwatershed to the next so that an additive
approach can eventually be applied to the larger basin.
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Protocol for Developing Sediment TMDLs
Table 3-2. Advantages and disadvantages of different TMDL watershed analysis scales
Large TMDL Study Units
(> 50 square miles)
Small TMDL Study Units
(< 50 square miles)
Advantages
Accounts for watershed processes that operate at
larger scales
More likely to account for cumulative effects
Avoids need to complete separate studies for multiple
tributaries
Easier to identify and address fine-scale source-impact
relationships and to identify needed control actions
Possible to use more accurate, data-intensive methods
Disadvantages
Confounding variables obscure cause-effect
relationships
Numeric target setting is harder for heterogeneous
waterbody features
Source estimation is more difficult because land areas
are more heterogeneous
Lag time between sediment discharge and in-stream
effects is potentialy longer, so effectiveness of source
controls is harder to assess
Analysis at coarse scale might cause TMDL to "miss"
source-impact relationships at fine scale
May miss cause-effect relationships detectable only at
broad scale (cumulative impacts)
May necessitate many separate TMDL studies in a
basin to cover the same area
Main problem may be big river
4. What temporal considerations affect TMDL
development?
Sediment TMDLs should consider seasonal and
interannual variations in pollutant discharges, receiving
water flows, and designated or existing use impacts.
Like most nonpoint source pollutants, sediment loadings
are not continuous in magnitude or effect and are likely
to increase as rainfall, runoff, and/or irrigation return
flows increase. However, land management activities
(e.g., cultivation) occurring during dry periods set the
stage for erosion and sediment delivery when
precipitation or irrigation runoff occurs. The seasonal
variability of sediment discharges and associated
designated or existing use impacts should be considered
during each phase of TMDL development.
Sediment impacts occur over different time scales,
depending on the designated or existing uses of concern.
Some uses (e.g., anadromous fish habitat) are much
more sensitive during certain times than at other times
(e.g., during the spawning and egg emergence life
stages). Other uses are more continuous and
consequently are sensitive to excess sediment impacts
throughout the year (e.g., drinking water or industrial
process water intakes). Finally, some designated or
existing uses suffer from cumulative effects of sediment
loading over long periods of time (e.g., reservoir storage
capacity, which affects water supply).
For many pollutants, TMDLs are developed for a
defined "critical flow" regime (usually low flow) when
the pollutant is believed to cause the greatest impacts.
The TMDL is then defined for this critical flow situation
on the assumption that it will be protective during other
flow regimes. The critical flow approach might be less
useful for sediment TMDLs because sediment impacts
can occur long after the time of discharge and sediment
delivery and transport can occur under many flow
conditions. Analysts should be aware of the flow
regimes of concern for sediment TMDLs. Although
sediment impacts can be substantial at low flows in
some situations (especially in some eastern and
midwestern waterbodies), sediment-related impacts are
often associated with higher-flow events (e.g., direct
effects on aquatic life, water supply intakes). Even if
high-flow impacts are insignificant, a TMDL would
need to consider flows associated with the time periods
in which sediment discharges of concern occur, which
are usually relatively high flow, high runoff periods.
High flows are considered to be the critical flows of
concern for sediment analyses in most situations. In
some circumstances, however, it might make sense to
consider flows over long periods of time as the "critical"
flow for TMDL calculation purposes (e.g., where long-
term sediment loads fill reservoirs and reduce storage
capacity).
Sediment discharges also vary substantially in their
timing, depending primarily on the sources of concern,
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Problem Identification
the watershed geology and landform, and the
precipitation/runoff patterns. Some sources are
vulnerable to erosion year-round (e.g., bank erosion and
continuously cultivated lands); other sources are
vulnerable only during and shortly after land-disturbing
activities (e.g., timber harvesting or construction
activities). In addition, watershed processes that affect
the magnitude, duration, and locations of sediment
discharges vary greatly over longer temporal scales. For
example, sediment transport mechanisms of greatest
concern in many watersheds recur relatively frequently,
often in conjunction with the bankfull flow event, which
may occur every 1 to 5 years (Wolman and Miller,
1960). In contrast, the dominant events contributing to
elevated levels of sediment transport and deposition in
other basins may occur only in response to infrequent
catastrophic events such as landslides or channel-
modifying flood events, which generally recur within
time scales of several decades to several centuries (e.g.,
some Northern California coastal watersheds).
Recommendations: The temporal variability of both
sediment impacts on designated or existing uses and
sediment discharges from different sources indicates
that careful consideration should be given to temporal
issues in TMDL development. Analysts should assess
whether TMDL development methods are capable of
accounting for temporal variability in watershed
processes. For example, use of suspended sediment or
turbidity as a sole TMDL indicator might not be
advisable for many watershed settings because these
measures are often highly variable through time and
difficult to use for trend-monitoring purposes. In
watersheds where sediment inputs are highly variable
and intensive monitoring is infeasible, these indicators
might be incapable of detecting the magnitude of
significant changes in sediment delivery and unable to
associate sediment discharges with designated or
existing use impacts. In such settings, indicators that
represent waterbody response to sediment loading over
time (e.g., substrate composition indicators or direct
measures of sediment loading from key sources) may be
preferable. This protocol provides additional guidance
related to time scale issues in later chapters.
5. What are the sediment sources and how do
they affect water quality?
The analyst should form an initial understanding of the
relative magnitude of the various sediment sources
during problem identification. This initial source
identification can often be based on existing
information; however, it is highly recommended that
analysts walk portions of streams and visit known or
suspected erosion sites if at all possible. The initial
source inventory will often be as simple as marking
down on a map the locations of known erosion problem
areas (e.g., landslide areas, gullies, eroding road
features, and stream reaches with eroding banks). A
qualitative assessment of the significance of hillslope
and in-stream sediment storage, along with changes in
channel structure in response to sediment load changes,
is also helpful.
In addition to assessing sediment sources, the initial
problem definition should begin to identify the specific
role that sediments play in affecting designated uses.
This analysis is important because many of the
impairments associated with sediment loadings can also
be caused by other stressors. For example, deposition of
fine sediments in pools can be associated with decreased
flows in addition to or instead of increased sediment
loadings. In addition, dissolved oxygen deficits in
spawning gravels, which can impair survival of eggs or
fry, can be associated with nutrient loading in addition
to fine sediment burial of spawning gravels. Sediments
might become the focus of watershed studies simply
because they are often the most visible stressor.
Recommendations: Inevitably, the role that sediments
play in affecting some waterbody impairments can be
determined only by using best professional judgment.
Monitoring data can be used to determine current levels
of sediments in streams or lakes, but a qualitative
judgment is sometimes the best means available to
assess the relationship among sediments, flows, channel
structure, and other factors. Analysts should use their
best judgment and consult with aquatic biologists and
other experts as appropriate.
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6. What margin of safety and uncertainty issues
must be considered? What level of accuracy
is needed?
Considerable uncertainty is usually inherent in
estimating sediment loading from nonpoint sources, as
well as predicting stream channel and designated or
existing use responses. The effectiveness of
management measures (e.g., agricultural BMPs) in
reducing loading varies depending on the location, the
severity of the problem being addressed, and other
practices being implemented. These uncertainties,
however, should not delay development of the TMDL
and implementation of control measures. EPA
regulations (40 CFR 130.2(g)) state that load allocations
for nonpoint sources are "best estimates of the loading
which may range from reasonably accurate estimates to
gross allotments, depending on the availability of data
and appropriate techniques for predicting the loading."
USEPA (1991a, 1999) advocated the use of a phased
approach to TMDL development as a means of
addressing these uncertainties. Under the phased
approach, load allocations and wasteload allocations are
calculated using the best available data and information,
recognizing the need for additional monitoring data to
determine if the load reductions required by the TMDL
lead to attainment of water quality standards. The
approach provides for the implementation of the TMDL
while additional data are collected to reduce uncertainty.
TMDLs also address uncertainty issues by incorporating
a margin of safety (MOS) into the analysis. The MOS is
a required component of a TMDL and accounts for the
uncertainty about the relationship between pollutant
loads and the quality of the receiving waterbody (CWA
section 303(d)(l)(c)). The MOS is either implicitly
accounted for by choosing conservative assumptions
about loading and/or water quality response or explicitly
accounted for during the allocation of loads. Table 3-3
lists several approaches available for incorporating an
MOS into sediment TMDLs.
During the problem identification process, the analyst
should decide at what point in the analysis the MOS will
be introduced. Often this decision can be made only by
using best professional judgment. The degree of
uncertainty associated with the selection and
measurement of indicators, source estimates, and water
quality response should be factored into this decision, as
well as the value of the resource and the anticipated cost
of controls. In general, a greater MOS should be
included when there is greater uncertainty in the
information used to develop the TMDL or when the
TMDL is for a high-value water. It might prove feasible
to include an MOS in more than one TMDL analytical
step. For example, relatively conservative numeric
targets and source estimates could be developed that, in
combination, create an overall MOS adequate to account
for uncertainty in the analysis.
Analysts should consider the level of precision needed
in the analysis. As a practical matter, analysts might
need to make trade-offs between (1) investing in more
precise analysis (presumably at higher cost) of different
TMDL elements and providing a smaller MOS (usually
providing greater management flexibility) and
(2) performing less precise analysis (presumably at
lower cost) and providing a larger MOS (presumably
constraining land management flexibility).
Many sediment TMDLs can be developed based on
existing, readily available data and information. Where
sufficient data are not available, TMDLs may be
developed based on modeling analysis or on simple
"screening-level" analysis in many cases. Where little
information about sediment causes and effects is
available, it is appropriate to account for the significant
Table 3-3. Approaches for incorporating the MOS into
sediment TMDLs
Type of
MOS
Explicit
Implicit
Available Approaches
Set numeric targets at more conservative levels
than analytical results indicate, corresponding to
some quantifiable MOS (e.g., 5% below
recommended criteria)
Add a safety factor to erosion and/or sediment
delivery estimates and expected sediment
reductions, corresponding to some quantifiable
MOS
Do not allocate a portion of available sediment
loading capacity (reserve for MOS)
Use conservative assumptions in derivation of
numeric targets
Use conservative assumptions in erosion rates,
land recovery rates following disturbance,
sediment delivery to waterbodies, and sediment
transport rates
Use conservative assumptions in analysis of
prospective feasibility of sediment management
practices and restoration activities
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uncertainty associated with TMDL analysis by
providing adequate margins of safety. In some cases,
providing larger margins of safety might result in
allocations that are not readily achievable. Several
approaches are available to address this problem. First,
more sophisticated analysis might be appropriate.
Where additional data or information is needed to use
more complex or data-intensive methods, it might be
more cost-effective to gather the information and use the
more complex methods than it would be to implement
more stringent allocations based on simpler analysis.
Where this is the case, a first-phase TMDL can often be
developed to provide a basis for further analysis while
initiating critical source control or restoration actions.
Because erosion and other key physical processes that
affect sediment impacts on designated or existing uses
are usually highly variable and difficult to characterize,
a significant degree of uncertainty is likely to emerge in
sediment TMDL development. Several strategies are
available to help address these uncertainties:
• Use a phased approach. Clarify that initial TMDLs
are based on limited information and that TMDLs
and implementation plans will be reviewed and
revised in the future based on monitoring results.
This approach clearly acknowledges uncertainty and
creates a framework for reviewing initial TMDL
hypotheses. This strategy is also a good means of
identifying information needs.
• Use multiple numeric targets and a "weight of
evidence " approach. Single-indicator TMDLs are
often difficult to relate to designated or existing uses
of concern or sediment sources. Multiple indicators
that, as a set, are believed to provide a richer basis
for interpreting water quality goals and linking goals
to source controls can be used in the TMDL. A
"weight of evidence" approach would be used to
interpret them; that is, evaluations would look at the
indicators as a group and would not consider
exceedance of one target as proof that a TMDL is
not working. If the weight of evidence approach is
taken, analysts are advised to clarify at the outset
how the responsible agency intends to evaluate
TMDL effectiveness as measured by multiple
indicators.
• Use hillslope targets to supplement in-stream
targets. Because it is difficult to associate
designated use problems or TMDL indicators and
targets with sediment sources, TMDLs can include
hillslope targets to supplement (but not supplant) in-
stream targets. Hillslope targets provide a TMDL
goal that might be easier to associate with sediment
source management.
• Use dynamic indicators and allocation approaches.
Sediment inputs tend to be quite variable across
time and space, and TMDL numeric targets and
allocations can be expressed in ways that recognize
and incorporate the dynamics of watershed
processes (e.g., sediment loading targets expressed
as a function of flow).
• Focus load allocations on load reductions related to
control actions. Where load allocations by source
are difficult to set but actions needed to reduce loads
are well understood, TMDL implementation plans
can incorporate more detail on actions to be taken
that are believed adequate to attain in-stream targets
and meet overall load reduction needs.
7. What are potential control options?
The problem identification should begin to identify
potential management alternatives. It is helpful to begin
thinking about key sources and the prospective
feasibility of controlling erosion from these sources.
Improvements already occurring should also be
considered when identifying possible control options. In
addition, analysts should begin to consider what options
will be adequate to address sediment-related
impairments. If no obvious level of sediment control
will achieve the designated use of the waterbody, the
appropriateness of the applicable water quality standards
should be evaluated.
If sediment source controls and/or restoration will be
able to address the impairment, the problem statement
should identify and stress the opportunity to take
advantage of other watershed protection efforts.
Opportunities include coordinating with various local,
state, tribal, territorial, and federal agencies along with
private landowners and stakeholder groups to avoid
duplicative or contradictory efforts. Other stakeholders
should also be encouraged to become involved with
development of the TMDL to contribute to the process
and to ensure that their concerns are addressed.
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8. What is the problem?
A summary problem statement should be drafted to help
frame the rest of the TMDL analysis and to help explain
the purpose and analytical approach for developing the
TMDL to interested parties. The problem statement
might need to be revised during development of the
TMDL to account for new information. Including the
problem statement with the TMDL submission helps
clarify the TMDL's scope and setting for readers who
are not familiar with the study area.
9.What changes does the proposed rule speak to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the problem
identification step, an approvable TMDL will need to
include the name and geographic location of the
impaired or threatened waterbody for which the TMDL
is being established. The TMDL will also need to list
the names and geographic locations of the waterbodies
upstream of the impaired waterbody that contribute
significant amounts of the pollutant for which the
TMDL is being established.
RECOMMENDATIONS FOR PROBLEM
IDENTIFICATION
• Identify events leading to the 303(d) listing and the
data to support the listing. Include any data or
anecdotal information that supports qualitative
approaches to develop the TMDL.
• Identify the specific role sediment plays in affecting
designated or existing uses, usually through
qualitative judgment and consultation with experts.
• Contact agency staff responsible for the waterbody
listing and collect any information they have
available.
• Prepare a flowchart or schematic detailing the
processes that might affect impairment of the
waterbody.
• Conduct an inventory of available information on
point or nonpoint sources using information
available from state or local agencies or databases.
• Identify the geographic scale of impairments.
• Identify temporal/seasonal issues affecting things
such as discharge rates, receiving water flows, and
designated or existing use impacts. Temporal
considerations will affect all subsequent stages of
TMDL development for sediments.
Identify and document all ongoing watershed
restoration or volunteer monitoring efforts in the
watershed.
Identify any characteristics or future uses of the
watershed or waterbody that might affect the TMDL
analysis.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
USEPA. TMDL Case Study Series.
. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1995a. Watershed protection: A statewide
approach. EPA 841-R-95-001. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1995b. Watershed protection: A projectfocus.
EPA 841-R-95-003. U.S. Environmental Protection
Agency, Washington, DC.
USEPA. 1996. TMDL development cost estimates: Case
studies of 14 TMDLs. EPA-R-96-001. U.S.
Environmental Protection Agency, Washington, DC.
USEPA 1999. Draft guidance for water quality-based
decisions: The TMDL process (second edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
Waters, T.F. 1995. Sediment in streams—Sources,
biological effects, and control. American Fisheries
Society Monograph 7. American Fisheries Society,
Bethesda, MD.
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Identification of Water Quality Indicators and Target Values
Objective: Identify numeric or measurable indicators
and target values that can be used to evaluate the TMDL
and the restoration of water quality in the listed
waterbody.
Procedure: Select one or more indicators that are
appropriate to the waterbody and local conditions. Key
factors to consider include both scientific and technical
validity, as well as practical issues such as cost and
available data. Identify target values for the indicator(s)
that represent achievement of water quality standards
and are linked (through acceptable technical analysis) to
the reason for waterbody listing.
OVERVIEW
To develop a TMDL, it is necessary to establish
quantitative measures that can be used to establish the
relationship between pollutant sources and their impact
on water quality. Such quantitative measures are called
indicators in this document. Examples of indicators for
a sediment TMDL include maximum turbidity or
suspended sediment concentrations, geometric mean
size of substrate particles, percentage of pool volume
occupied by fine sediments (Lisle and Hilton, 1992),
numbers of spawning fish, and percentage of eroding
streambanks. Once an indicator has been selected, a
target value for that indicator that distinguishes between
the impaired and unimpaired state of the waterbody
(e.g., no more than 15 percent fine sediment < 0.85 mm,
no more than 1000 tons/year sediment yield on average)
must be established. Although such discrete impaired or
unimpaired cutoffs do not exist in natural systems,
quantifiable goals are a necessary component of
TMDLs.
Key Questions to Consider for Identification of Water
Quality Indicators and Target Values
1.= What water quality standard(s) applies to the waterbody?=
2.= What factors affect indicator selection?^
3.= What water quality measures could be used as indicators? =
4.= What are appropriate target values for the chosen=
indicators?^
5. = How do the existing values compare to the target value? =
This chapter provides background on water quality
standards, lists a variety of factors that should be
addressed in choosing a TMDL indicator, provides
recommendations for setting target values under
different circumstances, and explains how to compare
existing and target conditions for each indicator. In
addition, this chapter identifies target values for the
indicator(s) that can be used to track progress toward the
restoration of designated uses. Figure 4-1 outlines an
approach for linking a water's impairment (e.g.,
nonattainment of designated use) to a TMDL.
KEY QUESTIONS TO CONSIDER FOR
IDENTIFICATION OF WATER QUALITY INDICATORS
AND TARGET VALUES
1. What water quality standards apply to the
waterbody?
Section 304(a) of the Clean Water Act (CWA), 33
U.S.C. 1314(a)(l), requires EPA to publish and
periodically update ambient water quality criteria. These
criteria are to ". . . accurately reflect the latest scientific
knowledge ... on the kind and extent of all identifiable
effects on health and welfare including, but not limited
to, plankton, fish, shellfish, wildlife, plant life . . . which
may be expected from the presence of pollutants in any
body of water . . . ." Water quality criteria developed
under section 3 04 (a) are based solely on data and
scientific judgments on the relationship between
pollutant concentrations and environmental and human
health effects. These recommended criteria provide
guidance for states and tribes in adopting water quality
standards under section 303(c) of the CWA. States and
authorized tribes are responsible for setting water
quality standards to protect the physical, biological, and
chemical integrity of their waters. The three components
of water quality standards include
• Designated uses (such as drinking water supply,
aquatic life protection, public recreation).
• Narrative and numeric criteria designed to protect
the uses.
• An antidegradation policy.
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Identification of Water Quality
Identify the Violation that Placed the
Waterbody on the 303(d) List
V
+ i
Numeric Water Nonnumeric Water
Quality Standard Quality Standard
, r Develop Supporting Indicators for Follow-up Monitoring ..
1 r 1
r
Develop TMDL Using Numeric Identify Potential
Standard Indicators
^
r
Select Target Value Protective of
Designated Uses
^
r
Develop TMDL Using Selected
Target Value
Figure 4-1. Factors for determining indicators and endpoints
For some waters, the indicators and target values needed
for TMDL development are already specified as numeric
standards in state water quality standards. An example
would be a state standard that specifies that turbidity in
a river designated for warm water aquatic life support
must not exceed 50 nephelometric turbidity units
(NTU). However, water quality standards vary
considerably from state to state and tribe to tribe and
often only narrative standards exist for sediment. In
these situations, development of the TMDL will require
the identification of one or more appropriate indicators
and associated target levels.
Where numeric targets are established for indicators
representative of narrative standards, the targets
themselves are not water quality standards; rather, they
are waterbody-specific interpretations of standards. For
example, a TMDL that addresses a narrative standard
prohibiting bottom deposits at levels that impair cold
water fish reproduction might include numeric channel
bottom indicators such as median particle size.
2. What factors affect indicator selection?
A variety of factors will affect the selection of
appropriate TMDL indicators. These factors include
scientific and technical validity, as well as those
associated with practical management considerations.
The importance of these factors will vary for each
waterbody, depending, for instance, on the time and
resources available to develop the TMDL, the
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Protocol for Developing Sediment TMDLs
availability of existing data, and the designated or
existing uses of the waterbody. Final selection of the
indicator is based on site-specific requirements.
Scientific or technical validity considerations
Indicators should be logically related to applicable water
quality standards and sensitive to the applicable
designated uses. Indicators will vary depending on
waterbody type. Indicators should also be sensitive to
geographic and temporal issues; they should be placed
or located where impacts occur. The indicators should
also be sensitive to when impacts occur. For example, if
water quality is impaired during certain times of the year
(e.g., drinking water intake fouling during snowmelt
runoff), the indicator should be chosen accordingly (e.g.,
turbidity during high flows). Indicators should be
sensitive to the temporal variability of sediment
processes and other driving processes active in the
watershed. The inherent temporal variability associated
with sediment impacts promotes indicators such as
macroinvertebrates or channel conditions, which
integrate over longer periods of time.
An indicator should also be helpful in linking pollutant
sources to indicator response (e.g., suspended sediment
data used as an indicator and as a component of
sediment budget development for source analysis). It
should also be technically robust; that is, the indicator
should be measurable and quantifiable, and
measurements of the indicator should be reproducible.
Practical considerations
Data collection should be as economical as possible
while still meeting monitoring objectives.
Indicators that can be suitably monitored using cost-
effective means should be considered. Indicators should
also be feasible to measure, given the capabilities of
monitoring personnel and the accessibility of the
monitoring site at the times when monitoring needs to be
done. Monitoring should introduce as little stress as
possible on the designated uses of concern. Since
comparability with previously collected information is
important, it is helpful to select an indicator that is
consistent with already-available data and for which
information concerning reference and natural
background conditions is available.
The choice of an indicator that is understandable to the
public is also desirable. Finally, the indicator should be
useful for addressing other pollutants of concern in the
analysis. For TMDLs that address pollutants in addition
to sediments, some indicators discriminate impacts from
the other pollutants as well as from sediment (e.g.,
biological indicators).
Number of indicators needed for sediment TMDLs
The watershed processes that cause adverse sediment
impacts are rarely simple. These processes often vary
substantially over time and space, affect designated uses
in more than one way (e.g., fish spawning and rearing
life stages), and are frequently difficult to relate to
specific sediment sources. It is often appropriate to
view sediment TMDLs as an iterative approach in which
assessment tools, planning decisions, and sediment
management actions are each evaluated over time to
ensure that they are reasonably accurate and successful
in addressing sediment concerns. In many watersheds,
more than one indicator and associated numeric target
might be appropriate to account for process complexity
and the potential lack of certainty regarding the
effectiveness of an individual indicator. Table 4-1 lists
examples of sediment TMDLs or similar projects that
used multiple indicators.
A single indicator might be appropriate in some settings.
For example, where drinking water source degradation
is the problem, it might be appropriate to establish a
single turbidity or suspended solids threshold above
which a water treatment plant must shut down or change
treatment strategies. It might be possible to link the
turbidity or suspended sediment indicator to source
analysis and allocation elements that would establish
straightforward BMP expectations. With adequate
monitoring and review over time, this simple approach
could prove effective in protecting drinking water
quality. Where the key concern is excessive filling of a
reservoir, it might be appropriate to establish an annual
average mass loading target above which reservoir life
span would be shortened more than stakeholders could
accept. Table 4-2 lists several sediment TMDLs that
used single indicators.
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Table 4-1. Examples of multiple indicators for TMDL targets and similar studies
Waterbody
Deep Creek, MT, TMDL=
(also addresses temperature^
and flow) =
South Fork Salmon River, ID,=
TMDL=
Pittsfield Lake, IL, Nonpoint=
Source-Clean Lakes Study=
Yager Creek, CA, Draft TMDL=
Indicators Selected
Percent fine sediment < 6.35 mm=
Number of trout =
Total suspended solids (TSS) load compared to that of=
reference stream =
Slope of discharge vs. TSS regression^
Percent of key reach with erosive banks =
Increased channel length=
Minimum flow=
Temperature^
Cobble embeddedness=
Percent fine sediment in gravels=
Photo point comparisons^
Tons of sediment per acre-ft discharge to lake=
Secchi diskdepths=
Concentration of total and volatile suspended solids=
Core Indicators
•= Percent fine sediments < 0.85 mm=
• Geometric mean particle size (D50) =
Secondary Indicators
• Percent fine sediments < 6.4 mm=
• Residual pool volume occupied by fine sediments^
(V*) =
• Width-depth ratios =
• Macroinvertebrate index=
• Miles of unimproved roads per mi2
• Volume of large woody debris per mile =
Rationale for Selection
Measures sand in spawning gravels=
Direct measure of designated or existing use=
Measures direct TSS impact on fish=
Dynamic TSS measure considers flow variation^
Measure of key sediment source=
Measure of restored channel form=
Measure of flow-related concern^
Direct measure of key fish stressor=
Spawning habitat measure =
Spawning habitat measure =
Show sediment feature changes^
Dynamic measure of sediment inputs and BMP=
effectiveness =
Measure lake clarity=
Measures total and organic sediment concentration^
• Measures fines in spawning gravels=
• Measure of spawning gravel condition^
• Measures sand in spawning gravels^
• Measures quality of pools used for rearing and=
refuge from predators^
• Measures channel recovery^
• Sensitive measure of habitat quality^
• Hillslope indicator of key source=
• Measures key factor influencing stream complexity^
and pool quality^
Table 4-2. Examples of a
jpropriate single-indicator sediment TMDLs
Waterbody
Ninemile Creek, MT=
Lemon Creek, AK=
Humboldt River, NV=
Indicator Selected
Number of trout redds per mile=
Turbidity under low-flow and high-flow conditions^
Total suspended sediment concentrations^
Rationale for Selection
Direct measure of quality of trout habitat=
Direct interpretation of state water quality standards^
Direct interpretation of state water quality standards^
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3. What water quality measures could be used as
indicators?
This section provides summaries of information on five
general categories of potentially useful TMDL
indicators. Each summary defines the indicator, reviews
its advantages and disadvantages, and makes
recommendations for use of the indicator. Following
the individual discussions of sediment indicator
categories, several tables are presented that compare the
suitability of different indicators for TMDL
development.
Water column sediment indicators
Two direct indicators and one indirect indicator of
sediment load in waterbodies have been used effectively
in watershed analysis and TMDL development—
suspended sediment, bedload sediment, and turbidity.
Suspended sediment refers to the fraction of sediment
load suspended in the water column. Bedload sediment
refers to the portion of sediment load transported
downstream by sliding, rolling, or bounding along the
channel bottom. In most cases, sediment particles
smaller than 0.1 mm in diameter are transported as
suspended load and sediment particles larger than 1 mm
are transported as bedload. Particles between 0.1 and 1
mm can be transported either as suspended load or as
bedload, depending on hydraulic conditions.
Turbidity is a measure of the amount of light that is
scattered or absorbed by a fluid, and it is used as a
measure of cloudiness in water. Turbidity is usually
associated with suspended sediment, but it can also be
caused by the presence of organic matter. Because
turbidity is easier to measure than suspended sediment,
many studies develop the correlation between TSS and
turbidity for sediment load estimation purposes and
measure turbidity as the primary indicator. However,
analysts should not assume a particular TSS-turbidity
correlation without evaluating the local relationship
between these variables based, if possible, on multiyear
data sets. In addition, as controls are installed, the TSS-
turbidity correlation might change.
Suspended sediment and turbidity are associated with
aquatic life use degradation in many settings. High
levels of suspended sediment can directly affect aquatic
species health. Suspended sediment has been widely
used as an indicator of sediment accumulation in
streambeds, which is also associated with aquatic life
impairment (Waters, 1995). In addition, high levels of
turbidity or suspended sediment are associated with
other use impacts, including contamination of drinking
water and industrial process water. Turbidity can also
directly affect aquatic species health. For example,
turbidity in midwestern smallmouth bass streams can
cause young fry to be displaced away from key feeding
areas due to loss of visual orientation.
Settings Where Water Column
Indicators Are Appropriate
Where the state has numeric standards for TSS or turbidity. =
Where suspended solids are the principal concern (e.g.,=
drinking water, industrial supply, or recreation). =
Where total sediment loading is a principal concern (e.g.,=
reservoir or estuary situations) or where sediment estimation^
methods based on suspended and bedload sediment analysis^
are used.=
Where existing data for these indicators are available and data=
for other candidate indicators are relatively difficult to obtain=
(e.g., as surrogate for concern over fine sediment in stream=
substrate). =
To help distinguish the relative importance of sediment=
discharge in different stream reaches (e.g., in Sycamore=
Creek, Michigan, TMDL). =
Where an indicator of sediment water quality upstream and=
downstream of a project area (e.g., a construction area) is=
needed.=
When flow data are also available since sediment indicators^
are generally flow-dependent. =
Turbidity or suspended sediment indicators may be used
in several ways in TMDL targets. For example, some
researchers have noted that some salmonids are
adversely affected by highly turbid flows that persist for
long periods of time. These researchers have proposed
the use of an indicator based on the level of turbidity or
suspended sediment associated with adverse fish
impacts and the duration of flows above that
turbidity/suspended sediment level. It might also prove
useful to set turbidity or suspended sediment targets as a
function of flow because turbidity would be expected to
increase naturally in response to rainfall-runoff events.
Early research on tributaries to South Fork Eel River,
California, indicates that when adjusted for flow,
turbidity levels in a relatively undisturbed reference
stream were significantly lower than turbidity levels in a
highly disturbed nearby stream.
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A variation on the use of suspended sediment
concentrations as a direct TMDL indicator is the use of
dynamic functions relating suspended sediment loads or
concentrations to waterbody flow. This approach was
used in the Deep Creek, Montana, TMDL, in which a
target was set based on the slope of the regression curve
identified by plotting flow against total suspended
sediment load. This approach acknowledges the fact
that sediment loading often varies substantially as a
function of flow (or other driving factors) and better
reflects system dynamics than static indicators.
However, two sediment curves with the same slope
could have significantly different intercepts or curve
forms. Where such functional relationships are used in
TMDLs, they should be derived based on site-specific or
comparable reference data.
Suspended and bedload sedimentation are often
evaluated as a component of sediment mass loading
studies (e.g., Rosgen, 1996; USDOI-BLM, 1993/1995).
Source analysis methods based on suspended and
bedload sediment estimation are discussed in Chapter 5.
Although bedload analysis is important to sediment
mass load studies, bedload sediment has some
disadvantages as a TMDL indicator. Bedload transport
rates are difficult to measure, are highly variable in
space and time, and might not clearly relate to
designated use impacts in particular settings
(MacDonald et al., 1991). Also, bedload as a proportion
of total sediment load varies substantially in different
settings (Rosgen, 1996). Significant experience has
been gained over the past few years, both in monitoring
bedload and in evaluating the accuracy of bedload
transport equations (see Reid and Dunne, 1996). Table
4-3 summarizes advantages and disadvantages of
various water column sediment indicators.
Measures of water clarity are in some ways the converse
of sediment or turbidity indicators. Water clarity is
often measured as the
water depth at which a
Secchi disk or other
reflecting material
becomes invisible from
the surface. This
indicator is widely used
to measure lake or
reservoir clarity.
TMDLs Using Water Column
Sediment Indicators
Lemon Creek, AK
Deep Creek, MT=
Sycamore Creek, Ml =
Humboldt River, NV=
Recommendations: Water column sediment indicators
will be appropriate in many TMDL settings, especially
when a numeric water quality standard for TSS or
turbidity has been established, or where sediment data
will be used as part of the source evaluation method.
These indicators should be useful in settings where
drinking water, other consumptive uses, and/or
recreation are the key designated use issues. In addition,
TSS and turbidity might be appropriate indicators in
warm water river and reservoir settings encountered in
much of the Midwest and South. Where cold water
aquatic habitat concerns prevail, these indicators might
be useful as secondary indicators to complement
streambed and geomorphic indicators, to monitor short-
term sediment impacts associated with specific areas,
and to estimate sediment yields. Bedload estimates
would be most useful as components of total sediment
yield estimation methods, and in settings where stream
channel changes are associated with bedload sediment
processes.
Where TMDLs are developed for lakes or reservoirs,
water clarity measures are recommended. Because state
water quality standards generally do not set numeric
standards for clarity indicators, analysts will need to set
targets for clarity as measured by Secchi disks based on
historical information or comparison to appropriate
reference sites.
If a water column sediment indicator is needed, analysts
should consider evaluating the relationship between TSS
and turbidity with the hope that a close correlation exists
and that turbidity can be used as a cheaper surrogate
indicator for TSS. It is usually best to base an analysis
of TSS-turbidity correlation on multiyear data since
substantial year-to-year variation can occur.
Streambed sediment indicators
A variety of indicators that measure different physical
attributes of waterbodies are available. Because so
much focus is placed on the adverse effects of sediment
aggradation or degradation of streambeds and the
associated use impacts on aquatic life, streambed
sediment indicators are assessed separately from other
stream channel indicators.
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Protocol for Developing Sediment TMDLs
Table 4-3. Advantages and disadvantages of water column sediment indicators
Advantages
Disadvantages
Intuitive appeal to the public (people can see the effect in many=
circumstances). =
Suspended sediment/turbidity impacts are primarily responsible for=
many designated use impacts. =
Because sediment indicator data can also be used to estimate^
sediment loads (e.g., through use of rating curve methods), the=
indicator can serve "double duty." =
Substantial experience as indicator of sediment problems from crop=
agriculture, urban runoff, and grazing. =
Extensive data are available in some watersheds (especially for=
suspended sediment). =
Difficulty in associating changes in TSS/turbidity with specific^
management activities. =
Large expected variation in time and space as function of=
precipitation, hydrograph, and other factors. =
Can be difficult or unsafe to measure during high flows. =
Difficulty in associating with some designated or existing use issues^
and establishing target conditions (e.g., habitat quality). =
A focus on suspended sediment might not address larger particle=
sizes that move as bedload.=
Bedload is difficult to measure accurately. =
Streamflow or discharge usually needs to be measured at the same=
time for the data to be useful. =
Difficult to distinguish human-caused changes. =
Streambed sediment quality indicators are based on the
theory that excessive or insufficient levels of fine
sediments or unnatural substrate size composition
directly and indirectly impair aquatic habitat in many
ways and during many key
life stages. These
indicators are used most
commonly in settings
where cold water fisheries,
anadromous fisheries, and
associated habitats are of
concern. For example,
excessive sediment
deposition can directly
TMDLs Using Streambed
Sediment Indicators
Deep Creek, MT
South Fork Salmon River, ID
Garcia River, CA=
South Fork Trinity River, CA=
Newport Bay, CA=
Simpson Timberlands=
Watersheds, WA (draft)
impair spawning success,
egg survival to emergence,
rearing habitat, and fish
escapement from streams, and it can indirectly
contribute to problems associated with water
temperature increases. The following is a partial list of
Streambed sediment indicators, the advantages and
disadvantages of which are summarized in Table 4-4:
Streambed particle size distribution indicators (e.g.,
percentage of fine sediments less than a certain
critical size, geometric mean or median particle size,
and the Fredle Index, another measure of central
tendency of particle size distribution).
Streambed coverage measures (e.g., embeddedness,
percent sandy or gravel bottom).
Streambed armoring or transport capacity measures
(e.g., comparison of surface versus subsurface
particle size; Dietrich et al., 1989).
Sediment supply measures (e.g., V*, percent of pool
volume occupied by fine sediment).
Recommendations: Substrate indicators are only a
subset of available geomorphic indicators and are not
fully indicative of geomorphic conditions of streams. In
many cases it will be appropriate to use substrate
indicators in association with other stream channel
condition/process indicators and hillslope indicators to
ensure that the indicators are sensitive to the entire
range of processes affecting sediment impairment.
Geology has a strong influence on substrate size
distribution. For example, granitic watersheds often
exhibit a natural bimodal size distribution. Therefore,
analysts should consider the link between watershed
geology and Streambed particle size classes.
Settings Where Streambed Sediment Indicators Are
Appropriate
Fine sediment in gravels is causing problems in spawning or=
egg emergence. =
Sediment accumulation around cobbles or gravels is degrading^
invertebrate and fish rearing habitat. =
Sediment accumulation in pools impairs hiding and rearing^
areas (especially where pool formation by woody debris is a=
secondary process). =
Because of access or high flow problems, only limited sampling^
is possible. =
Previously collected data are available. =
Generally, substrate indicators are recommended for
TMDLs focusing on protection of gravel bed aquatic
habitat. Specific indicators should be selected based on
a thorough understanding of the designated or existing
use impacts of primary concern (e.g., use pool indicators
where pool quality is a key issue). Because many riffle
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Identification of Water Quality
Table 4-4. Advantages and disadvantages of streambed sediment indicators.
