HomeMy WebLinkAbout2026.09.28 Council Workshop Packet22 / MONTH 2025
6. FISH AND WILDLIFE HABITAT CONSERVATION AREAS
(CHAPTER 28.20)
This chapter covers fish and wildlife habitat conservation area (FWHCA) regulations in PMC Sections
28.20.010 – 28.08.060. A summary of recommended updates is provided in Table 6; only sections where
updates are currently recommended have been included. A discussion of recommended updates is
provided after the table.
Table 6. Example code table summary.
Code Section Title Review Comment and
Recommendations
Reason for
Recommendation
PMC 28.20.010 Purpose Consider Including no net loss BAS, Commerce
Checklist
PMC 28.20.020 Fish and Wildlife Habitat
Conservation Area
designation and
classification criteria
1. Consider removing table listing all
FWHCAs
2. Consider separating the
classification sources into separate
section
1. BAS, Clarity
2. Bas, Clarity
PMC 28.20.030 Fish and wildlife habitat
conservation area rating
1. Consider removing section 1. Clarity
PMC 28.20.040 Determination of need
for fish and wildlife
habitat area detailed
study
1. Consider removing.
Determination addressed elsewhere
in code
1. Clarity
PMC 28.20.050 Fish and wildlife habitat
area detailed study
requirements
1. Consider including qualified
professional
2. Remove term fish and wildlife
critical area and replace with
FWHCA
3. Update critical area minimum
report requirements
1. Clarity, definition
change
2. Clarity
3. BAS
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Code Section Title Review Comment and
Recommendations
Reason for
Recommendation
PMC 28.20.060 Performance standards
minimum requirements
1. Consider adding riparian habitat
areas
2. Consider adding riparian habitat
area regulatory/performance
standards
1. BAS
6.1 Purpose (28.20.010)
The purpose section does not reference the requirement in WAC 365‑190‑180(1) for jurisdictions to
ensure no net loss of the functions and values of FWHCA. The City should consider revising the purpose
statement to explicitly include the no‑net‑loss requirement so that the section reflects state
expectations for protecting ecological functions and values.
6.2 Fish and wildlife habitat conservation area designation
and classification criteria (PMC 28.20.020)
6.2.1 Fish and Wildlife Habitat Area Classification
The City's FWHCA designation section does not comprehensively identify all fish and wildlife habitat
conservation areas recognized under WAC 365-190-130 and instead relies on a summarized list that
may omit certain state-designated habitat categories. For clarity and consistency with state guidance,
the City should consider revising the FWHCA designation section to explicitly identify all fish and
wildlife habitat conservation areas described in WAC 365-190-130. Incorporating the state habitat
categories directly into the code would improve transparency, reduce ambiguity, and help maintain
consistency with applicable state regulations and guidance documents.
6.2.2 Classification Sources and Mapping
Table 28.20.020(1) identifies resources used to designate habitat areas, but the sources are not
consolidated within the mapping section and could be expanded. The City should consider listing all
applicable mapping sources within the mapping section, including WDNR Natural Heritage Program
mapping data and anadromous and resident salmonid distribution maps contained in Habitat Limiting
Factors reports published by the Washington Conservation Commission. This would improve clarity
and provide a more comprehensive basis for critical area identification.
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6.3 Fish and wildlife habitat conservation area rating (PMC
28.20.030)
PMC 28.20.030 includes a habitat rating system that classifies habitat areas as either primary or
secondary. However, these ratings do not appear to be used elsewhere in the chapter to establish
differing protection standards, buffers, mitigation requirements, or review criteria. The City should
consider removing the habitat rating section to streamline the code and eliminate terminology that
does not have a clear regulatory function. This would improve clarity and reduce potential confusion
for staff, applicants, and decision-makers.
6.4 Determination of need for fish and wildlife habitat area
detailed study (PMC 28.20.040)
The City's FWHCA regulations include a separate section establishing when a detailed study is required.
However, PMC 28.12.120 already contains a citywide critical area screening and initial determination
process that serves a similar purpose. The City should consider removing or consolidating this section
with the general initial determination provisions to reduce redundancy and improve code clarity. This
would help ensure that critical area review is administered through a single, consistent process.
6.5 Fish and wildlife habitat area detailed study
requirements (PMC 28.20.050)
It is recommended to expand the critical area report requirements to include a description of habitat
protection measures, cumulative impacts assessment, monitoring, adaptive management, and
long‑term stewardship. Adding these elements ensures that reports address how habitat functions will
be protected and maintained over time, consistent with state agency expectations.
6.6 Performance standards minimum requirements (PMC
28.20.050)
The City currently does not establish riparian habitat area buffers. To facilitate implementation of
riparian habitat buffer standards, the City should consider adopting specific riparian habitat area
performance standards. These provisions could include standards for vegetative condition, buffer
averaging, increased buffer widths when warranted by site conditions, and functionally disconnected
buffers. Incorporating these performance standards would improve implementation of riparian habitat
area protections and allow buffer requirements to better reflect site-specific conditions.
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7. AQUIFER RECHARGE AREAS (CHAPTER 28.24)
This chapter covers aquifer recharge areas regulations in PMC Sections 28.24.010 – 28.24.090. A
summary of recommended updates is provided in Table 7; only sections where updates are currently
recommended have been included. A discussion of recommended updates is provided after the table.
Table 7. Example code table summary.
Code Section Title Review Comment and
Recommendations
Reason for
Recommendation
PMC 28.24.020 Aquifer recharge
designation criteria
Update WAC reference
Include DOE resources
Match designation and
vulnerability criteria to SMP
BAS, Clarity,
Consistency
PMC 28.24.030 General regulations Consider adding allowed
activities
Clarity
PMC 28.24.040 Determination of need
for aquifer recharge
area detailed study
Update list of resources
Add agricultural activities
Consistency, Clarity
PMC 28.24.050 Aquifer recharge
detailed study
requirements
Add mitigation Consistency, BAS
PMC 28.24.070 Performance standards
basic requirements
Include BMP’s BAS
7.1 General
Consider renaming section to “critical aquifer recharge area” (CARA) for consistency with WAC critical
area designations and SMP.
7.2 Aquifer Recharge Designation Criteria (PMC 28.24.020)
Update WAC reference.
Consider referencing the Department of Ecology’s confirmed or suspected contaminated groundwater
sites and associated map resources.
Add Designations per SMP
Consider revising the aquifer recharge area designation criteria to align with Table 29.01.540(2)(a),
Designation of Aquifer Recharge Areas, in the Pasco Shoreline Master Program (City of Pasco 2023) as
follows:
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(1) Wellhead Protection Areas pursuant to WAC 246-290 WA Department of Health, US Environmental
Protection Agency
(2) Areas designated for special protection pursuant to a groundwater management program, RCW
90.44, 90.48, and 90.54 and WAC 173-100 and 173-200 Ecology
(3) Areas overlying unprotected aquifers. Such aquifers shall be identified through any existing
competent hydrogeologic study USGS, WDNR
(4) Areas within identified unprotected aquifers but possessing the following characteristics:
a) Slopes less than 15%
b) Coarse alluvium or sand and gravel in the soil profile and no known impermeable layers (b)
WDFW
Add Vulnerability Assessment
Consider incorporating the vulnerability assessment criteria established in the Shoreline Master Program
(2023) to provide consistency between the City’s CAO and SMP and establish a clear framework for
evaluating the relative vulnerability of critical aquifer recharge areas.
High Vulnerability High significance aquifer recharge areas are areas with slopes of less than 15%
underlain by coarse alluvium or sand and gravel
Moderate Vulnerability Moderate significance aquifer recharge areas are: (1) Areas with slopes of less
than 15% underlain by fine alluvium, silt, clay, glacial till, or deposits from the electron mudflow (2) Areas
with slopes of 15% to 30% underlain by sand and gravel
Low Vulnerability Moderate significance aquifer recharge areas are: (1) Areas with slopes of 15% to 30%
underlain by silt, clay, or glacial till (2) Areas with slopes greater than 30%
7.3 General regulations (PMC 28.24.030)
Consider including a list of activities that are permitted outright within CARAs to provide greater clarity
and predictability for applicants. Clearly identifying exempt or allowed activities can improve code
usability, reduce uncertainty during project planning, and streamline the permit review process.
Examples of such activities are provided below:
Allowed uses (do not require approval or submission of a site assessment report)
All residential uses;
Development and improvement of parks, recreation facilities, open space, or conservation
areas resulting in less than five percent total site impervious surface area that do not increase
the use of a hazardous substance;
Public water systems;
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On-site domestic septic systems releasing less than 14,500 gallons of effluent per day and that
are limited to a maximum density of one system per one acre.
7.4 Determination of need for aquifer recharge area (PMC
28.24.030)
Consider updating the list of referenced information resources to reflect currently available and
accessible materials. The City of Pasco Wellhead Protection Area Plan does not appear to be publicly
available online and should be reviewed to confirm its continued applicability and availability as a
reference. Additionally, the City of Pasco Water System Plan appears to have been renamed the City of
Pasco Comprehensive Water System Plan and should be updated accordingly. Based on the resources
reviewed, none appear to specifically identify, map, or reference high significance aquifer recharge
areas, which may limit their usefulness in determining when the associated regulatory provisions apply.
It is recommended that the City consider developing or updating GIS mapping for its CARA
designations. Having readily accessible mapping would provide greater consistency in project review,
help applicants identify potential CARA requirements earlier in the permitting process, and reduce the
likelihood that potentially vulnerable aquifer recharge areas are overlooked.
Agriculture
Consider requiring new agricultural activities within critical aquifer recharge areas to be conducted in
accordance with applicable approved land management and conservation practices designed to
protect groundwater quality, including practices identified in the U.S. Department of Agriculture
(USDA) Natural Resources Conservation Service (NRCS) technical guides, as well as applicable local,
state, and federal regulations governing agricultural practices, as amended.
For new agricultural land uses that may affect critical aquifer recharge areas, consider requiring the
preparation of a detailed study, as appropriate, to evaluate potential risks to groundwater resources
and identify measures necessary to avoid or minimize impacts.
7.5 Aquifer recharge area detailed study (PMC 28.24.050)
Consider incorporating the following language from the Pasco Shoreline Master Program (PMC
29.01.540(5)(d)) to promote consistency between the City’s Critical Areas Ordinance and Shoreline
Master Program in the review and mitigation of potential impacts to critical aquifer recharge areas:
“The Detailed Study shall include a mitigation plan detailing how the activity will offset any impact on the
resource and control risk of contamination to the aquifer.”
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7.6 Performance standards basic requirements (PMC
28.24.070)
Consider referencing and requiring implementation of applicable Best Management Practices from the
Washington Department of Ecology’s Stormwater, Water Quality, Hazardous Waste, Wetland, and Solid
Waste Programs BMPs; Chapter 13.26A; and BMPs from the Washington Departments of Health,
Agriculture, Transportation, and State Conservation District Office to minimize impacts to CARAs.
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8. FLOOD HAZARD AREAS (CHAPTER 28.28)
This chapter covers flood hazard areas regulations in PMC Sections 28.28.010 – 28.28.040. A summary
of recommended updates is provided in Table 8; only sections where updates are currently
recommended have been included. A discussion of recommended updates is provided after the table.
Table 8. Example code table summary.
Code Section Title Review Comment and
Recommendations
Reason for
Recommendation
PMC 28.28..040 Management Address floodplain ecological
functions, flood storage,
groundwater recharge, floodplain
connectivity, channel migration
hazards, and climate resilience.
BAS
8.1 General (PMC 28.28.010)
Consider renaming section to “frequently flooded areas” for consistency with WAC critical area
designations
8.2 Management (PMC 28.28.040)
Designation criteria is limited to FEMA-mapped 100-year floodplains and does not fully reflect the
broader frequently flooded area definition in WAC 365-190-030. Current regulations emphasize flood
damage prevention and structural protection but contain limited provisions specifically addressing
floodplain ecological functions, flood storage, groundwater recharge, floodplain connectivity, channel
migration hazards, and climate resilience. Consideration should be given to expanding the flood
hazard area designation criteria, strengthening protection of natural floodplain processes, and
updating regulations to reflect contemporary floodplain management and climate adaptation
practices.