Advantages
Disadvantages
There is a relatively high level of experience^
using them (especially stream bottom particle=
size distribution indicators) =
Indicators effectively integrate sediment=
loading and transport effects, making it=
possible to obtain useful results based on=
annual sampling during the low-flow period. =
In some geologic settings, substrate indicators^
have proven effective in discriminating^
between disturbed and undisturbed hillslope=
areas (e.g., Knopp, 1993).=
Indicator sampling methods are relatively^
simple and do not require sophisticated=
equipments
Indicators allow for direct empirical=
association of specific indicators with specific^
cold-water fish life stage issues (e.g.,=
sediment in riffles as a measure of spawning^
gravel quality and sediment in pools as a=
measure of rearing habitat quality). =
Particle size is related to macroinvertebrate=
productivity^
• Some methods are difficult to replicate (e.g., cobble embeddedness).=
• Appropriate target or desired conditions for chosen indicators may vary substantially^
depending on local watershed and aquatic life characteristics, and indicator target values^
are not available for many parts of the country. It is inadvisable to apply target values=
selected in one part of the country to other areas without carefully considering whether the=
settings are comparable. =
• Substrate composition is a less important determinant of habitat quality in many parts of tne=
country, including naturally sandy-bottomed streams, low-gradient warm-water fishery^
streams, most lakes, and geologies with few fines. =
• Fine sediment accumulation might not be as critical a problem in many cold-water streams^
in the Midwest and East in which dissolved oxygen conditions are controlled more by=
ground water upwelling than by stream water infiltration (Waters, 1995).=
» Some substrate indicators are not easy to understand or to explain to the public. =
The following disdvantages are common pitfalls that can be avoided. =
• Not all substrate indicators are discriminating of all cold-water aquatic habitat impairment^
issues. For example, riffle substrate composition indicators might not be effective planning^
indicators in settings where other limiting factors (e.g., pool filling by fine sediment) prevail. =
• Focusing on a specific size of fine sediment (e.g., sediment < 0.85 mm) can result in=
failure to detect problems associated with other sediment sizes. =
• Not all data for an individual indicator are comparable because different sampling methods^
are commonly used to characterize particle size distribution (e.g., volumetric vs.=
gravimetric measurement, wet vs. dry weights or volumes, surface particle size vs. =
substrate core particle size, and sampling with shovels vs. sampling with McNeil cores). =
sediment indicators are closely related statistical
measures that can be evaluated without additional
sampling, it is recommended that multiple statistical
indicators of desirable particle size distribution be used
(e.g., percent fines less than 0.85 mm, less than 2 mm,
less than 6.4 mm, and/or geometric mean particle size).
Selection of multiple particle sizes for analysis is
particularly warranted in watersheds where the size
distribution of sediments expected to erode as a result of
future land management activities is not known
(Peterson et al, 1992). When monitoring and evaluating
results based on analysis of these indicators, it is
important to track and report raw data to facilitate
different statistical methods for substrate analysis.
Embeddedness indicators have been applied in Idaho
and Montana, particularly in watersheds dominated by
sedimentation associated with decomposed granitic soils
and where overwintering habitat quality is a primary
concern. Embeddedness indicators should be used with
caution in other areas, and care should be taken to use
quantitative measures of embeddedness to avoid errors
associated with qualitative embeddedness measurement
techniques (MacDonald et al., 1991). For example,
embeddedness may be an inappropriate indicator in
steep or very low gradient streams, or in silt- or clay-
dominated streams (MacDonald et al., 1991). Finally,
embeddedness is not a primary tool in most sediment
studies, in part because of its high spatial variability.
Pool indicators (e.g., V*) are useful in many settings
both as direct measures of problems associated with
pool habitat degradation and possibly as more general
indicators of excessive sediment loading in streams
(Lisle and Hilton, 1992). Several methods are
promising for TMDL development, although caution is
advised in applying general "rule of thumb" values in
setting pool indicator targets. (For example, setting a
V* target of 50 percent for all locations might be
inappropriate.) Although it has not been widely used
until recently, the V* method holds substantial promise
as a TMDL indicator because it is not flow-dependent
and it facilitates comparison between streams of
different sizes (Lisle and Hilton, 1992).
Although there are few TMDL examples where stream
bottom sediment indicators were used, their extensive
use in fishery protection projects suggests they will be
appropriate in many settings. Whatever method is
selected, the same sampling techniques should be used if
results are to be compared over time and space.
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Protocol for Developing Sediment TMDLs
TMDLs Using Other
Channel Indicators
Deep Creek, MT=
Garcia River, CA (draft)
Other channel condition indicators
Other channel indicators can also support TMDL
development because they help evaluate changes in
channel shape and structure that might be associated
with changes in key sedimentation and hydrologic
processes. These indicators
can be effective for TMDL
development because they
can be linked to key
designated uses (e.g., cold
water habitat) and to land
management activities (e.g.,
livestock grazing along
streambanks). By measuring key elements of stream
structure, these indicators provide a mechanism for
understanding the relative importance of physical
process interactions that occur within streams, and for
more thoughtfully planning goals for stream
management and actions to attain goals (Reid and
Dunne, 1996; Rosgen, 1996). The advantages and
disadvantages of channel condition indicators are
summarized in Table 4-5. Channel condition indicators
that might be appropriate for TMDL projects include
• Pool/riffle ratios
• Cross sections
• Width/depth ratios
• Sinuosity
• Gradient
• Entrenchment
• Thalweg profiles
• Channel scour
• Bank stability (measurement of which considers
vegetative cover and erosion features present)
• Pool measures (e.g., residual pool volume, percent
pools, and average residual pool depth).
Recommendations: Channel condition indicators can
effectively complement other sediment-related
indicators in many TMDL projects. Settings where
these indicators would be particularly relevant include
streams with cold-water habitat degradation issues,
drinking water intake issues, flow alteration due to
dams, irrigation water conveyance or extensive water
diversions, and/or substantial in-stream restoration
potential.
Analysts should use these indicators carefully. Because
interrelationships among channel condition indicators
are complex and poorly understood in many settings, it
is usually prudent to use several indicators to obtain a
more thorough representation of geomorphic conditions.
Focusing on just one or two channel characteristics
might not provide the degree of discrimination needed
for the indicator to be useful as an assessment and
monitoring tool. In addition, analysts should avoid
drawing premature conclusions concerning watershed
process interactions and associated problems based
solely on application of stream classification
methodologies (Kondolf, 1995; Miller and Ritter, 1996).
In-stream or channel indicators do not provide an
adequate substitute for hillslope sediment source
analysis (Reid and Dunne, 1996). However, the
converse is also true: hillslope indicators do not provide
an adequate substitute for in-stream measures. Hillslope
and in-stream indicators should be used to complement
each other in most settings.
Biological and habitat indicators
Biological metrics often provide discriminating
indicators for sediment TMDLs associated with
impairment of the aquatic habitat use. Because the
presence, diversity, and productivity of aquatic
organisms of concern can be used to infer the habitat
suitability characteristics, biological indicators can
complement physical and chemical indicators in many
TMDLs. Biological indicators can be used to detect the
effects of changes in key habitat characteristics (e.g.,
aggradation, degradation, changes in channel diversity)
on aquatic species.
Although it is possible to use bacteria and plant-related
indicators of aquatic habitat quality, this discussion
focuses on invertebrate- and fish-related indicators
because they are most likely to be of use in establishing
sediment TMDLs. Two general types of biological
assessment tools are available. First, a wide variety of
approaches focus on quantitative analysis of species
numbers, diversity, and productivity. For more detailed
guidance on biological indicator options and the
selection of specific indicators, see USEPA (1989) and
Platts et al. (1983). Second, several more qualitative or
quasi-quantitative methods have been developed that
integrate assessment of biological indicators with
physical indicators (chiefly channel condition factors)
and chemical indicators (e.g., temperature range) to
yield composite habitat quality indicators. These
methods include habitat typing (California Department
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Identification of Water Quality
Table 4-5. Advantages and disadvantages of other channel condition indicators.
Advantages
Disadvantages
Intuitive appeal to the public (people can see the effect in many=
circumstances). =
Suspended sediment/turbidity impacts are primarily responsible for=
many designated use impacts. =
Because sediment indicator data can also be used to estimate^
sediment loads (e.g., through use of rating curve methods), the=
indicator can serve "double duty." =
Substantial experience as indicator of sediment problems from crop=
agriculture, urban runoff, and grazing. =
Extensive data are available in some watersheds (especially for=
suspended sediment). =
Difficulty in associating changes in TSS/turbidity with specific^
management activities. =
Large expected variation in time and space as function of=
precipitation, hydrograph, and other factors. =
Can be difficult or unsafe to measure during high flows. =
Difficulty in associating with some designated or existing use issues^
and establishing target conditions (e.g., habitat quality). =
A focus on suspended sediment might not address larger particle=
sizes that move as bedload.=
Bedload is difficult to measure accurately. =
Streamflow or discharge usually needs to be measured at the same=
time for the data to be useful. =
Difficult to distinguish human-caused changes. =
of Fish and Game, 1994), assessment of proper
functioning condition (USDOI-BLM, 1993/1995), and
assessment of channel stability (Ohlander, 1991). Other
methods of this type are reviewed in Dissmeyer (1994).
Table 4-6 summarizes advantages and disadvantages of
biological indicators for TMDL development.
Recommendations: Biological indicators should be
considered for inclusion in sediment TMDL projects in
many settings. For example, fish indicators often
complement other TMDL indicators. However, because
numbers of fish are often influenced by factors beyond
sediment-related impacts, analysts should use caution in
selecting a fish-related indicator as the sole TMDL
indicator. In many settings, it is possible to design fish-
related indicators to help control for confounding
variables beyond sediment impacts. For example, the
indicator of trout redd counts per stream mile was
applied in the Ninemile Creek, Montana, TMDL by
establishing target levels based on conditions in a
neighboring, good-quality stream.
Invertebrate indicators have several characteristics that
TMDLs Where Too Little Sediment Is Present
In some settings, such as the Trinity River in California, fish habitat=
impairment is associated with diminished sediment supply and=
altered hydrologic regimes due to main stem dam construction. ln=
this type of setting, sediment supply shortages might result in=
channel bottom scour and erosion of spawning gravels. For TMDLs=
in scour settings, a different set of geomorphic and biological^
indicators might be needed to assess the degree of habitat impact=
and prospective solutions (e.g., management of dam releases and=
gravel replenishment). =
might make them preferable to fish indicators. They are
relatively abundant in many settings, are good
representatives of overall aquatic habitat condition, and
are relatively sensitive to changes in sedimentation. The
chief disadvantages of invertebrates include the
relatively high level of expertise needed to analyze
samples, the difficulty in collecting reliable samples, the
need to measure them at the same time of year as the
flow, and the difficulty of setting target conditions. In
Settings Where Biological Indicators Are Appropriate for
TMDL Development
Aquatic habitat uses are key concerns. =
Sufficient information is known about life histories and use of=
habitat. =
Quantitative methods have been locally tested and validated. =
Field personnel are trained in these methods and available for=
follow-up monitoring. =
Cause-effect relationships between sediment sources and in-=
stream habitat impacts are poorly understood. =
addition, the temporal and spatial variability of
invertebrate populations can be very high. In temperate
areas there is a strong seasonal variation in benthic
macroinvertebrate biomass, diversity, and composition,
and this variation must be considered when evaluating
the use of invertebrates as indicators (Rosenberg and
Resh, 1993). Additionally, benthic macroinvertebrate
populations are often very sensitive to changes in
substrate or other habitat characteristics, and this can
make it very hard to compare samples from different
streams or waterbodies. Local validation of invertebrate
monitoring methods is necessary to develop meaningful
target conditions over time or to compare conditions in
reference streams and the study area. Analysts should
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Protocol for Developing Sediment TMDLs
Table 4-6. Advantages and disadvantages of biological assessment indicators
Advantages
Disadvantages
Are often sensitive to the additive effects of multiple^
changes in hydrologic and erosion processes active in=
a watershed, including the effects of sediment=
discharges from multiple sources over time. =
Can reflect the recovery of aquatic habitats from past=
land disturbances and associated sediment inputs and=
can account for the effects of sediments stored in=
waterbody channels after discharge. =
Can be effective even if monitored rarely (e.g.,=
annually or during key life stage periods only). =
Provide direct measures of the designated or existing=
uses of concern in many projects and consequently^
have significant public appeal (especially fish counts). =
Qualitative methods might not yield results that can be reliably used for TMDL=
numeric targets. =
Often difficult to replicate results of qualitative assessment methods.^
Not very useful for distinguishing between stressors of concern (e.g., sediments, =
nutrients, temperature). =
Some methods are difficult to use and/or quantify (e.g., fish are difficult to count=
accurately). =
In many settings, so few fish are present that fish- related indicators cannot be=
reliably used.=
Fish indicators are very sensitive to confounding influences (e.g., effects of fishing=
within the watershed or in the ocean, in the case of anadromous fish; habitat=
stressors other than sediment [temperature]). =
Because many fish populations have been severely affected for substantial periods^
of time, it is difficult to set appropriate target conditions for fish counts. =
not assume that invertebrate indicators are always good
indicators of salmonid habitat conditions. Although
evaluations of invertebrate and fish measurements in
eastern streams have found good correlations, some
researchers in the Pacific Northwest have expressed
concern that invertebrate measurements provide poor
indicators of western salmonid habitat quality.
Qualitative and quasi-quantitative indicators (e.g.,
Ohlander, 1991; USDOI-BLM, 1993/1995) can greatly
assist in defining sediment problems and near-stream
sources. However, they might not prove viable as
TMDL indicators because results are often imprecise,
difficult to replicate, difficult to compare with target
levels, and not fully validated as designated use
assessment methods. Analysts should use caution in
applying such methods to derive TMDL numeric targets
for these reasons.
Riparian/hillslope indicators
Not all TMDL indicators must focus on the waterbody.
In many cases, it is difficult to analyze the relationship
between upslope sources of sediment and in-stream
impacts of sediment discharges. The hillslope-in-stream
connection is particularly difficult to evaluate in many
western coastal watersheds. Often these are highly
erosive, steep watersheds that are subject to extreme
variations in sediment-producing runoff events and in
which anadromous fisheries are the principal concern.
Riparian and hillslope indicators provide additional
indicators of environmental conditions associated with
designated or existing use protection; however, they
should be used to complement in-stream indicators and
not as substitutes for in-stream indicators. Riparian and
hillslope indicators would not suffice as lone TMDL
numeric targets because
they do not provide a
direct interpretation of
water quality standards,
which focus on in-stream
uses. See the Redwood
Creek TMDL case study
for an example
application of both in-
stream and hillslope indicators.
TMDLs Using Riparian/
Hillslope Indicators
Deep Creek, MT (bank stability)
Redwood Creek, CA=
South Fork Trinity River, CA=
San Diego Creek, CA
Riparian or upslope indicators represent a wide range of
influences on stream sediment quality:
• Riparian buffer width sizes and riparian vegetation
character.
• Amount of large woody debris present (e.g., number
or volume of wood pieces per mile).
• Disturbance indices such as Equivalent Roaded
Acreage (USDA Forest Service, 1988).
• Erosion hazard indices.
• Percent impervious land within zone adjacent to a
waterbody.
• Landslide area.
Depending on the context in which they are included in
a TMDL, riparian and hillslope indicators suitable for
TMDL numeric targets might not include actions,
BMPs, land management policies, or projects to be
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Identification of Water Quality
implemented to address riparian or hillslope sediment
issues. Such actions, practices, and projects do not
identify desired conditions; rather, they identify means
to accomplishing environmental objectives. In some
cases, the use of hillslope indicators will be related to
BMPs, such as when the hillslope indicator is related to
road crossing culvert sizes. It might be feasible in
limited circumstances to include such actions, practices,
and projects as part of the allocation process designed to
identify methods for attaining needed changes in
sediment processes. To help clarify the differences
between hillslope targets, allocations, and
implementation measures, Table 4-7 provides two
example applications. Advantages and disadvantages of
riparian and hillslope indicators are summarized in
4-8.
Settings Where Riparian/Hillslope
Indicators Are Appropriate
Bank erosion is a key sediment source. =
Grazing, recreation, or waterside development are key issues.
Woody debris is responsible for channel diversity and pool=
formation. =
Upslope/in-stream linkages are difficult to evaluate. =
Extensive prior monitoring of these indicators has been=
conducted. =
Riparian area land management options are likely to be key=
components of theTMDL implementation plans. =
Recommendations: Upslope and riparian indicators can
prove useful in many TMDLs, especially in settings
where in-stream or stream channel indicators are
particularly difficult to associate with sediment sources.
Inclusion of hillslope and riparian indicators in the suite
of indicators is recommended because they highlight
sediment problems before they happen and because
there is often a long lag time between hillslope
disturbance and downstream sediment impacts.
Although this class of indicators can often be effective
in improving stream condition, they can be difficult to
apply in settings where establishing target conditions is
problematic.
Comparisons of indicator candidates
Although selection of indicators is necessarily a site-
specific decision, Figure 4-2 offers some guidance on
selecting indicators that might be most appropriate for
different types of waterbodies and different designated
uses.
In general, the larger the TMDL study area, the more
likely it will be that indicators will need to be monitored
and target conditions established in multiple locations.
This is particularly true in settings where indicators
measured toward the bottom of the watershed are
incapable of detecting key designated use changes in
critical areas (e.g., upstream spawning areas) or of
establishing linkage with the source analysis and control
elements of the TMDL. Therefore, in larger study units
(e.g., > 50 mi2), the selection of indicators may be
influenced by the availability of future resources for
monitoring. Table 4-9 provides insights into addressing
indicator selection issues in large watersheds.
Tables 4-10 through 4-13 provide additional summary
comparisons of the candidate indicators. Table 4-10
reviews the sensitivity of indicators to key designated or
existing uses. Table 4-11 reviews the sensitivity of
indicators to primary sediment source management
activities. Table 4-12 compares candidate indicators
with respect to several key indicator evaluation criteria.
In addition to the indicator's sensitivity to designated
uses and sediment sources, key criteria include
practicality (relative ease of using the indicator), cost to
collect and interpret information, track record (degree of
productive experience using this indicator), public
understanding, and knowledge of reference conditions
(whether reference condition values are available from
comparable studies or literature sources). Table 4-13
considers the relative utility of available indicators with
respect to hydrologic, geomorphic, geologic,
topographic, and soil considerations. Indicator selection
requires careful consideration of the unique mix of
issues, opportunities, and characteristics present in each
watershed. Analysts are encouraged to use this
information as the starting point in an iterative process
and to consult key references and local experts in the
final selection of indicators.
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Protocol for Developing Sediment TMDLs
Table 4-7. Examples of in-stream and hillslope targets, allocations, and implementation measures
Indicators/ Targets
Allocations
Implementation Measures
Instream: =
• =Median particle size >12 mm=
•=<15% fines <0.85 mm=
Hillslope: =
• =Attain < 3 miles roads with erosion^
potential per mi2 study area=
Landowner 1: =
• =Reduce erosion-prone road mileage by 12=
miles=
Landowner 2: =
• =Reduce erosion-prone road mileage by 5 =
miles=
Landowner 1:=
• No new roads=
• Retire 5 miles of existing road=
Landowner 2:=
• Retire 2 miles of existing road=
• Retrofit 15 stream crossings^
Instream: =
•=V* < 0.2 =
•=>50 redds per mile=
Hillslope: =
• =Attain < 10% actively eroding^
streambanks=
Reduce length of eroding banks by=
Tributary 1:25%=
Tributary 2: 5%=
Tributary 3:10%=
Tributary 1: stream and bank restoration project=
Tributary 2: new riparian plantings and=
installation of stock watering tanks=
Tributary 3: new riparian fencing=
4. What are appropriate target values for the
chosen indicators?
For each numeric indicator used in a TMDL, a desired
or target condition needs to be established to provide
measurable goals and a clear linkage to water quality
standards attainment. Target values for some indicators
might already have been established through state water
quality standards (e.g., for turbidity). This is usually not
the case for indicators used in sediment TMDL
development. There are a variety of additional
mechanisms to determine appropriate target values. All
of the methods for setting target values require an
interpretation of what constitutes impaired versus
unimpaired conditions. In many cases this
determination is subjective (e.g., what level offish
habitat quality or water clarity is equated to "full
support" of designated uses?). Regardless of the
method used to establish the indicator values, it is
important to solicit input from as many stakeholders as
possible, including the public and regulatory agencies.
Stakeholder input is an important component of the
Watershed Approach (USEPA, 1996b), and it can be
particularly useful for interpreting narrative standards.
For example, in a stream designated for support of a
Table 4-8. Advantages and disadvantages of riparian and hillslo
ie indicators
Advantages
Disadvantages
Directly address key sources of concern (e.g., streambanks, roads, or=
timber harvest areas).=
Address key mitigating factors that may limit sediment delivery to streams=
(e.g., riparian buffers).=
Facilitate goal setting for large woody debris recruitment, a key factor in the=
maintenance of healthy stream conditions in many watershed types.=
Build connections with source analysis, which are critical to TMDL=
developments
Relatively easy to understand and measure (e.g., buffer width). =
Help address difficulty of linking sources to in-stream impacts by providing=
intermediate indicators. =
Usually do not have to be measured more than annually to yield useful=
informations
Quantitative indicators of this type (e.g., woody debris and=
bank stability) have not been widely demonstrated or applied. =
Setting desired conditions for these indicators would be=
difficult because some are not widely used as quantitative=
indicators. =
The linkage of upslope and riparian indicators to in-stream=
designated or existing use conditions has not been clearly=
established in most of the country (e.g., disturbance=
indicators). =
Some of these indicators (e.g., bank stability and woody=
debris) are relatively difficult and time-consuming to measure,
although they might not need to be measured often. =
First Edition: October 1999
4-13
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Identification of Water Quality
Sediment-^
Impaired =
Waterbodyx
Lake or Reservoir=
Aquatic Life=
Recreation =
Water Supply
Most
Sensitive =
Designated
Use
Aquatic Life = Recreation Water Supply= =
1. Biological 1. Turbidity/suspended
2. Substrate composition sediment
3. Channel structure 2. Secchi depth
4. Interstitial dissolved 3. Bottom deposit depth
oxygen
1. Turbidity/suspended
sediment
2. Channel structure
1. Biological
2. Turbidity/suspended
sediment
3. Secchi depth
4. Bottom deposit depth
1. Turbidity/suspended 1,
solids
2. Channel structure 2.
3. Substrate composition
Turbidity/suspended
solids
Bottom deposit depth
Figure 4-2. Guidelines for selecting indicators based on waterbody type and several designated uses.
cold water fishery, a biological indicator aimed at
assessing the health and diversity of the fish population
could be refined into a quantitative target based on
stakeholder consensus as to what constitutes a
sufficiently viable fishery.
Factors for establishing target conditions
Degree of experience applying the indicator(s) in the area
or in similar settings
Where local experience has been gained in applying
sediment indicators, it is often possible to identify target
conditions through analysis of historical conditions or
reference stream conditions in relatively high quality
parts of the watershed. Where less local or directly
analogous experience is available, it is appropriate to
establish more conservative targets.
Variability of conditions in the watershed
The larger the study area for the TMDL and the more
heterogeneous the waterbody characteristics in the
watershed, the more important it will be to consider
establishing multiple target conditions for the TMDL. It
might be useful to stratify the targets based on spatial
distinctions (e.g., key habitat areas vs. nonhabitat areas,
main stems vs. tributaries, or aggrading vs. degrading
reaches). Similarly, it might be necessary to account for
seasonal and interannual variations in setting target
conditions.
Margin of safety considerations
Determination of the margin of safety in the
establishment of target conditions should consider
provisions for monitoring and adaptive management.
Factors that should be considered in defining the margin
of safety include the expected accuracy or reliability of
the indicator for the local designated use and the degree
to which designated uses are rare or valuable.
4-14
First Edition: October 1999
-------
Protocol for Developing Sediment TMDLs
Table 4-9. Considerations in selecting indicator(s) for large watersheds
Resources Available
for Future Monitoring
Present or Future Resources Available to Develop TMDL
Low
Medium
High
None=
Biological indicator with very high=
margin of safety (MOS) =
Sediment or biological indicator witn=
analysis linkage to BMPs and high=
MOS=
Allocate resources for future=
monitoring and do less complex^
TMDL analysis^
Low=
Single sediment, substrate, or=
biological indicator with high MOS=
and annual monitoring^
Sediment or substrate indicator + =
biological or upland indicator with=
analysis linkage to BMPs, moderate^
MOS, and annual monitoring =
At least two indicators (per=
medium), extensive analysis of=
control/restoration effectiveness, =
moderate MOS, and annual =
monitoring. =
Multiple "target" points possible. =
Medium=
Sediment or substrate indicator + =
biological or upland indicator with=
high MOS and more frequent=
monitor! ng=
Sediment or channel^
indicator(substrate or other) + =
biological or upland indicator with=
analysis linkage to BMPs, moderate^
MOS and more frequent monitoring.
Multiple "target" points possible. =
At least two indicators (per=
medium), extensive analysis of=
control/ restoration effectiveness, =
moderate MOS and more frequent=
monitoring. =
Multiple "target" points possible. =
Watershed model as analytical tool.=
High=
Sediment or substrate indicator + =
biological or upland indicator with=
high MOS and frequent monitoring.
Multiple "target" points probable. =
Multiple indicators appropriate, =
including channel and biological^
metrics in multiple locations. =
Moderate to low MOS and frequent=
monitoring. Multiple "target" points=
probable. Watershed model as=
analytical tool. =
Multiple indicators appropriate, =
including channel and biological^
metrics in multiple locations. Robust=
analysis of linkage to BMPs. Low=
MOS and frequent monitoring. =
Multiple "target" points appropriate. =
Watershed model as analytical tool.=
Water quality standards
Several states have adopted numeric criteria for
suspended sediment concentrations or turbidity that can
be used as targets if the indicators are relevant to the
TMDL. Usually, these standards are set as either
absolute thresholds
(e.g., turbidity no
greater than 25 NTU)
or relative targets
(e.g., no turbidity
increases greater than
10 percent or 5 NTU
above background
conditions). These
standards are not
always easy to apply
given the spatial and temporal variability of suspended
sediment and turbidity, but they are related to designated
use concerns and often provide a ready basis for making
the required TMDL linkage to attainment of water
quality standards.
Information Sources for
Determining Indicator
Target Values
Water quality standards
Reference sites
Literature values
User surveys
Functional equivalents
Best professional judgment
Comparison to reference sites
One method for establishing target values is comparison
to reference sites—waterbodies that are representative
of the characteristics of the region and subject to
minimal human disturbance. Where narrative standards
are involved, assessing environmental conditions in
receiving waters often depends on comparing observed
conditions to expected conditions. This comparison is
typically done by comparing data collected from
impaired sites to similar data from the same sites
collected before impairment and/or from one or more
appropriate reference sites where designated uses are in
good condition. Conditions at the reference site (e.g.,
suspended sediment concentrations) can then be
interpreted as approximate targets for the indicators at
the impaired site. A disadvantage to this approach is
that it might not aid in determining an impairment
threshold. Reference sites may represent the completely
unaffected state, a relatively unaffected state, or
increasing degrees of existing impact.
First Edition: October 1999
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Table 4-10. Sensitivity of indicators to designated uses
Indicator
SEDIMENT=
Suspended =
Turbidity=
CHANNEL CHARACTERISTICS^
Bed Material Size=
GEOMORPHOLOGY MEASURES^
Width/Depth Ratio =
Cross Sections^
BankStability=
Pool Measures^
WOODY DEBRIS =
BIOLOGICAL INDICATORS^
Invertebrates^
Fish Counts =
Designated Uses
Domestic Water
Supply
1 =
1 =
3 =
4 =
4 =
3 =
4 =
4 =
3-4 =
4 =
Agricultural Water
Supply
1-2 =
2 =
4 =
4 =
4 =
4 =
4 =
4 =
3-4 =
4 =
Hydroelectric
Reservoir Storage
1 =
2 =
4 =
4 =
4 =
4 =
4 =
4 =
4 =
4 =
Recreation
1-2 =
1-2 =
3 =
2-3=
2-3=
1-2 =
2-3=
2 =
3 =
1 =
Cold-Water
Habitat
1-2 =
2-3=
1-2 =
1-2 =
1-2 =
1-2 =
1-2 =
1 =
1 =
1 =
Warm-Water
Habitat
1-2 =
1-2 =
1-2 =
2-3=
2-3=
1-2 =
1-2 =
1 =
1 =
1 =
KEY: 1 btee highly sensitive to indicator in most cases=
2= Use closely related and somewhat sensitive in most cases=
3= Use indirectly related and not very sensitive=
4= Use largely unrelated to indicator=
Source: MacDonald etal., 1991 =
-------
Table 4-11. Sensitivity of indicators to sediment sources
Indicator
SEDIMENT=
Suspended =
Turbidity=
CHANNEL CHARACTERISTICS^
Bed Material Size=
Embeddedness=
GEOMORPHOLOGY MEASURES^
Width-Depth Ratios=
Cross Sections^
BankStability=
Pool Measures^
WOODY DEBRIS =
BIOLOGICAL INDICATORS^
Invertebrates^
Fish Counts =
Potential Sediment Sources
Roads
1-2 =
1-2 =
1 =
1-3 =
2-3 =
2-3 =
2-3 =
1-2 =
3-4 =
1 =
1 =
Timber Harvest
2-3 =
2-3 =
1-2 =
1-3 =
2-3 =
2-3 =
1-2 =
1-3 =
1 =
1 =
2 =
Grazing
1-3 =
1-3 =
2-3 =
2-3 =
1-2 =
1-2 =
1 =
2 =
3-4 =
2 =
2 =
Crop
Agriculture
1-2 =
1-2 =
1-3 =
2-3 =
2 =
2 =
1-2 =
1-2 =
3-4 =
1 =
1-3 =
Urban Runoff
1-3=
1-2 =
2-4 =
2-4 =
1-3=
1-3=
1-3=
1-3=
2-3=
1 =
1-2 =
Construction
1 =
1 =
1-3 =
1-3 =
1-3 =
1-3 =
2-3 =
1-2 =
4 =
1 =
1-2 =
Sand and Gravel/
Placer Mining
1 =
1 =
1 =
1-3 =
1-2 =
1-2 =
2-3 =
1-2 =
3=
1-2 =
2-3 =
Handlock
Mining
3=
3=
3-4 =
3-4-
-4 =
2-4 =
2-4 =
2-4 =
3-4 =
1 =
1 =
KEY: 1 Erectly affected and highly sensitive=
2=Use closely related and somewhat sensitive=
3=Use indirectly related and not very sensitive=
4=Largely unaffected and insensitive=
Source: MacDonald etal., 1991 =
-------
Table 4-12. Comparison of sediment-related indicators for TMDL development
Indicator
SEDIMENT=
Suspended =
Turbidity=
CHANNEL CHARACTERISTICS^
Bed Material Size=
Embeddedness=
GEOMORPHOLOGY MEASURES^
Width/Depth Ratio =
Cross Sections^
Bank Stability =
Pool Measures^
WOODY DEBRIS =
BIOLOGICAL INDICATORS^
Invertebrates^
Fish =
Practicality
M-L=
H-M =
H =
H =
M =
M =
M-L=
H-M =
M-L=
M =
M =
Cost
H-M =
M =
L=
L=
L-M =
L-M =
M =
L-M =
M =
M-H =
M-H =
Track Record
G-F=
G-F=
G =
F=
F=
G-F=
F=
G =
F=
G-F=
G-F=
Public
Understanding
G-F=
G =
F=
F=
F-P =
F=
G =
G-F=
G =
G-F=
G =
Knowledge of
Reference
Conditions
G-F=
G-F=
G-F=
F-P =
G-F=
G-P =
F-P =
F=
F=
F=
F=
Comments
2,3 =
2 =
1 =
1 =
1 =
3 =
KEY: H= High =
M Medium =
L bew =
G= Good=
F Pair =
p= poor=
1 = Bestforfish designated or existing use=
2= Best for water supply=
3= Monitoring difficult=
-------
Table 4-13. Utility of sediment-related indicators for different environmental settings
Indicator
SEDIMENT=
Suspended =
Turbidity=
CHANNEL CHARACTERISTICS^
Bed Material Size=
Embeddedness=
Pool Measures^
GEOMORPHOLOGY MEASURES^
Channel Geometry^
BankStability=
WOODY DEBRIS =
BIOLOGICAL INDICATORS^
Invertebrates^
Fish =
Environmental Setting
Geology
Granitics
2 =
2-3 =
1 =
1 =
1 =
1-2 =
2 =
1-2 =
2 =
1-2 =
Basalts
2 =
2-3=
1-2 =
2 =
1-2 =
1-2 =
2 =
1-2 =
2 =
2 =
Sedimentary
2 =
1-2 =
1-2 =
2-3 =
1-2 =
1-2 =
2 =
1-2 =
2 =
2 =
Marine
2 =
2-3 =
1-2 =
2-3 =
1-2 =
1-2 =
2 =
1-2-
1-2 =
1-2 =
Glacial
1-2 =
2-2 =
2 =
2 =
1-2 =
1-2 =
2 =
1-2-
2 =
2 =
Topography
Low Slope
2 =
2 =
2 =
2-3 =
2-3 =
2-3 =
1-2 =
2-3 =
1-2 =
2-3 =
Steep
1-2 =
1-2 =
1-2 =
1-2 =
1 =
1-2 =
1-2 =
1-2 =
1-2 =
2 =
Over
Steep
2-3 =
2-3 =
1-2 =
1-2 =
1 =
2 =
1-2 =
1-2 =
1-2 =
2 =
Soils
More
Clays
2 =
1 =
1-2 =
2 =
2 =
2 =
2-3=
2 =
2-3=
More
Sandy
2 =
2-3 =
2-3 =
1-2 =
1-2 =
2 =
2-3 =
2 =
2 =
KEY: 1= SJearly useful; extensive record demonstrating sensitivity in this setting=
2 =Sometimes useful; limited or mixed record of use in this setting=
3= Probably not very useful; no or poor record of use in this setting=
-------
Table 4-13. Utility of sediment-related indicators for different environmental settings (continued)
Indicator
SEDIMENT=
Suspended =
Turbidity=
CHANNEL CHARACTERISTICS^
Bed Material Size=
Embeddedness=
Pool Measures^
GEOMORPHOLOGY MEASURES^
Channel Geometry^
BankStability=
WOODY DEBRIS =
BIOLOGICAL INDICATORS^
Invertebrates^
Fish =
Environmental Setting
Hydrology
Perennial
Flow
1-2 =
1-2 =
1-2 =
2 =
1-2 =
2 =
2 =
1-2 =
1 =
1-2 =
Intermittent/
Ephem. Flow
2-3=
2-3=
2 =
2-3=
2 =
2 =
2 =
2-3=
1-2 =
2-3=
Dom. by Major
Events
3=
3=
1-2 =
2 =
1-2 =
1-2 =
2 =
2-
1-2 =
2 =
Dom. by Frequent
Events
1-2 =
1-2 =
2 =
2 =
2 =
1-2 =
1-2 =
2-3=
1-2 =
2 =
Geomorphology
Sandy Bottom
1-2 =
1-2 =
3 =
3 =
2-3=
2 =
1-2 =
2-3=
2 =
2 =
Gravel/Cobble
2-3 =
2-3 =
1 =
1-2 =
1-2 =
1-2 =
2 =
1-2 =
1-2 =
1-2 =
KEY: 1= SJearly useful; extensive record demonstrating sensitivity in this setting=
2= Sometimes useful; limited or mixed record of use in this setting=
3= Probably not very useful; no or poor record of use in this setting=
-------
Protocol for Developing Sediment TMDLs
Selection of an appropriate reference site should reflect
a clear understanding of the overall system. The
reference sites may be within the study watershed or in
nearby or even distant watersheds, and they should be
selected based on careful comparison of key watershed
characteristics and processes (e.g., geology, soils,
topography, land use). In general, though, the most
useful reference sites are located within the watershed,
relatively near the point where impact is expected.
Reference sites may be difficult to find.
User surveys
Several states have used user surveys to determine
indicator target values, especially in lakes and
reservoirs. This approach is especially useful when the
designated use of the waterbody is recreational.
Waterbody users can be questioned concerning their
perceptions of water quality conditions and the quality
of the recreational experience. Survey results can be
correlated with simultaneous water quality
measurements to establish target values at the border
between acceptable and unacceptable conditions. For
example, if 50 percent of those surveyed agree that their
aesthetic enjoyment of a lake is impaired when water
clarity diminishes to less than 40 feet (measured with a
Secchi disk), this value could represent a possible clarity
(Secchi disk) target value. The survey approach
recognizes that such an assessment of the overall water
quality of a waterbody is highly subjective and can vary
considerably by region.
Literature Values
Several TMDLs have included numeric targets based on
information from research studies of the relationship
between the selected sediment indicator(s) and the
beneficial use of concern. For example, the Garcia
River, California, TMDL included numeric targets for
fine sediments based on reviews of several research
publications that evaluated the fine sediment levels at
which salmonid survival began to diminish.
Indicator relationships
In some cases, information is available to identify target
conditions for indicators that are functionally related to
the indicators selected for TMDL analysis. For
example, in the Silver Creek, Arizona, demonstration
TMDL, suspended sediment was the indicator of choice
for the TMDL because of its usefulness in developing
sediment budgets and the availability of data. Using
available turbidity and suspended sediment data for
Silver Creek, the relationship between turbidity and
suspended sediments was evaluated through regression
analysis. Because a close linear relationship was
observed, the TMDL target for suspended sediment was
determined as a watershed-specific function of the
turbidity.
Best professional judgment
It is sometimes infeasible to develop numeric targets
based on the methods described above because adequate
information is not available or relationships between
designated uses and selected indicators are not well
understood. In this case, it may be feasible to develop
target values based on the best professional judgment of
resource professionals involved in TMDL development.
To ensure that these targets are defensible, analysts are
advised to
• Consult with multiple experts with local experience
rather than relying on a single opinion.
• Thoroughly document the thinking underlying the
target, including assumptions, related experience, or
other factors considered in identifying the targets.
• Remember that targets must be set at levels that are
believed to result in full support of the impaired
designated uses (i.e., water quality "improvements"
might be inadequate).
• Design the TMDL as a phased TMDL that includes
a monitoring plan to assess whether the numeric
targets are appropriate for the particular situation.
Methods for expressing numeric targets
The dynamic interactions between the multiple
watershed processes that affect sediment delivery and
impacts in many streams may make it difficult to
establish individual target conditions. In general,
sedimentation problem solving is more likely to succeed
if it strives to mimic the natural ranges of watershed
process behaviors, including extreme events, which
cause adverse sediment impacts on designated uses
(Bisson et al., 1997). In many watersheds it is
reasonable to expect substantial spatial and temporal
variability in sediment indicators. Where this is the
case, it might be appropriate to express target conditions
for the watershed to account for expected variability in
First Edition: October 1999
4-21
-------
Identification of Water Quality
key watershed processes yet still provide measurable
goals for restoration and protection of designated or
existing uses overtime.
There may be resistance to developing "hard" targets if
it is perceived that they will limit land management
flexibility without having an adequately robust
analytical basis. Careful design of targets will help
ensure that the results are not perceived as arbitrary;
however, significant uncertainty regarding the precision
of the targets may exist in the best of circumstances. In
such circumstances, it might be appropriate to frame the
numeric indicators and associated target conditions as
testable hypotheses that will be reviewed and revised as
necessary over time. The TMDL process provides for
the inclusion of adequate margins of safety to account
for such uncertainties. If management flexibility is
reduced through the application of numeric targets, there
may be some incentives to conduct follow-up
monitoring and review to determine if targets are
appropriate or if they should be revised based on new
information.