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9. GEOLOGIC HAZARD AREAS (CHAPTER 28.32)
This chapter covers geologic hazard area regulations in PMC Sections 28.32.010 – 28.32.090. A
summary of recommended updates is provided in Table 9; only sections where updates are currently
recommended have been included. A discussion of recommended updates is provided after the table.
Table 9. Example code table summary.
Code Section Title Review Comment and
Recommendations
Reason for
Recommendation
PMC 28.32.060 Determination of need
for geologic hazard area
detailed study
Update mapping resources Consistency, clarity
9.1 Determination of need for geologic hazard area detailed
study (PMC 28.32.060)
The City of Pasco’s online GIS mapping and other available critical areas mapping resources do not
currently identify known or suspected erosion, landslide, seismic, or mine hazard areas. However, the
City’s online GIS includes a steep slopes layer that may assist in identifying areas with potential geologic
hazards. To improve consistency between the City’s mapping resources and the Critical Areas
Ordinance, consider updating or supplementing the available mapping resources to identify, where
data are available, the geologically hazardous areas designated under PMC 28.32.060(1).
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10. REFERENCES
City of Pasco. 2023. "Shoreline Master Program." City of Pasco, Washigton.
Ecology, the Corps, and EPA. 2021. Wetland Mitigation in Washington State - Part 1: Agency Policies and
Guidance (Version 2). Ecology Publication #21-06-003, Washington State Department of
Ecology.
ESA and Ross & Associates Environmental Consulting, Ltd. 2008. Making Mitigation Work: The Report of
the Mitigation that Works Forum. Publication #08-06-018, Washington State Department of
Ecology.
Facet. 2026. "Shrub-steppe Habitat Best Available Science." City of Pasco.
U.S. Army Corps of Engineers. 2010. Regional Supplement to the Corps of Engineers Wetland Delineation
Manual: Western Mountains, Valleys, and Coast Region (Version 2.0). ERDC/EL TR-10-3,
Wetlands Regulatory Assistance Program.
USDA, NRCS. 2024. Field Indicators of Hydric Soils in the United States: A Guid for Identifying and
Delineating Hydric Soils (Version 9.0). United States Department of Agriculture, Natural
Resources Conservation Service, in cooperation with the National Technical Committee for
Hydric Soils.
WDFW. 2008. Priority Habitat and Species List. Updated June 2023, Washington Department of Fish and
Wildlife, Olympia.
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APPENDIX A. Washington State Wetland Rating
System for Eastern Washington:
ɎɌɎɎ Update (Ecology
Publication No. ɎɎ -Ɍɒ -Ɍɍɐ )
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Washington State
Wetland Rating System
For Eastern Washington
2014 Update
October 2014 - Effective January 2015
Publication no. 14-06-030
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Publication and Contact Information
This report is available on the Department of Ecology’s website at
https://fortress.wa.gov/ecy/publications/SummaryPages/1406030.html
For more information contact:
SEA Program
P.O. Box 47600
Olympia, WA 98504-7600
Phone: 360-407-6600
Washington State Department of Ecology - www.ecy.wa.gov
o Headquarters, Olympia 360-407-6000
o Northwest Regional Office, Bellevue 425-649-7000
o Southwest Regional Office, Olympia 360-407-6300
o Central Regional Office, Yakima 509-575-2490
o Eastern Regional Office, Spokane 509-329-3400
This publication should be cited as:
Hruby, T. (2014). Washington State Wetland Rating System for Eastern Washington: 2014
Update. (Publication #14-06-030). Olympia, WA: Washington Department of Ecology.
To request ADA accommodation including materials in a format for the visually impaired, call
the SEA Program at 360-407-6600. Persons with impaired hearing may call Washington Relay
Service at 711. Persons with speech disability may call TTY at 877-833-6341.
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Washington State
Wetland Rating System
for Eastern Washington
2014 Update
by
Thomas Hruby, PhD
SEA Program
Washington State Department of Ecology
Olympia, Washington
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Wetland Rating System for Eastern WA: 2014 Update i
Effective January 1, 2015
Table of Contents
Preface ...................................................................................................................................................................... iii
Acknowledgements ............................................................................................................................................. iii
1. Introduction ...................................................................................................................................................... 1
Changes made to the 2004 Rating System in this update .............................................................. 2
Peer and public review of this update ................................................................................................... 4
2. Rationale for the Categories ........................................................................................................................ 5
2.1 Category I .................................................................................................................................................. 5
2.2 Category II ................................................................................................................................................ 9
2.3 Category III ............................................................................................................................................ 10
2.4 Category IV ............................................................................................................................................ 10
3. Overview for Users ...................................................................................................................................... 11
3.1 When to use the wetland rating system .................................................................................... 11
3.2 How the wetland rating system works ...................................................................................... 11
3.3 General guidance for using the Wetland Rating Form ......................................................... 11
4. Identifying Wetland Boundaries for Rating ....................................................................................... 15
4.1 Identifying unit boundaries in large contiguous wetlands in valleys (Depressional
and Riverine) ................................................................................................................................................ 17
4.2 Wetland units along the banks of streams or rivers ............................................................. 18
4.3 Identifying wetland units in a patchwork on the landscape (mosaic) ........................... 20
4.4 Identifying unit boundaries along the shores of lakes or reservoirs (Lake Fringe
wetlands only) ............................................................................................................................................. 21
4.5 Wetlands bisected by human-made features .......................................................................... 22
4.6 Cases when a wetland should not be divided .......................................................................... 23
4.7 Freshwater wetlands where only part of the wetland is a forest or a bog .................. 24
4.8 Very small wetlands .......................................................................................................................... 24
5. Detailed Guidance for the Rating Form: Scoring Functions ......................................................... 27
5.1 Classifying the wetland .................................................................................................................... 27
5.2 Classifying the plant communities ............................................................................................... 35
5.3 Water quality and hydrologic functions in Depressional wetlands (questions
starting with ‘D’) ......................................................................................................................................... 37
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Wetland Rating System for Eastern WA: 2014 Update ii
Effective January 1, 2015
5.4 Water quality and hydrologic functions in Riverine wetlands (questions starting
with ‘R’) ........................................................................................................................................................... 54
5.5 Water quality and hydrologic functions in Lake Fringe wetlands (questions starting
with “L”) .......................................................................................................................................................... 68
5.6 Water quality and hydrologic functions in Slope wetlands (questions starting with
“S”) .................................................................................................................................................................... 77
5.7 Habitat functions for all HGM classes (questions starting with ‘H’) ............................... 86
6. Detailed Guidance for the Rating Form: Wetlands With Special Characteristics .............. 105
References Cited ............................................................................................................................................... 119
Appendix A. Rating Form
Appendix B. WDFW Priority Habitats in Eastern Washington
Appendix C. Estimating Soil Texture
Appendix D. Modeling Functions and Values in This Rapid Method
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Wetland Rating System for Eastern WA: 2014 Update iii
Effective January 1, 2015
Preface
This document is an update of the Washington State Wetland Rating System for Eastern
Washington, published by the Department of Ecology in 2004 (Hruby, 2004a). This is the
third edition of the rating system for eastern Washington since the Department of Ecology
published the first one in 1991. The original document was published with the
understanding that modifications would be incorporated as we increase our understanding
of wetland systems, and as many different people use the rating system.
The need to update the previous version became apparent as we have learned more in the
last decade about how wetlands function and what is needed to protect them.
Furthermore, statistical analyses of the data collected during the use of the previous
version indicated that scoring functions from 0-100 could not be supported by the science.
The method can accurately document the levels at which wetlands function only to three
qualitative ratings of High, Medium, or Low.
We are calling this version an update of the 2004 edition rather than a revision because the
changes made are not as significant as those made between the 1993 and the 2004
versions. Much of the information and text remain the same and changes were made only if
new scientific information indicated changes were needed.
This update was initially published online as Publication # 14-06-018 in June 2014. It was
removed from the website to allow time for local jurisdictions to update relevant code
language and to correct typographical and formatting errors. Because typographical
changes were made to the rating form, we replaced the published version with a new
publication number, rather than issuing a notice of errata.
Acknowledgements
This document would not have been possible without the participation and help of many
people. The document is an update of existing tools, and thus represents the culmination of
two decades of development, review, and field testing. Special thanks go to the technical
committee of wetland experts and planners from local governments and Ecology’s
Wetlands Technical Advisory Group who helped develop the objectives for the rating
system in 2004, reviewed and field tested the Credit/Debit Method in 2010 (Ecology
publication #11-06-015), and provided feedback on the these tools. Special thanks to Joe
Rocchio of the Natural Heritage Program for refining our list of bog species and those found
in calcareous fens. We have also received valuable comments from 19 individuals and
organizations who took the time to review the draft sent out for public comment, and we
wish to acknowledge their efforts. These include: Suzanne Anderson, Confluence
Environmental Services, Kathy Curry, Geoff Gray, Grette Associates, Patricia Johnson,
Kennewick Irrigation District, Mike Layes, Torrey Luiting, Jeff Meyer, David Moore, Hugh
Mortensen, Brad Murphy, NW Ecological Services, Scott Rozenbaum, Rebecca Schroeder,
Lee Stragis, Doug Swanson, and Patrick Togher. Amy Yahnke edited the final draft. Thank
you all.
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Wetland Rating System for Eastern WA: 2014 Update iv
Effective January 1, 2015
Abbreviations for standard units of measure used in this document
inch = in centimeter = cm
foot = ft meter = m
mile = mi kilometer = km
acre = ac hectare = ha
horsepower = hp parts per thousand = ppt
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Wetland Rating System for Eastern WA: 2014 Update 1
Effective January 1, 2015
1. Introduction
The wetlands in Washington State differ widely in their functions and values. Some wetland
types are common, while others are rare. Some are heavily disturbed, while others are still
relatively undisturbed. All, however, provide some functions and resources that are valued.
These may be ecological, economic, recreational, or aesthetic. Managers, planners, and
citizens need tools to understand the resource value of individual wetlands in order to protect
them effectively.
Many tools have been developed to understand the functions and values of wetlands. The
methods range from detailed scientific analyses that may require many years to complete, to
the judgments of individual resource experts done during one visit to the wetland. Managers
of our wetland resources, however, are faced with a dilemma. Scientific rigor is often time
consuming and costly. Tools are needed to provide information on the functions and values of
wetlands in a time- and cost-effective way. One way to accomplish this is to categorize
wetlands by their important attributes or characteristics based on the collective judgment of
regional experts. Such methods are relatively rapid but still provide some scientific rigor
(Hruby, 1999).
This rating system was designed to differentiate among wetlands based on their sensitivity to
disturbance, their significance, their rarity, our ability to replace them, and the functions they
provide. The rating system, however, does not replace a full assessment of wetland functions
that may be necessary to plan and monitor a project of compensatory mitigation.
The intent of the rating categories is to provide a basis for developing standards for protecting
and managing the wetlands. Some decisions that can be made based on the rating include the
width of buffers needed to protect the wetland from adjacent development and permitted
uses in, and around, the wetland. Many local jurisdictions have included language on buffers
in their critical areas ordinances based on the 2005 guidance on wetland buffers (found in
Wetlands in Washington State – Volume 2: Guidance for Protecting and Managing Wetlands,
Publication #05-06-008). The update of the rating systems will provide a more accurate
rating of the functions and values of a wetland but keeps the same four wetland categories
used in the 2005 guidance. For the 2015-2019 critical areas ordinance update cycle, we are
not proposing any changes to the buffer widths recommended in the 2005 guidance, however
any buffer strategy that uses function scores to determine buffer widths will need to be
adjusted to use the new scores in the 2014 update.
The Washington State Wetland Rating System categorizes wetlands based on specific
attributes such as rarity, sensitivity to disturbance, and the functions they provide. These
attributes are not comparable, and thus cannot be rated on the same scale. Only the
functions are actually rated on a qualitative scale. The term “rating,” however, is being
kept in the title to maintain consistency with the previous editions.
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Wetland Rating System for Eastern WA: 2014 Update 2
Effective January 1, 2015
The rating system is intended for use primarily with vegetated, freshwater, wetlands as
identified using the federal wetland delineation manual and the appropriate regional
supplements. The rating system also does not characterize streambeds, riparian areas, and
other valuable aquatic resources.
The rating system also has not been calibrated to montane wetlands generally found above
3000 ft elevation. We do not recommend that the rating system be used to rate functions in
these montane wetlands.