In addition, it might make sense to establish both interim
and final numeric targets for the TMDL. The interim
targets may represent target levels believed to be
reasonably attainable in relatively short periods of time.
The final targets are set at levels at which designated
uses are protected and the actual desired condition for
the resource is represented. Under no circumstances do
interim targets replace final targets set at levels
necessary to attain water quality standards. Using both
interim and final targets is particularly well suited to
situations in which
• It might take many years to attain final targets and
water quality standards because of the slow response
of waterbodies to land use changes.
• Analysts and stakeholders want clearer short-term
measures to guide near-term implementation and
evaluate TMDL effectiveness (i.e., are we on the
right track?).
• The analytical basis for final target levels is weak.
Table 4-14 summarizes several possible approaches to
establishing numeric target levels for TMDLs. In
general, the objective in establishing target conditions is
to articulate the condition(s) for the TMDL indicators
that represents fully supported designated or existing
uses. Analysts should be creative in establishing ways to
achieve this objective while ensuring that the TMDL
approach is based on sound scientific principles.
Analysts developing targets for TMDLs for large
watershed areas should consider the potential need for
different targets for different areas or time frames. To
develop targets that address large study areas, several
approaches are available:
• Different target values can be established for
multiple measurement points (e.g., key habitat areas,
mouths of several tributaries, or areas where land
uses change).
• A different target may be set at a key watershed
outlet, critically vulnerable or sensitive area, or
other representative waterbody area.
• A range of values can be applied in the study area.
5. How do the existing values compare to the
target values?
The last step in establishing numeric targets is to
compare existing and target conditions for indicators
selected for the TMDL. This key step should not be
overlooked because it provides critical information that
can be used to evaluate whether watershed management
and restoration actions are likely to be effective in
attaining water quality standards. Although the
comparison might appear easy to make, in practice some
indicators are not as amenable to comparison as others.
The best approach to making comparisons is influenced
by the types of indicators selected, the approach to
articulating the target condition(s) for each indicator, the
spatial and temporal scales selected for the TMDL, and
the methods used to link numeric targets to other TMDL
elements. This section briefly reviews factors to
consider in making condition comparisons and discusses
some methods for making reasonable comparisons.
Key factors to consider in comparing numeric
targets with existing conditions
Variability in conditions within study area
If existing conditions for the selected indicators vary
substantially within the study area or at different times
of the year, the comparison method should be able to
account for spatial or temporal differences.
4-22
First Edition: October 1999
-------
Protocol for Developing Sediment TMDLs
Table 4-14. Methods for expressing numeric targets for TMDLs
Method
Absolute values or=
thresholds^
Conditional values=
Functional values=
Relative values =
Ranges of values=
Index values =
Example Application
• No more than 15% fine sediment > 0.85 mm in riffles (Garcia River, CA) =
• No net increase in sediment discharge above background (Mattole River, CA) =
• Depth of key refuge area no less than 6 feet deep (Newport Bay, CA) =
• Maximum 10% increased turbidity when background >50 NTU (AZ WQS) =
• 20% long-term reduction in average annual in-stream load compared to 1995 value (Deep
Creek, MT) =
• Suspended sediment load as function of flow (target is slope of TSS-flow regression equation) (Deep Creek, MT) =
• Average turbidity no greater than that measured simultaneously at paired reference stream
(Caspar Creek, CA) =
• 1 ,000-3,000 annual returning spawning Chinook salmon=
• Biological indicator index no greater than state index of biological integrity level for "full use support" (Waimanalo=
Stream, HI [draft]) =
• Acreages of aquatic habitat of different types in wildlife refuge (Newport Bay, CA) =
Level of accuracy needed in the condition comparison
Analysts should consider how the comparison will be
used to support the TMDL. In TMDL projects where
source reductions will be determined by comparing
existing and target conditions, it might be more
important to make relatively accurate comparisons.
However, in cases where source allocations are based
partly or completely on other factors, the comparison
could be relatively rough.
Theoretical basis for change in the indicator
Analysts should understand how changes in the selected
indicators are expected to occur in the study area (i.e.,
what are the driving forces of change in the watershed
and how do these forces manifest themselves in the
selected indicators?).
Methods for comparing existing and target
conditions
Direct comparison of data for existing and target levels
for indicators selected for the TMDL provides the most
straightforward method for estimating sediment
reductions needed to attain water quality standards.
However, the analyst should be careful in making such
comparisons, particularly if there is a strong analytical
basis for assuming a nonlinear pattern of change over
time in the indicators. Statistical analysis tools
(especially regression analysis) are particularly useful
for comparing existing and target conditions in many
settings. (See USEPA, 1997b, for additional information
on regression analysis for nonpoint source assessment.)
In addition, averaging existing conditions for indicator
values across the entire study area is inappropriate in
many settings because this practice can obscure
important differences in individual locations and make it
more difficult to identify source-to-in-stream impact
relationships. Table 4-15 presents a summary of
approaches for comparing existing and target conditions.
Note that these methods are not mutually exclusive.
In cases where the analytical uncertainty precludes
direct comparisons of existing and target conditions,
other approaches are more prudent. For example, a
TMDL could discuss the percentage of land area or
stream miles exceeding a TMDL indicator target level
rather than directly discussing the magnitude of the
exceedance. However, it is often useful to describe the
estimated magnitude of the problem to facilitate
development of allocations.
6. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the water quality
indicators and target values step, an approvable TMDL
will need to include the following information:
1. Identification of the pollutant for which the
TMDL is being established and quantification of
the maximum pollutant load that may be present
in the waterbody and still ensure attainment and
maintenance of water quality standards; and
First Edition: October 1999
4-23
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Identification of Water Quality
Table 4-15. Methods for comparing existing and target conditions for numeric targets
Methods and Rationale
Direct comparison of loads:
Best where load estimates and targets are reliable^
Percent reduction comparisons:
Best where absolute load estimates are rough or non-load-based=
indicators are used=
Factor comparisons:
Best where relationship between indicators and sources is not=
well established^
Indirect comparisons:
Best where indicator changes in response to driving forces that=
are nonlinear or poorly understood^
Examples
Existing (10 tons/year) - target (5 tons/year) = 5 ton/year needed reduction^
Existing (—10 tons/year) - target (~5 tons/year) = ~ 50% needed reduction^
Existing turbidity levels (75-125 NTU); target level (50 NTU); therefore, existing^
levels exceed target level by about a factor of 2=
Existing bioassessment index level = 30; target = 75. Comparison indicates^
waterbody is severely impaired but provides no basis for estimating needed =
sediment load reductions^
2. Identification of the amount or degree by which
the current pollutant load in the waterbody
deviates from the pollutant load needed to attain
or maintain water quality standards.
RECOMMENDATIONS FOR IDENTIFICATION OF
WATER QUALITY INDICATORS AND TARGET
VALUES
• If available, the numeric standard established in
water quality standards should be used as the TMDL
indicator and target value.
• Where no applicable numeric standard exists,
establish a target value through a combination of
literature values, reference waterbodies, additional
monitoring, stakeholder input, and the narrative
water quality standard. Document all assumptions
made in establishing the target.
• The chosen indicator should be sensitive to
geographic and temporal influences.
• Consider how many indicators are needed; single
indicators are appropriate for some situations (e.g.,
turbidity threshold for drinking water source), but
some watersheds might require the use of multiple
indicators to account for complex processes or a
lack of certainty regarding individual indicator
effectiveness.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
Chapman, D.W., and K.P. McLeod. 1987. Development
of criteria for fine sediment in the Northern Rockies
Ecoregion. EPA 910/9-87-162. U.S. Environmental
Protection Agency, Washington, DC.
MacDonald, L., A.W. Smart, and R.C. Wissmar. 1991.
Monitoring guidelines to evaluate effects of forestry
activities on streams in the Pacific Northwest and
Alaska. EPA 910/9-91-001. U.S. Environmental
Protection Agency, Region 10, Nonpoint Source
Section, Seattle, WA.
Peterson, N.P., A. Henry, and T.P. Quinn. 1992.
Assessment of cumulative effects on salmonid habitat:
Some suggested parameters and target condition.
Prepared for the Washington Department of Natural
Resources and The Coordinated Monitoring, Evaluation
and Research Committee, Timber Fish and Wildlife
Agreement. March 2.
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Source Assessment
Objective: Characterize the types, magnitudes, and
locations of sources of sediment loading to the
waterbody.
Procedure: Compile an inventory of all sources of
sediment to the waterbody. Sources may be identified
through assessment of maps, data, and reports and/or
field surveys. It is likely that a combination of
techniques will be needed depending on the complexity
of the source loading and watershed delivery processes.
After an inventory has been compiled, monitoring,
statistical analysis, modeling, or a combination of
methods should be used to determine the relative
magnitude of source loadings, focusing on the primary
and controllable sources of sediment.
OVERVIEW
The source assessment is needed to evaluate the type,
magnitude, timing, and location of loading of sediment
to a waterbody. A number of factors can be considered
in conducting the source assessment. These factors
include identifying the various types of sources (e.g.,
point, nonpoint, background), the relative location and
magnitude of loads from the sources, the transport
mechanisms of concern (e.g., runoff vs. mass wasting),
the routing of the sediment through the waterbody, and
the time scale of loading to the waterbody (i.e., duration
and frequency of sediment loading to receiving waters).
Of particular concern is what loading processes cause
the impairment of the waterbody of concern. The
evaluation of loading is typically performed using a
variety of tools, including existing monitoring
information, aerial photography analysis, simple
calculations, spreadsheet analysis using empirical
methods, and a range of computer models. The
selection of the appropriate method for determining
loads is based on the complexity of the problem, the
availability of resources, time constraints, the
availability of monitoring data, and the management
objectives under consideration. It is usually
advantageous to select the simplest method that
addresses the questions at hand, uses existing
monitoring information, and is consistent with the
available resources and time constraints for completing
the TMDL.
This chapter describes different types of sources,
identifies procedures for characterizing loadings, and
introduces a process for tool selection for TMDL
development. The source assessment process endorsed
in this protocol relies on many of the principles
associated with development of sediment budgets, as
described in Reid and Dunne (1996).
A sediment budget is an "accounting of the sources and
disposition of sediment as it travels from its point of
origin to its eventual exit from a drainage basin" (Reid
and Dunne, 1996). Sediment budget analyses are useful
both for the conceptualization of sediment problems and
as a tool for estimating sediment loadings. Full-scale
sediment budgeting provides an inventory of the sources
of sediment in a watershed and estimates sediment
production and delivery rates from each source.
Component processes are identified, and process rates
are usually evaluated independently of one another. All
of the relevant processes are quantified, including
hillslope delivery processes (creep, mass movement),
channel sources (e.g., bank collapse), in-channel storage,
bedload and suspended sediment transport capacity, and
net sediment yield from the basin (Figure 5-1). If the
effects of particular land use activities on each process
are known, the overall influence of a suite of existing or
planned land use activities can be estimated. Sediment
Key Questions to Consider for Source Assessment
1. What sources contribute to the problem?
2. How should sediment sources be grouped?
3. What technical and practical factors affect selection of
methods?
4. What is the appropriate source assessment method?
5. How do estimated source contributions compare with natural
or background levels?
6. How can the source assessment be described for TMDL
submittal?
7. What changes does the proposed rule speak to?
budgeting is particularly effective for evaluating
nonequilibrium situations, where channel loads do not
necessarily represent hillslope erosion rates. The time
and resources needed to develop a full sediment budget
will vary depending on the geographic scale and
required degree of accuracy, but it should be possible to
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Figure 5-1. Sedimentation process
develop rough sediment budgets
adequate for TMDL purposes (Reid
and Dunne, 1996).
Analysts are encouraged to
consider developing sediment
budgets because they can be used
to connect excess sediment load at
a point of impact to sources of
sediment generation and can thus
be used to target load reductions.
The analysis of sediment transport
rates included in full sediment
budgets is particularly helpful in
evaluating how changes in stream
structure (e.g., width-depth ratios)
might respond to changes in
sediment source management or
restoration activities. Sediment
budgets can usually be developed through (1) single
models that estimate erosion for multiple source
categories and assess in-stream processes and fate or
(2) a combination of different source estimation and fate
analysis methods for different sources or steps in
sediment movement through the system (Reid and
Dunne, 1996). It is important to note that detailed
sediment budgets are not needed for all sediment
TMDLs. For purposes of TMDL development, an
estimation of the major sources of sediment might be
adequate. This estimation can be done in several ways,
ranging in complexity and intensity from interpretation
of aerial photographs to on-the-ground surveys. Partial
sediment budgets identify sediment sources and provide
gross estimates of sediment delivery to waterbodies.
This level of detail allows prioritization of erosion
control efforts.
KEY QUESTIONS TO CONSIDER FOR SOURCE
ASSESSMENT
1. What sources contribute to the problem?
The development of a TMDL includes the identification
of the various sediment sources causing the impairment
in the listed waterbody. Sediment sources typically fall
into one of the following categories:
Agriculture
Silviculture (logged or burned areas)
Rangeland
Hillslope
Channel
Channel Transport
Net Watersh ed Sedim ent Yield
Construction sites
Roads
Urban areas
Landslide areas
In-stream sources (e.g., stream or lake banks)
Sedimentation can be divided into the following discrete
processes:
Weathering and erosion (liberation of soil or rock
particles from the soil or rock matrix).
Hillslope delivery (movement of eroded material to
the waterbody, minus upslope storage).
In-stream transport (movement of sediment
downstream in the waterbody).
In-stream storage (long- or short-term retention of
sediments in the stream channel).
Discharge or yield (movement of sediments out of
the study watershed).
Land use changes and disturbances that cause increased
sedimentation rates can also cause significant changes in
watershed hydrology. For example, vegetation removal
and soil compaction can cause a variety of hydrological
changes, including changes in infiltration rates, runoff,
and stream baseflows (Black, 1991; Spence et al., 1996).
These hydrologic changes can increase stream
vulnerability to channel and bank erosion, stress
fisheries during high flows, and increase stream
temperatures during dry periods.
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Sample Source Assessment Framework
This general framework for sediment source assessment has proven
useful in several assessment projects. Be aware, however, that
specific method(s) used to estimate sources will depend on the
situation.
Step 1. Define the suspected sources.
Step 2. Gather background information.
Step 3. Stratify the study area into areas of similar characteristics
to simplify source assessment in each area.
Step 4. Interpret existing information and data (e.g., sequential air
photography) to identify key sediment source areas and, in
some cases, to develop initial source estimates.
Step 5. Develop initial sediment source flowcharts.
Step 6. Conduct field work to verify initial estimates.
Step 7. Analyze data to develop or revise sediment source
estimates.
Step 8. Check results for reasonableness based on comparison
with similar areas (if feasible).
Step 9. Present loading estimates for major sources and, if
necessary, describe sediment transport and net yield from
study areas.
(Adapted from Reid and Dunne, 1996).
Although it is beyond the scope of this protocol to
address hydrologic changes associated with land
disturbance, TMDL analysts should consider these
effects when designing TMDLs. Refer to Reid (1996),
Dunne and Leopold (1978), Satterlund and Adams
(1993), Washington Forest Practices Board (1994), and
Regional Ecosystem Office (1995) for additional
guidance.
2. How should sediment sources be grouped?
Because sediment production is usually associated with
diffuse nonpoint sources, sediment source assessment
for TMDL development is often focused on source
groupings rather than individual land parcels. The
grouping approach is used because a parcel-by-parcel
analysis is usually infeasible or extremely expensive and
is not needed in all but the smallest study areas. For
many sediment TMDLs, load allocations will be
presented as "gross allotments," as outlined in the
TMDL regulation. The gross allotments are considered
appropriate when data and techniques for predicting the
loading are limited. Most sediment analysis methods
discussed in this protocol are based on source
categories. The grouping of sediment source categories
should be carefully considered in the source assessment
stage of TMDL development. The appropriate selection
of the various source categories will facilitate
completion of the subsequent linkage analysis and
allocation steps. Sources can be grouped by erosion
process, controllable versus uncontrollable sources,
ownership, subbasin, geology, or a combination of
factors. The source categories should account for the
relative magnitude of the loads, the potential
management options, and the capabilities of the
assessment and modeling tools under consideration.
The advantages and disadvantages of different source
groupings are summarized in Table 5-1.
3. What technical and practical factors affect
selection of source assessment methods?
A range of sediment source estimation methods are
available to assist in TMDL development. Some
methods provide estimates of sediment yield for entire
watersheds whereas others (e.g., the Revised Universal
Soil Loss Equation, or RUSLE) provide average annual
soil loss at the field scale. However, because sediment
sources vary tremendously in character and importance,
even within individual study areas, it might be necessary
to use different methods to evaluate individual sources.
The selection of the most appropriate method or
methods depends on the unique characteristics of
sources in the study area, how the information will be
linked to other TMDL elements, and, ultimately, how
sediment controls or restoration actions will be used to
address the problem.
Scientific and technical considerations
Key technical factors that should be considered in the
selection of methods include the proximity of key
sources to waterbodies (and critical designated use
areas), available data and information to support in-
stream sediment storage and transport analysis, the
dominant types of erosion processes and the methods
available for estimating hillslope storage and delivery
ratios, the timing and variability of erosion and sediment
transport processes, the attenuation of sedimentation
rates in response to recovery from disturbance, and the
degree of natural sedimentation. Scientific factors to
consider when selecting source estimation methods
include the following.
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Table 5-1. Advantages and disadvantages of sediment source grouping methods
Method
Advantages
Disadvantages
By Source Category
(e.g., roads, streambanks, forestland,
rangeland)
Supports use of different source assessment
methods for different sources, which might
be more sensitive to key watershed
processes which affect that source.
Supports GIS-based analysis methods that
rely on stratification of source areas into land
cells of unique characteristics.
Supports a differential focus of resources on
key sources, yielding more precise estimates
for key sources.
Allows allocation by category, which might
make it easier to evaluate feasibility of
controls and associated allocations.
Promotes stakeholder acceptance; helps
avoid the perception of "blame."
Different analysis methods used to
evaluate individual source types might be
difficult to meld and could complicate the
assessment of uncertainty of cumulative
analysis.
Might lead analysts to ignore key sources
based on erroneous preconceptions
concerning which source categories are
most important.
Might not lead to easy allocations to
different landowners or responsible
agencies.
By Subbasin or Geology
Allows use of sediment budgeting methods
that evaluate sediment loading and yield as a
function of suspended/ bedload sediment and
flow by tributary.
Helps target control efforts in key problem
areas, especially where most key sources are
located in a few subbasins or unstable
geologies.
Enables spatial association of key sources
with the most vulnerable areas (e.g., key
habitat areas).
Builds stakeholder support by helping to
avoid the perception of blame.
Might be useful only in estimating
sediment source contributions for large
areas, which could impede identification of
highest-priority sources.
Often ineffective in assessing source
issues where designated use concerns are
located near headwaters in tributaries, and
might result in missing key source
problems.
If areas are too large, this method might
not be capable of detecting significant
sediment flux changes or effects,
especially within short time intervals.
By Parcel
(e.g., by individual landowner or even subset
of ownership)
Enables direct allocations to responsible
landowners, thereby simplifying the task of
deciding who needs to do what.
Facilitates use of much readily available
information on sources often organized by
land owner in GIS framework.
Promotes "trading" solutions by clarifying
relative inputs from different ownerships.
Facilitates use of regulatory mechanisms
(e.g., local, state, or federal discharge
permits; timber harvest permits; grazing
allotments; or zoning programs) to ensure
that needed controls are implemented.
Potential creation of the appearance of
"locking in" allocations and removing
flexibility for landowners to negotiate the
most cost-effective allocation schemes.
Land ownership boundaries often follow
legal boundaries without regard for
geographic distinctions between land
characteristics, thereby complicating
source assessment on a watershed basis.
Potential perception that blame is being
cast for sedimentation problems, which
often diverts productive attention from
problem solving.
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Proximity of key sources to waterbodies
If bank erosion is considered a major and immediate
threat, it might be appropriate to focus more effort on
these sources and less effort on sources located farther
up slope. Alternatively, it might be appropriate to make
simplifying assumptions for the major sources, such as
assuming that most or all eroded sediment from these
sources reaches the waterbody.
Accuracy
Accuracy is important when estimates of how much
eroded sediment actually reaches waterbodies within the
assessment time frames (delivery ratios)are needed.
Methods for estimating sediment delivery ratios include
empirical estimates (see Reid, 1996, and Reid and
Dunne, 1996); deriving delivery ratios as a unique
function of key factors influencing sediment discharge
(e.g., slope and source distance from the waterbody
[Clarke and Waldo, 1986; Louisiana-Pacific
Corporation, 1996]); and extrapolation from delivery
ratios developed in other watersheds with similar
characteristics. Method accuracy varies widely. Some
methods are capable of producing estimates that are
accurate to within a factor of 2 or so (Reid and Dunne,
1996). Several more resource-intensive estimation
models are believed to be accurate to within 20 to 30
percent following calibration and validation (e.g., HSPF
and some other relatively complex models that estimate
long-term annual loads). Most modeled estimates may
be accurate to only within 50 to 100 percent (e.g.,
monthly or daily estimates). Other methods that focus
on specific sources of concern (e.g., Weaver and
Hagens[1996] road assessment method) are capable of
yielding relatively accurate estimates of potential future
erosion volumes. Simpler, screening-level methods
(e.g., models that apply simple default erosion rates or
regression relationships) are believed to be capable of
yielding order-of-magnitude estimates of total sediment
production along with estimates of relative inputs from
different sources.
Magnitude of source type
Methods should be focused on areas where designated
uses of concern are localized (e.g., spawning areas or
favored swimming areas). In these cases it might be
appropriate to focus the source assessment on upland
areas near or upstream from the waterbody area of
concern (Washington Forest Practices Board, 1994).
Erosion process
In-stream storage and transport analysis should be
accounted for when the net sediment yield from the
watershed is a TMDL indicator, the in-stream channel
structure and function have been disrupted by sediment
discharges, a large volume of sediment from past
discharges is working its way through the system, a
large proportion of total sediment in the system is stored
in-stream, or geomorphic analysis is needed to design
restoration actions. In-stream storage and transport
analysis is less important when the major project
concern is long-term sediment loading (e.g., to a lake or
estuary), indicators that do not focus on sediment
loading (turbidity) are used, and the project focus is
long-term erosion prevention (i.e., in-stream sediment
dynamics are of lesser concern).
When upland sediment storage substantially reduces the
amount of sediment that reaches streams or changes the
timing of sediment delivery, it is usually important to
select methods that account for upslope sediment
storage or estimate the sediment delivery ratio (the
percentage of eroded sediment that actually reaches the
waterbody). Although the use of "rule of thumb"
sediment delivery ratios should be used with caution
since it is based on long-term averages extrapolated
from lake studies.
Sediment source assessment methods should be selected
based on a clear understanding of the dominant
sediment-producing processes active in the watersheds
of concern. For example, in many parts of the
Northwest, Southwest, and Pacific Islands, erosion
processes tend to be associated with occasional large
storm events. Sediment discharges tend to vary
substantially from year to year in such settings. In
contrast, sediment discharges of concern are associated
with more regular precipitation and flow events in most
other parts of the country. Approaches available to
account for erosion associated with regular runoff
patterns or relatively frequent high-flow events (e.g.,
with 1- to 3-year return periods) usually estimate
sedimentation as a function of the distribution of rainfall
or flow events of different magnitudes and provide
cumulative erosion estimates.
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In watersheds dominated by very infrequent but extreme
runoff and sedimentation events, erosion is substantially
more difficult to predict. In these cases, it might be
preferable to select methods that estimate erosion
potential but do not attempt to directly estimate erosion
associated with specific future high-magnitude events
(see, for example, Weaver and Hagens, 1996).
Alternately, the TMDL could specify longer time steps
for averaging sediment inputs (e.g., as rolling averages
over a 5- to 15-year period) to account for interannual
variability in erosion rates.
Land management
Sedimentation rates associated with some land uses
(e.g., timber harvesting, construction, and some
cultivation practices) typically decline over time after
the land disturbance occurs and the land has a chance to
recover. To account for potential attenuation in
sedimentation rates in these cases, a sediment source
assessment might need to incorporate an attenuation
factor to avoid overestimating future erosion. Recovery
rates should be based on analogous local or reference
watershed experience whenever possible. Where
recovery rates used to estimate erosion attenuation are
based on general sources, a substantial margin of safety
might be needed to ensure that future sediment loads are
not underestimated. (See Reid, 1996; McGurk and
Fong, 1995; and Berg et al., 1996 for further information
and examples.) Sedimentation rates from farmland in
crop rotation can vary depending on the stage of crop
rotation.
The likelihood and timing of future land disturbances
should be considered. Although a watershed can
sometimes recover from one-time or widely disbursed
disturbances, the cumulative effect of multiple
disturbances may be that sedimentation rates remain
above levels of concern for decades or longer (see Berg
etal., 1996).
A source assessment might not need to define a specific
recovery or attenuation function. An analysis could link
individual estimates of sediment yield per disturbance
action (e.g., discrete timber harvesting event) with
overall targets above which watershed sediment yield is
excessive in any single period of time (Lewis and Rice,
1989, 1990; Louisiana-Pacific Corporation, 1996). If
the per entry factor and the sediment threshold are
linked, the variable management factor would be the
number and spatial distribution of timber harvest entries
and reentries planned in a watershed.
Background loading
Some erosion occurs in all watersheds, even those which
are completely undisturbed. Some watershed types are
extremely prone to periodic major sedimentation events.
Designated uses located in such settings have often
adapted to naturally high sediment conditions.
TMDLs need to distinguish sedimentation rates
associated with human activities in the study watershed
from those associated with naturally occurring (and
presumably uncontrollable) sediment sources. Human
land management activities can change the magnitude,
locations, and timing of land erosion or runoff events as
well as the key physical characteristics of receiving
waters. Methods sensitive to changes in the driving
forces that influence sedimentation (e.g., models like
RUSLE, HSPF, and WRENSS) will be useful in
comparing natural and anthropogenic sources if data
about key processes are available for the TMDL study
area and reference watersheds.
Methods that estimate sediment loading or yields as a
function of sediment concentration and streamflow (e.g.,
rating curves) are less useful in evaluating how existing
sedimentation rates differ from natural sedimentation
rates. Where rating curve methods are used, careful
comparison to reference watersheds (and the underlying
differences in land use or land characteristics) can assist
in comparing natural and human-caused sedimentation.
Direct erosion prediction methods might be able to
assess the degree to which erosion likelihood has, as a
result of human activity, been increased (e.g., due to
road construction in a vulnerable area) or decreased
(e.g., due to stabilization of an existing landslide
feature).
Practical considerations
Practical considerations include resources available
compared to level of effort needed to analyze the
sources, level of accuracy desired for the TMDL, and
stakeholder involvement and concerns. For most
TMDLs, the selection of appropriate methods for
TMDL development will rely on a combination of
scientific and practical considerations.
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Practical considerations include the following:
• Carefully consider data and resource demands
associated with all methods. Methods that require
unavailable technical expertise, data, or time should
not be selected.
• Assume that existing data will be adequate to
develop a reasonable first-phase source assessment.
(Plan according to the data in hand.) Relatively
crude estimates of sediment input sources might
provide adequate results for many TMDLs.
• Complex source assessment tools might be most
appropriate only where costs of controlling or
restoring sources are expected to be very high and
where refinement of source estimates might
substantially change allocations.
• Source assessment methods should be
understandable (e.g., models perceived as "black
boxes" are often difficult to explain), sensitive to or
capable of building upon previous local source
assessment work, and logically linked to other
TMDL elements.
4. What is the appropriate source assessment
method?
This section provides information on a range of
potentially useful sediment source assessment methods
that have been developed to
• Estimate actual or potential loading from hillslopes
and banks to receiving waters.
• Evaluate in-stream storage and transport of
sediment.
• Estimate the net sediment discharge (or yield) from
drainage basins.
The degree to which individual sediment TMDLs
address erosion and waterbody impairment by sediment
will depend on the overall approach taken in the TMDL
(e.g., the designated uses of concern, types of numeric
targets developed, key sources of concern, and land
management actions under consideration). Each type of
approach has its pros and cons. In general, methods that
more thoroughly account for both hillslope sediment
production and sediment transport and fate after erosion
occurs are likely to prove more useful in identifying the
sediment assimilative capacity of waterbodies than
methods that focus only on upslope source assessment.
However, other methods to assess assimilative capacity
and plan needed responses are available and are
potentially more cost-effective than full-scale sediment
budgets. In watersheds where past sediment budgeting
has been done, analysts should clarify the scope of the
work performed and take care not to assume that a
particular type of analysis was performed.
Source assessment methods
Source assessment methods vary widely with respect to
their applicability, ease of use, and acceptability.
Recognizing that many source assessment methods
exist, summaries of the methods were developed for
several categories. In some cases, the categories contain
a range of models that could arguably be placed into
multiple categories. The following categories are based
on expected uses of these methods in estimating soil
erosion, storage, and delivery in the context of TMDL
development:
1. Indices (do not provide load estimates but do
provide a guide for the TMDL)
Vulnerability
Future erosion
2. Erosion models
Source loading
Source loading and delivery processes
3. Direct estimations
Sediment budget
Rating curves
Statistical extrapolation
The following summaries present the key attributes of
the methods, review key advantages and disadvantages,
and make general recommendations concerning the use
of the model type for TMDL analysis.
Source sensitivity and erosion potential estimation
methods
A variety of methods are available for evaluating land
vulnerability, or sensitivity to erosion, sometimes as
associated with specific land management activities.
These methods do not directly yield sediment loading
estimates, but they can be used effectively to compare
the relative vulnerability of different areas to future
erosion or to target field work to make empirical
estimates of erosion potential. Some of these methods
yield indices or measures of watershed conditions that
might be associated with designated use condition (e.g.,
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Equivalent Roaded Acreage [McGurk and Fong, 1995]),
although these associations are poorly documented in
most parts of the country. It is possible to derive
methods that can provide such associations as both a
component of source assessment and a numeric target to
complement in-stream targets (see Chapter 4).
Most of these methods have been developed to address
watersheds in which timberland management and fishery
issues are primary concerns, although some habitat
condition inventory methods have similar
characteristics. This section briefly discusses examples
of methods that focus on sources that are often
important sediment causes.
Watershed analysis techniques have been developed to
evaluate watershed resource values, land use activity
impacts on those values, and opportunities to protect and
restore resource values through land use management
and restoration planning (e.g., Regional Ecosystem
Office, 1995; Washington Forest Practices Board,
1994.) Washington's Timber, Fish and Wildlife (TFW)
1994 approach entails assessments of watershed
condition according to key watershed processes with a
focus on fishery resource protection. Process
assessments are converted into numeric ranking factors.
Multiple ranking factors are then synthesized to yield
relative vulnerability rankings for different parts of the
study area, which then assist resource managers in
developing specific management and restoration
approaches or prescriptions.
The federal agency watershed analysis approach focuses
on a broader range of watershed and resource
management issues than fisheries and timberlands, and it
provides a general framework for quantification and
synthesis of watershed process assessment evaluations.
Unlike the TFW approach, the federal process is not a
decision-making process intended to lead directly to
land management planning decisions. Both the TFW and
federal watershed analysis approaches provide
opportunities to gather and evaluate information
concerning the relative significance of sedimentation
and sediment sources in a watershed, but they do not
necessarily yield quantitative estimates of past or future
sediment production.
Erosion vulnerability methods do not produce erosion or
sediment yield estimations, but instead index the
potential effects, including cumulative impacts of
management actions. Because sediment generation is
usually a major impact of forestry operations, these
methods can provide useful information in these
settings. For example, the Equivalent Roaded Area
(ERA) approach indexes potential impacts expected
from each activity to that expected from roads (USDA
Forest Service, 1988). A land use history is developed
for the watershed, sensitive sites are identified, and
ERAs are calculated for each activity with respect to the
mechanism thought to be of greatest concern. Values
are summed and normalized by area to calculate a total
ERA percentage, which is compared to an allowable
threshold identified for the watershed. If the calculated
ERA value is higher than the threshold, the watershed
may be singled out for further evaluation by other
means. Similar approaches have been used in other
parts of the country, including Equivalent Clearcut Area
(see Berg et al., 1996). In addition, specific disturbance
measures have been used to help characterize relative
erosion vulnerability in different subbasins within a
watershed study area (e.g., Black Butte River,
California, Watershed Analysis).
A simple forestland erosion hazard rating system
developed by the California Department of Forestry
(1990) evaluates the relative sensitivity of different land
areas to erosion as a function of soil characteristics,
geology, slope, vegetation, and rainfall ranges. This
approach produces maps of erosive hazard to guide
planning and field assessments in forestlands.
Landslides and other mass wasting features are critical
sources of erosion in many parts of the country. One
mass wasting assessment model used in the Pacific
Northwest estimates sensitivity of land areas to shallow
landslides as a function of precipitation, soil
characteristics, and topography (Dietrich et al., 1992,
1993; Montgomery and Dietrich, 1994). Based on
analysis of aerial photographs, geologic and landslide
maps, and digital elevation data, needed model inputs
can be developed. The model is capable of landslide
sensitivity rating maps and measures of slide areas, and
associated GIS coverages. This method has been used
in several watershed analysis projects in the Pacific
Northwest and California. Table 5-2 summarizes
advantages and disadvantages of this category of
methods.
Assessing future erosion requires identifying key
erosion features based on aerial photography analysis or
another screening method, then making field-based
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measurements of erosion potential of the largest future
sediment sources while evaluating the prospects for
restoration or mitigation actions. Most of the settings in
which this approach has been applied are Pacific
Northwest forest settings dominated by erosion
associated with logging roads and associated mass
wasting features (e.g., Redwood National Park,
California). It has not been extensively applied outside
this general setting, but it has the potential to address
watershed settings where other source concerns
predominate. Generally, these methods do not directly
predict when the erosion activity will occur; instead,
they target the assessment of key erosion features and
evaluate the feasibility of avoiding or mitigating the
future erosion effect (Weaver and Hagans, 1996). The
theory underlying this approach is that it is more
efficient to target future erosion sources for remedial
action than to evaluate past erosion locations, which are
probably not amenable to productive treatment. In
addition, the method probably works best in settings
where a relatively small group of potential sediment
sources will be responsible for most future erosion (e.g.,
road failures and mass wasting features), in contrast to
watersheds where erosion contributions are spread
evenly across the landscape (e.g., sheet and rill erosion
from cultivated land).
Recommendations: Where these methods have been
used extensively, analysts should consider exploring
ways to use the results in TMDL development or
assessment priority setting. Creative application of
these results could fit well with one or more TMDL
elements and could significantly assist in source
assessment. It is unlikely that any of these methods
provides a substitute for source measurement or
estimation through one or more of the other methods
discussed in this section. Future erosion estimation has
not been widely applied to date, but it offers great
promise for TMDL development in many settings. The
method is particularly appropriate in settings where
catastrophic sedimentation events are likely in key
disturbed areas in association with catastrophic events
(e.g., major storms and rain-on-snow events). The
method is less likely to be cost-effective in very large
watersheds (due to the prohibitive costs of field work) or
where highly disbursed erosion sources triggered by
commonplace driving forces predominate. However, it
might be feasible to use the approach in larger
watersheds if field work is targeted based on watershed
stratification and preliminary screening analysis (Reid
and Dunne, 1996).
Erosion process methods
Erosion process methods generally estimate
sedimentation through the application of sedimentation
prediction algorithms or erosion hazard ratings for
different land parcels. Most of these methods apply
models that estimate erosion as a function of several key
factors, potentially including soil characteristics,
topography, vegetation characteristics, and precipitation.
Many available methods are based on the Revised
Universal Soil Loss Equation (RUSLE) or one of its
many variants as applied by many agencies for erosion
estimation over the past decade (e.g., AGNPS,
SWRRBQ). Other methods commonly apply particle
detachment and washoff equations to estimate erosion
(e.g., HSPF, CREAMS, ANSWERS). Erosion process
models vary substantially in the sophistication and
technical expertise necessary to ensure proper
application. Table 5-3 presents a summary of the basic
differences in method sophistication.
This discussion distinguishes between models that focus
only on hillslope erosion (source loading models) and
models that account for both erosion and transport of
sediment out of the watershed (source loading and in-
stream process models).
Source loading models
Several commonly used methods provide estimates of
erosion from multiple sources, hillslope storage, and
sediment delivery to streams. Methods that have been
applied successfully include, but are not limited to, the
following:
USLE/RUSLE
AGNPS
BASINS-NPSM
WATSED
BOISED
Critical Sites Erosion Study (CSES)
WEPP
HSPF
SWAT
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Table 5-2. Advantages and disadvantages of source sensitivity estimation methods
Advantages
Disadvantages
Provide method for assessing relative significance of sediment
sources or source areas in settings where quantitative estimation of
past or future sediment sources is difficult due to the unpredictability
of erosion timing or magnitude or the difficulty of conducting
adequate field work.
Provide priority-setting framework for future assessment and
management planning.
Might be possible to establish thresholds of concern for certain
vulnerability measures, which could be used to develop numeric
targets and to assess need for source controls.
Measures of vulnerability and sensitivity do not yield direct measures
of past or future sedimentation from specific sources, which might
be easiest to use for TMDL development.
Use of these approaches for prediction purposes has not been well
established in most cases or has been explicitly discouraged (e.g.,
Equivalent Roaded Acreage).
Require substantial expertise to develop correctly and should include
field work as part of the analysis (which increases costs).
Accuracy of surrogate vulnerability measures has not been
confirmed in many settings. For many parts of the country (e.g.,
where forest land issues are not critical), these methods have not
been used at all.
Many models based on methods similar to the RUSLE
(Renard et al., 1997) have been used effectively to
evaluate erosion from cultivated areas in the East,
Southeast, and Midwest. Extensive discussion of these
methods is provided in USEPA (1997c) and is not
repeated here.
Source estimation models vary substantially in analysis
time steps. Some models (e.g., AGNPS and
ANSWERS) evaluate runoff associated with single
precipitation events, whereas others (e.g., HSPF and
SWAT) simulate sediment loadings using hourly or
daily time steps for longer time periods. Analysts
should be sensitive to the different time steps used by
models and should consider how the results of single-
event simulations will be integrated across time,
ensuring loadings are consistent with TMDL allocations.