Changes made to the 2004 Rating System in this update
Chapters 2-4 and the scoring for the site potentials in Chapter 5 are carried over from the
2004 version of the rating system. Some changes in these sections were made to reflect the
annotations added in 2007 and to include current definitions used by the Washington State
Department of Fish and Wildlife and the Natural Heritage Program at the Department of
Natural Resources.
The substantive differences between this version of the rating system and the 2004 version
are the conversion of scores for each function to ratings of High, Medium, or Low, and the
replacement of the Opportunity section with two new sections (Landscape Potential and the
Value). Only the ratings of functions are assigned a score rather than using the raw scores of
the indicators. The range of possible scores for a wetland category based on function was
reduced to 9-27 (from 1-100) to better reflect the accuracy of the method (see box on next
page).
The field indicators for Site Potential are the same as in the 2004 version of the rating system
and that were also kept in the more recent Credit/Debit Method developed by Ecology in
2012 (Ecology publication #11-06-015). The new sections on Landscape Potential and Value
in Chapter 5 of this update are the same as in the Credit/Debit Method. Also, we have added
calcareous fens to the description of peat systems (bogs) that are Category I wetlands in
eastern Washington (see Chapter 2).
A companion document, Washington State Wetland Rating System for Western Washington:
2014 Update should be used for wetlands in western Washington (Ecology publication
#14-06-029). The boundary between eastern and western Washington for the purpose of
rating wetlands is defined in WAC 222-16-010.
Eastern Washington means the geographic area in Washington east of the crest of the
Cascade Mountains from the international border to the top of Mt. Adams, then east of the
ridge line dividing the White Salmon River drainage from the Lewis River drainage and
east of the ridge line dividing the Little White Salmon River drainage from the Wind River
drainage to the Washington-Oregon state line.
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Wetland Rating System for Eastern WA: 2014 Update 3
Effective January 1, 2015
The distribution of categories of reference wetlands in the updated rating system
Data were collected at 90 wetlands to calibrate the rating system in 2004. Data from 86 of
these could be used to re-calibrate the scoring for this update. Some wetlands were lost
through natural and human alterations and some could not be re-located.
The range of scores for wetland categories based on functions in this update is between 9–
27 rather than the 0–100 possible in the 2004 version. This change was necessary because
a statistical analysis of data collected in the last decade indicated that rapid methods such
as these are not scientifically accurate beyond a qualitative rating of High, Medium, or Low
(unpublished data collected at reference sites during the calibration and field testing of the
method).
Choosing the score at which we separate levels of functioning is a decision that is based on
best professional judgment in rapid methods such as these. For example, in the 2004
Rating System we chose to call wetlands with a very high level of function (Category I)
those with a score of 70 or more, while those with a high level of function (Category II)
scored between 51 – 69, those with a moderate level of function (Category III) scored
between 30 – 50 points, and those with a low level of function (Category IV) scored less
than 30 points. These divisions were based on the judgment of the teams of wetland
experts that developed the rating system in 2004. It reflects the teams’ scientific
consensus on what is meant by very high, high, moderate, and low levels of functions after
visiting the reference sites. The divisions also reflected the teams’ observations that most
wetlands function at high or moderate levels and there are fewer that function at very high
or low levels.
The divisions between wetland categories based on levels of function in this update were
chosen to match as closely as possible the distribution of ratings found for the 86 reference
sites when rated using the 2004 method. However, given that the range of possible scores
was reduced, it was not possible to get the exact same distribution. We do consider,
however, that the scores used to place a wetland in a category were very close (see the
first page of the rating form in Appendix A for the scores of the different categories).
Number of Reference Wetlands in Each Category Based on Their Score for Functions
Category 2004 Rating System Updated Rating System
I 13 11
II 36 36
III 35 33
IV 6 6
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Wetland Rating System for Eastern WA: 2014 Update 4
Effective January 1, 2015
Peer and public review of this update
The 2004 version of the rating system went through a thorough peer and public review
process as did the Credit/Debit Method. The new sections on Landscape Potential and Value
were field tested for one year prior to publication in 2012. Over 40 individuals and groups
provided comments on the Credit/Debit Method. These comments and our responses can be
found at: https://fortress.wa.gov/ecy/publications/SummaryPages/1206005.html. In
addition to the 40 reviewers of the Credit/Debit Method, we received comments from 19
reviewers of a draft of this update.
The rating system is based on the best information available at this time and meets the needs
of “best available science” under the Growth Management Act.
We anticipate that the method will be further modified over time as we keep increasing our
understanding of our wetland resources.
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2. Rationale for the Categories
This rating system is designed to differentiate among wetlands based on their sensitivity to
disturbance, rarity, the functions they provide, and whether we can replace them or not. The
emphasis is on identifying those wetlands:
Where our ability to replace them is low.
That are sensitive to adjacent disturbance.
That are rare in the landscape.
That perform many functions well.
That are important in maintaining biodiversity.
The following description summarizes the rationale for including different wetland types in
each category. As a general principle, it is important to note that wetlands of all categories
have valuable functions in the landscape, and all are worthy of inclusion in programs for
wetland protection.
2.1 Category I
Category I wetlands are those that 1) represent a unique or rare wetland type; or 2) are more
sensitive to disturbance than most wetlands; or 3) are relatively undisturbed and contain
ecological attributes that are impossible to replace within a human lifetime; or 4) provide a
high level of functions. We cannot afford the risk of any degradation to these wetlands
because their functions and values are too difficult to replace. Generally, these wetlands are
not common and make up a small percentage of the wetlands in the region. Of the 86
wetlands used to field-test the current rating system, only 11 (13%) were rated as a Category
I.
In eastern Washington the following types of wetlands are Category I:
Alkali Wetlands. Alkali wetlands are characterized by the presence of shallow saline water
with a high pH. In eastern Washington these wetlands contain surface water with specific
conductance that exceeds 3000 micromhos/cm. These wetlands provide the primary habitat
for several species of migrant shorebirds and are also heavily used by migrant waterfowl.
They also have unique plants and animals that are not found anywhere else in eastern
Washington. For example, the small alkali bee that is used to pollinate alfalfa and onion for
seed production lives in alkali systems. Other bees used to pollinate fruits and vegetables are
generally too large to pollinate the small flowers of those commercially important plants.
Therefore, alkali wetlands are a valuable natural resource for agriculture in the western U.S.
and especially in eastern Washington (Delaplane & Mayer, 2000).
The salt concentrations in these wetlands have resulted from a relatively long-term process of
groundwater surfacing and evaporating. These conditions cannot be easily reproduced
through compensatory mitigation because the balance of salts, evaporation, and water inflows
are hard to reproduce, and to our knowledge has never been tried.
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Alkali wetlands are placed into Category I because they probably cannot be reproduced
through compensatory mitigation. No information was found on any attempts to create or
restore alkali wetlands. Any impacts to alkali wetlands will, therefore, probably result in a net
loss of their functions and values.
Wetlands of High Conservation Value (formerly called Natural Heritage Wetlands).
These Category I wetlands have been identified by scientists from the Washington Natural
Heritage Program (WNHP) as important ecosystems for maintaining plant diversity in our
state.
Wetlands that represent rare plant communities or provide habitat for rare plants are
uncommon in eastern Washington. As of March 2014, there are 946 Wetlands of High
Conservation Value in eastern WA; most of those sites are based on the presence of rare
plants (877); only 69 sites are based on plant communities (J. Rocchio, WNHP, personal
communication, March 2014). The total number of wetlands in eastern Washington, however,
is surprisingly high even in the arid parts of the region. The U.S. Fish and Wildlife Service
mapped 3124 wetlands in Lincoln County alone (Tiner et al., 2002). Unfortunately, we do not
have a good count of wetlands in other locations in the eastern part of the state.
If you find a rare plant species, rare plant community, or high-quality common plant
community that you believe would qualify the site as a Wetland of High Conservation Value
but is not currently documented in the WNHP database, you can submit the information to
them. If WNHP staff have the capacity to review the information, they will make a
determination about whether sufficient information exists to designate the site as a Wetland
of High Conservation Value. If WNHP does not respond within 30 days, then the wetland
cannot be rated as a Wetland of High Conservation Value. Information required for
documenting a new rare plant location can be found at:
http://www.dnr.wa.gov/Publications/amp_nh_sighting_form.pdf.
Visit WNHP’s website for resources to assist in classifying the plant community:
http://www1.dnr.wa.gov/nhp/refdesk/communities.html.
By categorizing these wetlands as Category I, we are trying to provide a high level of
protection to these important but rare wetlands. These natural systems and species will
survive in Washington only if we give them special attention and protection.
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Bogs and Calcareous Fens. Bogs and Calcareous Fens are Category I peat wetlands because
they are sensitive to disturbance and have not been successfully re-created through
compensatory mitigation.
Bogs are wetlands with peat soils and a low pH, usually a pH < 5. The chemistry of these
wetlands is such that changes to the water regime or water quality of the wetland can easily
alter their ecosystem. The plants and animals that grow in bogs are specifically adapted to
such conditions and do not tolerate changes well. Immediate changes in the composition of
the plant community often occur after the water regime changes. Minor changes in the water
regime or nutrient levels in these systems can have major adverse impacts on the plant and
animal communities (e.g., Grigal & Brooks, 1997).
In addition to being sensitive to disturbance, bogs are not easy to re-create through
compensatory mitigation. Researchers in northern Europe and Canada have found that
restoring bogs is difficult, specifically in regard to plant communities (Bolscher, 1995;
Grosvermier et al., 1995; Schouwenaars, 1995; Schrautzer et al., 1996; Mazerolle et al., 2006),
water regime (Grootjans & van Diggelen, 1995; Schouwenaars, 1995), and/or water
chemistry (Wind-Mulder & Vitt, 2000). In fact, restoration may be impossible because
changes to the biotic and abiotic properties preclude the re-establishment of bogs
(Schouwenaars, 1995; Schrautzer et al., 1996), although one study (Lucchese et al., 2010) did
find that a sphagnum layer did become re-established after 17 years. Furthermore, bogs
form extremely slowly, with organic soils forming at a rate of about 1 in per 40 years in
western Washington (Rigg, 1958).
Calcareous fens are a type of alkaline, rather than acidic, peat wetland. They are peat-
accumulating wetlands maintained by groundwater that have a neutral or high pH and high
concentrations of calcium and other alkaline minerals. Calcareous fens support rare plant
species tolerant of these unique chemical conditions (Calcareous Fen Technical Committee,
1994). The groundwater is typically rich in calcium and magnesium bicarbonates and
sometimes calcium and magnesium sulfates (Eggers & Reed, 1997). Calcareous fens are
thought to be one of the rarest wetland types in the United States (Eggers & Reed, 1997) and
appear to be one of the rarest peat wetland types in Washington State.
Within Washington, calcareous fens have been found only in the north central to northeastern
portion of the State. The Washington Natural Heritage Program has identified only 5
calcareous fens out of 946 Wetlands of High Conservation Value in their survey of eastern
We use the term bogs to represent a range of acidic peat wetlands. The criteria we
have been using in the rating system encompass a broader range of wetlands than what
many scientists consider to be true bogs. Many scientists consider bogs to be peat
wetlands that receive almost all of their water from rainfall (J. Rocchio, Washington
Natural Heritage Program, personal communication, March 2014). Since many of the
acidic peat wetlands in the state also get some of their water from the surrounding
landscape or groundwater, they cannot be considered as true bogs, but should rather be
called “acidic fens.” The criteria we use define a group of wetlands that should be called
acidic peatlands, but we are not changing the name in this update to avoid confusion and
because we have not changed the criteria for identifying bogs.
.
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Washington. As a result of their rarity, we have added calcareous fens to the other Category I
peat systems in this update.
Mature and Old-Growth Forested Wetlands with Slow Growing Trees. Mature and
old-growth forested wetlands over ¼ ac in size that are dominated by slow growing native
trees are Category I because these wetlands cannot be easily replaced through compensatory
mitigation. A mature forest of slow growing trees may require a century or more to develop,
and the full range of functions performed by these wetlands may take even longer (reviewed
in Sheldon et al., 2005).
Wetland species considered to be slow growing and native in eastern Washington are western
red cedar (Thuja plicata), Alaska yellow cedar (Chamaecyparis nootkatensis), pine spp. (mostly
western white pine, Pinus monticola), western hemlock (Tsuga heterophylla), Oregon white
oak (Quercus garryana), and Engelmann spruce (Picea engelmannii).
Forests with Stands of Aspen. Aspen stands in a forested area are Category I because their
contribution as habitat far exceeds the small acreage of these stands and relatively small
number of stems (Hadfield & Magelssen, 2004). Furthermore a mature stand of aspen and its
underground root system may be difficult to reproduce. Regeneration of aspen stands by
sexually produced seeds is an unusual phenomenon (Romme et al., 1997).
Aspen stands are also important because they represent a priority habitat as defined by the
State Department of Fish and Wildlife, “Priority habitats are those habitat types or elements
with unique or significant value to a diverse assemblage of species.” (Washington State
Department of Fish and Wildlife [WDFW],
http://wdfw.wa.gov/publications/00165/wdfw00165.pdf, accessed December 3, 2013).
NOTE: All wetlands are categorized as a priority habitat by the WDFW. Wetlands with aspen
stands, therefore, represent two priority habitats that coincide.
Wetlands That Perform Functions at High Levels. Wetlands scoring 22 points or more (out
of 27) from the rating of functions are Category I wetlands.
Not all wetlands function equally well, especially across the suite of functions performed. The
field questionnaire was developed to provide a method by which wetlands can be rated based on
their relative performance of different functions. Wetlands scoring 22 points or more were
judged to have the highest levels of functions. These wetlands are also relatively rare. Of the 86
wetlands used to calibrate the rating system in eastern Washington, only 11 (13%) scored 22
points or higher based on their functions.
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2.2 Category II
Category II wetlands are difficult, though not impossible, to replace, and provide high levels of
some functions. These wetlands occur more commonly than Category I wetlands, but still
need a relatively high level of protection. Category II wetlands in eastern Washington include:
Forested Wetlands in the Floodplains of Rivers. Forested wetlands are an important
resource in the floodplains of rivers, especially in the areas through which the river may flow
regularly (often called the channel migration zone). These wetlands are rated Category II, at a
minimum, because the questionnaire on functions does not adequately capture their unique
role in the ecosystem. Trees in the floodplains are critical to the proper functioning and the
dynamic processes of rivers. They influence channel form, and create pools, riffles, and side
channels that are essential habitat for many fish and other aquatic species. These trees also
create localized rearing and flood refuge areas, and contribute to the stabilization of the main
river channel (NRC, 2002).
Please note, however, that many forested wetlands in floodplains that have structurally
complex habitats may actually be a Category I based on their functions.
Mature and Old-Growth Forested Wetlands with Fast Growing Trees. Mature and
old-growth forested wetlands with over ¼ ac of forest dominated by fast growing native trees
are rated as Category II because they are hard to replace within the time frame of most
regulatory activities. The time needed to replace them is shorter than for forests with slow
growing trees, but still significant.
Native fast-growing wetland trees include:
Alders: Red (Alnus rubra), thinleaf (A. incana ssp. tenuifolia)
Cottonwoods: Narrowleaf (Populus angustifolia), black (P. balsamifera)
Willows: Peach-leaf (Salix amygdaloides), Sitka (S. sitchensis), Pacific (S. lasiandra)
Quaking aspen (Populus tremuloides)
Water birch (Betula occidentalis)
Vernal Pools. Vernal pools, also called rainpools, that are located in a landscape with other
wetlands, and that are relatively undisturbed during the early spring, are rated Category II
because the questionnaire on functions does not adequately capture their unique role in the
ecosystem.
Vernal pool ecosystems are formed when small depressions in the scabrock or in shallow soils
fill with snowmelt or spring rains. They retain water until the late spring when they dry out
as a result of reduced precipitation and increased evapotranspiration. The wetlands hold
water long enough throughout the year to allow some strictly aquatic organisms to flourish,
but not long enough for the development of a typical wetland environment (Zedler, 1987).
The Washington Natural Heritage Program has recognized the vernal pool ecosystem as an
important component of Washington's Natural Area System. Vernal pools in the scablands are
the first to melt in the early spring. This open water provides areas where migrating
waterfowl can find food while other, larger, bodies of water are still frozen. Furthermore, the
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open water provides areas for pair bonding in the waterfowl (R. Friesz, WDFW, personal
communication, 2002). Thus, vernal pools in a landscape with other wetlands provide an
important habitat function for waterfowl that requires a relatively high level of protection.
This is the reason why relatively undisturbed vernal pools in a mosaic of other wetlands are
Category II, and isolated, undisturbed vernal pools are Category III.
Wetlands That Perform Functions Well. Wetlands scoring between 19-21 points (out of 27)
on the questions related to the functions present are Category II wetlands. These wetlands were
judged to perform most functions relatively well, or performed one group of functions very well
and the other two moderately well.
2.3 Category III
Category III wetlands are wetlands with a moderate level of functions (scores between 16-18
points) and can often be adequately replaced with a well-planned mitigation project.
Wetlands scoring between 16-18 points generally have been disturbed in some ways, and are
often less diverse or more isolated from other natural resources in the landscape than
Category II wetlands.
2.4 Category IV
Category IV wetlands have the lowest levels of functions (scores less than 16 points) and are
often heavily disturbed. These are wetlands that we should be able to replace, and in some
cases, improve. However, experience has shown that replacement cannot be guaranteed in
any specific case. These wetlands may provide some important functions, and also need to be
protected.
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3. Overview for Users
3.1 When to use the w etland rating system
The rating system is designed as a rapid screening tool to categorize wetlands for use by
agencies and local governments in protecting and managing wetlands. It should be used only
on vegetated wetlands as defined using the delineation procedures in WAC 173-22-35. The
rating system does not try to establish the economic values present in a wetland; it only helps
to identify its sensitivity, rarity, and functions.
Two versions of the rating system have been developed, one for western Washington and one
for eastern. This broad division of the state into east and west may not reflect all regional
differences in the importance of wetlands. Developing special measures to protect locally
unique wetlands is recommended where local governments need to provide a level of
protection that would not be otherwise provided by the rating system.
3.2 How the w etland rating system w orks
The Wetlands Rating Form (the rating form) in Appendix A of this document asks the user to
collect information about the wetland in a step-by-step process. We recommend careful
reading of the guidance and taking one of the classes on the rating system given by the
Department of Ecology before filling out the form. A wetland may be rated in two different
categories based on the different criteria used in this method. It is important, therefore, to fill
out the entire rating form. If two categories can be applied to a wetland, it is the one that
provides the most protection that applies.
If you are interested in learning more about how the rating system was developed, details are
described in Hruby (2001, 2009). In addition, Appendix D discusses rapid methods for
characterizing functions and how this rating system was calibrated.
3.3 General guidance for using the Wetland Rating Form
Land-owner’s permission
It is important to obtain permission from the land owner(s) before going on their property.
Time Involved
Over the last decade the scientific community has standardized how we group assessment
methods based on the information collected and the time required (Kentula, 2007). The
rating system is classified as a “rapid method” or “Level 2 Assessment” (see definitions in box
on next page). We define rapid as usually taking no more than two people a half day in the
field and requiring no more than a half day of office preparation and data analysis to come to
an answer (Fennessy et al., 2004). In some cases, however, it may be necessary to visit the
wetland more than once. Some of the questions cannot be answered if the ground is covered
with snow or the surface water is frozen. If this is the case at the time a wetland is being
rated, it may be necessary to revisit the site later.
NOTE: We recommend that field work always be done by two people for reasons of safety.
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Several of the questions require analyzing and preparing figures. Aerial photographs
downloaded from the internet, topographic, or other maps are useful for preparing these
figures. The list of figures needed to correctly answer the questions is found on the back of the
first page of the rating form in Appendix A.
Experience and qualifications needed
It is important that the person completing the rating have experience in the identification of
natural wetland features, indicators of wetland function, vegetation classes, and some ability
to distinguish among different plant species. Reviewers of the rating system should also be
familiar with wetlands and how they function. We recommend that qualified wetland
consultants or wetland experts be used to rate most sites, particularly the larger and more
complex ones. This will help ensure that results are repeatable.
Training is highly recommended
In addition, we highly recommend that users of this method take the training provided by
the Department of Ecology on this method.
Users of this method who have not taken the training can expect that, on the average,
their scores for each function will be off by at least 1 point per function. This is based on
data collected during the calibration of the 2004 wetland rating systems and subsequent
training sessions. Untrained users will underestimate, or overestimate, the scores for
functions by 15%. This is an average, and actual differences may be as high as 40%.
Levels of Assessment
Wetland assessment techniques are classified as Levels 1, 2, or 3 based on the scope and
detail required to complete the assessment (Kentula, 2007). The levels are generally
defined as follows:
• Level 1 Assessment: Expert systems that use readily available digital data to define
ecological relationships based on best professional judgment.
• Level 2 Assessment: Rapid assessment based on data collection from easily
observable field indicators. A Level 2 assessment usually lasts less than four hours
in the field, has relatively simple metrics, and results in a single rating for each
wetland.
• Level 3 Assessment: Comprehensive assessment in which quantitative data are
collected on biological, physical, chemical and/or morphological aspects of the
ecosystem.
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Maps and figures
Some of the questions on the rating form can only be answered by drawing polygons on aerial
photos of the site and by calculating the relative area of these polygons (as a percent of total
area) within the wetland. Visual estimates of area can be prone to large errors as high as 40%.
The pictures or figures used to make these estimates have to be included with the
rating form for the rating to be considered as complete. A list of the figures and
photographs needed is provided in the rating form in Appendix A.
Rating the wetland
Each wetland can have several ratings: one resulting from its score for the functions and one
or more resulting from special characteristics it may have. The first page of the rating form
contains a box for recording each rating. This box should be filled out after completing the
form. If the wetland meets the criteria for two categories, select the one that will provide the
higher level of protection for the wetland.
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4. Identifying Wetland Boundaries for Rating
To begin, determine the location and approximate boundaries of all wetlands at the site you
are investigating. A surveyed delineation of the wetland is not necessary to rate the wetland,
unless this information is required for another part of your project. The boundary, however,
will need to be verified during the field visit. Boundaries that are not verified by a field survey
may cause problems in the scoring of the indicators. This is especially true in forested
wetlands where the boundaries are difficult to determine from aerial photographs.
The rating form identifies the information that needs to be included on aerial photos or maps
and submitted with the form. It is highly recommended that you obtain aerial photos of the
site.
The entire wetland has to be scored. Usually it is the entire delineated wetland that is
scored. Small areas within a wetland (such as the footprint of an impact) cannot be rated
separately. The method is not sensitive enough, or complex enough, to allow division of a
wetland into smaller units based on level of disturbance, property lines, or plant communities.
DO NOT SCORE ONLY THE PART BEING ALTERED OR MITIGATED (Figure 1).
Figure 1. Footprint of the impact is the red rectangle, but the unit for rating is the entire wetland (yellow
line).
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Furthermore, you do not subdivide a wetland into different hydrogeomorphic (HGM) classes if
more than one is present. A wetland with more than one HGM class within its boundary is
treated as one HGM class for rating (Figure 2). The second page of the classification key in
Appendix A provides guidance on how to classify wetlands having more than one HGM class
within its boundary.
Figure 2. A wetland with two HGM classes within the delineated boundary. This wetland is rated as a Lake
Fringe wetland.
There are, however, ecological criteria that can be used to separate very large wetlands into
smaller units for scoring. These criteria are described below.
If you do not have access to the entire wetland because the wetland includes different
properties or because parts of the site are impenetrable or not accessible, you should do the
best you can to answer the questions from aerial photos, using binoculars, or any other
additional information. Note your lack of access on the rating form and record which
questions are based on incomplete data.
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4.1 Identifying unit boundaries in large contiguous
wetlands in valleys (Depressional and Riverine)
Wetlands can often form large contiguous areas that extend over hundreds of acres. This is
especially true in river valleys where there is some surface water connection among all areas
of the floodplain. In these situations the initial task is to identify the wetland unit that will be
rated. A large contiguous area of wetland can be divided into smaller units using the criteria
described below.
The guiding principles for separating a wetland in a valley into different units are changes in
the water regime or a lack of wetland plants. Boundaries between different units should be
set at the point where the volume, flow, or velocity of the water changes abruptly. These
changes in water regime can be either natural or human-caused (anthropogenic). The
following sections describe some common situations that might occur. The criteria for
separating wetlands into different units are based on the observations made during the
calibration of the rating systems and the methods for assessing wetland functions. They
reflect the collective judgment of the teams of wetland experts that developed and calibrated
the methods.