Similar models such as BOISED, WATSED, R1/R4, and
WRENSS have focused primarily on forested watershed
sediment analysis. These models segment watersheds
into land types and land system inventories. Each land
parcel in the watershed is allocated erosion hazard
Table 5-3. Erosion process model comparisons.
Model Type/Examples
Key Capabilities and Limitations
Simple Methods:
EPA Screening Procedure
USGS Regression Procedure
RUSLE
WEPP
Aggregate large land areas (not RUSLE)
Large time steps, e.g., average annual (not RUSLE)
Estimation methods based on empirical relationships and expert judgment
Do not model delivery processes.
Generally reliable only for relative comparisons of sources, not load estimates
Limited data; no calibration requirements
Mid-Range Models:
BASINS-NPSM
AGNPS
ANSWERS
R1/R4
WATSED
BOISED
WRENSS
SWAT
Compromise between empirical and mechanistic models
Reliable for order of magnitude accuracy
Can interface with GIS framework
Moderate data and calibration requirements
Some capable of evaluating transport and/or control effectiveness
Detailed Models:
HSPF
SWMM
SWRRBQ
ANSWERS
SWAT
CREAMS
Can delineate sources at fine parcel scales
Can evaluate short time sequences/individual storm effects
Generally use mechanistic representations of key watershed functions to estimate erosion
Estimates generally accurate within factor of 1 to 2
Often work best in interface with GIS framework
Substantial data and calibration requirements
Usually capable of evaluating transport and/or possible control effectiveness
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potential and sediment delivery ratio values that allow
generation of erosion curves for each disturbance source
on the watershed. Estimates for this information are
ideally based on field information collected for the
specific purposes of the model. Absent such field data,
potential sources of information include erosion plot
studies, special-purpose studies (e.g., road and trail
erosion assessments), soil maps, erosion hazard potential
maps, Watershed Improvement Needs surveys
identifying disturbance types and sources, and fish
habitat surveys. As part of their routine operations, land
management agencies typically generate these types of
data sets.
A variation on these approaches is the Critical Sites
Erosion Study, a method that estimates the probability
that a site will yield more than a given sediment load if
the land is disturbed by timber harvest or road
construction (Lewis and Rice, 1989). This method was
used in a recent large-scale watershed assessment by
Louisiana-Pacific Corporation to evaluate potential
impacts of future timberland management plans
(Louisiana-Pacific Corporation, 1996). This method
recognizes that erosion in many settings is not even and
that the majority of measured erosion in such settings
comes from a relatively small number of critical sites. In
such settings, this type of method potentially enables the
analyst to focus on the watershed land areas most likely
to become major erosion sources and to obtain more
accurate estimates of potential sediment discharge.
Table 5-4 summarizes advantages and disadvantages of
hillslope source models for TMDL source assessment.
Recommendations: Erosion process models that focus
on upland areas can yield reasonable results for TMDL
analysis. They are appealing in many cases because
they can be applied without having to do extensive field
work. These models are probably most effective for
source analyses where the models have been applied and
calibrated in the past, where sediment fate and transport
after delivery is a less critical issue, and where
sedimentation is associated primarily with sheet and rill
erosion from relatively low-sloped lands. For example,
these methods typically work well in settings where
cropland erosion drains directly to reservoirs or lakes.
The broad, successful use of such models suggests that
they can be made to work within many project settings.
Such models should be used with caution in cases where
extreme watershed conditions predominate (e.g., very
steep topography, landslide-dominated erosion, radically
variable precipitation regimes). Other methods (e.g.,
R1/R4, WATSED) might be preferable in many
mountainous regions, the Pacific Northwest, and very
arid terrains (e.g., RUSLE). Where hillslope source
models are used, it is crucial either to calibrate and
subsequently validate the models to ensure reasonable
accuracy or to conduct follow-up monitoring to check
the reliability of the earlier results.
Table 5-4. Advantages and disadvantages of hillslope source models
Advantages
Disadvantages
Widely used in many parts of the country (especially the RUSLE-
based approaches).
Well accepted as a sediment prediction tool in many circumstances.
Detailed default parameters for many of the key model inputs are
widely available, which facilitates use of these approaches without
having to collect extensive data in many circumstances.
Needed data (e.g., soil composition) are widely available for many
parts of the country.
Provide relatively coarse or fine estimates of erosion depending on
project needs, spatial scales, and time steps chosen.
Simple methods can yield useful estimates of the relative importance
of different source areas, which might be sufficient for some TMDLs.
If more sophisticated models are used, it might be possible to
evaluate the relative sensitivity of different model factors in affecting
future erosion predictions. Based on such sensitivity analysis, it
might be possible to target controls or restoration at factors most
responsible for erosion effects.
Generally do not address or account for bank erosion.
Generally do not clearly account for hillslope sediment storage and
routing.
Downslope transport analysis often does not consider actual
complexity of transport processes.
Accuracy questionable for extremely steep watersheds in which
sedimentation is dominated by extreme climatic or geologic events.
Do not assist in the analysis of sediment fate after sediment reaches
waterbodies of concern, which may ignore key TMDL issues or
require additional in-stream analysis, especially linkage analysis.
Generally predict average annual or monthly gross loading rates.
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Source loading and delivery process models
Source loading and in-stream process models can be
used to estimate sediment erosion from multiple source
categories and movement to the water's edge (as with
the hillslope models described above). In addition, they
can provide a gross accounting of sediment transport
and in-stream storage to provide useful information
about net sediment yields from a watershed and
information about in-stream sediment fate (e.g., gross
degradation or aggradation). Care should be exercised
when using the transport and storage component of these
models because significant uncertainty is inherent in the
model results (e.g., erosion processes such as
streambank erosion are not accounted for in the models).
Models that incorporate both upland and in-stream
sediment analysis components include HSPF, SWMM,
SWRRBQ, DR3M, WRENSS, and SWAT. 5-5
summarizes advantages and disadvantages of the
hillslope source and in-stream process models.
Recommendations: Given the relatively high cost,
expertise, and effort associated with using these models,
they are most appropriate for large-scale watershed
projects with substantial, long-term resource support and
stakeholder commitment. The level of detail and
precision these models can provide are worthwhile in
settings where prospective sediment control and
restoration costs are high and stakeholders do not agree
on the best ways to proceed. The ability of these
methods to provide net sediment yield estimates may
prove useful in settings where the detailed field work
needed to complete some types of sediment budgets is
infeasible. In settings dominated by occasional extreme-
magnitude sedimentation and runoff events, however, it
might be best to assemble different source assessment
and sediment transport analysis methods for individual
sources of concern and combine the results to construct
sediment budgets. (See Reid and Dunne [1996] for
information on this approach.)
Direct measurement methods
These methods differ from the preceding methods
because the analysis is based on direct measurements of
past erosion rates and amounts. The general strategy of
this approach is that information on past erosion can be
used to characterize trends, to help predict future
erosion amounts, and to plan appropriate restoration and
prevention actions. Sediment budgets as described by
Reid and Dunne (1996) provide information on
individual source measurement methods and references.
Reservoir studies have been widely used to measure
overall watershed sediment yields and discharge rates
over time. This method entails the estimation of
sediment displacement of reservoir capacity over time to
yield a measure of total mass loading or watershed
loading rates overtime. For example, one study
calculated estimated total sedimentation rates per square
mile of watershed area in Northern California coastal
ranges based on reservoir studies (Phillip Williams
Associates, 1996).
Table 5-5. Advantages and disadvantages of hillslope and in-stream process models.
Advantages
Disadvantages
Ability to evaluate sediment fate in streams makes it possible to more
precisely identify when and where in-stream sediment loads are
expected to occur, and to evaluate designated use impacts as a result.
Helpful in cases where a substantial lag time between the onset of
erosion and the transport of sediment to key areas exists.
When used in concert with geomorphic analysis methods, model
results can assist in evaluating how changes in sedimentation and
hydrology associated with land use changes affect channel structure
and function.
Assist in evaluating prospective effectiveness of different source
control or restoration methods.
Relatively widely used in urban settings.
GIS interfaces often available to facilitate management of large data
sets.
Substantially more complicated to use than the models in the
preceding group.
Large amounts of local data are generally needed to calibrate and
validate the models.
Relatively little experience exists in their use.
Have not been widely used to examine rural or wildland settings.
Do not account for changes in stream morphology and sediment
transport capacity associated with long-term change in erosion and
hydrologic processes.
May need separate geomorphic analysis to evaluate the need to
make future changes in channel profile inputs to these models.
Difficult to predict transport and storage accurately, particularly in
large watersheds.
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At a smaller scale, many methods are available for
directly estimating erosion from sources such as:
• Bank erosion.
Slope erosion from timber harvest, construction or
other activities.
Headcut or gully erosion.
Landslides.
Road erosion and road-related mass wasting.
In-stream sources, including channel scour.
These methods usually entail the measurement of eroded
areas, placement of sediment traps to catch sediment
moving downhill, and/or pins or scour chains to detect
the removal of sediment from stream channels over
time. In many cases, hillslope sediment volumes can be
directly measured or inferred by measuring void spaces
or erosion around datable vegetation. Advantages and
disadvantages of these methods are summarized in
5-6.
Recommendations: This group of methods can be very
useful to build an overall estimate of sediment loading
rates (e.g., reservoir studies), to evaluate erosion
patterns associated with specific sources (based on bank
or upslope erosion estimates) or areas (based on
comparisons between source monitoring done in
different areas), or to validate estimates derived using
other methods (particularly sediment budgeting
methods). In general, these methods should not be
uniformly assumed to provide reliable future erosion
estimates given the potential future variability of key
watershed processes.
Rating curves and other statistical extrapolation
methods
Rating curve methods generally estimate total sediment
loading past a measurement point as a function of three
variables—streamflow, suspended sediment
concentration, and bedload transport. Separate
suspended load and bedload rating curves are developed
in many cases, and bedload rating curves are often not
developed because of bedload sampling difficulties.
Functional relationships among these variables are
usually estimated through regression analysis and used
to estimate average annual or seasonal sediment loading.
For example, in a situation where a modest number of
data points are available relating flow, TSS, and
sometimes bedload, it is often feasible to develop
statistically reliable regression functions. Then, the
overall sediment load can be estimated by applying
Table 5-6. Advantages and disadvantages of direct measurement methods.
Advantages
Disadvantages
Provide direct measures of sedimentation from specific sources.
Over long time scales, can be used to develop estimates of long-
term erosion rates in some cases.
Effectively complement the use of other source estimation methods
that do not address all sources of concern (e.g., Sycamore Creek,
Ml, study directly measured bank erosion to complement modeled
estimates of erosion from agricultural and urban areas).
May be possible to derive useful results for some sources by
establishing collection traps or pins, then measuring the results
annually or seasonally, if longer time steps are acceptable for TMDL
development.
Reservoir studies can provide a more accurate means of estimating
the relative proportion of total sediment load that moves downstream
as bedload and as suspended load (Reid, 1996).
Reservoir studies can provide fairly reliable long-term average
loading rates per unit area of watershed in many places (which can
also assist with model validation or establishment of reference
conditions.)
Some data are better than no data.
Can apply results to other, analogous areas.
Can use data to calibrate/validate models.
Easy to measure sediment in areas where landslides are responsible
for most sediment.
Direct measures are often time- and resource-intensive to develop.
Difficult to generalize based on data collected because it is difficult
to determine if sampling sites are representative of watershed
conditions as a whole or of similar sources within the watershed.
Sediment traps can miss substantial amounts of sediment eroded
uphill if they are spaced too widely or if sediment moves through
channels or gullies that pass between traps.
Many watersheds of interest for TMDLs either have no reservoirs to
study or have no nearby watersheds containing reservoirs for use
in establishing sedimentation rates based on analogous
circumstances.
Past erosion rates and total loadings might provide a poor basis for
estimating future rates and loadings if key watershed processes or
characteristics change in the future.
Past erosion evaluation might miss substantial erosion potential if
monitoring is not done during time periods when most erosion
occurs (often the case with site-specific erosion studies that do not
account for the effect of extreme climatic or runoff events).
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these functions to a continuous (or more frequently
monitored) flow record based on the frequency
distribution of flows of different magnitudes. For
example, a sediment budget was developed for the
Trinity River, California, based on the rating curve
method (USDOI-BLM, 1995). Refer to USDA
Agricultural Research Service (1975) for additional
information on using rating curves to estimate sediment
yield.
Variations on the traditional rating curve approach
include the following:
• Annual rating curves, which may facilitate analysis
of changes in sediment yield associated with land
management changes or temporal variability
(Ketcheson, 1986).
• Time-integrated rating curves, which ignore
streamflow fluctuations and integrate sediment
transport rates overtime (Ketcheson, 1986).
• A sediment supply-based model that uses a
suspended sediment rating curve and supply
depletion function to account for load declines
during individual storms or runoff seasons (Van
Sickle and Beschta, 1983).
Similar methods might be available to extrapolate
localized sediment loading information. For example, a
sedimentation load or rate estimated for one tributary
area of a larger watershed could be used to estimate an
overall load or rate for the rest of the watershed if key
characteristics of the smaller study unit and larger
watershed are comparable and flow data are available
for the larger watershed. Care should be taken in
extrapolating results derived for a small area to a larger
watershed area, or from a short time period to a longer
time frame, to account for differences in operation of
key watershed processes (e.g., hydrology and
precipitation) at larger spatial scales or within longer
time frames. Table 5-7 summarizes advantages and
disadvantages of rating curves and other statistical
extrapolation methods.
Recommendations: Used with care, rating curves and
other extrapolation methods can provide a cost-effective
approach to source assessment, particularly in large-
scale TMDL studies where tributary-by-tributary source
analyses are adequate. Rating curve approaches are
particularly appealing in areas where they have been
used in the past or are commonly used by stakeholder
agencies and groups. This method is less appropriate in
systems where sediment discharge is dominated by
infrequent, large-magnitude events (e.g., mass wasting
and flood events triggered by extreme precipitation
events because the flow-TSS relationship observed at
lower flows might not account for these processes.
Rating curve construction should be preceded by careful
suspended sediment sampling covering a representative
range of storm or runoff events, if possible. Bedload
sampling (or an appropriate substitute method of
estimating the bedload portion of the total load) should
also be considered (see Reid and Dunne, 1996; Rosgen,
1996). Analysts should validate and refine rating curves
over time to account for changes and improvements
made possible by additional monitoring. Finally, it
might be appropriate to complement rating curve
analysis with more detailed source assessment in the
highest-priority sediment source tributaries identified by
the rating curve analysis, as a later phase of the TMDL
project.
Comparisons of source estimation methods
Source assessment method selection requires careful
consideration of the unique mix of issues, opportunities,
and characteristics present in each watershed, and it is
inappropriate to select methods based solely on the
cursory evaluations provided in this document. Analysts
are encouraged to use this information as a starting point
and to consult key references and local experts for
assistance in the final selection of methods.
5. How do estimated source contributions
compare with natural or background levels?
Where feasible, the source assessment should also
compare projected sediment loadings with natural or
background levels of sediment loading. This type of
comparison greatly facilitates the linkage of sediment
source assessment with numeric targets. (See Chapter 6
for details on linkages.) A sediment loading comparison
provides an additional basis for determining the degree
to which sediment loadings differ from levels needed to
support designated uses, thereby assisting in identifying
the needed levels of sediment reduction. In many
settings it is possible to estimate natural or background
sediment production in the study area. Such estimates
can be developed by assessing sedimentation rates
measured in relatively undisturbed areas of the
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Table 5-7. Advantages and disadvantages of rating curves and statistical extrapolation methods.
Advantages
Disadvantages
Rating Curves
• Widely used.
• Based on locally obtained empirical information.
• Substantial degree of statistical validity.
• Ability to relate suspended, bedload and total sediment loading
(frequently subdivided by tributary watershed) offers a ready method
of linking a commonly used sediment endpoint (suspended sediment
or turbidity as a surrogate) to a source estimation tool.
• Sensitive to spatial and temporal variability in sediment loading (by
relating loads to flows) (e.g., Deep Creek, MT).
• Reasonably accurate for estimating source loads on tributary-by-
tributary basis.
Other Extrapolation Methods
• Statistical extrapolation methods allow screening-level source analyses
for large land areas without having to invest in detailed analysis of
each land area.
• Assists in targeting the most significant source areas of concern for
further assessment and action without waiting for the results of lengthy
detailed analysis.
Rating Curves
• Data sources needed for rating curves (flow, suspended sediment, and
bedload sediment) are highly variable and often difficult to measure
accurately.
• Statistically significant results are often difficult to obtain.
• Unless careful sampling designs are followed, it is easy to obtain a
skewed sampling of sedimentation events, which could easily lead to
underestimation or, occasionally, overestimation of sediment loading.
• Bedload factor is often misinterpreted. Proportion of sediment
transported in bedload varies widely among stream types and between
events within a stream.
• Rating curve approaches that ignore bedload or assume a bedload
portion of total load without careful analysis are likely to produce
inaccurate results (Reid and Dunne, 1996; Rosgen, 1996).
• Rating curve approach does not help analyze key watershed
processes influencing sediment production.
• Difficult to determine respective influences of sediment supply and
channel transport capacity on changes in sediment yields.
• Might not assist in source assessment by source category ownership;
tributary scale might not be fine enough.
Other Extrapolation Methods
• Key statistical assumptions that should be met to draw robust
conclusions are not met in many studies (e.g., flow and discharge
data points are often not independent of each other).
• Easy to miss fundamental differences in the characteristics of small
study areas and the larger land areas or time scales for which
extrapolations are developed. Where differences are not taken into
account, large, difficult-to-detect errors might occur.
watershed or in comparable reference watersheds, or
estimated based on reviews of appropriate literature
sources. (See Reid and Dunne [1996] for additional
information.) These comparisons might not be
absolutely necessary for all TMDLs, particularly where
other methods are available for clearly determining the
degree to which existing and projected sedimentation
conditions depart from target levels.
6. How can the source assessment be described
for TMDL submittal?
The source assessment should yield estimates of
sediment loading from different sources within the study
area. These results can be expressed in terms of
expected sediment loadings per unit of time. If the
source assessment results are expressed in terms other
than mass loads per unit of time, the TMDL should
describe why the alternative approach is used. In
addition, if the source assessment also includes
evaluations of in-stream sediment fate and transport
and/or net sediment yield from the watershed, the
TMDL should describe these results. Ideally, the source
assessment results include estimates of sediment loading
in total and by source, taking into account temporal
variations in sediment delivery. Finally, if the source
assessment includes comparisons of projected and
natural or background sediment loadings, these results
should also be presented in the TMDL document.
7. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the source assessment
step, an approvable TMDL will need to include an
identification of the source categories, source
subcategories, or individual sources of the pollutant for
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which the wasteload allocations and load allocations are
being established.
RECOMMENDATIONS FOR SOURCE ASSESSMENT
Using all available information, develop a
comprehensive list of the potential and actual
sediment sources to the waterbody. Develop a plan
for identifying and accounting for the load
originating from the identified sources in the
watershed.
Use GIS or maps to document the location of
sources and the processes important for delivery to
the waterbody.
Identify all government agencies and non-
government organizations active in the watershed
and conduct interviews and collect information.
Group sources into some appropriate and
manageable unit (e.g., by delivery mechanism,
location, rate) for evaluation using the available
resources and analytical tools.
Ideally, monitoring data should be used to estimate
the magnitude of loads from various sources. In the
absence of such data, some combination of literature
values, best professional judgment, and appropriate
empirical techniques or models will be necessary.
In general, the simplest approach that provides
meaningful predictions should be used.
Sediment source assessment methods should be
selected based on a clear understanding of the
dominant processes in the watershed.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
• Dissmeyer, G.E. 1994. Evaluating the effectiveness
of forestry best management practices in meeting
water quality goals or standards. USFS
Miscellaneous Publication 1520. U.S. Department
of Agriculture, Forest Service, Washington, DC.
• Regional Ecosystem Office. 1995. Ecosystem
analysis at the watershed scale. Version 2.2. U.S.
Government Printing Office: Regional Ecosystem
Office, Portland, OR. 1995-689-120/21215.
Reid, L.M., and T. Dunne. 1996. Rapid evaluation
of sediment budgets. Catena Verlag, Reiskirchen,
Germany.
USEPA. 1997. Compendium of tools for watershed
assessment and TMDL development. EPA 841-B-
97-006. U.S. Environmental Protection Agency,
Washington, DC.
Washington Forest Practices Board. 1994. Standard
methodology for conducting watershed analysis
under chapter 222-22 WAC. Version 2.1,
November 1994. Washington Forest Practices
Board, Olympia, WA.
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Linkage Between Water Quality Targets and Sources
Objective: Define a linkage between the selected water
quality targets and the identified sources to determine
total assimilative capacity for sediment loading or total
load reduction needed.
Procedure: Determine the cause-and-effect relationship
between the water quality target and the identified
sources through data analysis, best professional
judgment, models, or previously documented
relationships. Use the linkage to determine what
sediment loads or conditions are acceptable to achieve
the desired level of water quality. Develop approaches
for determining an appropriate margin of safety.
OVERVIEW
One of the essential components of developing a TMDL
is to establish a relationship (linkage) between the
indicators and numeric targets and the estimated
loadings. This linkage makes it possible to determine
the capacity of the waterbody to assimilate sediment
load and still support its designated uses. Based on this
analysis, allowable loads or needed load reductions can
be allocated among key sources. The link between in-
stream uses, as evaluated through numeric targets, and
sources, as evaluated through the source analysis, can be
established by using one or more analytical tools.
Ideally, the link will be based on long-term monitoring
data that indicate the waterbody's response to flow and
loading conditions. More often, however, the link must
be established by using a combination of monitoring
data, statistical and analytical tools (including
simulation models), and best professional judgment. It
is difficult to draw accurate linkages between hillslope
processes and in-stream conditions, and it will be
necessary at times to base linkages on qualitative
analysis relying on professional judgment.
Key Questions to Consider for Linkage of Water Quality
Targets and Sources
1. What is an appropriate level of analysis?
2. What is an appropriate method for linkage?
3. What is the linkage and what is the resulting estimated loading
capacity or needed load reduction?
This section provides recommendations regarding
appropriate techniques for establishing the source-
indicator link. As with the prediction of sources, the
analysis can be conducted using methods ranging from
simple to complex.
KEY QUESTIONS TO CONSIDER FOR LINKAGE
BETWEEN WATER QUALITY TARGETS AND
SOURCES
1. What is an appropriate level of analysis?
Choice of an analytical tool to link the sediment loads to
the TMDL indicator(s) depends on the interaction of a
number of technical and practical factors. Suggestions
on how to address these factors were included in the
numeric targets and source analysis chapters and are not
repeated here. Key factors to consider in determining
the appropriate level of analysis for TMDL linkages
include the following:
• The types of indicators and source analysis tools
used in the sediment analysis, and other watershed
processes that influence sedimentation dynamics in
the study area.
• Physical and hydraulic characteristics of the
waterbody (e.g., lake versus stream).
• Geomorphic characteristics of the waterbody and
degree to which waterbody structure is stable.
• Temporal representation needs. (Are seasonal
averages sufficient, or must dynamic events on a
shorter time scale or key time periods [e.g., fish life
stages] be evaluated?)
• Spatial representation needs. (Are there significant
spatial variations in the indicator and does spatial
variability in the waterbody [e.g., key spawning
areas] need to be represented?)
• User requirements (including availability of
resources, time constraints, and staff familiarity
with specific analysis techniques).
• Stakeholder interests and outreach needs.
• Level of accuracy needed.
Different TMDLs will need varying degrees of accuracy
in establishing linkages between sediment sources and
in-stream targets, depending on the precision in each of
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the methods used in individual TMDL elements and the
needs of the stakeholder community. It is difficult to
characterize the degree of accuracy associated with
different linkage methods; however, this guidance
provides a rough sense of the relative accuracy each
method provides.
Settings where linkage accuracy is more important
Where relatively accurate methods are used throughout
the TMDL, they might lend themselves to, and assist in,
establishing clear linkages. Clear linkages may be
particularly important for a TMDL where finality and
certainty are sought—where the TMDL is supposed to
be "right" on the first try. In addition, where sediment
problems are very serious, watershed issues are
contentious, or stakeholders disagree about sediment-
related issues and potential solutions, more precise
linkages between TMDL elements might be needed for
several reasons. In many cases, TMDLs become
contentious because the financial stakes for involved
stakeholders are high. Clearer linkages can assist
stakeholders in understanding why particular sediment
sources and impacts need to be addressed, make the
TMDL more defensible if challenged, and provide a
more rigorous basis for future monitoring design.
Settings where linkage accuracy is less important
If each TMDL element is relatively crude, it might be
enough to explain the theoretical linkage between
elements and not expect direct quantitative linkages.
This approach could be particularly appropriate in
settings where the TMDL is to be done in phases and a
strong commitment to adaptive management over time
exists. Moreover, stakeholder expectations are an
important consideration here. Where watershed issues
are not highly controversial and the stakeholder
community seems ready to take effective action, specific
linkages might not need to be established in advance
with a high degree of precision. In this type of situation,
adequate linkages should be made to inform the design
and implementation of follow-up "hypothesis-based"
monitoring and adaptive management. Finally, precise
linkages might be less important in watersheds where
the problem is not very serious and where modest action
would be adequate. Where qualitative approaches to
linkage are used, the TMDL should document all
assumptions, theories that provide the basis for linkage,
expert and literature citations, and provisions for follow-
up monitoring.
2. What is an appropriate method for linkage?
Many approaches to linking or synthesizing the
elements of a TMDL are available. Some of these
approaches were reviewed in the discussion of source
analysis approaches. This section briefly reviews a
range of possible approaches and discusses examples.
For more detailed discussions of linkage principles and
methods, see Washington Forest Practices Board (1994),
Regional Ecosystem Office (1995), Reid (1996), and
Dissmeyer (1994).
Potential Linkage Methods
Mathematical Linkages
Process Model Linkages
Empirical Linkages
Linkage by Inference
Index Linkages
Mathematical linkages
Linkages between
numeric targets and
source loadings can often
be determined through
quantitative analysis of
the TMDL elements and underlying data used to
develop these elements. A variety of straightforward
arithmetic and statistical analyses are available. Where
these approaches are used, it is recommended that
analysts identify a theoretical basis for the relationship
between indicators and the sources of concern. In
addition, where these relationships are not well
understood, it might be appropriate to frame the linkages
as testable hypotheses to be further evaluated through
follow-up monitoring and evaluation. In most cases,
mathematical linkages provide moderately accurate
results.
Direct arithmetic linkages can be drawn between
numeric target and source analysis elements in some
cases. For example, a linear association can be
established between in-stream and upslope analysis (see
Silver Creek, Arizona, example in inset box). Analysts
should take care to examine the theoretical basis for
assuming particular functional relationships between in-
stream conditions and upslope sediment production
measures. In some cases it is reasonable to assume
linear functional relationships, whereas data
transformations might be needed in other cases to
establish meaningful functions. (See USEPA [1997b]
for more information on evaluation of functional
relationships through regression analysis.)
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Linkage in Silver Creek, AZ, TMDL Study
In a pilot TMDL analysis for Silver Creek, sediment loading reduction targets were
estimated through the following ratio:
existing instream sediment concentration existing sediment loadings
desired instream sediment concentration ~ target sediment loadings
Sediment loading reduction targets were then derived by subtracting target loading
levels from existing loading levels (Source: LimnoTech, 1993).
For TMDLs in which numeric targets include functional
relationships (e.g., the slope of the TSS/flow regression
curve in the Deep Creek, Montana, TMDL), it might be
feasible to examine the distance between the regression
curve derived for the study area and the comparable
curve calculated for a reference stream to determine how
much change is needed in sediment delivery, transport,
or net sediment yield to attain the targets.
In-stream and upslope sediment analysis linkages can
also be developed with more rigorous methods. Several
studies have linked in-stream and upslope indicators
through the use of statistical regression analysis. For
example, a study in the Sierra Nevada range of
California (McGurk and Fong, 1995) found a reasonably
robust relationship between aquatic invertebrates and
equivalent roaded acreage (ERA) measures, which
helped to evaluate the utility of the ERA method and
appropriate threshold levels.
In a study of northern California coastal streams
(Knopp, 1993), a statistical link was drawn between
watershed disturbance, as measured by a crude sediment
budget analysis, and several in-stream sediment
indicators, including geometric mean particle size, V*,
and riffle-armor stability index, to evaluate the ability of
in-stream metrics to discriminate between relatively
disturbed and undisturbed watersheds (and associated
historical sediment production). Other approaches are
possible and should be considered in cases where
relatively robust data sets are available and statistical
analysis of these data sets can be undertaken. By
examining the differences between conditions in the
study area and in reference sites, it should be feasible to
estimate needed load reductions.
Process model linkages
Mechanistic or process models may also be
used to draw relatively accurate linkages
between TMDL elements in many cases. For
example, sediment budgeting methods that
estimate net sediment discharge from a
watershed could be used to identify the degree
of change in sedimentation processes needed
for those processes to mimic natural
conditions. The sediment budgeting analysis
in the South Fork Salmon River, Idaho,
indicated that the river system was beginning to recover
from large historical sediment inputs, but that the river
lacked the hydraulic energy needed to move
accumulated in-stream sediments out of the system.
This finding led analysts to design a sediment input
reduction strategy that would reduce sediment loading to
the stream, thereby enabling the river to gradually
remove excess in-stream sediments. By accounting for
the different components of sediment movement through
a system (erosion, upslope storage, delivery to streams,
in-stream storage, transport, and net sediment
discharge), these methods enable the analyst to
quantitatively estimate load reduction needs and
compare the effectiveness of alternative sediment
management options.
In addition, process models that directly use sediment
indicators can often provide a framework for linkage of
in-stream endpoints based on sediment measures and
sediment source and allocation analysis. Several of the
more complex models discussed in the source analysis
section (e.g., HSPF, SWRRBQ, EFDC, GSTARS,
SWMM, and possibly AGNPS) might be capable of
providing this framework.
Empirical linkages
A variety of empirical linkage approaches are possible.
For example, in projects that use suspended sediment
load as an target, it might be feasible to link source
analysis, allocation, and numeric target elements by
simply ensuring that the sum of expected loads from
significant sources does not exceed the allowable load at
a downstream compliance point, as calculated by a
function of suspended sediment and flow data. This
approach would also facilitate the identification of total
allowable loads or total sediment load reductions
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needed. Significant uncertainty is likely to exist in each
component of the empirical linkages and will vary
depending on the quality of data sets.
Another empirical linkage approach is to use thresholds
of concern for upland or in-stream indicators and an
adaptive management approach to land management in
the future that links exceedance of one or more
thresholds with a management decision. For example, a
TMDL could reference a management approach by
stating that if a disturbance index or substrate
composition indicator threshold were exceeded, specific
actions would be taken (e.g., cease the activity or use
more protective management practices) at specific times.
If the case can be made that the adaptive response to
exceeding a threshold is significantly more protective
than the initial land use activity causing sedimentation,
this approach could provide an adequately robust
framework for TMDL linkage and eventual success
(e.g., Louisiana-Pacific Corporation, 1996).
Linkage by inference
In some cases, indirect inferences of relationships
between TMDL elements may suffice. For example, an
in-stream analysis might show that relatively modest
reductions (say, 10 to 20 percent) in sediment discharge
are needed to attain established sediment targets. If the
source analysis and allocation elements could be linked
to show that very large reductions (e.g., 50 to 75
percent) in sediment inputs are expected to result from
planned management and restoration actions, the rough
comparison of the elements could be construed to infer
the adequacy of the overall TMDL approach. A
theoretical connection should be established or
hypothesized based on expert judgment or literature
references to support linkages made through indirect
inferences. Such inferred linkages are likely to be quite
crude, but they might be adequate in some situations.
Index linkages
There are a variety of approaches to combining physical
and biological assessment tools to assist in linking
TMDL elements. These methodologies provide a
systematic framework for conducting and synthesizing
biological, physical, and chemical measurements of
habitat characteristics. Examples that have been used in
settings where sediment contamination is a key concern
include EPA's Rapid Bioassessment Protocols (USEPA,
1989), the Fish and Wildlife Service's Index of Biotic
Integrity (McMahon, 1983), and various habitat typing
methods (e.g., California Department of Fish and Game,
1994). In some cases, these methods provide guidance
on determining whether existing conditions are "good
enough" or whether habitat is impaired (e.g., McMahon,
1983).
These methods are most useful in linking disparate
numeric indicators to create composite rankings of
habitat quality. The methods also have potential for
establishing target conditions for multiple indicator
projects where aquatic habitat is impaired by sediments
(and potentially other stressors). These methods do not
directly lend themselves to estimation of total
assimilative capacity, but could conceivably be used to
infer estimates of sediment reductions needed.
Linking multiple indicators or multiple source
assessment methods
As discussed in the previous chapters, multiple
indicators and/or multiple source analysis methods
could be needed to ensure that the analysis of
complicated watershed settings adequately accounts for
complex in-stream sediment impacts and the complex
watershed processes that drive sediment loading. It is
rarely necessary to link all indicators in a seamless,
logical fashion. Likewise, not all indicators need to be
linked with the entire source analysis and associated
allocations. The objective should be to define adequate
linkages to provide logical coherence to the project
without straining scientific credibility or burdening an
already complicated analysis project. Several linkage
approaches might be adequate for this purpose.
One strategy is to link like indicators with like source
analysis elements (e.g., bank erosion targets linked with
bank erosion measures and controls in the Deep Creek,
Montana, TMDL). A second strategy is to first
synthesize estimates of sediment loads from different
sources that were developed with different methods
(e.g., through a sediment budget), then link the overall
sediment loading estimate with the in-stream indicators
for purposes of reduction and allocation planning (e.g.,
Sycamore Creek, Michigan).
Another approach is to use watershed analysis methods
as a linkage framework (e.g., Washington's TFW
approach and the federal watershed analysis
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procedures). These methods hold substantial promise as
integrating mechanisms where they are being
implemented, although linkages between aquatic
resource impacts and land management patterns that
contribute to those impacts have rarely been established
through rigorous methods.
3. What is the linkage and what is the resulting
estimated loading capacity or needed load
reduction?
The linkage analysis should show how numeric targets
and source analysis results relate to each other and how
they combine to yield estimates of sediment assimilative
capacity or needed sediment load reductions. An
example linkage analysis is provided below. The
example illustrates how professional judgment
combined with simple arithmetic comparisons of
existing and target conditions can be used to link
numeric targets and source analysis results to estimate
assimilative capacity. This estimate provides the basis
for the allocation of loads or load reduction plans to be
devised in the next TMDL step.
In this example, the target values are based on
conditions at a reference site. The indicators chosen are
percent fines, geometric median particle size, and
average pool depth; the target values for the indicators
are established at the values of the reference site.
A sediment budget for the impaired watershed shows
that the estimated annual sediment loading is
80 tons/mi2. To determine a rough estimate of the
needed load reductions, the existing conditions can be
compared to the target conditions. The percentage of
fine sediment is 60 percent greater, the median particle
size is 30 percent smaller, and the average pool depth is
30 percent shallower. The average departure of existing
conditions from target conditions is therefore 40 percent
((60% + 30% + 30%)/3). Based on expert interpretation
and assuming that linear comparisons are valid, one
approach to load reduction needs would be to specify
that existing loads should be reduced by an equivalent
percentage, or that loads should be reduced by 40
percent to approximately 48 tons/mi2.
Indicator
Target (Reference)
Level*
% fine sediment < 0.85 mm 11%
Median particle size 20 mm
Average pool depth 2 m
Existing
Condition*
18%
15 mm
1.5m
* A range of values for each indicator and target is likely in actual
settings; single values are used here to simplify the presentation.
Recommendations for Linkage of Water Quality
Targets and Sources
• Use all available and relevant data; ideally, the
linkage will be supported by monitoring data,
allowing the analyst to associate waterbody
responses with flow and loading conditions.
• Selection of an appropriate technique must be made
on a site-specific basis and should consider the
nature of the indicator to be evaluated, hydraulic
characteristics of the waterbody, user requirements,
relevant temporal and spatial representation needs,
and stakeholder interests.
• When selecting a technique to establish a
relationship between sources and water quality
response, usually, the simplest technique that
adequately addresses all relevant factors should be
used.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
Dissmeyer, G.E. 1994. Evaluating the effectiveness of
forestry best management practices in meeting water
quality goals or standards. USES Miscellaneous
Publication 1520. U.S. Department of Agriculture, U.S.
Forest Service, Washington, DC.
Regional Ecosystem Office. 1995. Ecosystem analysis at
the watershed scale. Version 2.2. U.S. Government
Printing Office: 1995-689-120/21215 Regional
Ecosystem Office, Portland, OR.
USEPA. 1997c. Compendium of tools for watershed
assessment and TMDL development. EPA 841-B-97-
006. U.S. Environmental Protection Agency,
Washington, DC.
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Washington Forest Practices Board. 1994. Standard
methodology for conducting watershed analysis under
chapter 222-22 WAC. Version 2.1, November 1994.
Washington Forest Practices Board, Olympia, WA.
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Allocations
Objective: Using total assimilative capacity developed
in the linkage component, develop recommendations for
the allocation of loads among the various point and
nonpoint sources, while accounting for uncertainties in
the analyses (MOS) and, in some cases, a reserve for
future sources.
Procedure: Determine the allocations based on
identification of the acceptable loading (loading
capacity), the margin of safety, and the estimated loads
from significant sources. The available load is then
allocated among the various sources.
OVERVIEW
A TMDL is legally defined as the sum of wasteload
allocations to point sources, load allocations to nonpoint
and natural background sources, and a margin of safety
considering seasonal variation (40 CFR 130.2).
Although there are many ways to express TMDLs, the
concept of allocation is central to the TMDL process
because it reinforces the importance of identifying what
sources need to be addressed to attain water quality
standards. Therefore, sediment TMDLs should clearly
provide for allocations by source of maximum allowable
loads, needed load reductions, or, in some cases, source
control actions.1
Pollutant allocations (e.g., maximum allowable loads or
needed load reductions per unit of time) are strongly
recommended where feasible. The allocations provide a
framework for identifying specific source reduction
levels. In most TMDLs, the allocation element does not
identify specific implementation measures; rather, those
measures are identified in an implementation plan that is
legally distinct from the TMDL. The implementation
plan is often developed concurrently with the TMDL
and sometimes as a follow-up activity. It is usually
advantageous to develop the implementation plan at the
same time as the TMDL to
Make efficient use of assessment and planning
resources and the time of participants.
Increase the likelihood that actions needed to
implement the TMDL will actually be carried out.
Improve the analytical basis for concluding that
allocations will be effective in meeting TMDL
targets.
Key Questions to Consider for Allocations
1. What key factors affect selection of allocation method(s)?
2. What is an appropriate allocation method?
3. How are allocations described in the TMDL document?
4. What changes does the proposed rule speak to?
Although some sediment TMDLs might determine a need to
increase sediment loading to address an impairment, this analysis
focuses on the more likely scenario that sediment reductions will be
needed to address the designated use problem(s).
Allocations should be accompanied by adequate
documentation to provide reasonable assurance that the
changes in sediment dynamics in the watershed
(reductions, increases, or redistributions) needed to
implement the TMDL allocations will be implemented
and will result in the attainment of water quality
standards. To provide the reasonable assurance needed,
the TMDL submittal usually includes an analysis
showing that the sum of allocations does not exceed the
waterbody's assimilative capacity for sediment as
identified in the linkage step. In addition, some analysis
showing the feasibility of implementing proposed
allocations should be provided if possible. This section
reviews key factors to consider in the allocation process
and discusses several allocation approaches.
KEY QUESTIONS TO CONSIDER FOR ALLOCATIONS
1. What key factors affect selection of allocation
method (s)?
The following factors usually influence the selection of
an allocation approach.
Types of sources and management options
Allocations should usually be organized along the same
lines as the source analysis and linkage elements (e.g.,
by source category, tributary area, land parcel, or
possibly a combination of these). Following the same
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approach in the allocation step usually eases the task of
demonstrating that the sum of allocated reductions or
management actions offers reasonable assurance of
success, defined in this case as eventual attainment of
numeric targets. It might not be necessary to devise
allocations for each source category, tributary, or land
area if action taken to address a subset of sources shows
clear likelihood of success.
Analysts should also consider how sediment sources are
expected to be controlled and tailor allocations
accordingly. For example, in a case where erosion from
roads is the key source of concern, an allocation could
be expressed in different ways depending on how such
erosion is to be controlled. If the focus is on prevention
of road-related erosion through replacement of failing
culverts, the allocation could be done in terms of total
tons of avoided sediment loading to be realized through
culvert management. Alternatively, if road-related
erosion is to be controlled by reducing the miles of
active roads per square mile, the allocation could be
expressed in terms of percent reductions in sediment
loading by tributary watersheds.
In another example, sediment runoff from fields under
multiple-stage crop rotation varies depending on which
crop is planted at any one time. TMDL allocations
should therefore be designed to ensure that sediment
production associated with the maximum sediment
production stage of the rotation does not exceed
acceptable levels (Davenport, 1983).
Equity issues
Allocations entail distribution of sediment control needs
or expectations among different point and nonpoint
sources. Because costs of controlling different sources
can vary substantially, the allocation analysis should
consider whether the allocations create reasonably fair
distributions of control costs. Analysts might want to
develop cost/benefit analyses of potential control actions
to assist in fairly distributing control costs.
Typically, responsible parties are more likely to carry
out actions needed to implement TMDLs if they feel
their share of the sediment control burden is fair.
Therefore, analysts are advised to consult with affected
stakeholders during the development of allocations.
Many methods for developing allocations that result in
equitable control burdens are available. Refer to
USEPA (1991a, 1991b, 1999) for additional guidance on
allocation development.
Variability in loads and impacts
Allocations should be developed with an understanding
of spatial and temporal variability in sediment loading
and designated use impacts. The allocations should be
established at levels that ensure that designated uses are
protected at critical time periods and in key locations
(e.g., allowance of zero anthropogenic sediment
discharge to stream reaches containing spawning
grounds during spawning periods).
Margin of safety issues
As discussed in the introduction, the margin of safety
(MOS) required in each TMDL can be addressed
implicitly through inclusion of conservative analytical
assumptions or methods or explicitly through
reservation of a portion of the available loading to
account for uncertainty. The explicit MOS approach is
usually addressed during the allocation phase. In cases
where the TMDL provides the required MOS through
implicit analysis assumptions, the allocation section
should indicate that this approach makes the need for an
explicit reservation of loading capacity as an MOS
unnecessary. Tha allocation section should also identify
the conservative assumptions used in the analysis and
explain how they adequately account for uncertainties.
Where an explicit allocation is reserved as an MOS, the
analysis should discuss why this reservation is adequate
to account for uncertainty present in the TMDL.
Future Growth
Recognizing that in some watersheds there will be
growth that results in increased loadings, some TMDLs
may allocate a portion of the loading capacity for this
growth. In this situation, the State will make the
specific allocation to a facility in the future when the
loading increases occur. Current guidance clarifies that
any reserved allocation for future growth cannot also be
used as a margin of safety.
On August 23, 1999, EPA published proposed rules that,
when finalized, will require that an approvable TMDL
must include an allowance for future growth which
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accounts for reasonably foreseeable increases in
pollutant loads, or otherwise state that there is no
capacity for growth. States, Territories, and authorized
Tribes will need to include future growth in their
allocation strategy and carefully document their
decision-making process. The TMDL documentation
should clearly explain the implications of the growth
allocation decision on new and existing point and
nonpoint sources of a pollutant. It should also explain
what other local planning processes may be affected.
Needs for stakeholder involvement and public
outreach
Since the reason for establishing sediment TMDLs is to
set the stage for productive action, TMDL allocations
that clearly define needed load reductions are more
likely to be understood and supported by stakeholders.
If allocations are vague and the roles of agencies,
landowners, and other stakeholders are not clear,
misunderstandings might arise later and project
effectiveness could suffer. The best ways to ensure
stakeholders' support for allocations are to involve them
in allocation development early, to fully document the
basis for each allocation, and to show how the
allocations "add up" to provide an effective overall plan.
Implementation and reasonable assurance issues
Feasible allocations should be supported by information
or analysis providing reasonable assurance that their
implementation will occur and that TMDL targets will
be met. Where point source discharges are concerned, it
might be enough to cite the regulatory basis for point
source permitting and to explain that a permit will be
required. With nonpoint sources, it is sometimes
difficult to demonstrate that a set of management
measures or restoration projects can be developed to
achieve the projected load reductions (EPA 199la).
(EPA's August 1997 policy memorandum [USEPA,
1997a] discusses implementation issues for waters
impaired solely or primarily by nonpoint sources.) The
relationship between land management activities and
sediment processes is complex and not easy to quantify
through simple measures. Therefore, creativity and
flexibility might be needed to build a record supporting
the feasibility and adequacy of proposed allocations. In
general, the greater the demand for specific assurances
that allocations are feasible and that associated actions
will be implemented, the more likely it will be that
specific quantitative allocations linking sediment
loading caps, reductions, or other source control targets
need to be associated with specific management actions.
In some projects, reasonable assurance that the load
reduction will be achieved might be related to
stakeholders agreeing on the watershed's problems and
the implementation of appropriate solutions.
Many methods can be used to document the basis for
allocations and to assess their expected feasibility.
Documentation will be most effective if it explains
(1) why the allocations, when attained, will result in
sediment loads that do not exceed waterbody
assimilative capacity as identified in the linkage element
and (2) how the allocations will be implemented.
Documentation may be based on modeling results or
other rigorous quantitative analysis showing why a
certain allocation meshes with total allowable loads or
needed sediment reductions. However, less
sophisticated approaches might also work in some
settings. For example, in a case where a sediment
loading percentage reduction target needs to be met
through BMP implementation, the analyst could show
literature values regarding effectiveness found in BMP
guidance documents. Good sources of information about
sediment BMPs and their effectiveness include EPA's
management measures guidance (USEPA, 1993), USDA
Forest Service conservation handbooks (e.g., USDA
Forest Service, 1988), NRCS Field Office technical
guides, and state BMP handbooks (e.g., Platts, 1990). In
addition, reference could be made to results from similar
projects. If a similar project was effective, analysts
might have a sound basis for suggesting that the same
control or restoration approaches would work. Where a
strong adaptive management component is planned for
the project, less rigorous documentation of the expected
effectiveness of the allocations could be adequate.
In cases where implementation of actions associated
with allocations is expected to occur under the auspices
of a regulatory mechanism (e.g., timber harvest plans,
grazing allotments, construction permit, or storm water
permit), it might be helpful to describe how the actions
are factored into the regulatory framework. Such a
description would help bolster the analysis supporting
the allocations.
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2. What is an appropriate allocation method?
Many methods are available to establish effective
allocations. The first step in establishing allocations is to
determine the segments and sources that require
allocations to achieve water quality standards. Sources
where allocations are needed might be evident based on
screening-level analyses. However, the actual
establishment of allocations will depend on many
factors, such as decisions about whether reductions
should be spread out across all sources or applied to a
few targeted sources. Each TMDL will likely have its
own criteria for making these decisions (e.g., magnitude
of impact, degree of management control now in place,
feasibility, probability of success, costs). For sediment
TMDLs, analysts should consider the following options
as a starting point for expressing allocations:
• Maximum allowable loads
• Percentage reduction targets
• Performance-based actions or practices
However, other allocation options are available and
should be explored.
Maximum allowable loads
Specific allocation of maximum allowable mass loads to
specific source categories, tributaries, or channel types
or from specific parcels, erosion process categories (e.g.,
landslides), or distinct geologic types are the allocation
approaches most commonly used in sediment TMDLs
(e.g., Garcia River, California, Simpson Timberlands,
Washington [draft]). Specific allocations of loading
caps or other thresholds offer relatively precise targets
and a clear basis for monitoring. Given the variability
of sediment dynamics in many systems, it might not be
feasible or wise to set allocations in this manner because
they might not reflect the expected imprecision in the
target and source analysis components of some TMDLs.
If these targets are framed as preliminary hypotheses to
be tested and adjusted if necessary over time, they might
be more defensible and will likely receive a more
positive response from stakeholders. Another approach
to addressing expected variability in loadings over time
is to set allocations for relatively long time steps (e.g.,
average annual sediment load per square mile) expressed
as a multiyear rolling average (e.g., 10-year rolling
average for Redwood Creek, California, TMDL). This
approach recognizes that annual or seasonal loads will
vary substantially in response to different precipitation
patterns.
The disadvantage is that this approach creates a
significant lag time between the implementation of
TMDL-related sediment controls and the review of the
effectiveness of those controls. Some TMDLs address
this disadvantage by incorporating sensitive monitoring
triggers as numeric targets. For example, the Newport
Bay/San Diego Creek TMDLs include numeric targets
for maintenance of wetland habitat types that are
sensitive to change due to sediment loading. If the
acreage of any particular habitat type in a key wildlife
refuge changes more than 1 percent, the TMDL
implementation plan requires the state to immediately
review the TMDL for potential revisions. It might also
be possible to use turbidity or suspended sediment
targets to provide more sensitive numeric targets.
(Targets of this type are discussed in the numeric targets
section in Chapter 4.)
Percentage reduction targets
As an alternative to maximum allowable loads,
allocations can be expressed in terms of percentage
reductions in sediment loading allocated among sources
(e.g., Deep Creek, Montana). Percent reduction targets
enable the analyst to account for the uncertainties and
variabilities in the analysis of dynamic watershed
settings while providing a quantitative basis for
allocations and subsequent monitoring. The simplicity
of this approach is appealing in many settings.
However, it might be more difficult to measure
attainment of percent reduction targets because this
approach might require more complicated monitoring
than that used for some other methods. For this approach
to work, estimates of baseline sediment loading
conditions by source are needed to determine the
appropriate percentage reductions needed. Relatively
simple baseline estimates might be adequate for this
purpose.
Allocations based on performance of actions or
practices
In some cases, allocations can be expressed in terms of
project performance expectations (e.g., tons of
sedimentation avoided due to road improvements)
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associated with specific projects or management
practices, which, as a group, "add up" to meet overall
sediment management goals (e.g., South Fork Salmon
River, Idaho, and Chalk Creek, Utah [USEPA, 1996c)].
This allocation approach usually entails estimating the
erosion reduced or avoided as a result of implementing
specific practices. Project performance expectations
offer tangible connections to specific management or
restoration actions in specific places. This approach
facilitates the identification of specific action based on
allocations and the monitoring of project effectiveness.
Its main drawback is that it is often difficult to show
how the projected sum of avoided sedimentation from
multiple projects adds up to reasonable assurance that
overall source reduction or in-stream targets can be
attained. This approach might work best where the
expected magnitude of sediment control actions
significantly exceeds the needed sediment reductions.
A related allocation approach identifies in detail the
practices to be implemented to address specific sources
of concern. Provided with the action plan is a rationale
that shows why the set of identified actions is expected
to be adequate to attain the total sediment load
reductions needed (as identified during the linkage
phase of the TMDL). This rationale could be based on
the professional judgment of resource experts involved
in TMDL and implementation planning; modeling
results; literature and agency guidance that provide
estimates of BMP and restoration effectiveness in
sediment control; and experience with similar sediment
control projects.
Because this approach lacks the direct allocation of
loads or load reductions and instead shows how
allocation of actions is adequate to attain necessary load
reductions, the approach is most appropriate under the
following circumstances:
• Stakeholders strongly support the actions to be
taken, and there is reasonable assurance that the
actions will occur (e.g., landowner and funding
commitments are in place, actions are required by
permits or ordinances).
• Adequate information concerning BMP or
restoration project effectiveness is available to
support an argument that the actions will be
adequate to attain needed load reductions.
• Follow-up monitoring is included as part of the
TMDL and implementation plan.
3. How are allocations described in the TMDL
document?
Individual allocations by source should be identified,
along with any allocation characteristics that account for
variability in source inputs or in-stream impacts (e.g.,
seasonal variations in allowed loads). The rationale
supporting the allocations should be described in
adequate detail to show that the allocations will result in
attainment of water quality standards and that their
implementation is feasible. Uncertainties in the analysis
should also be discussed. Where implementation
planning is done concurrently with allocation, it might
be appropriate for the allocation section to reference the
implementation plan to further explain the intended
approaches for addressing sources. In most cases,
however, the document should clearly distinguish the
allocations from the implementation actions.
4. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the allocation step, an
approvable TMDL will need to include the following
information:
1. Wasteload allocations to each industrial and
municipal point source permitted under §402 of
the Clean Water Act discharging the pollutant
for which the TMDL is being established;
wasteload allocations for storm water, combined
sewer overflows, abandoned mines, combined
animal feeding operations, or any other
discharges subject to a general permit may be
allocated to categories of sources, subcategories
of sources or individual sources; pollutant loads
that do not need to be allocated to attain or
maintain water quality standards may be
included within a category of sources,
subcategory of sources or considered as part of
background loads; and supporting technical
analyses demonstrating that wasteload
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allocations when implemented, will attain and
maintain water quality standards;
2. Load allocations to nonpoint sources of a
pollutant, including atmospheric deposition or
natural background sources. If possible, a
separate load allocation must be allocated to
each source of natural background or
atmospheric deposition; load allocations may be
allocated to categories of sources, subcategories
of sources or individual sources. Pollutant loads
that do not need to be allocated may be included
within a category of sources, subcategory of
sources or considered as part of the background
load. Supporting technical analyses must
demonstrate that load allocations, when
implemented, will attain and maintain water
quality standards;
3. A margin of safety expressed as unallocated
assimilative capacity or conservative analytical
assumptions used in establishing the TMDL;
e.g., derivation of numeric targets, modeling
assumptions, or effectiveness of proposed
management actions which ensures attainment
and maintenance of water quality standards for
the allocated pollutant;
4. Consideration of seasonal variation and high
and low flow conditions such that water quality
standards for the allocated pollutant will be met
during all design environmental conditions;
5. An allowance for future growth which accounts
for reasonably foreseeable increases in pollutant
loads; and
6. An implementation plan, which may be
developed for one or a group of TMDLs.
Minimum Elements of an Approvable Implementation
Plan
Whether an implementation plan is for one TMDL or a
group of TMDLs, it must include at a minimum the
following eight elements:
• Implementation actions/management measures:
a description of the implementation actions
and/or management measures required to
implement the allocations contained in the
TMDL, along with a a description of the
effectiveness of these actions and/or measures in
achieving the required pollutant loads or
reductions.
Time line: a description of when activities
necessary to implement the TMDL will occur. It
must include a schedule for revising NPDES
permits to be consistent with the TMDL. The
schedule must also include when best
management practices and/or controls will be
implemented for source categories,
subcategories and individual sources. Interim
milestones to judge progress are also required.
Reasonable assurances: reasonable assurance
that the implementation activities will occur.
Reasonable assurance means a high degree of
confidence that wasteload allocations and /or
load allocations in TMDLs will be implemented
by Federal, State or local authorities and /or
voluntary action. For point sources, reasonable
assurance means that NPDES permits (including
coverage under applicable general NPDES
permits) will be consistent with any applicable
wasteload allocation contained in the TMDL.
For nonpoint sources, reasonable assurance
means that nonpoint source controls are specific
to the pollutant of concern, implemented
according to an expeditious schedule and
supported by reliable delivery mechanisms and
adequate funding.
Legal or regulatory controls: a description of
the legal authorities under which
implementation will occur (as defined in 40
CFR 130.2(p)). These authorities include, for
example, NPDES, Section 401 certification,
Federal Land Policy and Management programs,
legal requirements associated with financial
assistance agreements under the Farm Bills
enacted by Congress and a broad variety of
enforceable State, Territorial, and authorized
Tribal laws to control nonpoint source pollution.
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Time required to attain water quality standards:
an estimate of the time required to attain water
quality. The estimates of the time required to
attain and maintain water quality standards must
be specific to the source category, subcategory
or individual source and tied to the pollutant for
which the TMDL is being established. It must
also be consistent with the geographic scale of
the TMDL, including the implementation
actions.
Monitoring plan: a monitoring or modeling plan
designed to determine the effectiveness of the
implementation actions and to help determine
whether allocations are met. The monitoring or
modeling plan must be designed to describe
whether allocations are sufficient to attain water
quality standards and how it will be determined
whether implementation actions, including
interim milestones, are occurring as planned.
The monitoring approach must also contain an
approach for assessing the effectiveness of best
management practices and control actions for
nonpoint sources.
Milestones for attaining water quality
standards: a description of milestones that will
be used to measure progress in attaining water
quality standards. The milestones must reflect
the pollutant for which the TMDL is being
established and be consistent with the
geographic scale of the TMDL, including the
implementation actions. The monitoring plan
must contain incremental, measurable
milestones consistent with the specific
implementation action and the time frames for
implementing those actions.
TMDL revision procedures: a description of
when TMDLs must be revised. EPA expects that
the monitoring plan would describe when failure
to meet specific milestones for implementing
actions or interim milestones for attaining water
quality standards will trigger a revision of the
TMDL.
RECOMMENDATIONS FOR ALLOCATIONS
• Allocations should be accompanied by adequate
documentation to provide reasonable assurance that
the suggested changes will result in attainment of
water quality standards.
• It might be helpful to organize allocations along the
same lines as source assessment and linkage (e.g.,
by source category or land parcel).
• Involve affected stakeholders in developing
allocations.
• Clarify whether the margin of safety is implicit or
explicit and explain the rationale behind the
decision.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1991b. Technical support document for water
quality-based toxics control. EPA/505/2-90-001. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1993. Guidance specifying management
measures for sources of nonpoint pollution in coastal
waters. EPA 840-B-92-002. U.S. Environmental
Protection Agency, Washington, DC.
USEPA 1999. Draft guidance for water quality-based
decisions: The TMDL process (second edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
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Follow-up Monitoring and Evaluation
Objective: Define the monitoring and evaluation plan to
validate TMDL elements, assess the adequacy of control
actions to implement the TMDL, and provide a basis for
reviewing and revising TMDL elements or control
actions in the future.
Procedure: Identify the key questions that a monitoring
plan needs to address and evaluate monitoring options
and the feasibility of implementing a monitoring
program. Describe the specific monitoring plan,
including timing and location of monitoring activities,
parties responsible for conducting monitoring, and
quality assurance/quality control procedures. Describe
the schedule for reviewing monitoring results to
consider the need for TMDL or action plan revisions,
and discuss the adaptive management approach to be
taken. The monitoring component of a TMDL results in
a description of monitoring and adaptive management
plan objectives, methods, schedules, and responsible
parties.
OVERVIEW
Sediment-related impacts on designated uses are often
difficult to characterize. For this reason, sediment
TMDLs are likely to have significant uncertainty
associated with selection of numeric targets and
estimates of source loadings and waterbody assimilative
capacity. Recognizing the inherent uncertainty, EPA
has encouraged the development of TMDLs using
available information and data with the expectation that
a monitoring plan will be developed and submitted with
the TMDL (USEPA, 1991a, 1999). This approach
allows proceeding with source controls while additional
monitoring data are collected to provide a basis for
reviewing and revising the TMDL. This "adaptive
management" approach enables stakeholders to move
forward with resource protection based on reasonably
rigorous planning and assessment.
The monitoring and adaptive management plan is a
central element of TMDLs and is highly advisable for
all sediment TMDLs. This chapter discusses key factors
to be considered in developing the monitoring plan and
suggests additional sources of guidance on monitoring
plan development.
Many types of monitoring activities should be
considered when developing the monitoring plan
(MacDonald et al., 1991). The types of monitoring
programs and their definitions as used in this document
are from monitoring guidelines developed by
MacDonald et al. (1991). They include
• Baseline monitoring
• Implementation monitoring
• Effectiveness monitoring
• Trend monitoring
• Validation monitoring
Baseline monitoring characterizes existing conditions
and provides a basis for future comparisons. Baseline
monitoring should also include information on source
controls in place in the watershed, including the types of
controls present, where they are located, and general
information on their past effectiveness in controlling
erosion. This type of monitoring is not always
necessary for the monitoring plan. Usually, some
baseline data that were considered during TMDL
development already exist.
Implementation monitoring ensures that identified
management actions (such as specific BMPs or resource
restoration or enhancement projects) are undertaken.
Implementation monitoring is often cited as the most
cost-effective of the monitoring types because it
provides information on whether BMPs are being
installed or implemented as intended. This type of
monitoring will not provide a link to in-stream water
quality.
Effectiveness monitoring is used to assess whether the
source controls had the desired effect. Specific projects
that potentially affect water quality conditions should be
monitored to determine their immediate on-site effects.
Trend monitoring is used to assess changes in conditions
over time relative to the baseline and identified target
values. Trend monitoring is critical, assuming the other
elements of the TMDL are appropriately developed. It
addresses the changing conditions in the waterbody that
result from TMDL-specific activities, as well as other
land management activities over time. This is the most
critical component of the monitoring program since it
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also documents progress toward achieving the desired
water quality conditions.
Validation monitoring is used to validate source analysis
and linkage methods. This type of monitoring provides
a different data set that can be used to provide an
unbiased evaluation of the overall performance of
methods or models used in the analysis.
A monitoring program includes the following elements,
which should be addressed in the monitoring plan:
• The specifications for the location and timing of
monitoring.
• The types of monitoring techniques to be used.
• The standard operating procedures and appropriate
quality assurance protocols.
• Procedures for the storage of collected information
and for internal and public access to such
information.
• Analytical techniques and objectives for the
interpretation and analysis of information gathered.
• A process for refining and modifying the monitoring
design in response to changing objectives and
improved information.
• A designated laboratory with sufficient capacity and
appropriate levels of certification.
It is not possible to provide details on the factors that
should be considered in development of monitoring
plans for all environments in this document. Instead,
this document provides a review of general monitoring
considerations and factors that might help to optimize
data collection and interpretation in the context of
TMDL development.
Key Questions to Consider for Follow-up Monitoring and
Evaluation
1. What key factors influence monitoring plan design?
2. What are some of the potential monitoring approaches for
sediment TMDLs?
3. What is included in an appropriate monitoring plan?
4. What is an appropriate adaptive management plan, including
review and revision schedule?
5. What constitutes an adequate monitoring plan?
KEY QUESTIONS TO CONSIDER FOR FOLLOW-UP
MONITORING AND EVALUATION
1. What key factors influence monitoring plan
design?
Many factors influence the necessary rigor of a
monitoring plan. For example, in watersheds where
limited data are available for TMDL development, a
more robust monitoring plan that outlines the steps to be
taken to refine problem identification or confirmation
might be necessary. In watersheds where the problem is
better understood and source controls are in place, it
might be more desirable for the monitoring plan to focus
on monitoring source control implementation. Some of
the key factors that influence the development of a
monitoring plan include the following:
• What specific TMDL elements need evaluation?
• How can tracking of implementation of source
controls be included in the monitoring plan?
• How can stakeholder involvement and goals be
included?
• How can existing monitoring activities, resources,
and capabilities be fully utilized?
What specific TMDL elements need evaluation?
TMDL problem identification, indicators and numeric
targets, source estimates, and allocations might need
reevaluation to determine whether they are accurate and
effective. The monitoring plan should define specific
questions to be answered about these components
through the collection of monitoring information. The
following factors/questions should be considered when
determining on which components additional or new
monitoring should be focused:
• Are the selected indicators and numeric targets
capable of detecting designated use impacts and
responses to control actions?
• What is the level of confidence in the
characterization of baseline or background
conditions?
• Were the data used to establish the numeric targets
of sufficient quality to reasonably represent the
appropriate desired conditions for designated uses of
concern? Was uncertainty in the data within an
acceptable range for the type of data?
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• Was the source assessment comprehensive or are
other sources suspected? Have sources been
accurately estimated?
• Was the linkage between sources and in-stream
impacts accurately characterized? Did the
characterization rely heavily on screening-level
analyses due to a lack of data? Would additional
data provide any significant improvements to the
analyses?
• Were the erosion and hydrologic processes that
affect sediment production or impacts on designated
uses accurately characterized?
• Where reference sites were used to help determine
TMDL targets and load reduction needs, were
reference site conditions accurately characterized?
Would the analysis benefit from comparison to
additional reference sites or from additional data
collected from reference sites?
How can tracking of implementation of source
controls be included in the monitoring plan?
It is often important to determine whether actions
identified in the implementation plan were actually
carried out (implementation monitoring) and whether
these actions were effective in reaching the desired
condition as outlined in the TMDL (effectiveness
monitoring).
Specific questions to be considered when developing the
monitoring plan include the following:
• What types of implementation problems are
expected? Will specific landowners require special
attention (e.g., landowners not party to the TMDL)
or technical support?
• How can implementation monitoring be conducted
in large watersheds?
• How will the implementation monitoring results be
assessed and used in revising the TMDL?
• Will the implementation monitoring include any
assessment of BMP effectiveness?
How can stakeholder involvement and goals he
included?
Watershed stakeholders often participate in follow-up
monitoring, and their interests, in addition to TMDL
analysis, should be considered in devising monitoring
plans. Monitoring plans should address the following:
• What stakeholder/volunteer groups are willing to
participate in monitoring efforts?
• Where are likely locations for stakeholder/volunteer
monitoring efforts?
• What types of data are amenable to collection by
stakeholders or volunteers?
• How will data from stakeholders or volunteers be
used in the TMDL revision?
How can existing monitoring activities, resources,
and capahilities he fully utilized?
Analysts should identify existing and planned
monitoring activities in an effort to address TMDL
monitoring needs in concert with other efforts,
particularly where a long-term monitoring program is
envisioned, the study area is large, or water quality
agency monitoring resources are limited. Staff
capabilities and training should also be considered to
ensure that monitoring plans are feasible. Factors to
consider include the following:
• What data collection efforts are ongoing in the
watershed? What kinds of data have been collected
and what methods have been used?
• What other types of programs or studies are ongoing
or planned in the watershed that were not identified
in the original TMDL analysis? Will data collected
Characteristics of Effective Monitoring Plan
Quantifiable approach. Results must be discernible over time
so that they can be compared to previous or reference
conditions.
Appropriate in scale and application, and relevant to designated
or existing uses and the TMDL methods.
Adequately precise, reproducible by independent investigators,
and consistent with scientific understanding of the problems
and solutions.
Able to distinguish among many different factors/sources (e.g.,
roads, mass wasting, agricultural practices, urban runoff, in-
stream historical loads).
Understandable to the public and supported by stakeholders.
Feasible and cost-effective.
Anticipatory of potential future conditions and climatic
influences.
Minimally disruptive to the designated uses during data
collection.
Conductive to reaching and sustaining conditions that support
the designated or existing use.
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by the programs or studies be of any use in a
TMDL revision? Does the potential exist for
pooling data collection and analysis resources?
• Were the data used in the original TMDL analysis?
If not, why were the data omitted?
• Are known volunteer monitoring groups active in
the watershed? In the region?
In addition to the factors presented above, many other
practical considerations influence the design and
development of a monitoring plan. Practical constraints
include problems with access to monitoring sites due to
landowner restrictions, physical barriers (e.g.,
topography), seasonal weather concerns, and concerns
about indirect impacts of monitoring on habitat. Other
factors influencing the design of monitoring plans and
different types of monitoring of interest for TMDLs are
discussed in detail in MacDonald et al. (1991).
2. What are some of the potential monitoring
approaches for sediment TMDLs?
The protocol chapters concerning numeric targets,
source analysis, and linkage discuss several analysis
approaches that could provide the basis for monitoring
parameter selection. Potential monitoring parameters
are discussed in detail in MacDonald et al. (1991), Reid
and Dunne (1996), and other monitoring texts.
Approaches that might prove useful for TMDL and
implementation plan monitoring include, but are not
limited to, the following areas:
• Monitoring of channel condition and bed material to
assess changes in channel structure and substrate
composition.
• Aerial photography to assess changes in channel
structure and erosion sources.
• Suspended load, bedload, and flow data to assess
changes in sediment concentrations and mass loads.
• Biological indicators (e.g., invertebrates, fish
populations, spawning rates, redd counts).
• Riparian and streambank indicators (e.g., woody
debris, vegetation, erosion features).
• Hillslope erosion features (e.g., mass wasting
features, gullies).
• Drainage features (e.g., reservoir, settlement basin,
and drainage channel sediment levels).
• Calibrated models that can be used to simulate the
implementation of controls. This approach can
provide an interim evaluation of the potential
effectiveness of different implementation
approaches and the adequacy of different TMDL
elements.
3. What is included in an appropriate monitoring
plan?
The first step in developing an appropriate monitoring
and adaptive management plan is to clearly identify the
goals of the monitoring program. It might be possible to
accomplish several of these monitoring goals
simultaneously. For example, the primary need in most
TMDLs will be to document progress toward achieving
the numeric targets. During this process, the additional
information collected might lead to a better
understanding of the processes, suggesting a revision to
the source analysis that would better pinpoint the
sediment problem and lead to faster attainment of water
quality improvements, or it might be that a particular
restoration or enhancement project did not produce the
desired effects and some changes to it should be
undertaken.
Other guidelines for developing a monitoring plan
include the following:
• Address the relationships between the monitoring
plan and the TMDL's numeric targets, source
analysis, linkages, and allocations, as well as the
implementation plan.
• Articulate specific questions to be answered in the
form of monitoring hypotheses, and explain how the
monitoring program will answer those questions.
• Explain any assumptions being made.
• Discuss the likely effects of episodic events.
• The design can be delineated by source type, by
geographical area, and/or by ownership parcel.
• Describe the monitoring methods to be used and
provide the rationale for selection of these methods.
• Define monitoring locations and frequencies, and
list who will be responsible for conducting the
monitoring.
• Develop an appropriate Quality Assurance Project
Plan. Detail sampling methods, selection of sites,
and analysis methods consistent with accepted
quality assurance/quality control practices. Have
the monitoring plan peer-reviewed if possible. (For
more information, refer to USEPA, 1994a, 1994b.)
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4. What is an appropriate adaptive management
plan, including review and revision schedule?
The plan should contain a section addressing the
adaptive management component. This section should
discuss when and how the TMDL will be reviewed. If
possible, the plan should describe criteria that will guide
TMDL review and revision. For example, the plan
could identify expected levels of progress toward
meeting TMDL numeric targets at the time of the initial
review, stated in terms of interim numeric targets or
interim load reduction expectations. In addition, the
plan could identify "red flag" thresholds for key
indicators that would signal fundamental threats to
designated or existing uses and perhaps trigger a more
in-depth review of the TMDL and implementation plan
components. The adaptive management plan can also
contain provisions for modifying the monitoring plan.
The adaptive management component does not need to
schedule every conceivable TMDL review; it should be
adequate to indicate the estimated frequency of review
and identify a specific date for the initial review. It
would be difficult to reliably forecast how often TMDL
reviews will be needed, especially where problems
might take several decades (or longer) to remediate.
5. What constitutes an adequate monitoring plan
for the TMDL document?
Because monitoring and adaptive management will be
key elements of most sediment TMDLs, the TMDL
should contain a monitoring and adaptive management
plan (USEPA, 1991a, 1999). The plan should
incorporate each of the components discussed above
along with the rationale for the monitoring and adaptive
management approach. The plan should clearly indicate
the monitoring goals and hypotheses, the parameters to
be monitored, the locations and frequency of
monitoring, the monitoring methods to be used, the
schedule for review and potential revision, and the
parties responsible for implementing the plan. If it is
infeasible to develop the monitoring plan in detail at the
time of TMDL adoption, it might be adequate to identify
only the basic monitoring goals, the review time frame,
and the responsible parties while committing to develop
the full monitoring plan in the near future.
6. What changes does the proposed rule speak
to?
On August 23, 1999, EPA published proposed rules that
specify that approvable TMDLs must include at a
minimum ten elements. Within the monitoring step, an
approvable TMDL will need to include a monitoring
plan as part of the implementation plan. The monitoring
plan needs to determine the effectiveness of control
actions and/or management measures being
implemented and whether the TMDL is working, as well
as a procedure that will be followed if components of a
TMDL must be refined. The plan should clearly
indicate the monitoring goals and hypotheses, the
parameters to be monitored, the locations and frequency
of monitoring, the monitoring methods to be used, the
schedule for review and potential revision, and the
parties responsible for implementing the plan. It must
contain incremental, measurable targets consistent with
the specific implementation action and the time frames
for implementing those actions. This information is
needed to adequately assess whether the specified
actions are sufficient to attain water quality standards.
The following are key factors to consider when
developing a TMDL monitoring plan:
• Need to evaluate specific TMDL components.
TMDL problem identification, indicators, numeric
targets, source estimates, and allocations might need
reevaluation to determine whether they are accurate
and effective. The monitoring plan should define
specific questions to be answered about these
components through the collection of monitoring
information.
• Need to evaluate implementation actions. It is often
important to determine whether actions identified in
the implementation plan were actually carried out
(implementation monitoring) and whether these
actions were effective in attaining TMDL
allocations (effectiveness monitoring). Specific
questions to be answered concerning
implementation actions should be articulated as part
of the monitoring plan.
• Stakeholder goals for monitoring efforts.
Watershed stakeholders often participate in
follow-up monitoring, and their interests, in addition
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to TMDL analysis, should be considered in devising
monitoring plans.
• Existing monitoring activities, resources, and
capabilities. Analysts should identify existing and
planned monitoring activities to address TMDL
monitoring needs in concert with these efforts,
particularly where a long-term monitoring program
is envisioned, the study area is large, or water
quality agency monitoring resources are limited.
Staff capabilities and training should also be
considered to ensure that monitoring plans are
feasible.
• Practical constraints to monitoring. Monitoring
options can be limited by practical constraints (e.g.,
problems with access to monitoring sites and
concerns about indirect impacts of monitoring on
habitat).
RECOMMENDATIONS FOR FOLLOW-UP
MONITORING AND EVALUATION
• Clearly identify the goals of the monitoring
program.
• Define specific questions to be answered concerning
the evaluation of individual TMDL elements.
• If possible, coordinate with other existing or
planned monitoring activities.
• Determine which type or types of monitoring (e.g.,
implementation, trend) are appropriate for
accomplishing the desired goals.
• Develop an appropriate quality assurance plan;
follow-up monitoring should be designed to yield
defensible data that can support future analysis.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document).
MacDonald, L., A.W. Smart, and R.C. Wissmar. 1991.
Monitoring guidelines to evaluate effects of forestry
activities on streams in the Pacific Northwest and
Alaska. EPA 910/9-91-001. U.S. Environmental
Protection Agency, Region 10, Nonpoint Source
Section, Seattle, WA.
USEPA. 1992. Monitoring guidance for the national
estuary program. EPA 842 B-92-004. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1996. Nonpoint source monitoring and
evaluation guide. Draft final, November 1996. U.S.
Environmental Protection Agency, Office of Water,
Washington, DC.
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Protocol for Developing Sediment TMDLs
Assembling the TMDL
Objective: Clearly identify components of a TMDL
submittal to support adequate public participation and to
facilitate TMDL review and approval.
Procedure: Compile all pertinent information used to
develop the TMDL and prepare the final submittal. The
final submittal should be supported by documentation
for all major assumptions and analyses.
OVERVIEW
It is important to clearly identify the "pieces" of the
TMDL submittal and to show how they fit together to
provide a coherent planning tool that can lead to
attainment of water quality standards for sediment-
related water quality impairments. Where TMDLs are
derived from other analyses or reports, it is helpful to
develop a separate document or chapter that ties
together the TMDL components and shows where
background information can be found.
RECOMMENDATIONS REGARDING CONTENT OF
SUBMITTALS
Section 303(d) of the CWA and EPA's implementing
regulations specify that a TMDL consists of the sum of
wasteload allocations for future and existing point
sources and load allocations for future and existing
nonpoint sources and natural background, considering
seasonal variation and a margin of safety. These loads
are established at levels necessary to implement
applicable water quality standards with seasonal and
interannual variation and a margin of safety. Experience
indicates, however, that information in addition to the
statutory and regulatory requirements is useful to ensure
adequate public participation and to facilitate EPA
review and approval. Since the state and EPA are
partners in the TMDL development process, it is in their
best interest to work together to determine how much
supporting information is needed in the TMDL
submittal.
Recommended Minimum Submittal Information
The following list of elements provides a suggested
outline for TMDL submittals:
1. Submittal Letter
• Each TMDL submitted to EPA should be
accompanied by a submittal letter stating that
the submittal is a draft or final TMDL submitted
under section 303(d) of the CWA for EPA
review and approval.
2. Problem Statement
Waterbody name and location.