Wetland units in a series of depressions in a valley
Wetlands that form ponded depressions in river corridors may contain constrictions where
the wetland narrows between two or more depressions. The key consideration is the
direction of flow through the constriction. If the water moves back and forth freely it is not a
Examples of Changes in Water Regime
Berms, dikes, cascades, rapids, falls, and culverts.
Features that change flow, volume, or velocity of water over short distances.
The presence of drainage ditches that significantly reduce water detention in one
area of a wetland.
More detailed data are needed to adequately assess functions in only a part of a
wetland
The rating of an entire wetland unit rather than just the part of it being mitigated or
impacted is a trade-off made between scientific rigor and the need for a rapid method.
None of the rapid methods developed by Ecology (the rating systems and function
assessment methods) are rigorous enough to adequately assess the functions of only a
small area within a wetland unit. We did numerous tests of this question, and both
methods produced invalid results when applied to small areas within a wetland. More
detailed data are needed to adequately assess functions in only a part of a wetland. This
would require monitoring and measuring the actual processes taking place in different
parts of a wetland rather than characterizing the structural indicators present, and would
certainly require monthly sampling for at least one year.
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separate unit. If the flow between depressions is unidirectional, down-gradient, and has a
change in elevation from one part to the other, then a separate unit should be created. The
justification for separating wetlands increases as the flow between two areas becomes more
unidirectional and has a higher velocity. Constrictions can be natural or human-made (e.g.,
culverts) (Figure 3). Generally, if the high water mark in the lower wetland is 6 in or more
lower than the high water mark in the upper wetland, then the two should be considered as
separate units for rating.
4.2 Wetland units along the banks of streams or rivers
In eastern Washington, linear wetlands contiguous with a stream or river may be broken into
units using criteria based on either hydrologic factors or the distribution of plants. Figure 4
presents a diagram of how wetland units might be separated along a stream corridor based on
change in the water regime. Three changes in water regime are illustrated: 1) a weir or dam,
2) a series of rapids, and 3) a tributary coming into the main stream that increases the flow
significantly (generally > 25%).
NOTE: Unit 1 in Figure 4 should be classified as a Depressional wetland. Units 2, 3, and 4
would probably be Riverine or Slope, depending on the area of overbank flooding.
Figure 5 illustrates how units can be separated based on the distribution of plants. Units can
be separated when: 1) wetland plants disappear and are replaced with unvegetated bars or
banks for at least 50 ft along the stream, and 2) the wetland plant community is less than 5 ft
wide along the shore for at least 100 ft.
Unit 1
Area 2a
Area 2b
Figure 3. Determining depressional wetland units along a stream corridor with constrictions.
Areas 2a and 2b should be rated as one unit.
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Figure 4. Determining wetland units in a riverine system based on changes in water regime.
Figure 5. Determining wetland units in a riverine setting based on reduced plant cover. In this case, the
river is wider than 17 ft and the vegetated wetlands on either side are rated separately.
Unit 3
Unit 4
Unit 1
Unit 2
Wetland Unit 1
Wetland Unit 2 Wetland Unit 3
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In cases when a wetland contains a stream or river, you must also decide whether the stream
or river is a part of the wetland. Use the following guidelines to make your decision:
Wetland on one side only — If the wetland unit is contiguous with, but only on one side
of, a river or stream, do not include the river as a characteristic of the wetland unit for
rating.
Wetland on both sides of a wide stream or river — If the river or stream has an
unvegetated channel that is more than 17 ft (5 m) wide, and there are contiguous
wetland areas on both sides, treat each side as a separate unit for rating. Do not
include the river as a characteristic of the wetland unit for rating.
Wetland on both sides of a narrow river or stream — If the river or stream has an
unvegetated channel less than 17 ft (5 m) wide, and there are contiguous vegetated
wetlands on both sides, treat both sides together as one unit, and include the river as a
characteristic of the wetland.
4.3 Identifying w etland units in a patchwork on the
landscape (mosaic)
If the wetland area being scored contains a mosaic of wetlands and uplands, the entire mosaic
should be considered one unit for rating when:
Each patch of wetland is less than 1 ac (0.4 ha), AND
Each patch is less than 100 ft (30 m) away from the nearest wetland, AND
The total area delineated as vegetated wetland is more than 50% of the total area of
wetlands and uplands, open water, and river bars around which you can draw a polygon
(see Figure 6), AND
There are at least three patches of wetland that meet the size and distance thresholds.
If these criteria are not met, each wetland area should be considered as a separate unit for this
method (see Figure 6).
NOTE: One of the most common mosaic landscapes in eastern Washington is formed by
riparian wetlands in the floodplains of rivers and streams. In this landscape, vegetated
wetlands, as defined by the delineation manual, are interspersed with “uplands” of
cottonwood or willow. In this case, use the criteria above. Treat the entire area as a
wetland if the areas that meet the criteria for wetlands are greater than 50% of the total
area. In this landscape the cottonwoods growing outside the wetland patches, but within
the mosaic, should be included as features of the wetland.
Unit 3
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4.4 Identifying wetland unit boundaries along the
shores of lakes or reservoirs (Lake Fringe wetlands
only)
Lakes or reservoirs will often have a fringe of wetland plants along their shores. Different
areas of this vegetated fringe can be separated into different units if there are gaps where the
width of plants narrows or they disappear completely. Use the following criteria for
separating units along a lakeshore.
Only the vegetated areas along the lake shore are considered part of the wetland unit for
rating. Open water within areas of plants are considered to be part of the wetland, but open
water that separates patches of plants along a shore is not considered to be part of the
wetland (Figure 7).
If only some parts of the lakeshore are vegetated with wetland plants, separate the vegetated
parts into different units at the points where the wetland plants thin out to less than a foot in
width for at least 33 ft (10 m) (Figure 8).
NOTE: If the open water is less than 20 ac, the entire area (open water and any other
vegetated areas) is considered as one wetland unit, and is a Depressional or Riverine wetland.
Figure 1
Wetland
Unit boundary
Total wetland area < 50% of polygon – each wetland is
a separate unit
Figure 6. Determining unit boundaries
when wetlands are in small patches.
Each wetland polygon should be
scored separately when the total area
is less than 50% wetland.
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Figure 7. Lake Fringe wetland showing open water that is included within the wetland boundary
Figure 8. Absence of wetland plants along the shore of a lake that separates the wetlands into two units for
rating.
4.5 Wetlands bisected by human-made features
When a Depressional wetland is divided by a human-made feature, such as a road
embankment, the wetland should not be divided into different units if there is a level surface-
water connection between the two parts of the wetland. Water should be able to flow equally Unit 1
Open water outside
the boundary of unit
being rated.
Open water inside the
boundary of unit
being rated.
Break in wetland
vegetation
Unit 1
Unit 2
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well between the two areas. For example, if there is a wetland on either side of a road with a
culvert connecting the two, and both sides of the culvert are partially or completely
underwater for most of the year, the wetland should be treated as one unit. Make the down-
gradient wetland a separate unit, however, if the bottom of the culvert is above the high water
marks in the receiving wetland, or the high water marks on either side of the road or dike
differ by more than 6 in of elevation.
4.6 Cases w hen a w etland should not be divided
Differences in land use within a wetland should not be used to define units unless they
coincide with the circumstances described above. Many functions that wetlands perform are
independent of the land use in the wetland. For example, a Depressional wetland has
approximately the same amount of live storage whether the surface is a shrub community or a
pasture.
Furthermore, the rating system used in this method is not robust enough to capture slight
differences in habitat functions within different portions of the same wetland unit. Attempts
were made during the calibration of the 2004 Wetland Rating System (Hruby, 2004a) to score
different portions of a wetland unit based on differences in land use, but the results did not
provide an accurate representation of the system. This compromise is necessary in order to
make the tool rapid and easy to use. For example, if half a wetland has been recently cleared
for farming and the other half left intact, the entire area functions as, and should be
categorized as, one unit. Figure 9 shows a wetland that is a lawn along one side and a wetland
plant community on the other side. In this case, the entire wetland should be rated as one
unit.
Figure 9. A wetland with two land uses and separated by a fence. The entire wetland should be treated as
one unit.
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4.7 Freshwater w etlands where only part of the w etland
is a forest or a bog
Freshwater wetlands may be rated as Category I because they contain a smaller area of bogs,
calcareous fens, or mature or old-growth forest. If the entire wetland (including the bog and
forested areas) scores between 16 and 21 points for its functions (Table 1), it may be possible to
assign a dual rating to the wetland (Category I/II, Category I/III).
Table 1. Situations where dual ratings may be possible.
Rating Based on
Special Characteristics
Score for Functions
22-27
Score for Functions
19-21
Score for Functions
16-18
Cat. I bog Not possible – Cat. I I/II I/III
Cat. I forest Not possible – Cat. I I/II I/III
To develop a dual rating you will need to establish a boundary within the wetland that clearly
establishes the area that is the Category I bog or forest. If you are unable to clearly map the
boundaries between the forest or bog and the rest of the wetland, it may be impossible to assign a
dual rating.
Dual ratings are acceptable only when a wetland contains a small area of bog, calcareous fen, or
forest. Wetlands that are Category I, Wetlands of High Conservation Value, and Alkali
wetlands cannot be assigned a dual rating.
The criteria to be used in establishing the boundary between the Category I part of a wetland and
those that are either Category II or III are as follows:
For wetland areas that are Category I as a result of the presence of a forest, the boundary
between categories should be set at the edge of the forest.
For wetland areas that are Category I because they are Bogs or Calcareous Fens, the
boundary between categories should be set where the characteristic vegetation of these
peatlands changes (i.e., most of the plants that are specifically adapted to acidic and
calcareous peatlands are replaced with more common wetland species) and/or where the
organic soils become shallow (less than 16 in).
4.8 Very small w etlands
Users often question the effectiveness of using rapid methods in wetlands that are ¼ ac or
less. One tree or shrub may be all that is needed in a small wetland to score points on the
rating form for certain questions. The data collected during the calibration of the rating
systems, however, indicate that wetlands smaller than a ¼ ac can be rated accurately. The
smallest wetlands rated during the calibration were about 1/10 ac in size (see Figure 10 for an
example of a small wetland that is about 1/10 ac in size), and all were judged by the field teams
to be adequately characterized.
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Figure 10. A Slope wetland near Padilla Bay that is approximately 1/10 ac in size.
At present, the accuracy of the scoring has not been tested for wetlands smaller than 1/10 ac,
but the method may be applicable to even smaller wetlands because the scoring of water
quality and hydrologic functions is not dependent on the size or the habitat niches in the
wetland.
For example, the ability of a square yard of organic soil in a wetland to remove nitrogen is not
dependent on the size of the wetland. A square yard of soil in a wetland of 1/10 ac can be just
as effective at performing a function as a square yard in a large wetland. The same is true for
the hydrologic functions. A small wetland that stores 3 ft of water during a flooding event is
more effective, on a per acre basis, than a large wetland that stores only 1 ft. The larger
wetland may store a larger volume overall, but it is the volume per unit area that needs to be
characterized. Impacts to wetlands are usually calculated by area. For example, an impact to
1/10 ac of a wetland that stores 3 ft of water needs to be mitigated by replacing a similar
amount of storage (i.e., 3 ft over 1/10 ac). It makes no difference if the size of the wetland
impacted is ¼ ac, 10 ac, or 100 ac.
The field testing, however, indicated that the method will not work well for scoring habitat
functions in wetlands smaller than 1/10 ac (4000 ft2). For example, one large tree may cover
400 ft2 of a 4,000 ft2 wetland and this would give it a "forested" class. It is not expected,
however, that the tree will provide functions to the same level as a forested class in a larger
wetland. On the other hand, wetlands that are larger than 1/10 ac are adequately
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characterized. This is based on the consensus of the different teams (function assessment and
rating) that went out into the field when we were developing the methods.
Also, very small wetlands may not provide good habitat for some of the larger wildlife species
such as otter or beaver, but they are known to provide critical habitat for many smaller
species. For example, amphibians were found using and breeding in wetlands as small as 270
ft2 in the Palouse region of northern Idaho (Monello and Wright 1999).
Thus, very small wetlands may be less important for large wildlife but more important for
smaller wildlife. Since the methods were judged to be accurate for wetlands as small as a 1/10
of an acre, the review team and the Department of Ecology staff decided not to develop
additional questions for very small wetlands less than 1/10 ac in size. Very small wetlands can
be rated with the understanding that the results are not as robust as in larger wetlands.
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5. Detailed Guidance for the Rating Form:
Scoring Functions
This chapter provides detailed guidance for answering the questions on the rating form
(Appendix A). The questions are listed in the order they appear on the form. Results from
each section should be summarized on the first page of the form. More than three-fourths of
the questions are the same as, or similar to, those used in the previous version of the
Washington State Wetland Rating System for Eastern Washington (Ecology publication #04-
06-015).
A correctly filled out Wetland Rating Form requires maps or figures to correctly answer the
questions. Most of these maps are needed to estimate the area covered by different
environmental indicators, but several can be combined in one figure. The second page of the
rating form lists the figures and photographs needed to correctly fill out the form.
NOTE: Do not estimate area visually without a graphic aid such as a gridded overlay.
Visual estimates of area can be off by 30-40% and this will change the results.
5.1 Classifying the w etland
Scientists have come to understand that wetlands can perform functions in different ways.
The way wetlands function depends to a large degree on hydrologic and geomorphic
conditions (Brinson, 1993). As a result, we group wetlands into categories based on the
geomorphic and hydrologic characteristics that control many functions. This classification
system is called the Hydrogeomorphic (HGM) Classification.
The rating system described here uses only the highest grouping in the HGM classification
(i.e., wetland class). The more detailed methods for assessing wetland functions developed
for eastern and western Washington (Hruby et al., 1999; Hruby et al., 2000) refine this
classification and subdivide some of the classes further.
A classification key is provided with the rating form to help you identify whether the wetland
is Lake Fringe, Slope, Riverine, or Depressional. The key contains eight questions that need to
be answered sequentially. Each question is described below in more detail than that found in
the key.
Question 1: Lake Fringe Wetlands
Lake Fringe wetlands are on the water side of the Ordinary High Water Mark (OHWM) of
lakes. Lake Fringe wetlands are separated from other wetlands based on the area and depth
Training is highly recommended
An analysis of data collected during training sessions and field tests suggest that untrained
users of this method can expect that, on the average, their scores will be off by at least 4
points out 27. One-third of untrained users will have errors of 8 points or more.
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of open water adjacent to them. If the area of open water (without vegetation) next to a
vegetated wetland is larger than 20 ac (8 ha), and more than 10 ft (3 m) deep over 30% of the
open water areas, the wetland is considered to be Lake Fringe. The criterion here is 20 ac of
open water without any vegetation. If the water levels fluctuate, the depth criterion has to be
met for at least 9 months of the year in a year with average rainfall. This definition of lakes is
different than in the Shoreline Management Act (SMA). The Shoreline Management Act
requires that a water body have 20 ac within the OHWM in order to be considered a lake
under shoreline jurisdiction. Thus, a 20 ac shallow pond that is completely vegetated would
be a lake under the SMA but a Depressional wetland for the purpose of this method.
The definition of lakes in this rating system is based on limnological characteristics and not
the criteria used in the SMA. Lakes have different environmental processes than do small
ponds (e.g., stratification, spring turnover, etc.). In general, these processes occur in eastern
Washington only in systems that have at least 20 ac of open water that is deeper than 10 ft.
Wetlands found along the shores of large reservoirs such as those found behind dams are also
considered to be Lake Fringe. Figure 11 shows a Lake Fringe wetland along the shores of a
reservoir on the Snake River with a narrow band of wetland shrubs along the shore. Although
the area was once a river valley, these wetlands function more like Lake Fringe wetlands
rather than Riverine wetlands. The technical teams developing the 2004 Wetland Rating
Systems (Hruby, 2004a; b) decided to include wetlands along the shores of reservoirs as Lake
Fringe if they meet the thresholds for open water and depth.
Figure 11. Lake Fringe wetland along the shores of a reservoir on the Snake River with a narrow band of
wetland shrubs along the shore.
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Question 2: Slope Wetlands
Slope wetlands occur on slopes where groundwater surfaces and begins running along the
surface, or immediately below the surface. Water in these wetlands flows only in one
direction (down the slope) and the gradient is steep enough that the water is not impounded.
The downhill side of the wetland is always the point of lowest elevation in the wetland. Figure
12 shows a Slope wetland along the Columbia River that formed where the slope of the
hillside changed and caused groundwater to come to the surface.
Slope wetlands with surface flows can be distinguished from Riverine wetlands by the lack of
a defined stream bed with banks. Slope wetlands may develop small rivulets along the
surface, but they serve only to convey water away from the wetland. There is no surface flow
coming into the wetland through channels. Also, Slope wetlands do not impound water except
in very small depressions that may form on the surface. These are only a few inches in
diameter and a few inches deep.
Some Slope wetlands can only be identified by their vegetation. For example, in the Palouse
region, you may find a small swale that collects groundwater percolating through the loess
(windblown) soils. The only indication that a wetland is present is the stand of cattails
growing in the swale (Figure 13). Such swales are not considered to be Riverine wetlands
because there are no indications of a channel with defined banks nor indications of overbank
flooding.
Figure 12. Slope wetland along the Columbia River identified by the presence of wetland plants (Carex spp.
and Juncus spp.). Wetland occurs where there is a major break in this slope of the hillside.
Break in slope
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Figure 13. Slope wetland in Pullman identified by cattails in a swale (red arrow).
Question 3: Riverine Wetlands
Riverine wetlands occur in valleys associated with stream or river channels. They lie in the
active floodplain, and have important hydrologic links to the flows in the river or stream.
Their proximity to the river facilitates both the rapid transfer of floodwaters in and out of the
wetland, and the import and export of sediments. The distinguishing characteristic of
Riverine wetlands in eastern Washington is that they are flooded by overbank flow from the
river at least once every 10 years. Riverine wetlands, however, may also receive significant
amounts of water from other sources such as groundwater and slope discharges.
Wetlands that lie in floodplains but are not flooded at least once every 10 years by the stream
are not classified as Riverine. Also, wetlands behind dikes are usually disconnected from the
active floodplain and are no longer regularly flooded. In cases where wetlands in floodplains
are not flooded frequently enough to meet the flooding criterion, they should be classified as
Depressional or Slope.
In eastern Washington, the technical committee developing the rating system decided that the
frequency of overbank flooding needed to call a wetland Riverine is at least once in 10 years
(10 yr return frequency). This is in contrast to western Washington where a wetland has to
be flooded at least once every 2 years to be considered Riverine. The decision to reduce the
flooding frequency for Riverine wetlands is based on the observations that the region is often
subject to periods of drought that may last several years. In periods of drought, wetlands that
are an integral part of the river system may not get flooded. Even during periods of drought,
however, they still function as an integral part of the river system because they are connected
to the underground flows in the valley (hyporheic flows).
Most Riverine wetlands in eastern Washington are relatively easy to identify because they lie
directly within the channel as vegetated bars (Figure 14), vegetated channels (Figure 15), or
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are old oxbows within the floodplain (Figure 16). The Riverine wetlands in the northeastern
part of the state (Ferry, Stevens, Pend Oreille Counties) may be harder to identify because the
broad valleys there were formed by glaciers rather than the existing rivers. The valley around
Colville, for example, is, or used to be, all a wetland. These wetlands, however, are mostly
Slope wetlands rather than Riverine. The floodplain of the Colville River is a narrow band
within the much larger valley created by the glaciers.
Many Riverine wetlands are associated with rivers that are very dynamic. Their proximity to
the river facilitates the rapid transfer of floodwaters in and out of the wetland, and the import
and export of sediments. Riverine wetlands are often replaced by Depressional or Slope
wetlands near the headwaters of streams and rivers, where the channel (bed) and bank
disappear, and overbank flooding grades into inundation by surface or groundwater. In
headwaters, the dominant source of water becomes surface runoff or groundwater seepage.
For the purposes of classification, wetlands that show evidence of frequent overbank flooding,
even if from an intermittent stream, are considered Riverine even if they receive water from
surface flows or groundwater.
Wetlands that are created in a stream channel by impounded water from an obstruction such
as a beaver dam, weir, or debris dam are considered to be Depressional rather than Riverine.
The major hydrologic factor that maintains and provides the structures in these systems is the
ongoing flow that is impounded. The overbank flooding is not as important a factor. A
wetland would be considered Riverine, however, if the dam or weir impounds water for only a
short time, such as a single storm. The impounded water must be present for at least 2
months every year to be considered Depressional.
However, a Riverine wetland may have depressions where water is maintained by high levels
of groundwater (hyporheic waters). If it is flooded at least once every 10 years it still should
be classified as Riverine. The difference between a Depressional and Riverine wetland in
such cases may be subtle. The wetland is Depressional if the impounded water is maintained
by a physical feature (dam, weir, or log jam) that raises the water level in the floodplain. If the
water is impounded in a depression that is below the general surface, then it would be
Riverine.
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Figure 14. Vegetated river bars on the Touchet River that are classified as Riverine wetlands because the
depressions in them get flooded at least once every 10 years.
Figure 15. Riverine wetland in the Palouse where the entire channel is vegetated between the banks and is
a wetland. This channel has only seasonal flow. It is dry by late summer.
Impoundment created by a beaver
dam has increased the amount of
open water in this wetland.
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Figure 16. Oxbow wetland on the Colville River that is classified as Riverine.
Question 4: Depressional Wetlands
Depressional wetlands occur in topographic depressions where the elevation of the surface
within the wetland is lower than in the surrounding landscape. The shapes of Depressional
wetlands vary, but in all cases, the movement of surface water and shallow subsurface water
is toward the lowest point in the depression. The depression may have an outlet, but the
lowest point in the wetland is somewhere within the boundary, not at the outlet.
Depressional wetlands can sometimes be hard to identify because the depressions in which
they are found are not very evident. By working through the key it may not be necessary to
look at topographic maps, or try to identify that the lowest point of the wetland is in the
middle. If a wetland has surface ponding, even if only for a short time, and does not meet the
criteria for Lake Fringe or Riverine wetlands, it can be classified as Depressional. Vernal pools
and Alkali wetlands are also classified as Depressional wetlands.
A wetland where there is no surface ponding, such as a true bog without any open water,
would also be classified as Depressional. Such wetlands may be difficult to differentiate from
Slope wetlands, but are probably rare in eastern Washington. All of the Depressional
wetlands visited as part of the function assessment project and the calibration of the rating
system have had some surface water ponding during part of the year.
Question 5: Wetland Is Hard to Classify
Sometimes it is hard to determine whether the wetland unit you are scoring meets the criteria
for a specific wetland class. You may find characteristics of several different
hydrogeomorphic classes within one wetland boundary. For example, seeps at the base of a
slope often grade into a Riverine wetland, or a small stream within a Depressional wetland
has a zone of flooding along its sides that would be classified as Riverine.
If you have a wetland with the characteristics of several HGM classes present within its
boundaries, use Table 2 to identify the appropriate class to use for rating. Use this table only
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if the area encompassed by the “recommended” class is at least 10% of the total area of
wetland being rated. For example, if a Slope wetland grades into a Riverine wetland and the
area of the Riverine wetland is ¼ of the total wetland unit you are rating, use the questions for
Riverine wetlands. However, if the area that would be classified as Riverine is less than 10%
(e.g., ½ ac of a 10 ac unit is frequently flooded), use the questions for the Slope wetlands. The
same applies for other combinations of classes. A unit in which the depressional area is only
5% of the entire unit that is otherwise a slope should be rated as a Slope wetland. If, however,
the area classified as Depressional is 15% of the area of the unit it should be rated as
Depressional.
Table 2. Classification of wetlands with multiple hydrogeomorphic classes for the purpose of rating their
functions.
HGM classes found within one
wetland unit
HGM Class to use if area of
this class > 10% total area of
unit
Slope + Riverine Riverine
Slope + Depressional Depressional
Slope + Lake Fringe Lake Fringe
Depressional + Riverine Depressional
Depressional + Lake Fringe Depressional
Riverine + Lake Fringe Riverine
If you are still unable to determine which of the above criteria apply to your wetland, or you
have more than two HGM classes within a wetland boundary, classify the wetland as
Depressional. Hydrologically complex wetlands found in eastern Washington during the
calibration of the methods have always had some features of Depressional wetlands, and thus,
could be classified as Depressional.