A map is especially useful if information
displayed indicates the area covered by the
TMDL (e.g., watershed boundary or upper and
lower bounds on the receiving stream segment)
and the location of sources.
Waterbody section 303(d) list status (including
pollutant of concern for the TMDL).
Watershed description (e.g., the land cover/land
use, geology/hydrology).
3. Applicable Water Quality Standards and Water
Quality Numeric Targets
Description of applicable water quality
standards including designated use(s) affected
by the pollutant of concern, numeric or narrative
criteria, and the antidegradation policy.
If the TMDL is based on a target other than a
numeric water quality criteria, provide a
description of the process used to derive the
target.
4. Pollutant Assessment
Source inventory with location of
Background
Point sources
Nonpoint sources
Supporting documentation for the analysis of
pollutant loads from each of the sources.
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Assembling the TMDL
5. Linkage Analysis
Rationale for the analytical method used to
establish the cause-and-effect relationship
between the numeric target and the identified
pollutant sources.
Supporting documentation for the analysis (e.g.,
basis for assumptions, strengths and weaknesses
in the analytical process, results from water
quality modeling).
6. TMDL and Allocations
• Total Maximum Daily Load (TMDL)1
The TMDL is expressed as the sum of the
WLAs, the LAs, and the MOS (if an explicit
MOS is included).
If the TMDL is expressed in terms other
than mass per time, an explanation should
be provided for the selection of the other
appropriate measure.
Wasteload Allocations (WLAs)2
Loads allocated to existing and future point
sources.
An explanation of any WLAs based on the
assumption that loads from a nonpoint
source will be reduced.
If no point sources are present, the WLA
should be explicitly expressed as zero.
Load Allocations (LAs)2
Loads allocated to existing and future
nonpoint sources.
Loads allocated to natural background,
where it is possible to separate them from
nonpoint sources.
If there are no nonpoint sources or natural
background, the LA should be explicitly
expressed as zero.
Seasonal Variation1
Description of the method chosen to
account for seasonal and interannual
variation.
Margin of Safety1
An implicit MOS is accounted for through
conservative assumptions in the analysis. To
justify this type of MOS, an explanation of
the conservative assumptions used is
needed.
An explicit MOS is incorporated by setting
aside a portion of the TMDL as the MOS.
Critical Conditions2
Critical conditions associated with flow,
loading, beneficial use impacts, and other
water quality factors are considered.
7. Follow-Up Monitoring Plan
• Recommended component for TMDLs.
Describes the additional data to be collected
to determine if load reductions in the TMDL
lead to attainment of water quality
standards.
8.
9.
Required by statute.
Required by regulation.
Public Participation2
Description of public participation process used.
• Summary of significant comments received and
the responses to those comments.
Implementation Plan
Implementation plans help establish the basis for
approval of TMDLs. They include reasonable
assurances that the load allocations in the
TMDL for nonpoint sources will be achieved.
Supplementary TMDL Submittal Information
In addition to the information described above, TMDL
submittals can be improved by preparing supplemental
information, including a TMDL summary memorandum,
a TMDL executive summary, a TMDL technical report,
and an administrative record. The effort required to
develop these documents should be minimal because
they are largely a repackaging of information contained
in the TMDL submittal. For example, the TMDL
executive summary would be prepared for inclusion in
the TMDL technical report but would also be ideal for
press releases or distribution to the public.
The TMDL summary memorandum provides an
overview of all the essential regulatory elements of a
TMDL submittal. This overview can facilitate
regulatory and legal review. The summary memo should
include the following information:
Waterbody (name, size) and location
• Pollutant of concern
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Protocol for Developing Sediment TMDLs
• Primary pollutant source(s)
• Applicable water quality standards
• Major data/information sources
• Linkage analysis and load capacity
• WLA, LA, MOS, critical condition, background
concentrations, consideration of seasonal variation
• Implementation
• Reasonable assurance
• Follow-up monitoring
• Public participation
The TMDL executive summary provides an overview of
the TMDL, the conclusions and implications, the
analyses, and the background. This document is useful
for public information, news releases, and public
hearing announcements.
The TMDL technical report provides a compilation of
the information sources, technical analyses,
assumptions, and conclusions. This document provides
a summary of the technical basis and rationale used in
deriving the TMDL. A sample report outline might
include the following sections:
1. Executive Summary
2. Introduction
3. TMDL Indicators and Numeric Targets
4. Water Quality Assessment
5. Source Assessment
6. Linking the Sources to the Indicators/Targets
7. Allocation
8. Implementation
9. Monitoring
10. References
The administrative record provides the technical
backup, sources of information, calculations, and
analyses used in deriving the TMDL. After-the-fact
explanations or justifications of EPA's decisions are
generally not permitted. A typical administrative record
might include the following:
• Spreadsheets
• Modeling software, input/output files
Description of the methodology/models used,
and a description of the data used for the
models.
• References
List or index of all documents relied upon by
the state or EPA in making decision.
• Reports
Including any EPA documents i.e., national/
regional guidance, interpretations, protocols,
technical documents relied upon in making
decision.
Comments/correspondence from outside parties
and EPA's or state's responses, including copies
of public notice seeking comment, and final
decision document.
• Communication
Documentation of communication between EPA
and the state or EPA and other federal agencies
regarding the TMDL.
• Paper calculations
• Maps (working copies)
Public Participation
Public participation is a requirement of the TMDL
process and is vital to a TMDL's success. The August
23, 1999, proposed regulation states that the public must
be allowed at least 30 days to review and comment on a
TMDL prior to its submission to EPA for review and
approval. In addition, with its TMDL submittal, a State,
Territory, or authorized Tribe must provide EPA with a
summary of all public comments received regarding the
TMDL and the State's, Territory's, or authorized Tribe's
response to those comments, indicating how the
comments were considered in the final decision.
EPA believes, however, that stakeholders can contribute
much more than their comments on a specific TMDL
during the public review process. Given the
opportunity, stakeholders can contribute credible, useful
data and information about an impaired or threatened
water body. They may also be able to raise funds for
monitoring or to implement a specific control action
and/or management measure.
More importantly, stakeholders can offer insights about
their community that may ensure the success of one
TMDL allocation strategy over an alternative, as well as
the success of follow-up monitoring and evaluation
activities. Stakeholders possess knowledge about a
community's priorities, how decisions are made locally,
and how different residents of a watershed interact with
one another. A thorough understanding of the social,
political, and economic issues of a watershed is as
critical to successful TMDL development as an
understanding of the technical issues. States, Territories,
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Assembling the TMDL
and authorized Tribes can create a sense of ownership
among watershed residents and "discover® innovative
TMDL strategies through a properly managed public
participation process.
Each State, Territory and authorized Tribe is required
to establish and maintain a continuing planning process
(CPP) as described in section 303(e) of the Clean Water
Act. A CPP contains, among other items, a description
of the process that the State, Territory or authorized
Tribe uses to identify waters needing water quality
based controls, a priority ranking of these waters, the
process for developing TMDLs, and a description of the
process used to receive public review of each TMDL.
EPA encourages States, Territories, and authorized
Tribes to use their CPP as the basis for establishing a
process for public participation, involvement, and in
many cases leadership, in TMDL establishment. On a
watershed level, the continuing planning process allows
programs to combine or leverage resources for public
outreach and involvement, monitoring and assessment,
development of management strategies, and
implementation.
RECOMMENDED READING
(Note that the full list of references for this chapter is
included at the end of the document.)
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDL process. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Assessment and
Watershed Protection Division, Washington, DC.
USEPA 1999. Draft guidance for water quality-based
decisions: The TMDL process (Second Edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
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APPENDIX: Case Studies
Deep Creek, Montana, TMDL
Redwood Creek, California, TMDL
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Appendix: Case Studies
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Protocol for Developing Sediment TMDLs
TMDL Summary: Deep Creek, Montana1
Waterbody Type:
Pollutant:
Designated Uses:
Size of Waterbody:
Size of Watershed:
Water Quality Standards:
Indicators:
Analytical Approach:
Stream
Temperature, Sediment
Recreation, Aquatic Life,
Agriculture
Main stem length: 24 miles
87.7 square miles
Narrative
Sediment load, erosive
banks, channel length,
substrate fines, spawning
trout, water temperature,
minimum flow
Slope of discharge vs. TSS
regression
TMDL Submittal Elements
Loading Capacity: Set as a measurable goal of
several TMDL targets, including
suspended sediment load,
amount of erosive banks,
substrate fines and fish counts.
Load Allocation: 50 percent reduction in percent
of reach consisting of erosive
banks, reestablishment of lost
channel length, reduction in fine
sediments, increase the number
of female rainbow trout captured
at weir, decrease the number of
days where maximum
temperatures exceed 73 degrees
F, target low flows in each
reach.
Wasteload Allocation: Zero; no point sources
Seasonal Variation: Inherent in analysis
Margin of Safety: Implicit
Introduction
Deep Creek, a major tributary of the Missouri River
located in Townsend, Montana, provides spawning and
rearing habitat for rainbow trout and brown trout. Deep
Creek is classified by the state of Montana as "B-l,"
which is "suitable for drinking, culinary and food
processing purposes, after conventional treatment;
bathing, swimming and recreation; growth and
propagation of salmonid fishes and associated aquatic
life, waterfowl and furbearers; and agricultural and
industrial water supply."
EPA Region 8 approved a sediment TMDL for Deep
Creek in 1996. This TMDL illustrates a number of
important points. First, it demonstrates how the phased
TMDL process can be used to initiate mitigation
activities even when there is incomplete knowledge of
sediment sources and loading rates. Second, it provides
an example of an approved TMDL in which quantitative
estimates of assimilative capacity and specific numeric
load allocations to individual sediment sources are
satisfied through the specification of performance
targets, such as percent reduction of length of erosive
streambanks, which relate implicitly to load reductions.
The TMDL is therefore a dynamic plan of action, not
just a static allocation of loads. Finally, this sediment
TMDL might be more properly thought of as a plan for
addressing degraded stream geomorphology, of which
sediment is only one aspect. By focusing on
geomorphological aspects, the TMDL is able to
simultaneously address a variety of interrelated
stressors, including excess sediment loading, elevated
temperatures, and degradation of physical habitat.
Problem Identification
A cover memo should describe the waterbody as it is
identified on the state's section 303(d) list, the pollutant
of concern, and the priority ranking of the waterbody.
The TMDL submittal must include a description of the
point, nonpoint, and natural background sources of the
pollutant of concern, including the magnitude and
All information contained in this summary was obtained from Endicott and McMahon, 1996.
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Appendix-1
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Appendix: Case Studies
location of the sources. The TMDL submittal should
also contain a description of any important assumptions,
such as (1) the assumed distribution of land use in the
watershed; (2) population characteristics, wildlife
resources, and other relevant characteristics affecting
pollutant characterization and allocation, as applicable;
(3) present and future growth trends, if this factor was
taken into consideration in preparing the TMDL; and
(4) an explanation and analytical basis for expressing
the TMDL through surrogate measures, if applicable.
Deep Creek supports the valuable Missouri
River/Canyon Ferry Reservoir cold-water trout fishery.
The Canyon Ferry Reservoir is one of the most heavily
fished bodies of water in Montana, and the condition of
the fishery has long been a concern of the Montana
Department of Fish, Wildlife & Parks (MDFWP).
Detailed studies were undertaken in connection with
mitigation of impacts associated with the construction of
Toston Dam on the Missouri River. Construction of the
dam had isolated a stretch of the Missouri River
between the dam and Canyon Ferry Reservoir, leaving
Deep Creek as one of the few spawning streams in the
isolated reach. A major physical barrier to spawning
trout was remedied in 1991 by routing Montana Ditch
under Deep Creek with a siphon. Despite the Montana
Ditch routing effort, however, concerns over habitat
quality remained.
The Natural Resources Conservation Service (NRCS)
developed an inventory of watershed land use using
aerial photographs and analyzed the condition and
stability of the channel by applying a Rosgen
geomorphological analysis. Intensive monitoring of
flows, temperature, suspended sediment, and chemical
water quality was conducted between 1988 and 1994 at
a variety of locations within Deep Creek. Biological
data include trout counts at the Montana Ditch siphon
and redd counts taken by the MDFWP. Rapid
Bioassessment Protocol (RBP) analyses of benthic
macroinvertebrate communities have also been
performed in several reaches of Deep Creek. These data
provide the basis for development of the TMDL and are
summarized in Endicott and McMahon (1996).
Designated uses of Deep Creek include recreation,
support for aquatic life, and agricultural water supply,
but the major concern leading to the TMDL was support
for the trout fishery. Analysis of the available chemical,
physical, and biological data led to the formation of a set
of interlinked hypotheses explaining the poor support of
designated uses, summarized by Endicott and McMahon
(1996) as follows:
. . . aquatic life in Deep Creek is impaired by
several types of habitat degradation. Degraded
instream habitat and water quality in Deep
Creek is the result of degradation of riparian
vegetation communities and dewatering. Bank
stability is poor throughout the lower reaches
resulting in bank collapse, loss of meander
bends, stream entrenchment and high suspended
and deposited fine sediment. Water
temperatures become elevated due to limited
riparian shading and dewatering. Dewatering
may also impair migration of juvenile salmonids
to the Missouri River. The combined effects of
degradation on Deep Creek results in impacts on
aquatic life which can be seen in the low
production of juvenile trout and alteration in
communities of benthic macroinvertebrates [in
downstream reaches]. . . .
These various types and sources of degradation are
linked because all reflect modifications to the natural
form of the stream channel and the stream's riparian
area. Thus, the set of linked causes of nonsupport are
addressed through a TMDL for sediment and stream
geomorphology. It is noted that in addition to the
TMDL for sediment, TMDLs (and target values) for
lack of flow and for temperature2 have also been
established for Deep Creek. Although each TMDL is
designed to address separate concerns, all three are
interrelated since the impacts of both reduced flow and
temperature are closely linked to the impacts addressed
in the sediment TMDL.
Description of the Applicable Water Quality
Standards and Numeric Water Quality Target
The TMDL submittal must include a description of the
applicable state water quality standard, including the
designated use(s) of the waterbody, the applicable
numeric or narrative water quality criterion, and the
Montana has no absolute temperature standards, but has established
standards that prevent certain excursions from natural ambient
temperature values.
Appendix-2
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Protocol for Developing Sediment TMDLs
antidegradation policy. This information is necessary
for EPA to review the load and wasteload allocations
required by the regulation. A numeric water quality
target for the TMDL (a quantitative value used to
measure whether the applicable water quality standard is
attained) must be identified. If the TMDL is based on a
target other than a numeric water quality criterion, a
description of the process used to derive the target must
be included in the submittal.
As is the case with many sediment TMDLs,
management of Deep Creek is framed in terms of
attainment of narrative standards and designated uses,
and no numeric water quality standards are relevant to
the problem. How then were target values of water
quality indicators established? The Deep Creek TMDL
developers (Endicott and McMahon, 1996) state "while
the title 'TMDL' implies that. . . goals are expressed in
terms of concentrations or levels of a given pollutant, a
TMDL can be phrased in terms of any quantifiable goal
related to the aquatic system. For example, a TMDL
can be defined as established decreases in eroding bank
or measured increases in trout recruitment." This broad
interpretation is justified in light of EPA's guidance for
phased TMDLs. EPA (1991) suggests use of a phased
approach for TMDLs for water quality-limited
waterbodies where loading estimates are based on
limited information. Further, EPA regulations (40 CFR
130.2(g)) define load allocations for nonpoint sources as
"best estimates of the loading which may range from
reasonably accurate estimates to gross allotments
The phased approach requires adaptive management
where initial load allocations or mitigation strategies are
established based on best estimates and are subsequently
refined as responses to these actions are observed.
For Deep Creek, water quality indicators were identified
and associated target values were developed based on
problem identification using the available information
and professional judgment and with the expectation that
the targets would be revised through additional
monitoring and adaptive management. The use of more
than one indicator was desirable for Deep Creek to
account for system complexity, multiple stressors, and
the lack of certainty regarding the effectiveness of each
indicator and its numeric target values. Additionally,
the use of multiple indicators allows tracking of both
source control and attainment of uses, even though there
is uncertainty in the exact linkage between sources and
uses.
Five broad categories are applicable to sediment TMDL
indicators: (1) water column indicators, (2) streambed
sediment indicators, (3) biological indicators, (4)
channel condition indicators such as channel form and
stability, and (5) riparian and hillslope indicators. For
Deep Creek, four different indicators and associated
target values were proposed. The indicators and targets
are listed below with the applicable TMDL indicator
category in parentheses.
1. Suspended sediment load (a water column sediment
indicator). Obtain a measurable reduction in
suspended sediment load by decreasing the slope
and intercept of the regression line between
discharge and total suspended solids (TSS) by half
in 4 out of 5 years or by demonstrating no
significant difference in daily TSS load between
Deep Creek and an unimpaired reference stream
during spring runoff in 4 out of 5 years. The utility
of using the reference reach daily TSS load
approach may not be as great as that of the discharge
vs. TSS relationship approach because the daily TSS
load approach is more limited in terms of
acknowledging the variability of the system.
Because Deep Creek is a dynamic system that
experiences significant loading during wet weather
events, the discharge vs. TSS relationship may be
more relevant.
2. Substrate fines (streambed sediment indicator).
Reduce substrate fines (<6.35 mm) in spawning
riffles from 50 percent to 30 percent over the next 5
years.
3. Spawning trout (biological indicator). Meet a target
of 3,000 spawning female wild trout per year
entering Deep Creek from the Missouri River over
the next 10 years.
4. Water temperature. Reduce water temperature
extremes so that temperatures do not exceed 73 °F
for more than 10 days per year along the length of
Deep Creek.
In addition to the four indicator targets noted above,
three other quantifiable goals associated with
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Appendix: Case Studies
achievement of the specified in-stream targets were
identified and set as the TMDL for Deep Creek. For
this type of TMDL, it is important to understand that the
indicator target values are reasonable benchmarks for
measuring progress, rather than enforceable goals.
Source Assessment
The geographic scope of the TMDL is the entire Deep
Creek watershed. Within this general geographic area,
however, the TMDL focuses on specific critical areas
identified by a source assessment. The source
assessment for Deep Creek is based on a reach-by-reach
analysis of channel condition and geomorphology. It
includes historical analysis of changes in stream length
and sinuosity based on the review of aerial photographs
and the estimation of stability for each erosive bank
based on streambank inventories of each reach of Deep
Creek.
The analysis indicates that unstable banks are a key
source of the sediment loading that results in impairment
of uses. A detailed, reach-by-reach analysis of channel
morphology and bank stability identified critical areas
for mitigation and established a basis for prioritizing
initial control efforts. Accordingly, the priorities
identified for remediation include the prevention of
additional loss of channel length and the stabilization of
streambanks and riparian areas that are significant
sources of sediment in the most highly impacted
reaches.
The source assessment reflects the working hypotheses
of causes of use impairment in Deep Creek.
Degradation of habitat condition in Deep Creek was
originally caused by a combination of increased
watershed sediment loads, reduction in flow volume,
and some artificial channel straightening. These
stressors initiated a complex chain of geomorphological
events, which led to loss of meanders, shortening of the
stream and incision into the floodplain, and erosion of
streambanks. Increased bedload requires increased
hydraulic energy for transport, resulting in straightening
of the stream; increasing gradient, width, and
wavelength; and decreasing depth. Increasing gradient,
however, results in undermining of banks, generation of
additional sediment load, and a cycle of continued
degradation, which cannot be addressed through upland
watershed controls alone. In the short term, eroding
banks represent the major source of stressor loading to
Deep Creek and thus are the priority for the first phase
of a phased TMDL.
Loading Capacity: Linking Water Quality and
Pollutant Sources
As described in EPA guidance, a TMDL describes the
loading capacity of a waterbody for a particular
pollutant. EPA regulations define loading capacity as
the greatest amount of loading that a waterbody can
receive without violating water quality standards (40
CFR 130.2(f)). The TMDL submittal must describe the
rationale for the analytical method used to establish the
cause-and-effect relationship between the numeric target
and the identified pollutant sources. In many
circumstances, a critical condition must be described
and related to physical conditions in the waterbody (40
CFR 130.7(c)(l)). Supporting documentation for the
analysis must also be included, including the basis for
assumptions, strengths and weaknesses in the analytical
process, and results from water quality modeling, so that
EPA can properly review the elements of the TMDL that
are required by the statute and regulations.
The linkage analysis should establish the cause-and-
effect relationships between measurable water quality
targets and identified sources. There are various ways
of drawing this linkage, including the use of a
cause/effect model to predict the result of applying
source control with respect to meeting targets,
monitoring data to associate waterbody responses to
flow and loading conditions, statistical and analytical
tools, and best professional judgment. Another option is
to use a reference reach approach that takes conditions
from a healthy stream and establishes them as targets for
the unhealthy stream. Using the reference reach
approach, conditions may have to be normalized or
otherwise adjusted for the unhealthy stream, but the
approach can be helpful in establishing sediment criteria
as well as sediment TMDLs and in providing the linkage
between source control and targets.
For Deep Creek, this established linkage consists
primarily of analysis of observations (including
statistical analyses) and best professional judgment,
although a reference reach approach was used to
establish a linkage between suspended sediment load
and sediment sources. A qualitative analysis of
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Protocol for Developing Sediment TMDLs
probable geomorphic response was determined to be the
most feasible and appropriate method for Deep Creek.
It is noted that a lack of a quantitative linkage is
acceptable in the case of a phased TMDL that
emphasizes adaptive management, as is the case for the
Deep Creek TMDL.
Allocations
EPA regulations require that a TMDL include wasteload
allocation (WLAs), which identify the portion of the
loading capacity allocated to existing and future point
sources (40 CFR 130.2(g)). If no point sources are
present or the TMDL recommends a zero WLA for point
sources, the WLA must be listed as zero. The TMDL
may recommend a zero WLA if the state determines,
after considering all pollutant sources, that allocating
only to nonpoint sources will still result in attainment of
the applicable water quality standard. In preparing the
WLA, it is not necessary that every individual point
source have a portion of the allocation of pollutant
loading capacity. But it is necessary to allocate the
loading capacity among individual point sources as
necessary to meet the water quality standard. The
TMDL submittal should also discuss whether a WLA is
based on an assumption that loads from a nonpoint
source or sources will be reduced. In such cases, the
state will need to demonstrate reasonable assurance that
the nonpoint source reductions will occur within a
reasonable time.
EPA regulations require that a TMDL include load
allocations (LAs), which identify the portion of the
loading capacity allocated to existing and future
nonpoint sources and to natural background (40 CFR
130.2(h)). LAs may range from reasonably accurate
estimates to gross allotments (40 CFR 130.2(g)). Where
it is possible to separate natural background from
nonpoint sources, separate LAs should be made and
described. If there are neither nonpoint sources nor
natural background or the TMDL recommends a zero
LA, an explanation must be provided. The TMDL may
recommend a zero LA if the state determines, after
considering all pollutant sources, that allocating only to
point sources will still result in attainment of the
applicable water quality standard.
The statute and regulations require that a TMDL include
a margin of safety to account for any lack of knowledge
concerning the relationship between effluent limitations
and water quality (CWA § 303(d)(l)(C), 40 CFR
130.7(c)(l)). EPA guidance explains that the MOS may
be implicit, i.e., incorporated into the TMDL through
conservative assumptions in the analysis, or explicit, i.e.,
expressed in the TMDL as loadings set aside for the
MOS. If the MOS is implicit, the conservative
assumptions in the analysis that account for the MOS
must be described. If the MOS is explicit, the loading
set aside for the MOS must be identified.
The statute and regulations require that a TMDL be
established with seasonal variations. The method
chosen for including seasonal variations in the TMDL
must be described (CWA § 303(d)(l)(C), 40 CFR
For many TMDL, allocations consist of assigning
specific, quantitative load allocations and wasteload
allocations, expressed in terms of mass per time loading
rates, to each source of a stressor. In some cases this
will involve development of allocations for each
individual facility and landowner. Allocations,
however, are not necessarily equivalent to identifying
"who is to blame." Instead, the basic objective is to
develop recommendations for load reductions that are
distributed among the various sources while
demonstrating that implementation of the allocations
will achieve numeric targets.
In the case of Deep Creek, the primary immediate
threats are due to unstable banks and loss of meanders,
regardless of what processes initiated geomorphic
disturbance in the stream. The allocation consists in
large part of determining which streambanks have the
greatest potential to contribute sediment loads and then
planning stabilization for these high-priority banks.
Therefore, the allocation is expressed in terms of
relative threat rather than a known loading rate. Bank
stabilization activities for Deep Creek will consist of
installing juniper revetments, planting vegetation, and
excluding cattle from riparian areas. One management
practice implemented in 1992 that has eliminated a
major sediment source was the improvement of the
annual start-up and shut-down practices of the
Broadwater-Missouri ditch (Endicott and McMahon,
1996). This best management practice (BMP) has
significantly decreased sediment pulses from the ditch to
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Appendix-5
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Appendix: Case Studies
Deep Creek and provides a good example to consider for
similar systems.
The TMDLs established for Deep Creek are intended to
indicate the level of pollutant reduction needed to
achieve the in-stream targets (e.g., regarding substrate
fines, spawning trout) and are related to a decrease in
the intensity of sediment loading. The TMDLs
developed for Deep Creek are as follows:
1. Percentage of eroding bank. Decrease the
percentage of eroding streambanks by 50 percent
over the next 10 years, with target conditions
established by reach.
2. Channel length. Over the next 5 years, reestablish
2,275 feet of channel length in meanders (25 percent
of the length of channel that has been lost to
meander reduction and degradation since 1955).
3. Minimum flow. Maintain minimum flows of not less
than 9 cubic feet per second (cfs) in the lower and
upper reaches of Deep Creek and not less than 3 cfs
in the middle reaches.
Although the discrepancy between the four indicator
target values and the three TMDL values may be
considered slight, the differentiation helps to clarify
which indicators are more indicative of suitable fish
habitat and a healthy trout population (i.e., four target
values) and which are more indicative of source control
(i.e., three TMDL values). The indicator target values
are linked to the designated uses of the waterbody and
relevant narrative provisions in the state water quality
standards and, therefore, can be used to measure success
toward meeting those standards and attaining designated
uses. The TMDL values represent the sediment load
reductions needed to meet target values and achieve
water quality standards.
Within the phased TMDL process, the ability to achieve
numeric targets is uncertain, although the proposed
remediation efforts represent a good faith attempt to
achieve these targets. It is fully expected that
management strategies and the specific allocations
implied by these management strategies are likely to
change as monitoring continues.
Monitoring Plan for TMDLs Developed Under the
Phased Approach
EPA's 1991 document, Guidance for Water Quality-
Based Decisions: The TMDL Process (EPA 440/4-91-
001), calls for a monitoring plan when a TMDL is
developed under the phased approach. The guidance
provides that a TMDL developed under the phased
approach also needs to provide assurances that nonpoint
source control measures will achieve expected load
reductions. The phased approach is appropriate when a
TMDL involves both point and nonpoint sources and the
point source WLA is based on an LA for which
nonpoint source controls need to be implemented.
Therefore, EPA's guidance provides that a TMDL
developed under the phased approach should include a
monitoring plan that describes the additional data to be
collected to determine if the load reductions required by
the TMDL lead to attainment of water quality standards.
A plan for continued monitoring is a key and required
component of any phased TMDL. The Deep Creek
TMDL recognizes the importance of monitoring to
guide the adaptive management process and includes
detailed proposals for monitoring in accordance with the
general goals specified by Endicott and McMahon
(1996):
... the proposed monitoring tools cover aspects
of water quality, channel morphology, substrate
characteristics, and aquatic biota. Monitoring
protocols should be applied yearly for between 5
and 10 years . . . following treatment. While not
all the proposed monitoring procedures . . . need
to be implemented, it is important to design a
monitoring protocol for each of the TMDL
targets. In addition, because landowner
involvement is so important to the success of
this [TMDL], monitoring tools that can be
implemented by landowners should be
considered.
Endicott and McMahon (1996) recommend the
following monitoring components and techniques for
analyzing and tracking progress in Deep Creek:
• Annual completion by landowners along Deep
Creek of the riparian monitoring questionnaire
developed by the Montana Riparian Association.
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Protocol for Developing Sediment TMDLs
The questionnaire is designed to assess the
effects of land management on riparian stream
conditions and troubleshoot problems like
excessive soil erosion.
• Monitoring total suspended sediment and discharge
through spring runoff. This monitoring will support
the relationship between discharge and TSS and the
calculation of the yearly load of suspended
sediment.
• Continued monitoring of water temperature to assess
progress toward temperature targets, including the
installation of recording thermographs in the 11
reaches of Deep Creek.
• Measurement of substrate sedimentation by
methods, including substrate core sample analysis,
Wolman pebble counts, and photo series of substrate
at specified locations.
• Measurement of channel morphology changes at
permanent transect locations.
• Establishment of a photographic record of fluvial
and habitat changes at permanent photo points.
• Continued counts of fish at the permanent weirs at
the Montana Ditch siphon coupled with monitoring
of artificial redds and the completion of a basin fish
and fish habitat survey.
• Continued application of the RBPs to assess changes
in habitat conditions and benthic macroinvertebrate
communities.
Implementation Plans/Reasonable Assurances
On August 8, 1997, Bob Perciasepe issued a
memorandum, "New Policies for Establishing and
Implementing Total Maximum Daily Loads (TMDLs),"
which directs EPA regions to work in partnership with
states to achieve nonpoint source load allocations
established for 303(d)-listed waters impaired solely or
primarily by nonpoint sources. To this end, the
memorandum asks that regions assist states in
developing implementation plans that include
reasonable assurances that the nonpoint source load
allocations established in TMDLs for waters impaired
solely or primarily by nonpoint sources will in fact be
achieved; a public participation process; and recognition
of other relevant watershed management processes. In a
water impaired by both point and nonpoint sources,
where a point source is given a less stringent wasteload
allocation based on an assumption that nonpoint source
load reductions will occur, reasonable assurance must be
provided for the TMDL to be approvable. This
information is necessary for EPA to review the load and
wasteload allocations required by the regulation.
Although implementation plans are not approved by
EPA, they help establish the basis for EPA's approval of
TMDLs.
In a water impaired solely by nonpoint sources,
reasonable assurances are not required for a TMDL to
be approvable. For such nonpoint source-only waters,
states are encouraged to provide reasonable assurances
regarding achievement of load allocations in the
implementation plans described in section 7, above. As
described in the August 8, 1997, memorandum, such
reasonable assurances should be included in state
implementation plans and "may be non-regulatory,
regulatory, or incentive-based, consistent with
applicable laws and programs." Endicott and McMahon
(1996) recommend a variety of stream restoration
activities along Deep Creek that would increase bank
stability, decrease erosion, and increase the health of the
fishery by reducing sediment stresses and improving fish
habitat to meet water quality targets. Based on existing
data, a number of reach specific recommendations for
remediation on Deep Creek are proposed. Restoration
implementation activities include the channel
modifications, installation of juniper revetments,
riparian BMPs, willow plantings, widening of riparian
zone width, increases in channel length, and fencing to
exclude livestock from the stream and riparian areas.
References
Endicott, C.L., and T.E. McMahon. 1996. Development
of a TMDL to reduce nonpoint source sediment
pollution in Deep Creek, Montana. Report to Montana
Department of Environmental Quality.
Contact: Bruce Zander, Region 8 TMDL Coordinator * United States
Environmental Protection Agency Region 8 * 999 18th Street Suite
500 • Denver, CO 80202 • (303) 312-6846 •
zander.bruce@epa.gov
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Appendix-7
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Appendix: Case Studies
Appendix-8
First Edition: October 1999
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Protocol for Developing Sediment TMDLs
TMDL Summary: Redwood Creek, California
Waterbody Type:
Pollutant:
Designated Uses:
Size of Waterbody:
Size of Watershed:
Stream
Sediment
Cold freshwater habitat;
migration of aquatic organisms;
estuarine habitat; community,
military, or individual system
use, including drinking water;
maintenance of rare, threatened,
or endangered plant or animal
species; spawning, reproduction,
and/or early development
63 miles long
285 square miles
Water Quality Standards: Narrative
Indicators:
Analytical Approach:
Introduction
In-stream - percent fines, percent
riffles, pool depth, median
particle size diameter, large
woody debris
Hillslope - stream crossings,
road culvert sizing, land/road fill
stability, road surfacing/
drainage, road inspection,
maintenance, decommissioning,
road location, and timber harvest
methods.
Partial sediment budget;
reference reach comparison
Redwood Creek watershed is a 285-mi2 forested
watershed in Humboldt County in northwestern
California. Redwood Creek flows into the Pacific
Ocean near Orick, California. The watershed is narrow
and elongated (65 miles in length and 4 to 7 miles wide)
with mostly mountainous and forested terrain.
Elevations within the watershed range from sea level to
5,300 feet. Redwood National Park composes the lower
portion of the watershed, and timber and livestock
production are the primary land uses upstream of the
park. Redwood Creek is designated for use as a cold
water fishery. The creek has historically supported large
numbers of coho salmon, chinook salmon, steelhead
trout, and other fish species.
USEPA Region 9 approved the sediment TMDL for
Redwood Creek in December 1998. This summary is
based on information contained in Redwood Creek
Sediment Total Maximum Daily Load (USEPA, 1998).
TMDL Submittal Elements
Loading Capacity:
Load Allocation:
Wasteload Allocation:
Seasonal Variation:
Margin of Safety:
1,900 tons/square mile/year
1,900 tons/square mile/year
Zero - No point sources
Inherent annual and seasonal
variation in the delivery of
sediment to streams
Implicit through conservative
assumptions
Problem Identification
A cover memo should describe the waterbody as it is
identified on the state's section 303(d) list, the pollutant
of concern, and the priority ranking of the waterbody.
The TMDL submittal must include a description of the
point, nonpoint, and natural background sources of the
pollutant of concern, including the magnitude and
location of the sources. The TMDL submittal should
also contain a description of any important assumptions,
such as (1) the assumed distribution of land use in the
watershed; (2) population characteristics, wildlife
resources, and other relevant characteristics affecting
pollutant characterization and allocation, as applicable;
(3) present and future growth trends, if this factor was
taken into consideration in preparing the TMDL; and (4)
an explanation and analytical basis for expressing the
TMDL through surrogate measures, if applicable.
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Appendix-9
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Appendix: Case Studies
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Redwood Creek watershed was listed on California's
1992 section 303(d) list as impaired due to
sedimentation, the levels of which violated the existing
water quality objective for protecting designated uses,
particularly the cold water fishery. Accelerated erosion
and other causes of sedimentation are adversely
affecting the migration, spawning, reproduction, and
early development of coho salmon, chinook salmon, and
steelhead trout.
Because the native fishery of Redwood Creek is largely
free of the effects of non-native aquatic species or
hatchery stocks, the creek's ability to support fish
populations is determined primarily by habitat quality
and availability. The Redwood Creek TMDL for
sediment addresses habitat quality impacts associated
with excessive sediment, specifically pool quality,
gravel quality (for spawning and food production), and
changes in channel structure contributing to increased
temperature. Although Redwood Creek is prone to
storm-induced erosional events and the watershed has
natural geologic instability, land management activities
have accelerated the natural erosion process,
overwhelming the stream channel's ability to efficiently
remove the excess sediment.
Specific in-stream problems in Redwood Creek include
fine sediment in spawning gravels, channel aggradation,
lack of suitable pools for rearing habitats, stream
channel instability, and physical barriers to migration.
Specific hillslope problems in the watershed include
improperly designed or maintained roads, sediment from
unstable areas, removal of riparian trees, and loss of
large woody debris.
Description of the Applicable Water Quality
Standards and Numeric Water Quality Target
The TMDL submittal must include a description of the
applicable state water quality standards, including the
designated use(s) of the waterbody, the applicable
numeric or narrative water quality criterion, and the
antidegradation policy. This information is necessary
for EPA to review the load and wasteload allocations
required by the regulation. A numeric water quality
target for the TMDL (a quantitative value used to
measure whether the applicable water quality standard is
attained) must be identified. If the TMDL is based on a
target other than a numeric water quality criterion, a
description of the process used to derive the target must
be included in the submittal.
The state of California has established water quality
objectives (WQOs) to protect designated uses. The
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First Edition: October 1999
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Protocol for Developing Sediment TMDLs
WQO that addresses settleable material and sediment is
as follows:
Water shall not contain substances that result in
deposition of material that causes nuisance or
adversely affect beneficial uses.
The suspended sediment load and suspended
sediment discharge rate of surface water shall not be
altered in such a manner as to cause nuisance or
adversely affect beneficial uses.
Because the applicable water quality standards are
narrative, it was necessary to identify some measurable
parameters (indicators) to evaluate the relationship
between pollutant sources and their impact on water
quality. The analysts then quantified numeric target
values for the indicators that represent conditions that
meet water quality standards and support designated
uses. Various types of indicators are available for
sediment, including water column, streambed/channel,
biological, and hillslope indicators.
The numeric targets developed for the Redwood Creek
sediment TMDL inlcuded both streambed targets and
hillslope targets (Tables I and 2). The in-stream
streambed numeric targets represent adequate aquatic
habitat conditions for salmonid reproductive success.
Hillslope targets provide additional indicators of
environmental conditions associated with designated use
protection. The hillslope indicators complement in-
stream indicators and reflect the watershed erosional
conditions. They represent land management conditions
associated with erosional processes and erosion rates
that are not excessively accelerated by human activities.
The numeric targets were based on scientific literature,
available monitoring data for the basin, and best
professional judgment. The numeric targets interpret
the narrative water quality standards to:
Describe the physical conditions of Redwood Creek
and the surrounding hillslope s that relate to the
designated use.
Assist in estimating the creek's capacity to receive
future sediment inputs and still support designated
uses.
Compare existing and target conditions for
sediment-related indicators.
Provide a framework for future data analysis and
review of the TMDL or implementation plan.
Assist in evaluating the effectiveness of land
management and restoration actions in adequately
reducing erosion and subsequent sediment loading
to the creek.