Once you have classified the wetland, you will need to answer only the questions that pertain
to the HGM class of the wetland being rated. The first letter of the question on the rating form
identifies the wetland class for which the question is intended:
D = Depressional or Flats
R = Riverine
L = Lake Fringe
S = Slope
The guidance in the following sections is divided according to the HGM class of the wetland
being rated. Each question on the rating form is addressed in turn.
NOTE: The questions for scoring habitat functions are labeled [H] and apply to all HGM
classes of wetlands.
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5.2 Classifying the plant communities
Several questions on the data sheet ask you to classify the plant communities found within the
wetland unit. This should not be confused with classifying the wetland as described earlier.
The rating system uses several different classification schemes for plant communities; only
one of which is the commonly used Cowardin classification (Cowardin et al., 1979). The
Cowardin classification is the most complex one and is described in more detail below. You
will need to carefully read the description of each question to ensure that you use the
classification scheme appropriate for that question. Use caution in filling out the rating
form because the thresholds for scoring, as well as the way in which plants are
classified, differ among the questions.
The Cowardin Classification
Cowardin plant classes are distinguished by the uppermost layer of plants (forest, shrub, etc.)
that provides more than 30% surface cover within part or all of a wetland. This area is often
called a Cowardin polygon when mapping the distribution of plants. If the total cover of
plants is less than 30%, the area does not have a Cowardin plant class. Areas with less than
30% plant cover should be categorized as open water or sand/mud flats. If the plants are
deciduous and you are rating the wetland during periods when leaves have fallen, try to
reconstruct what the cover would be when the plants are fully leafed-out. A deciduous forest
of alder would still be considered a forest using the Cowardin classification even in winter
when there are no leaves present and the cover may be less than 30%.
Plant names used in the rating system: The rating system identifies some specific plants
as indicators. For example, lists of species found in bogs and calcereous fens are provided
in the identification key in Chapter 6. The plant names listed in the rating system are those
found in the United States Department of Agriculture (USDA) PLANTS Database
(http://plants.usda.gov) and are current as of August 2014. Plant names change based on
new information from genetics, morphology, and historical records. The reference
databases we commonly use for plant names are sometimes in disagreement. For example,
at the time of this publication, USDA PLANTS Database, Integrated Taxonomic Information
System (ITIS; http://www.itis.gov/), and US Army Corps of Engineers National Wetland
Plant List (NWPL; http://rsgisias.crrel.usace.army.mil/NWPL/) disagree on the names of
some common wetland species. We used the USDA PLANTS Database because it is familiar
to many users of the rating system, provides a map of where each species is located, lists
wetland indicator status where available, includes moss species, and acknowledges
subspecies and variety names. Though we consider NWPL an authority on wetland
indicator status, it does not distinguish among different subspecies and variety names, and
it does not include mosses. Likewise, ITIS is an authority on the current taxonomic standing
of plant names, but it does not provide a map. When distinguishing among plants with
similar names, a map of the plants’ distributions is sometimes helpful Therefore, we have
chosen the PLANTS database as the most useful for the rating system. Where plant names
in the PLANTS database differ from NWPL, the synonym is provided in parentheses.
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This method uses only four of the major Cowardin plant classes to map the plant communities
in a wetland. These are:
Forested class: An area (polygon) in the wetland unit where the canopy of woody
plants over 20 ft (6 m) tall (such as cottonwood, aspen, cedar, etc.) covers at least 30% of
the ground. Trees need to be at least partially rooted in the wetland in order to be
counted toward the estimates of cover (unless the unit is a mosaic of small wetlands as
described in Section 4.3 and the trees are on hummocks between the wetlands). Some
small wetlands may have a canopy over the unit but the trees are not rooted within the
wetland. In this case the wetland does not have a Forested class.
Scrub-shrub class: An area (polygon) in the wetland unit where woody plants less than
20 ft (6 m) tall are the top layer of plants. To count, the shrub plants must provide at
least 30% cover and be the uppermost layer. Examples of common shrubs in western
Washington wetlands include the native roses, young alder, young cottonwoods,
hardhack (Spiraea), willows, and red-osier dogwood.
Emergent class: An area (polygon) in the wetland unit covered by erect, rooted
herbaceous plants excluding mosses and lichens, and where total cover of shrubs and
trees is less than 30%. These plants have stalks that will support the plant vertically in
the absence of surface water during the growing season. These plants are present for
most of the growing season in most years. To count, the emergent plants must provide
at least 30% cover of the ground and be the uppermost layer. Cattails and bulrushes are
good examples of plants in the Emergent class.
NOTE: The definition of emergent plants used by Cowardin is different from the one
used in delineation for determining the boundaries between “vegetated wetlands” and
“vegetated shallows”.
Aquatic Bed class: An area (polygon) in the wetland unit where rooted aquatic plants,
such as lily pads, pondweed, etc., cover more than 30% of the surface of the standing
water. These plants grow principally on or below the surface of the water for most of the
growing season in most years. This is in contrast to the emergent plants described above
that have stems and leaves that extend above the water most of the time. Aquatic bed
plants are found only in areas where there is seasonal or permanent ponding or
inundation. Lemna spp. (duckweed) is not considered an aquatic bed species because it
is not rooted. Aquatic bed plants do not always reach the surface and care must be taken
to look into the water.
NOTE: Sometimes it is difficult to determine whether a plant found in the water is an
aquatic bed species or an emergent species. A simple criterion to separate emergent and
aquatic bed plants most of the time is to observe whether the stalk will support the plant
vertically in the absence of water. If so, it is emergent. If, however, the stalk is not strong
Herbaceous plants are defined as seed-producing species that do not develop
persistent woody tissue (stems and branches). Many herbaceous species die back at
the end of the growing season.
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enough to support the plant when water is removed, it is considered an aquatic bed
species.
Examples of how different areas might be classified are given below.
An area of trees (mapped as a polygon on your aerial photograph) within the wetland
unit having a 50% cover of trees and with an understory of shrubs that have a 60% cover
would be classified as a Forest. The trees are the highest layer of plants and meet the
minimum requirement of 30% cover.
An area with 20% cover of trees overlying a shrub layer with 60% cover would be
classified as Scrub-shrub. The trees do not meet the requirement for minimum cover.
An area where trees or shrubs each cover less than 30%, but together have a cover
greater than 30% is classified as Scrub-shrub.
When trees and shrubs together cover less than 30% of an area, the polygon is classified
based on the next highest plant class that has a 30% cover. This would be either
Emergent or Aquatic Bed.
5.3 Water quality and hydrologic functions in
Depressional wetlands (questions starting with ‘D’)
D 1.0 Does the site have the potential to improve water quality?
D 1.1 Characteristics of surface water outflows from the wetland (This indicator is used
for both the water quality and the hydrologic functions):
As you walk around the edge of the Depressional wetland, note carefully if there are any
indications that surface water leaves the wetland and flows farther down-gradient. The
question is relatively easy to answer if you find a channel. Many Depressional wetlands in
eastern Washington, however, have outflows only during the wet season or during summer
thunderstorms (seasonally or intermittently flowing). These are harder to locate and identify
because they have no banks. Some indicators of seasonal outflows are as follows:
Rationale for indicator: Pollutants that are in the form of particulates (e.g., sediment, or
phosphorus that is bound to sediment) will be retained in a wetland with no outlet.
Wetlands with no outlet are scored the highest for this indicator. An outlet that flows only
seasonally is usually better at trapping particulates than one that is flowing all the time
because there is no chance for a downstream release of particulates for most of the year (a
review of the scientific literature on the trapping potential of wetlands is found in Adamus
et al., 1991).
Each polygon with a wetland unit can only have one Cowardin class. For this reason, it is
useful to map the Cowardin classes on an aerial photo. This will avoid the common mistake
of counting emergent plants under a canopy of trees or shrubs as a separate class.
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A swale at one end of a depression that has a gradient away from the wetland and that
has wetland vegetation in it (Figure 17).
A section along the circumference of the wetland where the herbaceous vegetation is all
lying in one direction and perpendicular to the circumference (last year’s reed
canarygrass in Figure 17 is oriented in the direction of the outflow).
A ditch that has been dug to drain the wetland.
Figure 17. The seasonal outflow of a depressional wetland. The swale is dry for most of the year, but is
filled with reed canarygrass. The arrow points in the direction of the outflow.
You are asked to characterize the surface outlet in one of three ways, and these are:
Wetland has no surface water outlet. You find no evidence that water leaves the
wetland on the surface. The wetland lies in a depression in which the water never goes
above the edge (Figure 18).
Wetland has an intermittently flowing, or highly constricted, outlet. Intermittently
flowing means that surface water flows out of the wetland during the wet season
(seasonal outflow) or during heavy thunderstorms. A Depressional wetland with
occasional outflow resulting from stormwater runoff from an adjacent developed area is
considered to have intermittent flow as well. Highly constricted outlets are those that
are small or heavily incised, narrow channels anchored in steep slopes. In general, you
will find marks of flooding or inundation 3 ft or more above the bottom of the outlet if
the outlet is severely constricted. Another indicator of a severely constricted outlet is
evidence of erosion of the down-gradient side of the outlet.
Wetland has a permanently flowing, unconstricted, surface outlet. This means that
the wetland is a depression along a permanently flowing stream or is the point of
groundwater discharge that does not dry out. This includes Depressional wetlands
where ditches act as the outlet and where the water level fluctuations are less than 3 ft.
Reed
canarygrass
that is
oriented in
the direction
of the
outflow.
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One can expect that some “permanent” flows dry up during periods of drought. In
general, water should be flowing all year in 8 years out of 10 to be considered
permanent.
NOTE: If you cannot find or do not have access to an outlet in the Depressional wetland,
assume it is intermittently flowing when rating it.
Figure 18. A depressional wetland on a basalt plateau with no surface water outlet.
D 1.2 The soil 2 in below the surface is a true clay or true organic soil.
If the unit is found within an area that is mapped as an organic or clay soil by the National
Resource Conservation Service (NRCS) on their county soil maps, consider the unit to have
clay or organic soils. If it is not mapped as an organic or clay soil, you will need to take at least
one sample at the site and determine its composition.
To look at the soil: Dig a small hole within the wetland boundary and pick a sample from the
area that is about 2-3 in below the duff layer. Usually it is best to sample the soil toward the
middle of the wetland rather than at the edge. Do not sample the soil under areas of
permanent ponding. Avoid picking up any of the duff or recent plant material that lies on the
surface. Determine whether the soil is organic or clay. If you are unfamiliar with the methods
for doing this, a key for clay soils is provided in Appendix C.
NOTE: There is no scaling for this question based on the size of the patch of soil. This
simplification is necessary because it is not possible to develop a reproducible map of
different soils in a wetland unit within the time frame for doing a rating.
Rationale for indicator: Clay soils and organic soils are good indicators that a wetland
can remove a wide range of pollutants from surface water. The uptake of dissolved
phosphorus and toxic compounds through adsorption to soil particles is highest when soils
are high in clay or organic content (Mitsch & Gosselink, 1993). We only consider the type
of soil near the surface because this is where the soil actually has contact with the surface
waters carrying the pollutants. This is where most of the chemical and biological reactions
occur.
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See the NRCS web page on soils for more descriptions on how to identify soils:
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/?cid=nrcs142p2_05358
0#simplified
D 1.3 Characteristics and distribution of persistent plants (Emergent, Scrub-shrub,
and/or Forested classes):
Use the Cowardin classification of plants for this question. You are looking for the areas
that would be classified as Emergent, Scrub-shrub, or Forested (see Section 5.2). These are all
persistent types of plants; those species that normally remain standing at least until the
beginning of the next growing season (Cowardin et al., 1979). Emergent plants do not have to
be alive at the time of the site visit to qualify as persistent. The dead stalks of emergent
species will provide a vertical structure to trap pollutants as well as live stalks.
You are asked to characterize the plants in terms of how much area within the wetland unit is
covered by persistent, ungrazed or unmowed plants. There are three size thresholds used to
score this characteristic: more than 1/10 of the wetland unit is covered in persistent plants;
more than ½ of the wetland unit is covered; or more than 95% of the wetland unit is covered.
You will need to draw the area of persistent plants on a map or aerial photo before you can
feel confident that your estimates are accurate. NOTE: This question applies only to
persistent plants that are not grazed or mowed (or if grazed or mowed, the plants are
taller than 6 in).