Source Assessment
Ten categories of sediment delivery were identified for
the Redwood Creek watershed, eight of which were
characterized as controllable, as follows:
Table 1. In-stream numeric targets representing desired conditions for Redwood Creek
Indicator
Percent fines <0.85 mm in riffle crests offish-bearing
streams
Percent fines <6.5 mm in riffle crests offish-bearing streams
Percent of stream length in riffles
Pool depth in main stem Redwood Creek reaches with pool-
riffle morphology
Depths of pools in 3rd and 4th order tributaries with pool-
riffle morphology
Median particle size diameter (d50) from riffle crest surfaces
Percent fines <2 mm at riffle crest surfaces in fish-bearing
streams
Large woody debris in any watercourse capable of
transporting sediment to a higher-order watercourse
Numeric Target
<14%
<30%
<25%-30% of stream reaches in riffles (reach gradient <2%)
mean depth of pools at low flow >2 m
mean depth of pools at lowflow>1-1.5 m
>37 mm (minimum for a reach)
>69 (mean for a reach)
<10%-20%
Improving trend toward increased large woody debris
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Appendix-11
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Appendix: Case Studies
Table 2. Hillslope numeric targets representing desired conditions for Redwood Creek
Indicator
Road stream crossings with diversion potential
Road culvert/crossing sizing
Landing and road fill stability
Road surfacing and drainage
Road inspection, maintenance, and decommissioning
Road location in inner gorge or unstable headwall areas
Use of clearcut and/or tractor yarding timber harvest
methods
Numeric Target
No crossings have diversion potential (i.e., all crossings are
reconfigured permanently to ensure that no diversion will occur).
All culverts and crossings are sized to pass the 50-year flood and
associated sediment and debris. In addition, crossings and
culverts in the snow zone are sized large enough to
accommodate flows and associated sediment and debris caused
by precipitation and snowmelt runoff.
All landings and road fills (e.g., sidecasts) that are on slopes
>50% and could potentially deliver sediment to a watercourse are
pulled back and stabilized.
All roads have surfacing and drainage facilities or structures that
are appropriate to their patterns and intensity of use.
All roads are inspected and maintained annually or
decommissioned. Decommissioned roads (roads which are
closed, abandoned, or obliterated) are hydrologically
maintenance-free.
Roads are not located in steep inner gorge or unstable headwall
areas except where alternative road locations are unavailable.
Clearcut or tractor yarding harvest methods are not used in steep
inner gorge, unstable, or streamside areas unless a detailed
geological assessment is performed that shows there is no
potential for increased sediment delivery to watercourses as a
result of using these methods.
Controllable:
• Erosion associated with roads, skid trails, and
landings
• Gully erosion
• Bare ground erosion associated with human
activities
• Streambank erosion associated with human
activities
• Tributary landslides (road-related)
• Tributary landslides (harvest-related)
• Main stem landslides
• Debris torrents
Uncontrollable:
Tributary landslides (naturally occurring)
Other naturally occurring mass movements (e.g.,
earth flows, block slides)
In evaluating these sources, analysts determined the
following information:
Estimate of average annual sediment loads per
square mile for the entire Redwood Creek
watershed.
Estimates of average annual sediment loads per
square mile for three "reference" tributary
watersheds within the Redwood Creek basin.
Estimates of historical sediment loading rates from
each erosional process category in the watershed.
Geomorphic research and monitoring programs of the
National Park Service and the USGS provide two
general types of sediment source information for
Redwood Creek: (1) measurements of erosional
processes within the watershed and (2) records of
sediment transport in Redwood Creek and some
tributaries. The measurements of erosional processes
were used to estimate the relative contributions of
different source categories to overall sediment loading,
and as the basis for allocating sediment source
Appendix-12
First Edition: October 1999
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Protocol for Developing Sediment TMDLs
reductions and the TMDL. The records of sediment
transport were used to estimate overall sediment loading
rates for the watershed and localized loading rates for
three tributaries. The overall loading rate provided the
baseline against which TMDL-related sediment
reductions were calculated. The localized tributary
loading rate information assisted in estimating the future
loading capacity of Redwood Creek and the overall
sediment discharge reductions needed to protect
designated uses. A more detailed discussion of the
source assessment, including estimated sediment loads,
is contained in USEPA (1998).
Loading Capacity: Linking Water Quality and
Pollutant Sources
As described in EPA guidance, a TMDL describes the
loading capacity of a waterbody for a particular
pollutant. EPA regulations define loading capacity as
the greatest amount of loading that a waterbody can
receive without violating water quality standards (40
CFR 130.2(f)). The TMDL submittal must describe the
rationale for the analytical method used to establish the
cause-and-effect relationship between the numeric target
and the identified pollutant sources. In many
circumstances, a critical condition must be described
and related to physical conditions in the waterbody (40
CFR 130.7(c)(l)). Supporting documentation for the
analysis must also be included, including the basis for
assumptions, strengths and weaknesses in the analytical
process, and results from water quality modeling, so that
EPA can properly review the elements of the TMDL that
are required by the statute and regulations.
To determine the magnitude of in-stream sediment
problems and the associated levels of sediment source
reductions needed to address sediment problems, it is
important to evaluate the cause-and-effect relationship
between water quality targets and sediment sources.
Assessment of the loading capacity of Redwood Creek
and of the necessary reductions in sediment loading
from sources to meet water quality standards requires
the following two analytic methods:
Qualitative comparison of existing and historical
conditions (related to numeric targets).
Quantitative comparison of average sediment
loading rates per square mile, in highly affected and
relatively unimpaired areas of the watershed.
The Redwood Creek sediment TMDL recognizes that
inferring linkages between hillslope erosion processes
and in-stream impacts based on the methods used might
produce uncertain results. Because of the lack of direct
linkages or reliable methods for modeling those
linkages, these inferential methods are necessary to
compare existing and desired conditions and to estimate
the level of sediment reduction needed to meet water
quality standards.
Because of limited historical data, it was not feasible to
quantitatively compare historical and target conditions
for in-stream indicators. A qualitative analysis of
existing conditions related to water quality targets (e.g.,
percent fines, pool depth) indicated that in-stream
conditions are inadequate to support a healthy habitat
and that reductions in sediment loading are necessary to
support designated uses.
To quantitatively compare existing and "reference"
conditions, three tributary subwatersheds within the
Redwood Creek watershed were identified and used as
reference watersheds. Each reference subwatershed
represented different underlying geologies. The
loadings from each of the reference conditions were then
extrapolated to those areas of the entire watershed
having comparative geologies to estimate a single
"reference watershed" loading rate for the whole
Redwood Creek watershed. Comparison of the existing
watershed sediment loading and the "reference
watershed" loading values indicated that a reduction of
approximately 60 percent in sediment loading was
needed to achieve "reference" conditions. Therefore,
the sediment loading capacity for Redwood Creek was
determined to be 40 percent of the historical average
annual loading rate, or 1,900 tons/mi2/yr.
Allocations
EPA regulations require that a TMDL include wasteload
allocations (WLAs), which identify the portion of the
loading capacity allocated to existing and future point
sources (40 CFR 130.2(g)). If no point sources are
present or the TMDL recommends a zero WLA for point
sources, the WLA must be listed as zero. The TMDL
may recommend a zero WLA if the state determines,
after considering all pollutant sources, that allocating
only to nonpoint sources will still result in attainment of
First Edition: October 1999
Appendix-13
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Appendix: Case Studies
the applicable water quality standard. In preparing the
WLA, it is not necessary that every individual point
source have a portion of the allocation of pollutant
loading capacity. But it is necessary to allocate the
loading capacity among individual point sources as
necessary to meet the water quality standard. The
TMDL submittal should also discuss whether a WLA is
based on an assumption that loads from a nonpoint
source or sources will be reduced. In such cases, the
state will need to demonstrate reasonable assurance that
the nonpoint source reductions will occur within a
reasonable time.
EPA regulations require that a TMDL include load
allocations (LAs), which identify the portion of the
loading capacity allocated to existing and future
nonpoint sources and to natural background (40 CFR
130.2(h)). LAs may range from reasonably accurate
estimates to gross allotments (40 CFR 130.2(g)). Where
it is possible to separate natural background from
nonpoint sources, separate load allocations should be
made and described. If there are neither nonpoint
sources nor natural background or the TMDL
recommends a zero LA, an explanation must be
provided. The TMDL may recommend a zero LA if the
state determines, after considering all pollutant sources,
that allocating only to point sources will still result in
attainment of the applicable water quality standard.
The statute and regulations require that a TMDL include
a margin of safety to account for any lack of knowledge
concerning the relationship between effluent limitations
and water quality (CWA § 303(d)(l)(C), 40 CFR
130.7(c)(l)). EPA guidance explains that the MOS may
be implicit, i.e., incorporated into the TMDL through
conservative assumptions in the analysis, or explicit, i.e.,
expressed in the TMDL as loadings set aside for the
MOS. If the MOS is implicit, the conservative
assumptions in the analysis that account for the MOS
must be described. If the MOS is explicit, the loading
set aside for the MOS must be identified.
The statute and regulations require that a TMDL be
established with seasonal variations. The method
chosen for including seasonal variations in the TMDL
must be described (CWA § 303(d)(l)(C), 40 CFR
Allocations for the Redwood Creek sediment TMDL are
based on erosion processes, which are mostly associated
with land use activities. The load allocations for erosion
processes are expressed as long-term annual average
loads per square mile for the entire watershed. The
TMDL is expressed as a 10-year rolling annual average,
allowing for the large interannual variability in sediment
loading. The TMDL of 1,900 tons/mi2/year is equal to
the loading capacity determined in the linkage analysis.
The individual load allocations were based on EPA's
assessment of the controllability of loadings from
different source categories. The controllable fraction of
total loads from each source category was estimated, and
the remaining loads were summed and compared to the
TMDL. (Controllable sources of sediment were defined
as those which are associated with human activity and
will respond to mitigation, altered land management, or
restoration.) The analysis indicated that the application
of reasonable practices plus reduction by the
controllable load would result in a decrease that is
adequate to meet the TMDL. There are no known point
sources in the Redwood Creek watershed, so the
waste load allocation is zero.
Estimates of controllable percentages of loads were
derived from field work in the watershed and in nearby
watersheds, documented results of sediment control
practices within the watershed, literature references, and
professional experience.
The Redwood Creek TMDL uses a series of
conservative assumptions to fully account for the margin
of safety. These assumptions include selection of in-
stream numeric target levels, use of hillslope targets,
proportion of bedload in total sediment load, sediment
storage in the main stem of Redwood Creek, comparison
of sediment loading from reference streams with that
from Redwood Creek as a whole, association of
hillslope sources with human causes, and estimation of
loading capacity.
Seasonal variation is inherent in the delivery of sediment
to stream systems. For this reason, the allocations in the
Redwood Creek TMDL are designed to apply to the
sources of sediment, not to the movement of sediment
across the landscape or the delivery of sediment directly
to the stream channel.
Appendix-14
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Protocol for Developing Sediment TMDLs
Monitoring Plan for TMDLs Developed Under the
Phased Approach
EPA's 1991 document, Guidance for Water Quality-
Based Decisions: The TMDL Process (EPA 440/4-91-
001), calls for a monitoring plan when a TMDL is
developed under the phased approach. The guidance
provides that a TMDL developed under the phased
approach also needs to provide assurances that nonpoint
source control measures will achieve expected load
reductions. The phased approach is appropriate when a
TMDL involves both point and nonpoint sources and the
point source WLA is based on an LA for which
nonpoint source controls need to be implemented.
Therefore, EPA's guidance provides that a TMDL
developed under the phased approach should include a
monitoring plan that describes the additional data to be
collected to determine if the load reductions required by
the TMDL lead to attainment of water quality standards.
The monitoring recommendations suggest an agreement
between the state's Regional Water Quality Control
Board and Redwood National Park (and possibly other
agencies) to jointly develop and implement a monitoring
plan. It is anticipated that the monitoring plan will
coordinate existing monitoring efforts within the
watershed.
The monitoring plan will distinguish different
monitoring needs for different stream types and hillslope
locations. Priorities for monitoring tributaries and main
stem reaches with spawning/rearing habitat should
include
Pebble counts at riffle crests
Large woody debris inventories
Thalweg and cross section measures
Suspended sediment and possible bedload sediment
at mouths of key tributaries
Bulk sampling of substrate composition at riffle
crests at a subset of established sites
Priorities for monitoring in the larger portions of
Redwood Creek should include
Thalweg profiles and cross sections
Large woody debris inventories
Suspended and bedload suspended sediment
Additional indicators that should be considered for
monitoring programs include
Substrate permeability
Turbidity
Bed mobility measures
Hillslope monitoring should provide adequate
information to update the sediment budget every 10 to
15 years. All monitoring plans should include detailed
descriptions of the monitoring protocols and data
management efforts.
Implementation Plans
On August 8, 1997, Bob Perciasepe issued a
memorandum, "New Policies for Establishing and
Implementing Total Maximum Daily Loads (TMDLs),"
which directs EPA regions to work in partnership with
states to achieve nonpoint source load allocations
established for 303(d)-listed waters impaired solely or
primarily by nonpoint sources. To this end, the
memorandum asks that regions assist states in
developing implementation plans that include
reasonable assurances that the nonpoint source load
allocations established in TMDLs for waters impaired
solely or primarily by nonpoint sources will in fact be
achieved; a public participation process; and recognition
of other relevant watershed management processes.
Although implementation plans are not approved by
EPA, they help establish the basis for EPA's approval of
TMDLs.
Reasonable Assurances
EPA guidance calls for reasonable assurances when
TMDLs are developed for waters impaired by both point
and nonpoint sources or for waters impaired solely by
nonpoint sources. In a water impaired by both point and
nonpoint sources, where a point source is given a less
stringent wasteload allocation based on an assumption
that nonpoint source load reductions will occur,
reasonable assurance must be provided for the TMDL to
be approvable. This information is necessary for EPA to
review the load and wasteload allocations required by
the regulation.
In a water impaired solely by nonpoint sources,
reasonable assurances are not required for a TMDL to
First Edition: October 1999
Appendix-15
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Appendix: Case Studies
be approvable. For such nonpoint source-only waters,
states are encouraged to provide reasonable assurances
regarding achievement of load allocations in the
implementation plans described in section 7, above. As
described in the August 8, 1997, Perciasepe
memorandum, such reasonable assurances should be
included in state implementation plans and "may be non-
regulatory, regulatory, or incentive-based, consistent
with applicable laws and programs."
References
USEPA. 1998. Redwood Creek Sediment Total
Maximum Daily Load. U.S. Environmental Protection
Agency, Region 9, Water Division, San Francisco, CA.
Contact: Dave Smith, Region 9 TMDL. Coordinator
United States Environmental Protection Agency
75 Hawthorne Street • San Francisco, CA 94105
(415) 744-2012 * smith.davidw@epa.gov
Appendix-16
First Edition: October 1999
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Protocol for Developing Sediment TMDLs
References
Note: This bibliography includes references cited in the
protocol and other selected references. EPA is currently
developing a more extensive annotated bibliography of
references concerning sediment water quality analysis
and management, which will be made available under
separate cover.
Berg, N.H., K.B. Roby, and B.J. McGurk. 1996.
Cumulative watershed effects: Applicability of available
methodologies to the Sierra Nevada. In Vol. Ill,
Assessments, commissioned reports, and background
information, Sierra Nevada Ecosystem Project: Final
report to Congress. University of California, Davis,
Centers for Water and Wildland Resources.
Bisson, P.A., G.H. Reeves, R.E. Bilby, and R J. Naiman.
1997. Watershed management and Pacific salmon:
Desired future conditions. In Pacific salmon and their
ecosystems—Status and future options, ed. Stouder,
Bisson, and Naiman. Chapman and Hall, New York.
Black, 1991. Watershed Hydrology. Englewood Cliffs,
New Jersey
California Department of Fish and Game. 1994. Coho
salmon habitat impacts—Qualitative assessment
technique for registered professional foresters. Draft
no. 2, November 1994.
California Department of Forestry. 1990. Forest
practice rules, technical rule addendum No. 1.
Chapman, D.W., and K.P. McLeod. 1987. Development
of criteria for fme sediment in the Northern Rockies
Ecoregion. EPA 910/9-87-162. U.S. Environmental
Protection Agency, Washington, DC.
Clarke, C.D., and P.O. Waldo. 1986. Sediment yield
from small and medium watersheds. In Proceedings of
the Fourth Interagency Sedimentation Conference, pp.
3-19 to 3-28.
Davenport, T.E. 1983. Soil erosion and transport
dynamics in the Blue Creek Watershed, Pike County,
Illinois. IEPA/WPC/83/004. Illinois Environmental
Protection Agency.
Dietrich, W.E., J.W. Kirchner, H. Ikeda, and F. Iseya,
1989, Sediment supply and the development of the
coarse surface layer in gravel-bedded rivers, Nature,
v.340,no. 6230, p. 215-217.
Dietrich, W.E., C.J. Wilson, D.R. Montgomery, J.
McKean, and R. Beaver. 1992. Erosion thresholds and
land surface morphology. Geology 20:675-79.
Dietrich, W.E., C.J. Wilson, D.R. Montgomery, and J.
McKean 1993. Analysis of erosion thresholds, channel
networks, and landscape morphology using a digitized
terrain. Journal of Geology 101(2):259-78.
Dissmeyer, G.E. 1994. Evaluating the effectiveness of
forestry best management practices in meeting water
quality goals or standards. U.S. Forest Service
Miscellaneous Publication 1520. U.S. Department of
Agriculture Forest Service, Washington, DC.
Dunne, T., and L.B. Leopold. 1978. Water in
environmental planning. W.H. Freeman and Co., San
Francisco, CA.
Endicott, C.L., and T.E. McMahon. 1996. Development
of a TMDL to reduce nonpoint source sediment
pollution in Deep Creek, Montana. Report to Montana
Department of Environmental Quality.
Gomez, B., and M. Church. 1989. An assessment of
bed load sediment transport formulae for gravel bed
rivers. Water Resources Research 25(6): 1161-1186.
Ketcheson, G.L. 1986. Sediment rating equations: An
evaluation for streams in the Idaho Batholith.
Intermountain Research Station General Technical
Report INT-213. U.S. Department of Agriculture Forest
Service, Ogden, UT.
Knopp, C. 1993. Testing indices of cold water fish
habitat. California North Coast Regional Water Quality
Control Board, Santa Rosa, CA.
Kondolf, G.M. 1995. Geomorphological stream
classification in aquatic habitat classification: Uses and
limitations. Aquatic Conservation 5:27-141.
First Edition: October 1999
References-1
-------
References
Lewis and Rice. 1989. Critical sites erosion study. Vol.
II. Site conditions related to erosion on private
timberlands in Northern California. Report of a
cooperative investigation by the California Department
of Forestry and U.S. Forest Service PSW Forest and
Range Experiment Station.
Lewis and Rice. 1990. Estimating erosion risk on forest
lands using improved methods of discriminant analysis.
Water Resources Research 26(8): 1721-33.
Limno-Tech, Inc. 1993. Silver Creek, AZ
demonstration TMDL. Prepared for U.S. Environmental
Protection Agency, Region 9.
Lisle, T., and S. Hilton. 1992. The volume of fine
sediment in pools: An index of sediment supply in
gravel-bed streams. Water Resources Bulletin
28(2):371-383.
shallow landsliding.
30:1153-71.
Water Resources Research
Louisiana-Pacific Corporation.
analysis manual. Samoa, CA.
1996. Watershed
MacDonald, L. 1992. Sediment monitoring: Reality and
hope. Presented at EPA/USFS Technical Workshop on
Sediments, February 3-7, 1992, Corvallis, OR.
MacDonald, L., A.W. Smart, and R.C. Wissmar. 1991.
Monitoring guidelines to evaluate effects of forestry
activities on streams in the Pacific Northwest and
Alaska. EPA 910/9-91-001. U.S. Environmental
Protection Agency, Region 10, Nonpoint Source
Section, Seattle, WA.
McGurk, B.J., and D.R. Fong. 1995. Equivalent roaded
area as a measure of cumulative effect of logging.
Environmental Management 19(4): 609-621.
McMahon, T.E. 1983. Habitat suitability index
models: Coho salmon. FWS/OBS-82/10.49. U.S.
Department of the Interior, Fish and Wildlife Service,
Washington, DC.
Miller, J.R., and J.B. Ritter. 1996. An examination of
the Rosgen classification of natural rivers. Catena
27:295-99.
Montgomery, D.R., and W.A. Dietrich. 1994. A
physically based model for the topographic control on
Naiman, R.J., and R.E. Bilby. 1998. River ecology and
management. Springer-Verlag New York, Inc.
Ohlander, C.A. 1991. Water resources analysis: T-
Walk—water quality monitoring field manual and
tables. U.S. Department of Agriculture Forest Service,
Region 2.
Peterson, N.P., A. Henry, and T.P. Quinn. 1992.
Assessment of cumulative effects on salmonid habitat:
Some suggested parameters and target condition.
Prepared for the Washington Department of Natural
Resources and The Coordinated Monitoring, Evaluation
and Research Committee, Timber Fish and Wildlife
Agreement. March 2.
Phillip Williams Associates. 1996. Garcia river gravel
management plan. San Francisco, CA.
Platts, W. S. 1990. Managing fisheries and wildlife on
rangelands grazed by livestock. Nevada Department of
Wildlife, Reno, NV.
Platts, W.S., W.F. Megahan, and G.W. Minshall. 1983.
Methods for evaluating stream, riparian, andbiotic
conditions. General Technical Report INT-183. U.S.
Department of Agriculture, Forest Service, Ogden, UT.
Regional Ecosystem Office. 1995. Ecosystem analysis
at the watershed scale. Version 2.2. U.S. Government
Printing Office: 1995-689-120/21215. Regional
Ecosystem Office, Portland, OR.
Reid, M. 1996. Evaluating timber management effects
on land uses and values in Northwest California. Draft,
December 3.
Reid, M. 1997. Comparative analysis of watershed
analysis methods for TMDL analysis. Draft, May 1997.
Reid, L.M., and T. Dunne. 1996. Rapid evaluation of
sediment budgets. Catena Verlag, Reiskirchen,
Germany.
Reiser, D.W., and T.C. Bjornn. 1979. 1. Habitat
requirements of anadromous salmonids. In Influence of
References-2
First Edition: October 1999
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Protocol for Developing Sediment TMDLs
forest and rangeland management of anadromous fish
habitat In the western United States and Canada, ed.
W.R. Meehan. General Technical Report PNW-96. U.S.
Department of Agriculture Forest Service.
Reiser, D.W., and J.B. Bradley. 1992. Fine sediment
intrusion and salmonid habitat. In Advances in hydro-
science and engineering, Vol. 1., ed. Sam S.Y. Yang.
Renard, K.G., G.R Fpster, G.A. Weesies, O.K. McCool,
and B.C. Yoder, coordinators. 1997. Predicting Soil
Erosion by Water: A Guide to Conservation Planning
With the Revised Universal Soil Loss Equation
(RUSLE). U.S. Department of Agriculture, Agriculture
Handbook No. 703, 404 pp.
Rosenburg, D.M., and V.H.Resch. 1993. Freshwater
biomonitoring and benthic macroinvertebrates.
Chapman & Hull, New York.
Rosgen, D. 1996. Applied river morphology. Wildland
Hydrology Books, Pagosa Springs, CO.
Satterlund D.R., and P.W. Adams, 1993. Wildland
Watershed Management. 2nd edition. New York.
Spence, B.C., G.A. Lomnicky, R.M. Hughes, and R.P.
Novitzki. 1996. An ecosystem approach to salmonid
conservation. TR-4501-96-6057. ManTech
Environmental Research Services, Corp. National
Marine Fisheries Service, Portland, OR.
USDA Agricultural Research Service. 1975. Present and
prospective technology for predicting sediment yield
and sources. In Proceedings, Sediment Yield Workshop.
1972. Oxford, MS.
USDA Forest Service. 1988. Cumulative off-site
watershed effects analysis. In USDA Forest Service
Region 5 soil and water conservation handbook. FSH
2509.22. U.S. Department of Agriculture Forest Service,
San Francisco, CA.
USDA Forest Service, PSW Region. 1996. Stream
condition inventory protocol version 3.4. Draft, June 27,
1996.
USDOI-BLM. 1993/1995. Process for assessing
proper functioning condition. TR1737-9. Revised 1995.
U.S. Department of the Interior, Bureau of Land
Management, Washington, DC.
USDOI-BLM. 1995. Mainstem Trinity River
Watershed analysis. U.S. Department of the Interior,
Bureau of Land Management, Washington, DC.
USEPA. 1989. Rapid bioassessment protocols for use
in streams and rivers: Benthic macroinvertebrates and
fish. EPA/444/4-89-001. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1991a. Guidance for water quality-based
decisions: The TMDLprocess. EPA 440/4-91-001.
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1991b. Technical support document for water
quality-based toxics control. EPA/505/2-90-001. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1992a. TMDL case study: Sycamore Creek,
Michigan. EPA841-F-92-012. U.S. Environmental
Protection Agency, Office of Water, Assessment and
Watershed Protection Division, Washington, DC.
USEPA. 1992b. TMDL case study: South Fork of the
Salmon River, Idaho. U.S. Environmental Protection
Agency, Office of Water, Assessment and Watershed
Protection Division, Washington, DC.
USEPA. 1992c. Monitoring guidance for the National
Estuary Program. EPA 842 B-92-004. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1993. Guidance specifying management
measures for sources of nonpoint source pollution in
coastal waters. EPA 840-B-92-002. U.S. Environmental
Protection Agency, Washington, DC.
USEPA. 1994a. EPA requirements for quality
assurance project plans for environmental data
operations. EPA QA/R-5. Draft interim final, August
1994. U.S. Environmental Protection Agency, Quality
Assurance Management Staff, Washington, DC.
USEPA. 1994b. Guidance for the data quality
objectives process. EPA QA/G-4. EPA/600/R-96/055.
U.S. Environmental Protection Agency, Office of
Research and Development, Washington, DC.
First Edition: October 1999
References-3
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References
USEPA. 1995a. Watershed protection: A statewide
approach. EPA 841-R-95-001. U.S. Environmental
Protection Agency, Washington DC.
USEPA. 1995b. Watershed protection: A project focus.
EPA 841-R-95-003. U.S. Environmental Protection
Agency, Washington DC.
USEPA. 1996a. TMDL development cost estimates:
Case studies of 14 TMDLs. EPA-R-96-001. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1996b. Watershed approach framework. EPA-
840-5-96-001. U.S. Environmental Protection Agency,
Washington, DC.
USEPA. 1996c. Chalk Creek Watershed project
implementation plan—Continuation project summary
sheet, 1996. U.S. Environmental Protection Agency,
Region 8, Denver, CO.
USEPA. 1996d. Nonpoint source monitoring and
evaluation guide. Draft final, November 1996. U.S.
Environmental Protection Agency, Office of Water,
Washington, D.C.
USEPA. 1997a. New policies for establishing and
implementing Total Maximum Daily Loads (TMDLs).
U.S. Environmental Protection Agency, Washington,
DC.
USEPA. 1997b. Linear regression for nonpoint source
pollution analysis. EPA-841-B-97-007. U.S.
Environmental Protection Agency, Washington, DC.
USEPA. 1997c. Compendium of tools for watershed
assessment and TMDL development. EPA 841-B-97-
006. U.S. Environmental Protection Agency,
Washington, DC.
USEPA 1998. Redwood Creek Sediment Total
Maximum Daily Load. US Environmental Protection
Agency, Region 9, Water Division, San Francisco, CA.
USEPA 1999. Draft Guidance for Water Quality-based
Decisions: The TMDL Process (Second Edition). EPA
841-D-99-001. U.S. Environmental Protection Agency,
Washington, DC.
Vanoni, V.A., ed. 1975. Sedimentation engineering.
American Society of Civil Engineers, New York, NY.
Van Sickle, J., and RL. Beschta. 1983. Supply-based
models of suspended sediment transport in streams.
Water Resources Research 19(3):768-778.
Washington Forest Practices Board. 1994. Standard
methodology of conducting watershed analysis under
chapter 222-22 WAC. Version 2.1, November 1994.
Washington Forest Practices Board, Olympia, WA.
Waters, T.F. 1995. Sediment in streams—Sources,
biological effects, and control. American Fisheries
Society Monograph 7. American Fisheries Society,
Bethesda, MD.
Weaver, W., and D. Hagans. 1996. Sediment
treatments and road restoration: Protecting and restoring
watersheds from sediment-related impacts. In Healing
the watershed—A guide to the restoration of watersheds
and native fish in the west. Pacific Rivers Council, Inc.
White, W.R., H. Milli, and A.D. Crabbe. 1978.
Sediment transport: An appraisal of available methods.
UK Hydraulics Research Station Report 119.
Hydraulics Research Station, Wallingford, UK.
Wolman, M.G., and J.P. Miller. 1960. Magnitude and
frequency offerees in geomorphic processes. Journal
of Geology 68:54-74.
Young, M.K., et al. 1991. Selection of measures of
substrate composition to estimate survival to emergence
of salmonids and to detect changes in stream substrate.
North American Journal of Fisheries Management
11:339-346.
References-4
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Protocol for Developing Sediment TMDLs
KEY TO ACRONYMS
AGNPS Agricultural Nonpoint Source
Pollution Model
ANSWERS Areal Nonpoint Source Watershed
Environment Response Simulation
BASINS Better Assessment Science Integrating
Point and Nonpoint Sources
BLM Bureau of Land Management
BMP best management practice
CFR Code of Federal Regulations
CREAMS Chemical, Runoff, and Erosion from
Agricultural Management Systems
CSES Critical Sites Erosion Study
CWA Clean Water Act
DR3M Multi-Event Urban Runoff Quality
Model
D50 diameter of 50th percentile particle
found through stream substrate
sampling
EMAP Environmental Monitoring and
Assessment Program
ERA equivalent roaded acreage
FEMAT Federal Ecosystem Management
Team
GIS Geographic Information System
GWLF Generalized Watershed Loading
Functions
HSPF Hydrologic Simulation Program-
Fortran
LA load allocation (for nonpoint sources
in TMDLs)
MOS margin of safety, a required TMDL
element
NAWQUA National Water Quality Assessment
project led by USGS
NPDES National Pollutant Discharge
Elimination System
NPS nonpoint source
NRCS Natural Resource Conservation
Service
NTU nephelometric turbidity units
PL-566 Public Law 566, which established the
USDA Small Watersheds program
QA/QC quality assurance/quality control
RBP rapid bioassessment protocol
RUSLE revised universal soil loss equation
SWAT Soil Water Assessment Tool
SWMM Storm Water Management Model
SWRRBWQ Simulator for Water Resources in
Rural Basins- Water Quality
TMDL total maximum daily load
TSS total suspended solids or sediment
USDA United States Department of
Agriculture
USDOI United States Department of the
Interior
USEPA United States Environmental
Protection Agency
USFS United States Forest Service
USGS United States Geological Survey
USLE universal soil loss equation
V* measure of residual pool volume
occupied by fine sediments
WLA waste load allocation (for point
sources in TMDLs)
WQS water quality standards
WRENSS Water Resources Evaluation of Non-
point Silvicultural Sources
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Acronyms
Acronyms-2
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Protocol for Developing Sediment TMDLs
GLOSSARY
Acute toxicity. A chemical stimulus severe enough to
rapidly induce an effect; in aquatic toxicity tests, an
effect observed within 96 hours or less is considered
acute. When referring to aquatic toxicology or human
health, an acute effect is not always measured in terms
of lethality.
Adaptive management. Approach where source
controls are initiated while additional monitoring data
are collected to provide a basis for future review and
revision of the TMDL (as well as management
activities).
Adsorption-desorption. Adsorption is the process by
which nutrients such as inorganic phosphorous adhere to
particles via a loose chemical bond with the surface of
clay particles. Desorption is the process by which
inorganic nutrients are released from the surface of
particles back into solution. Adsorption differs from
absorption in that absorption is the assimilation or
incorporation of a gas, liquid, or dissolved substance
into another substance.
Advanced secondary treatment. Biological or
chemical treatment processes added to a secondary
treatment plant including a conventional activated
sludge to increase the removal of solids and BOD.
Typical removal rates for advanced secondary plants are
on the order of 90 percent removal of solids and BOD.
Advanced waste treatment (AWT). Wastewater
treatment process that includes combinations of physical
and chemical operation units designed to remove
nutrients, toxic substances, or other pollutants.
Advanced, or tertiary, treatment processes treat effluent
from secondary treatment facilities using processes such
as nutrient removal (nitrification, denitrification),
filtration, or carbon adsorption. Tertiary treatment plants
typically achieve about 95 percent removal of solids and
biochemical oxygen demand (BOD) in addition to
removal of nutrients or other materials.
Advection. Bulk transport of the mass of discrete
chemical or biological constituents by fluid flow within
a receiving water. Advection describes the mass
transport due to the velocity, or flow, of the waterbody.
Aerobic. Environmental conditions characterized by the
presence of dissolved oxygen; used to describe
biological or chemical processes that occur in the
presence of oxygen.
Aggradation. The raising of the bed of a watercourse
by the deposition of sediment.
Allocations. That portion of a receiving water's loading
capacity that is attributed to one of its existing or future
pollution sources (nonpoint or point) or to natural
background sources. (A wasteload allocation [WLA] is
that portion of the loading capacity allocated to an
existing or future point source, and a load allocation
[LA] is that portion allocated to an existing or future
nonpoint source or to natural background source. Load
allocations are best estimates of the loading, which can
range from reasonably accurate estimates to gross
allotments, depending on the availability of data and
appropriate techniques for predicting loading.)
Alluvium. Sediment deposited by flowing water, such
as in a riverbed, floodplain, or delta.
Ambient water quality. Natural concentration of water
quality constituents prior to mixing of either point or
nonpoint source load of contaminants. Reference
ambient concentration is used to indicate the
concentration of a chemical that will not cause adverse
impact to human health.
Anadromous. Migrating up rivers from the sea to breed
in fresh water.
Anaerobic. Environmental condition characterized by
zero oxygen levels. Describes biological and chemical
processes that occur in the absence of oxygen.
Anoxic. Aquatic environmental conditions containing
zero or little dissolved oxygen. See also anaerobic.
Anthropogenic. Pertains to the [environmental]
influence of human activities.
Anti-degradation Policies. Policies that are part of
each state's water quality standards. These policies are
designed to protect water quality and provide a method
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Glossary
of assessing activities that may impact the integrity of
waterbodies.
Aquatic classification system. Assigns a classification
to a waterbody reflecting the water quality and the
biological health (integrity). Classification is
determined through use of biological indices (see IBI).
Examples of classifications include oligosaprobic
(cleanest water quality) and polysaprobic (highly
polluted water).
Aquatic ecosystem. Complex of biotic and abiotic
components of natural waters. The aquatic ecosystem is
an ecological unit that includes the physical
characteristics (such as flow or velocity and depth), the
biological community of the water column and benthos,
and the chemical characteristics such as dissolved
solids, dissolved oxygen, and nutrients. Both living and
nonliving components of the aquatic ecosystem interact
and influence the properties and status of each
component.
Assimilative capacity. The amount of contaminant
load that can be discharged to a specific waterbody
without exceeding water quality standards or criteria.
Assimilative capacity is used to define the ability of a
waterbody to naturally absorb and use a discharged
substance without impairing water quality or harming
aquatic life.
Background levels. Levels representing the chemical,
physical, and biological conditions that would result
from natural geomorphological processes such as
weathering or dissolution.
BASINS (Better Assessment Science Integrating
Point and Nonpoint Sources). A computer-run tool
that contains an assessment and planning component
that allows users to organize and display geographic
information for selected watersheds. It also contains a
modeling component to examine impacts of pollutant
loadings from point and nonpoint sources and to
characterize the overall condition of specific watersheds.
Bedload sediment. Portion of sediment load
transported downstream by sliding, rolling, bouncing
along the channel bottom. Generally consists of particles
>1 mm.
Benthic. Refers to material, especially sediment, at the
bottom of an aquatic ecosystem. It can be used to
describe the organisms that live on, or in, the bottom of
a waterbody.
Benthic organisms. Organisms living in, or on, bottom
substrates in aquatic ecosystems.
Best management practices (BMPs). Methods,
measures, or practices that are determined to be
reasonable and cost-effective means for a land owner to
meet certain, generally nonpoint source, pollution
control needs. BMPs include structural and
nonstructural controls and operation and maintenance
procedures.
Bioaccumulation. The process by which a compound
is taken up by an aquatic organism, both from water and
through food.
Bioassessment. Biological assessment; the evaluation of
an ecosystem using integrated assessments of habitat
and biological communities in comparison to
empirically defined reference conditions.
Bioavailability. A measure of the physicochemical
access that a toxicant has to the biological processes of
an organism. The less the bioavailability of a toxicant,
the less its toxic effect on an organism.
Biochemical oxygen demand (BOD). The amount of
oxygen per unit volume of water required to bacterially
or chemically oxidize (stabilize) the oxidizable matter in
water. Biochemical oxygen demand measurements are
usually conducted over specific time intervals (5, 10, 20,
30 days). The term BOD generally refers to a standard
5-day BOD test.
Biological criteria. Also known as biocriteria,
biological criteria are narrative expressions or numeric
values of the biological characteristics of aquatic
communities based on appropriate reference conditions.
Biological criteria serve as an index of aquatic
community health.
Biomass. The amount, or weight, of a species, or group
of biological organisms, within a specific volume or area
of an ecosystem.
Glossary-2
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Protocol for Developing Sediment TMDLs
Boundary conditions. Values or functions representing
the state of a system at its boundary limits.
Calcareous. Pertaining to or containing calcium
carbonate.
Calibration. The process of adjusting model
parameters within physically defensible ranges until the
resulting predictions give a best possible good fit to
observed data.
Carbonaceous. Pertaining to or containing carbon
derived from plant and animal residues
Cation exchange capacity. The sum total of
exchangeable cations that a soil can adsorb. Expressed
in centimoles per kilogram of soil (or of other adsorbing
material such as clay.)
Channel. A natural stream that conveys water; a ditch
or channel excavated for the flow of water.
Channel improvement. The improvement of the flow
characteristics of a channel by clearing, excavation,
realignment, lining, or other means in order to increase
its capacity. Sometimes used to connote channel
stabilization.
Channel stabilization. Erosion prevention and
stabilization of velocity distribution in a channel using
jetties, drops, revetments, vegetation, and other
measures.
Chloride. An atom of chlorine in solution; an ion
bearing a single negative charge.
Chronic toxicity. Toxicity impact that lingers or
continues for a relatively long period of time, often
one-tenth of the life span or longer. Chronic effects
could include mortality, reduced growth, or reduced
reproduction.
Clean sediment. Sediment that is not contaminated by
chemical substances. Pollution caused by clean sediment
refers to the quantity of sediment, as opposed to the
presence of pollutant-contaminated sediment.
Clean Water Act (CWA). The Clean Water Act
(formerly referred to as the Federal Water Pollution
Control Act or Federal Water Pollution Control Act
Amendments of 1972), Public Law 92-500, as amended
by Public Law 96-483 and Public Law 97-117, 33
U.S.C. 1251 et seq. The Clean Water Act (CWA)
contains a number of provisions to restore and maintain
the quality of the nation's water resources. One of these
provisions is section 303(d), which establishes the
TMDL program.
Coastal Zone. Lands and waters adjacent to the coast
that exert an influence on the uses of the sea and its
ecology, or whose uses and ecology are affected by the
sea.
Colluvium. Soil and rock debris on a hillslope that has
been transported from its original location.
Completely mixed condition. A condition in which no
measurable difference in the concentration of a pollutant
exists across a transect of the waterbody (e.g., the
concentration does not vary by 5 percent).
Concentration. Amount of a substance or material in a
given unit volume of solution; usually measured in
milligrams per liter (mg/L) or parts per million (ppm).
Concentration-based limit. A limit based on the
relative strength of a pollutant in a wastestream, usually
expressed in milligrams per liter (mg/L).
Conservative substance. A substance that does not
undergo any chemical or biological transformation or
degradation in a given ecosystem.
Contamination. The act of polluting or making impure;
any indication of chemical, sediment, or biological
impurities.
Continuous discharge. A discharge that occurs without
interruption throughout the operating hours of a facility,
except for infrequent shutdowns for maintenance,
process changes, or other similar activities.
Conventional pollutants. As specified under the Clean
Water Act, conventional contaminants include
suspended solids, coliform bacteria, high biochemical
oxygen demand, pH, and oil and grease.
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Glossary
Cost-share program. A program that allocates project
funds to pay a percentage of the cost of constructing or
implementing a best management practice. The
remainder of the costs are paid by the producer.
Cross-sectional area. Wet area of a waterbody normal
to the longitudinal component of the flow.
Critical condition. The critical condition can be
thought of as the "worst case" scenario of environmental
conditions in the waterbody in which the loading
expressed in the TMDL for the pollutant of concern will
continue to meet water quality standards. Critical
conditions are the combination of environmental factors
(e.g., flow, temperature, etc.) that results in attaining and
maintaining the water quality criterion and has an
acceptably low frequency of occurrence.
Cryptosporidium. See protozoa.
Decay. The gradual decrease in the amount of a given
substance in a given system due to various sink
processes including chemical and biological
transformation, dissipation to other environmental
media, or deposition into storage areas.
Decomposition. Metabolic breakdown of organic
materials; the formation of by-products of
decomposition releases energy and simple organic and
inorganic compounds. (See also, Respiration.)
Design stream flow. The stream flow used to conduct
steady-state waste load allocation modeling.
Designated uses. Those uses specified in water quality
standards for each waterbody or segment whether or not
they are being attained.
Deterministic model. A model that does not include
built-in variability: same input will always equal the
same output.
Detritus. Any loose material produced directly from
disintegration processes. Organic detritus consists of
material resulting from the decomposition of dead
organic remains.
Diagenesis. Production of sediment fluxes as a result of
the flux of particulate organic carbon in the sediment
and its decomposition. The diagenesis reaction can be
thought of as producing oxygen equivalents released by
various reduced species.
Diel ("die'-el"). Involving a 24-hour period.
Dilution. The addition of some quantity of less
concentrated liquid (water) that results in a decrease in
the original concentration.
Direct runoff. Water that flows over the ground
surface or through the ground directly into streams,
rivers, and lakes.
Discharge. Flow of surface water in a stream or canal
or the outflow of groundwater from a flowing artesian
well, ditch, or spring. Can also apply to discharge of
liquid effluent from a facility or to chemical emissions
into the air through designated venting mechanisms.
Discharge Monitoring Report (DMR). Report of
effluent characteristics submitted by a municipal or
industrial facility that has been granted an NPDES
discharge permit.
Discharge permits (NPDES). A permit issued by the
U.S. EPA or a State regulatory agency that sets specific
limits on the type and amount of pollutants that a
municipality or industry can discharge to a receiving
water; it also includes a compliance schedule for
achieving those limits. It is called the NPDES because
the permit process was established under the National
Pollutant Discharge Elimination System, under
provisions of the Federal Clean Water Act.
Dispersion. The spreading of chemical or biological
constituents, including pollutants, in various directions
from a point source, at varying velocities depending on
the differential in-stream flow characteristics.
Dissolved oxygen (DO). The amount of oxygen that is
dissolved in water. This term also refers to a measure of
the amount of oxygen available for biochemical activity
in a waterbody, and is an indicator of the quality of that
water.
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Protocol for Developing Sediment TMDLs
Dissolved oxygen sag. Longitudinal variation of
dissolved oxygen representing the oxygen depletion and
recovery following a waste load discharge into a
receiving water.
Diurnal. Actions or processes having a period or a
cycle of approximately one tidal-day or are completed
within a 24-hour period and which recur every 24 hours.
Domestic wastewater. Also called sanitary wastewater,
consists of wastewater discharged from residences and
from commercial, institutional, and similar facilities.
Drainage basin. A part of a land area enclosed by a
topographic divide from which direct surface runoff
from precipitation normally drains by gravity into a
receiving water. Also referred to as a watershed, river
basin, or hydrologic unit.
Dry ravel. Sloughing of sediment due to loss of
cohesion in surface materials.
Dynamic model. A mathematical formulation
describing and simulating the physical behavior of a
system or a process and its temporal variability.
Dynamic simulation. Modeling of the behavior of
physical, chemical, and/or biological phenomena and
their variation over time.
Ecoregion. A physical region that is defined by its
ecology, which includes meteorological factors,
elevation, plant and animal speciation, landscape
position, and soils.
Ecosystem. An interactive system that includes the
organisms of a natural community association together
with their abiotic physical, chemical, and geochemical
environment.
Effluent. Municipal sewage or industrial liquid waste
(untreated, partially treated, or completely treated) that
flows out of a treatment plant, septic system, pipe, etc.
Effluent guidelines. Technical EPA documents that set
effluent limitations for given industries and pollutants.
Effluent limitation. Restrictions established by a state
or EPA on quantities, rates, and concentrations in
pollutant discharges.
Effluent plume. Delineates the extent of contamination
in a given medium as a result of a distribution of
effluent discharges (or spills). Usually shows the
concentration gradient within the delineated areas or
plume of flow of contaminants.
Embeddedness. The degree to which fine sediments
fill the spaces (interstices) between rocks on the
substrate.
Empirical model. Use of statistical techniques to
discern patterns or relationships underlying observed or
measured data for large sample sets. Does not account
for physical dynamics of waterbodies.
Endpoint. An endpoint (or indicator/target)is a
characteristic of an ecosystem that may be affected by
exposure to a stressor. Assessment endpoints and
measurement endpoints are two distinct types of
endpoints commonly used by resource managers. An
assessment endpoint is the formal expression of a valued
environmental characteristic and should have societal
relevance (an indicator). A measurement endpoint is the
expression of an observed or measured response to a
stress or disturbance. It is a measurable environmental
characteristic that is related to the valued environmental
characteristic chosen as the assessment endpoint. The
numeric criteria that are part of traditional water quality
standards are good examples of measurement endpoints
(targets).
Enhancement. In the context of restoration ecology,
any improvement of a structural or functional attribute.
Enteric. Of or within the gastrointestinal tract.
Environmental Monitoring and Assessment Program
(EMAP). A USEPA program to monitor and assess the
ecological health of major ecosystems, including surface
waters, forests, near-coastal waters, wetlands,
agricultural lands, arid lands, and the Great Lakes, in an
integrated, systematic manner. Although EMAP has
been curtailed somewhat during recent years, the
program is designed to operate at regional and national
scales, for decades, and to evaluate the extent and
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Glossary
condition of entire ecological resources by using a
common sampling framework to sample approximately
12,500 locations in the conterminous United States.
Epiphyte. A plant growing on another plant; more
generally, any organism growing attached on a plant.
Estuary. Brackish-water areas influenced by the tides
where the mouth of a river meets the sea.
Estuarine number. A nondimensional parameter
accounting for decay, tidal dispersion, and advection
velocity; used for classification of tidal rivers and
estuarine systems.
Existing use. Use actually attained in the waterbody on
or after November 28, 1975, whether or not it is
included in the water quality standards (40 CFR 131.3).
Fate of pollutants. Physical, chemical, and biological
transformation in the nature and changes of the amount
of a pollutant in an environmental system.
Transformation processes are pollutant-specific.
Because they have comparable kinetics, different
formulations for each pollutant are not required.
Feedlot. A confined area for the controlled feeding of
animals. Tends to concentrate large amounts of animal
waste that cannot be absorbed by the soil and, hence,
may be carried to nearby streams or lakes by rainfall
runoff.
First-order kinetics. The type of relationship
describing a dynamic reaction in which the rate of
transformation of a pollutant is proportional to the
amount of that pollutant in the environmental system.
Flocculation. The process by which suspended
colloidal or very fine particles are assembled into larger
masses or floccules that eventually settle out of
suspension.
Fluvial geomorphology. The effect of rainfall and
runoff on the form and pattern of riverbeds and river
channels.
Flux. Movement and transport of mass of any water
quality constituent over a given period of time. Units of
mass flux are mass per unit time.
Forcing functions. External empirical formulation used
to provide input describing a number of processes.
Typical forcing functions include parameters such as
temperature, point and tributary sources, solar radiation,
and waste loads and flow.
Fry. Young, newly hatched fish.
Geochemical. Referring to chemical reactions
involving earth materials such as soil, rocks, and water.
Geomorphology. The study of the evolution and
configuration of landforms.
Gradient. The rate of change of the value of one
quantity with respect to another; for example, the rate of
decrease of temperature with depth in a lake.
Ground water. The supply of fresh water found
beneath the earth's surface, usually in aquifers, which
supply wells and springs. Because ground water is a
major source of drinking water, there is growing concern
over contamination from leaching agricultural or
industrial pollutants and leaking underground storage
tanks.
Gully erosion. The erosion process whereby water
accumulates in narrow channels and, over short periods,
removes the soil form this narrow area to considerable
depths, ranging from 1-2 feet to as much as 75-100 feet.
Half-saturation constant. Nutrient concentration at
which the growth rate of a population of a species or
group of species is half the maximum rate.
Half-saturation constants define the nutrient uptake
characteristics of different phytoplankton species. Low
half-saturation constants indicate the ability of the algal
group to thrive under nutrient-depleted conditions.
Heterotroph. An organism that uses organic carbon for
the formation of its cell tissue, e.g., is unable to
synthesize organic compounds from inorganic substrates
for food and must consume organisms or their products.
Bacteria are examples of heterotrophs;
photosynthesizing organisms are not.
Hillslope Targets. Quantitative measure that links the
upslope sources of sediment and instream impacts of
sediment discharge.
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Hydrodynamic model. Mathematical formulation used
in describing fluid flow circulation, transport, and
deposition processes in receiving water.
Hydrograph. A graph showing variation of in stage
(depth) or discharge of water in a stream over a period
of time.
Hydrologic cycle. The circuit of water movement from
the atmosphere to the earth and its return to the
atmosphere through various stages or processes, such as
precipitation, interception, runoff, infiltration, storage,
evaporation, and transpiration.
Hydrology. The study of the distribution, properties,
and effects of water on the earth's surface, in the soil
and underlying rocks, and in the atmosphere.0
Hydrolysis. A chemical reaction that occurs between a
substance and water resulting in the cleaving of a
molecular bond and the formation of new bonds with
components of the decomposed water molecule; a
reaction of water with a salt to create an acid or a base.
Hyetograph. Graph of rainfall rate during a storm
event.
Hypolimnetic oxygen depletion rate. The
hypolimnetic oxygen depletion rate describes changing
dissolved oxygen concentrations in the hypolimnion
(lowest stratum) of lakes and reservoirs. Dissolved
oxygen concentrations in the hypolimnion are especially
significant because of their effect on fish.
Index of Biotic Integrity (IBI). The IBI uses
measurements of the distribution and abundance or
absence of several fish species types in each waterbody
for comparison. A portion of a waterbody is compared
to a similar, unimpacted waterbody in the same
ecoregion.
Indicator. A measurable quantity that can be used to
evaluate the relationship between pollutant sources and
their impact on water quality.
Indirect discharge. A nondomestic discharge
introducing pollutants to a publicly owned treatment
works.
Infiltration capacity. The capacity of a soil to allow
water to infiltrate into or through it during a storm.
Initial mixing zone. The region immediately
downstream of an outfall where effluent dilution
processes occur. Because of the combined effects of the
effluent buoyancy, ambient stratification, and current,
the prediction of initial dilution can be complex.
In situ. In place; in situ measurements consist of
measurements of components of processes in a full-scale
system or a field, rather than in a laboratory.
Interstitial water. Water contained in the interstices,
which are the pore spaces or voids in soils and rocks,
i.e., ground water.
Irrigation. Applying water or wastewater to land areas
to supply the water and nutrient needs of plants.
Irrigation return flow. Surface and subsurface water
that leaves a field after the application of irrigation
water.
Karst geology. Solution cavities and closely-spaced
sinkholes formed as a result of dissolution of carbonate
bedrock.
Kinetic processes. Description of the rates and modes
of changes in the transformation or degradation of a
substance in an ecosystem.
Land application. Discharge of wastewater onto the
ground for treatment or reuse. (See: irrigation)
Leachate. Water that collects contaminants as it
trickles through wastes, pesticides, or fertilizers.
Leaching can occur in farming areas, feedlots, and
landfills, and can result in hazardous substances entering
surface water, groundwater, or soil.
Leachate collection system. A system that gathers
leachate and pumps it to the surface for treatment.
Light saturation. The optimal light level for algae and
macrophyte growth and photosynthesis.
Loading, Load, Loading rate. The total amount of
material (pollutants) entering the system from one or
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Glossary
multiple sources; measured as a rate in weight per unit
time.
Load allocation (LA). The portion of a receiving
water's loading capacity that is attributed either to one
of its existing or future nonpoint sources of pollution or
to natural background sources. Load allocations are best
estimates of the loading, which can range from
reasonably accurate estimates to gross allotments,
depending on the availability of data and appropriate
techniques for predicting the loading. Wherever
possible, natural and nonpoint source loads should be
distinguished. (40 CFR 130.2(g))
Loading capacity (LC). The greatest amount of
loading that a water can receive without violating water
quality standards.
Longitudinal dispersion. The spreading of chemical or
biological constituents, including pollutants,
downstream from a point source at varying velocities
due to the differential in-stream flow characteristics.
Low-flow (7Q10). Low-flow (7Q10) is the 7-day
average low flow occurring once in 10 years; this
probability-based statistic is used in determining stream
design flow conditions and for evaluating the water
quality impact of effluent discharge limits.
Margin of Safety (MOS). A required component of the
TMDL that accounts for the uncertainty about the
relationship between the pollutant loads and the quality
of the receiving waterbody (CWA section
303(d)(l)(C)). The MOS is normally incorporated into
the conservative assumptions used to develop TMDLs
(generally within the calculations or models) and
approved by EPA either individually or in state/EPA
agreements. If the MOS needs to be larger than that
which is allowed through the conservative assumptions,
additional MOS can be added as a separate component
of the TMDL (in this case, quantitatively, a TMDL =
LC=WLA + LA + MOS).
Mass balance. An equation that accounts for the flux of
mass going into a defined area and the flux of mass
leaving the defined area. The flux in must equal the flux
out.
Mass loading. The quantity of a pollutant transported to
a waterbody.
Mass wasting. Downslope transport of soil and rocks
due to gravitational stress.
Mathematical model. A system of mathematical
expressions that describe the spatial and temporal
distribution of water quality constituents resulting from
fluid transport and the one, or more, individual
processes and interactions within some prototype
aquatic ecosystem. A mathematical water quality model
is used as the basis for waste load allocation evaluations.
Maximum depth. The greatest depth of a waterbody.
Mean depth. Volume of a waterbody divided by its
surface area.
Mineralization. The transformation of organic matter
into a mineral or an inorganic compound.
Mitigation. Actions taken to avoid, reduce, or
compensate for the effects of environmental damage.
Among the broad spectrum of possible actions are those
which restore, enhance, create, or replace damaged
ecosystems.
Monitoring. Periodic or continuous surveillance or
testing to determine the level of compliance with
statutory requirements and/or pollutant levels in various
media or in humans, plants, and animals.
Monte Carlo simulation. A stochastic modeling
technique that involves the random selection of sets of
input data for use in repetitive model runs. Probability
distributions of receiving water quality concentrations
are generated as the output of a Monte Carlo simulation.
Narrative criteria. Nonquantitative guidelines that
describe the desired water quality goals.
National Pollutant Discharge Elimination System
(NPDES). The national program for issuing, modifying,
revoking and reissuing, terminating, monitoring, and
enforcing permits, and imposing and enforcing
pretreatment requirements, under Sections 307, 402,
318, and 405 of the Clean Water Act.
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Natural waters. Flowing water within a physical
system that has developed without human intervention,
in which natural processes continue to take place.
Nonpoint source. Pollution that is not released through
pipes but rather originates from multiple sources over a
relatively large area. Nonpoint sources can be divided
into source activities related to either land or water use
including failing septic tanks, improper animal-keeping
practices, forest practices, and urban and rural runoff.
Numeric target. A measurable value determined for
the pollutant of concern which, if achieved, is expected
to result in the attainment of water quality standards in
the listed waterbody.
Numerical model. Model that approximates a solution
of governing partial differential equations which
describe a natural process. The approximation uses a
numerical discretization of the space and time
components of the system or process.
One-dimensional model (1-D). A mathematical model
defined along one spatial coordinate of a natural water
system. Typically 1-D models are used to describe the
longitudinal variation of water quality constituents along
the downstream direction of a stream or river. In writing
the model, it is assumed that the cross-channel (lateral)
and vertical variability is relatively homogenous and
can, therefore, be averaged over those spatial
coordinates.
Organic matter. The organic fraction that includes
plant and animal residue at various stages of
decomposition, cells and tissues of soil organisms, and
substance synthesized by the soil population. Commonly
determined as the amount of organic material contained
in a soil or water sample.
Outfall. The point where water flows from a conduit,
stream, or drain.
Oxidation. The chemical union of oxygen with metals
or organic compounds accompanied by a removal of
hydrogen or another atom. It is an important factor for
soil formation and permits the release of energy from
cellular fuels.
Oxygen demand. Measure of the dissolved oxygen
used by a system (microorganisms) in the oxidation of
organic matter. (See also Biochemical oxygen
demand.)
Oxygen depletion. A deficit of dissolved oxygen in a
water system due to oxidation of organic matter.
Oxygen saturation. The natural or artificial reaeration
or oxygenation of a water system (water sample) to
bring the level of dissolved oxygen to maximum
capacity. Oxygen saturation is greatly influenced by
temperature and other water characteristics.
Partition coefficient. A constant symbolizing the ratio
of the concentration of a solute in the upper of two
phases in equilibrium to its concentration in the lower
phase. Chemicals in solution are partitioned into
dissolved and particulate adsorbed phase based on their
corresponding sediment-to-water partitioning
coefficient.
Pathogen. Disease-causing agent, especially
microorganisms such as bacteria, protozoa, and viruses.
Peak runoff. The highest value of the stage or
discharge attained by a flood or storm event; also
referred to as flood peak or peak discharge.
Periphyton. Microscopic underwater plants and animals
that are firmly attached to solid surfaces such as rocks,
logs, pilings, and other structures.
Permit. An authorization, license, or equivalent control
document issued by EPA or an approved Federal, state,
or local agency to implement the requirements of an
environmental regulation; e.g., a permit to operate a
wastewater treatment plant or to operate a facility that
may generate harmful emissions.
Permit Compliance System (PCS). Computerized
management information system which contains data on
NPDES permit-holding facilities. PCS keeps extensive
records on more than 65,000 active water-discharge
permits on sites located throughout the nation. PCS
tracks permit, compliance, and enforcement status of
NPDES facilities.
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Glossary
Phased approach. Under the phased approach to
TMDL development, LAs and WLAs are calculated
using the best available data and information
recognizing the need for additional monitoring data to
accurately characterize sources and loadings. The
phased approach is typically employed when nonpoint
sources dominate. It provides for the implementation of
load reduction strategies while collecting additional
data.
Point source. Pollutant loads discharged at a specific
location from pipes, outfalls, and conveyance channels
from either municipal wastewater treatment plants or
industrial waste treatment facilities. Point sources can
also include pollutant loads contributed by tributaries to
the main receiving water stream or river.
Pollutant. Dredged spoil, solid waste, incinerator
residue, sewage, garbage, sewage sludge, munitions,
chemical wastes, biological materials, radioactive
materials, heat, wrecked or discarded equipment, rock,
sand, cellar dirt and industrial, municipal, and
agricultural waste discharged into water. (CWA Section
502(6)).
Pollution. Generally, the presence of matter or energy
whose nature, location, or quantity produces undesired
environmental effects. Under the Clean Water Act, for
example, the term is defined as the man-made or man-
induced alteration of the physical, biological, chemical,
and radiological integrity of water.
Pool. Portion of a stream with reduced current velocity,
often with deeper water than surrounding areas ans with
a smooth surface.
Postaudit. A subsequent examination and verification
of model predictive performance following
implementation of an environmental control program.
Pretreatment. The treatment of wastewater to remove
or reduce contaminants prior to discharge into another
treatment system or a receiving water.
Primary productivity. A measure of the rate at which
new organic matter is formed and accumulated through
photosynthesis and chemosynthesis activity of producer
organisms (chiefly, green plants). The rate of primary
production is estimated by measuring the amount of
oxygen released (oxygen method) or the amount of
carbon assimilated by the plant (carbon method).
Primary treatment. A basic wastewater treatment
method that uses settling, skimming, and (usually)
chlorination to remove solids, floating materials, and
pathogens from wastewater. Primary treatment typically
removes about 35 percent of biochemical oxygen
demand (BOD) and less than half of the metals and toxic
organic substances.
Privately owned treatment works. Any device or
system that is (a) used to treat wastes from any facility
whose operator is not the operator of the treatment
works and (b) not a POTW.
Protozoa. A phylum or subkingdom including all
single-celled animals with membrane- bound organelles;
they may be aquatic or parasitic, with or without a test,
solitary or colonial, sessile or free-swimming, moving
by cilia, flagella, or pseudopodia.
Public comment period. The time allowed for the
public to express its views and concerns regarding
action by EPA or states (e.g., a Federal Register notice
of a proposed rule-making, a public notice of a draft
permit, or a Notice of Intent to Deny).
Publicly owned treatment works (POTW). Any
device or system used in the treatment (including
recycling and reclamation) of municipal sewage or
industrial wastes of a liquid nature that is owned by a
state or municipality. This definition includes sewers,
pipes, or other conveyances only if they convey
wastewater to a POTW providing treatment.
Raw sewage. Untreated municipal sewage.
Reaction rate coefficient. A constant describing the
rate of transformation of a substance in an
environmental medium characterized by a set of
physical, chemical, and biological conditions such as
temperature and dissolved oxygen level.
Reaeration. The net flux of oxygen occurring from the
atmosphere to a body of water with a free surface.
Receiving waters. Creeks, streams, rivers, lakes,
estuaries, ground-water formations, or other bodies of
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water into which surface water and/or treated or
untreated waste are discharged, either naturally or in
man-made systems.
Redd. Nest made in gravel, consisting of a depression
hydraulically dug by a fish for egg deposition (and then
filled) and the associated gravel mounds.
Reference sites. Waterbodies that are representative of
the characteristics of the region and subject to minimal
human disturbance.
Reserve capacity. Pollutant loading rate set aside in
determining stream waste load allocation accounting for
uncertainty and future growth.
Residence time. Length of time that a pollutant remains
within a section of a stream or river. The residence time
is determined by the streamflow and the volume of the
river reach or the average stream velocity and the length
of the river reach.
Restoration. Return of an ecosystem to a close
approximation of its presumed condition prior to
disturbance.
Riffle. A rocky shoal or sand bar located just below the
surface of the water.
Rill erosion. An erosion process in which numerous
small channels of only several centimeters in depth are
formed; occurs mainly on recently cultivated soils.
Riparian areas. Areas bordering streams, lakes, rivers,
and other watercourses. These areas have high water
tables and support plants that require saturated soils
during all or part of the year. Riparian areas include
both wetland and upland zones.
Riparian vegetation. Hydrophytic vegetation growing
in the immediate vicinity of a lake or river closely
enough so that its annual evapotranspiration constitutes
a factor in the lake or river regime.
Riparian zone. The border or banks of a stream.
Although this term is sometimes used interchangeably
with floodplain, the riparian zone is generally regarded
as relatively narrow compared to a floodplain. The
duration of flooding is generally much shorter, and the
timing less predictable, in a riparian zone than in a river
floodplain.
Roughness coefficient. A factor in velocity and
discharge formulas representing the effects of channel
roughness on energy losses in flowing water. Manning's
"n" is a commonly used roughness coefficient.
Rotating biological contactor (RBC). A wastewater
treatment process consisting of a series of closely
spaced rotating circular disks of polystyrene or
polyvinyl chloride. Attached biological growth is
promoted on the surface of the disks. The rotation of
the disks allows contact with the wastewater and the
atmosphere to enhance oxygenation.
Runoff. That part of precipitation, snow melt, or
irrigation water that runs off the land into streams or
other surface water. It can carry pollutants from the air
and land into receiving waters.
Scoping modeling. A method of approximation that
involves simple, steady-state analytical solutions for a
rough analysis of a problem.
Scour. To abrade and wear away. Used to describe the
weathering away of a terrace or diversion channel or
streambed. The clearing and digging action of flowing
water, especially the downward erosion by stream water
in sweeping away mud and silt on the outside of a
meander or during flood events.
Secondary treatment. The second step in most
publicly owned waste treatment systems, in which
bacteria consume the organic parts of the waste. It is
accomplished by bringing together waste, bacteria, and
oxygen in trickling filters or in the activated sludge
process. This treatment removes floating and settleable
solids and about 90 percent of the oxygen-demanding
substances and suspended solids. Disinfection is the
final stage of secondary treatment. (See Primary
treatment, Tertiary treatment.)
Sediment. Particulate organic and inorganic matter that
accumulates in a loose, unconsolidated form on the
bottom of natural waters.
Sediment delivery. Contribution of transported
sediment to a particular location or part of a landscape.
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Glossary
Sediment oxygen demand (SOD). The solids
discharged to a receiving water are partly organics, and
upon settling to the bottom, they decompose
anaerobically as well as aerobically, depending on
conditions. The oxygen consumed in aerobic
decomposition represents another dissolved oxygen sink
for the waterbody.
Sediment production. Delivery of colluvium or
bedrock from hillslope to stream channel. The
production rate is evaluated as the sum of the rates of
colluvial bank erosion and sediment transport across
channel banks.
Sediment yield. Amount of sediment passing a
particular point (e.g., discharge point of the basin) in a
watershed per unit of time.
Sedimentation. Process of deposition of waterborne or
windborne sediment or other material; also refers to the
infilling of bottom substrate in a waterbody by sediment
(siltation).
Septic system. An on-site system designed to treat and
dispose of domestic sewage. A typical septic system
consists of a tank that receives waste from a residence or
business and a system of tile lines or a pit for disposal of
the liquid effluent (sludge) that remains after
decomposition of the solids by bacteria in the tank; must
be pumped out periodically.
Sewage fungus. Proliferations of bacteria and/or fungi
that may form feathery, cotton-wool-like growths in
streams and rivers that have high concentrations of
dissolved organic compounds.
Sewer. A channel or conduit that carries wastewater
and stormwater runoff from the source to a treatment
plant or receiving stream. "Sanitary" sewers carry
household, industrial, and commercial waste. "Storm"
sewers carry runoff from rain or snow. "Combined"
sewers handle both.
Sheet erosion. Also Sheetwash. Erosion of the ground
surface by unconcentrated (i.e. not in rills) overland
flow.
Sheetwash. Also Sheet erosion. Erosion of the ground
surface by unconcentrated (i.e. not in rills) overland
flow.
Simulation. The use of mathematical models to
approximate the observed behavior of a natural water
system in response to a specific known set of input and
forcing conditions. Models that have been validated, or
verified, are then used to predict the response of a
natural water system to changes in the input or forcing
conditions.
Sinuosity. The degree to which a river or stream bends.
Slope. The degree of inclination to the horizontal.
Usually expressed as a ratio, such as 1:25 or 1 on 25,
indicating one unit vertical rise in 25 units of horizontal
distance, or in a decimal fraction (0.04); degrees (2
degrees 18 minutes), or percent (4 percent).
Sorption. The adherence of ions or molecules in a gas
or liquid to the surface of a solid particle with which
they are in contact.
Spatial segmentation. A numerical discretization of
the spatial component of a system into one or more
dimensions; forms the basis for application of numerical
simulation models.
Stabilization pond. Large earthen basin used for the
treatment of wastewater by natural processes involving
the use of both algae and bacteria.
Steady-state model. Mathematical model of fate and
transport that uses constant values of input variables to
predict constant values of receiving water quality
concentrations.
Stoichiometric ratio. Mass-balance-based ratio for
nutrients, organic carbon and algae (e.g.,
nitrogen-to-carbon ratio).
STORET. U.S. Environmental Protection Agency
(EPA) national water quality database for STORage and
RETrieval (STORET). Mainframe water quality
database that includes physical, chemical, and biological
data measured in waterbodies throughout the United
States.
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Storm runoff. Storm water runoff, snowmelt runoff,
and surface runoff and drainage; rainfall that does not
evaporate or infiltrate the ground because of impervious
land surfaces or a soil infiltration rate lower than rainfall
intensity, but instead flows onto adjacent land or
waterbodies or is routed into a drain or sewer system.
Stratification (of waterbody). Formation of water
layers each with specific physical, chemical, and
biological characteristics. As the density of water
decreases due to surface heating, a stable situation
develops with lighter water overlaying heavier and
denser water.
Streamflow. Discharge that occurs in a natural channel.
Although the term "discharge" can be applied to the
flow of a canal, the word "streamflow" uniquely
describes the discharge in a surface stream course. The
term streamflow is more general than "runoff" as
streamflow may be applied to discharge whether or not
it is affected by diversion or regulation.
Stream restoration. Various techniques used to
replicate the hydrological, morphological, and
ecological features that have been lost in a stream due to
urbanization, farming, or other disturbance.
Stressor. Any physical, chemical, or biological entity
that can induce an adverse response.
Substrate. Refers to bottom sediment material in a
natural water system.
Surface area. The area of the surface of a waterbody;
best measured by planimetry or the use of a geographic
information system.
Surface runoff. Precipitation, snowmelt, or irrigation
water in excess of what can infiltrate the soil surface and
be stored in small surface depressions; a major
transporter of nonpoint source pollutants.
Surface water. All water naturally open to the
atmosphere (rivers, lakes, reservoirs, ponds, streams,
impoundments, seas, estuaries, etc.) and all springs,
wells, or other collectors directly influenced by surface
water.
Suspended solids or load. Organic and inorganic
particles (sediment) suspended in and carried by a fluid
(water). The suspension is governed by the upward
components of turbulence, currents, or colloidal
suspension. Suspended sediment usually consists of
particles <0.1 mm, although size may vary according to
current hydrological conditions. Particles between 0.1
mm and 1 mm may move as suspended or be deposited
(bedload).
Technology-based limitations. Industry-specified
effluent limitations applied to a discharge when it will
not cause a violation of water quality standards at low
stream flows. Usually applied to discharges into large
rivers.
Technology-based standards. Effluent limitations
applicable to direct and indirect sources that are
developed on a category-by-category basis using
statutory factors, not including water quality effects.
Temperature coefficient. Rate of increase in an
activity or process over a 10 degree Celsius increase in
temperature. Also referred to as the Q10.
Tertiary treatment. Advanced cleaning of wastewater
that goes beyond the secondary or biological stage,
removing nutrients such as phosphorus, nitrogen, and
most biochemical oxygen demand (BOD) and suspended
solids.
Thalweg. Deepest part of a stream channel.
Three-dimensional model (3-D). Mathematical model
defined along three spatial coordinates where the water
quality constituents are considered to vary over all three
spatial coordinates of length, width, and depth.
Topography. The physical features of a geographic
surface area including relative elevations and the
positions of natural and man-made features.
Total Maximum Daily Load (TMDL). The sum of the
individual wasteload allocations (WLAs) for point
sources, load allocations (LAs) for nonpoint sources and
natural background, plus a margin of safety (MOS).
TMDLs can be expressed in terms of mass per time,
toxicity, or other appropriate measures that relate to a
state's water quality standard.
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Glossary
Transit time. In nutrient cycles, the average time that a
substance remains in a particular form; ratio of biomass
to productivity.
Transport of pollutants (in water). Transport of
pollutants in water involves two main processes: (1)
advection, resulting from the flow of water, and (2)
diffusion, or transport due to turbulence in the water.
Tributary. A lower order stream compared to a
receiving waterbody. "Tributary to" indicates the largest
stream into which the reported stream or tributary flows.
Turbidity. A measure of opacity of a substance; the
degree to which light is scattered or absorbed by a fluid.
Turbulent flow. A flow characterized by agitated and
irregular, random-velocity fluctuations.
Turbulence. A type of flow in which any particle may
move in any direction with respect to any other particle
and not in a smooth or fixed path. Turbulent water is
agitated by cross current and eddies. Turbulent velocity
is that velocity above which turbulent flow will always
exist and below which the flow may be either turbulent
or laminar.
Two-dimensional model (2-D). A mathematical model
defined along two spatial coordinates where the water
quality constituents are considered averaged over the
third remaining spatial coordinate. Examples of 2-D
models include descriptions of the variability of water
quality properties along: (a) the length and width of a
river that incorporates vertical averaging of depth, or (b)
length and depth of a river that incorporates lateral
averaging across the width of the waterbody.
Ultimate Biochemical Oxygen Demand (UBOD or
BODu). Long-term oxygen demand required to
completely stabilize organic carbon in wastewater or
natural waters.
Uncertainty factors. Factors used in the adjustment of
toxicity data to account for unknown variations. Where
toxicity is measured on only one test species, other
species may exhibit more sensitivity to that effluent. An
uncertainty factor would adjust measured toxicity
upward and downward to cover the sensitivity range of
other, potentially more or less sensitive species.
Unstratified. Indicates a vertically uniform or
well-mixed condition in a waterbody. See also stratified.
Use Attainability Analysis (UAA). A structured
scientific assessment of the factors affecting the
attainment of the use which may include physical,
chemical, and economic factors as described in section
131.10(g). (40CFR131.3)
Validation (of a model). Process of determining how
well the mathematical model's computer representation
describes the actual behavior of the physical process
under investigation.
Verification (of a model). Testing the accuracy and
predictive capabilities of the calibrated model on a data
set independent of the data set used for calibration.
Virus. Submicroscopic pathogen consisting of a nucleic
acid core surrounded by a protein coat. Requires a host
in which to replicate (reproduce).
Volatilization. Process by which chemical compounds
are vaporized (evaporated) at given temperature and
pressure conditions by gas transfer reactions. Volatile
compounds have a tendency to partition into the gas
phase.
Wasteload allocation (WLA). The portion of a
receiving water's loading capacity that is allocated to
one of its existing or future point sources of pollution.
WLAs constitute a type of water quality-based effluent
limitation (40 CFR 130.2(h)).
Wastewater. Usually refers to effluent from a sewage
treatment plant. See also domestic wastewater.
Wastewater treatment. Chemical, biological, and
mechanical procedures applied to an industrial or
municipal discharge or to any other sources of
contaminated water in order to remove, reduce, or
neutralize contaminants.
Water quality. The biological, chemical, and physical
conditions of a waterbody. It is a measure of a
waterbody's ability to support beneficial uses.
Water quality-based effluent limitations. Effluent
limitations applied to dischargers when mere
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technology-based limitations would cause violations of
water quality standards. Usually WQBELs are applied
to discharges into small streams.
Water quality-based permit. A permit with an
effluent limit more stringent than one based on
technology performance. Such limits may be necessary
to protect the designated use of receiving waters (e.g.,
recreation, irrigation, industry or water supply).
Water quality criteria. Levels of water quality
expected to render a body of water suitable for its
designated use, composed of numeric and narrative
criteria. Numeric criteria are scientifically derived
ambient concentrations developed by EPA or states for
various pollutants of concern to protect human health
and aquatic life. Narrative criteria are statements that
describe the desired water quality goal. Criteria are
based on specific levels of pollutants that would make
the water harmful if used for drinking, swimming,
farming, fish production, or industrial processes.
Water quality-limited segments. Those water
segments which do not or are not expected to meet
applicable water quality standards even after the
application of technology-based effluent limitations
required by sections 301(b) and 306 of the Clean Water
Act (40 CFR 130.29(j)). Technology-based controls
include, but are not limited to, best practicable control
technology currently available (BPT) and secondary
treatment.
Water quality standard. Law or regulation that
consists of the beneficial designated use or uses of a
waterbody, the numeric and narrative water quality
criteria that are necessary to protect the use or uses of
that particular waterbody, and an anti-degradation
statement.
Watershed-based trading. Watershed-based trading is
an efficient, market-driven approach that encourages
innovation in meeting water quality goals, but remains
committed to enforcement and compliance
responsibilities under the Clean Water Act. It involves
trading arrangements among point source dischargers,
nonpoint sources, and indirect dischargers in which the
"buyers" purchase pollutant reductions at a lower cost
than what they would spend to achieve the reductions
themselves. Sellers provide pollutant reductions and
may receive compensation. The total pollution
reduction, however, must be the same or greater than
what would be achieved if no trade occurred.
Watershed protection approach (WPA). The
USEPA's comprehensive approach to managing water
resource areas, such as river basins, watersheds, and
aquifers. WPA has four major features—targeting
priority problems, stakeholder involvement, integrated
solutions, and measuring success.
Watershed-scale approach. A consideration of the
entire watershed, including the land mass that drains
into the aquatic ecosystem.
Watershed. A drainage area or basin in which all land
and water areas drain or flow toward a central collector
such as a stream, river, or lake at a lower elevation.
Wetland. An area that is saturated by surface water or
ground water with vegetation adapted for life under
those soil conditions, as in swamps, bogs, fens, marshes,
and estuaries.
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