An easy way to estimate the amount of persistent plants is to map the areas that are open
water, covered with aquatic bed plants, mudflats, or rock on an aerial photograph. Also
include areas that are grazed because much of the vertical structure of wetland plants is
removed when plants are grazed. The remaining area is then, by default, the area of
persistent plants. Figure 19 shows a Depressional wetland in which persistent plants cover
between 1/10 and 1/3 of the area of the wetland. The remainder is open water.
NOTE 1: To meet the requirement for a Cowardin plant class, a polygon within the wetland
unit needs at least 30% cover of the specified plant type (forest, shrub, etc.). However, to
count the Cowardin polygon as an indicator in the rating system, the polygon itself has to meet
a size threshold. The threshold is 10% of the area of the unit if the unit is smaller than 2.5 ac
or at least ¼ ac if the unit is larger.
Rationale for indicator: Plants enhance sedimentation by acting like a filter, and cause
sediment particles to drop to the wetland surface (review in Adamus et al., 1991). Plants
in wetlands can take on different forms and structures. The intent of this question is to
characterize how much of the wetland is covered with plants that persist throughout the
year and provide a vertical structure to trap or filter out pollutants. It is assumed,
however, that the effectiveness at trapping sediments and pollutants is severely reduced if
the plants are grazed.
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NOTE 2: If the unit has just been mowed or grazed, but you suspect this occurs infrequently,
you will need to determine whether the plants in the wetland are 6 in or less at the time when
the wetland is receiving surface waters that transport sediment and pollutants. If the grazing
occurs in summer (because the area is too wet for cattle in the winter), but the plants have
time to grow again before the flood season, then the unit is ungrazed because the plants will
meet the height threshold at the time of inundation. If, however, the grazing pressure is
intense enough that the grass does not have time to recover before the wet season, then it
should be considered grazed. The same question can be asked of seasonal mowing or haying.
Figure 19. A depressional wetland where persistent vegetation is between 1/10 and 1/3 the area of the
wetland.
D 1.4 Characteristics of seasonal ponding or inundation:
To answer this question you will need to estimate how much of the wetland is seasonally
ponded with water. Areas that are seasonally ponded must be inundated for at least 2
consecutive months, but then dry out for part of the year. Because the seasonally ponded area
will change from year to year, try to estimate what the average condition might be in 5 out of
10 years.
Rationale for indicator: The area of the wetland that is seasonally ponded is an
important characteristic in understanding how well it will remove different forms of
nitrogen that cause eutrophication. The highest levels of nitrogen transformation occur in
areas of a wetland that undergo a cyclic change between oxic (oxygen present) and anoxic
(oxygen absent) conditions. The oxic regime is needed so certain types of bacteria can
change nitrogen that is in the form of ammonium ion (NH4+) to nitrate, and the anoxic
regime is needed for denitrification (changing nitrate to nitrogen gas) (Mitsch & Gosselink,
1993). The area that is seasonally ponded is used as an indicator of the area in the wetland
that undergoes this seasonal cycling. The soils are oxygenated when dry but become
anoxic during the time they are flooded.
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One way to estimate this area is to make a sketch of the boundary of the wetland unit, and on
this diagram draw the outside edge of the area you believe has surface water during the wet
season. If the wetland also has permanent surface water, you will have to draw this and
subtract it when making your estimate (see Figure 20).
Figure 20. Sketch showing the boundaries of areas that are seasonally ponded and permanently ponded.
The answer to question D 1.4 for this wetland is that the area seasonally ponded is more than ½ the total
area of the wetland.
The boundary of seasonal ponding will usually coincide with the delineated boundary of the
wetland in Depressional wetlands of eastern Washington. This edge is often very distinct on
the Columbia Plateau.
There may be periods of time when a Depressional wetland is flooded very briefly during
exceptionally heavy rainfall or snowmelt. This area of brief ponding should not be counted as
seasonal ponding. For example, if a site is visited during the wet season and wetland
vegetation is inside the area of ponding, then the area outside of the wetland vegetation line is
probably only ponded for a short time and may not meet the criteria used in delineating a
wetland.
During the dry season, the boundary of areas ponded for several months (seasonal ponding)
will have to be estimated by using indicators such as:
Marks on trees and shrubs of water/sediment/debris (Figure 21). The boundary of
seasonal ponding can be estimated by extrapolating a horizontal line from this mark to
the edge of the wetland.
Water stained vegetation lying on wetland surface. For example, downed fragments of
bulrushes and cattails that are dark gray or near black in color.
Dried algae left on the stems of emergent vegetation and shrubs and on the wetland
surface (Figures 22 and 23).
Boundary of
permanent
ponding
Upper edge of seasonal ponding that in this unit
coincides with the unit boundary
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Figure 23. Algae left hanging on vegetation as wetland dried out. The top of the algae marks the vertical
extent of seasonal ponding. The boundary of seasonal ponding can be estimated by extrapolating a
horizontal line from this mark to the edge of the wetland.
NOTE: Avoid making visual estimates of area covered by seasonal ponding when standing at
the wetland edge. These estimates can be very inaccurate. Drawing the boundary on an aerial
photograph and then using a graphic tool such as a grid to calculate area is a more accurate
way to estimate area. A Global Positioning System (GPS) that has been corrected for
positional inaccuracies can also be used to locate the boundaries and estimate area.
Figure 21. Water mark on tree
showing vertical extent of
seasonal ponding.
Figure 22. Small depressional wetland covered with
algae. The edge of the algae marks the area that is
seasonally ponded.
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D 2.0 Does the landscape have the potential to support the water quality function
of the site?
Wetlands can remove many pollutants from waters coming into them. It is the removal of this
excess pollution that is considered to be a valuable function for society. The landscape
surrounding the wetland will determine, to some degree, how well a wetland improves water
quality. If the wetland receives a heavy load of pollutants from the surrounding areas, it will
function to its maximum capacity. However, if there are no pollutants coming in, the wetland
cannot remove them, even if it has the necessary physical and chemical characteristics. Thus,
the Landscape Potential for the function is related to the amount of pollutants that come into
the wetland from the surrounding areas. Qualitatively, the level of pollutants can be
correlated with the level of disturbance, development, and intensity of agriculture in the
landscape. For example, relatively undisturbed watersheds will carry much lower sediment
and nutrient loads than those that have been impacted by development, agriculture, or
logging practices (Hartman et al., 1996; Reinelt & Horner, 1995).
D 2.1 Does the wetland unit receive stormwater discharges?
Answer YES to the question if you see any pipes coming into the wetland from the
surrounding land. These are usually stormwater discharges. Also, look on the aerial
photograph of the wetland and its surroundings for stormwater ponds. If you see any ponds,
determine if their discharges can get into the wetland. Stormwater may come into the unit by
way of a stream or ditch as well as a pipe. Stormwater can also come into a Depressional
wetland in runoff from parking lots or roads even if no pipes are present. If you see evidence
that such runoff comes into the wetland answer YES to this question.
D 2.2 Is more than 10% of the area within 150 ft of the wetland in land uses that
generate pollutants in surface runoff (agricultural, pasture, residential,
commercial, urban)?
Use your aerial photo and draw a line around the unit that is 150 ft from the edge of the
wetland you have mapped for rating. Answer YES to this question if you find the listed uses
within 150 ft of the wetland and they cover more than 10% of the area within this 150 ft
Rationale for indicator: Farming, grazing, golf courses, residential areas, commercial
areas, and urban areas, in general, are major sources of pollutants (reviewed in Sheldon et
al., 2005). The review also found that a well-vegetated buffer of 150 ft will only remove
60-80% of some pollutants from surface runoff into a wetland. Thus, pollutants from such
land uses will probably reach the wetland unit if they are within 150 ft of the wetland.
Rationale for indicator: Stormwater coming from residential or developed areas is often
discharged into wetlands. Untreated stormwater is a source of many different pollutants
(reviewed in Sheldon et al., 2005). Furthermore, stormwater ponds do not remove all
pollutants leaving them, even those constructed recently (Mallin et al., 2002). Thus, any
stormwater discharge into a wetland increases the pollutants coming into it.
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perimeter around the wetland. Use a graphic aid, such as an acetate overlay with a grid or
dots, to estimate area. Visual estimates are not accurate enough and may result in significant
errors.
D 2.3 Are there septic systems within 250 ft of the wetland?
Use the aerial photograph of the unit to determine if there are any residences within 250 ft of
the wetland. Septic systems are still in common use in many areas of eastern Washington that
are outside city boundaries. If your wetland is within a city limit, you will need to check with
the local planning office to determine if the area has sewers serving the houses or if they are
still on septic systems. If you are outside city limits in areas with lots of ½ ac or larger, you
can assume the houses are on septic systems.
D 2.4 Are there other sources of pollutants coming into the wetland that are not listed
in questions D 2.1–D 2.3?
Answer YES to the question if you can identify any source of pollutants in the groundwater or
surface water coming into the wetland caused by human activities. Identify the source of the
pollution on the rating form. Wetlands can receive polluted waters even if they have large,
well-vegetated buffers. For example, a stream that drains areas where pollutants are released
far from the unit can pass through the wetland. Also, silt fences often do not prevent all the
sediment from reaching the wetland during construction. Other sources of pollutants may be
pesticide spraying on golf courses, particulates in exhausts from airplanes or motor vehicles,
and pesticides used in mosquito control.
Activities that generate pollutants within the wetland itself, such as grazing, also count for a
YES for this question. Cattle, sheep, or large native herbivores such as elk grazing within the
wetland are a source of pollutants. Also, answer YES to this question if the wetland has a
larger pond that is commonly used by migrating waterfowl. Waterfowl droppings are a
source of both excess nutrients and bacteria.
Rationale for indicator: The sources of pollutants listed in questions D 2.1-D 2.3 may not
be the only sources coming into the wetland unit from the surrounding landscape. In
addition, sources of pollutants can be within the wetland unit itself. For example,
pollutants are discharged within the wetland if it is used for grazing.
Rationale for indicator: Septic systems can pollute groundwater because nitrogen is not
removed underground. Plumes of nitrogen from septic systems can be traced at least 250
ft in the groundwater (Aravena et al., 1993).
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D 3.0 Is the water quality improvement provided by the site valuable to society?
D 3.1 Does the wetland discharge directly to a stream, river, or lake that is on the
303(d) list?
To answer this question you will need to access the Department of Ecology’s website that lists
all the bodies of water that do not meet water quality standards
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html. Use the Map Tool to
locate your site. Determine from the aerial photograph or the map on the Ecology website if
the wetland unit you are rating is within at least 1 mi up-gradient of any aquatic resource
mapped as not meeting water quality standards and has a surface water channel, ditch, or
other discharge leading to it (red lines or polygons on the map).
D 3.2 Is the wetland in a basin or sub-basin where water quality is an issue in some
aquatic resource (i.e., there is an aquatic resource in the basin that is on the 303(d) list)?
To answer this question you will need to access the Department of Ecology’s website that lists
all the bodies of water that do not meet water quality standards
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html . Determine from the
aerial photo if the wetland unit you are rating is in the contributing basin of any aquatic
resource mapped as not meeting water quality standards. To find the boundaries of
contributing basins in the area, consult with the planning department of the local jurisdiction.
If this information is not available, use the guidance for mapping contributing basins
described in question D 5.3.
Rationale for indicator: Wetlands can mitigate the impacts of pollution even if they do
not discharge directly to a polluted body of water. Wetlands can remove nitrogen from
groundwater as well as surface water. They can also trap airborne pollutants. Thus,
wetlands can provide an ecosystem service and value to our society in any basin and sub-
basin that has pollution problems. The removal of pollutants by wetlands is judged to be
more valuable in basins where other aquatic resources are already polluted or have
problems with eutrophication.
Rationale for indicator: The phrase "303(d) list" is short for the list of impaired waters
(stream segments, lakes) that the Clean Water Act requires all states to submit to the
Environmental Protection Agency (EPA) every two years. In Washington, we identify all
waters where pollution controls are not sufficient to attain or maintain applicable water
quality standards. Wetlands that discharge directly to these polluted waters are judged to
be more valuable than those that discharge to unpolluted bodies of water because their
role in cleaning up the pollution is critical for reducing further degradation of water
quality.
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D 3.3 Has the site been identified in a watershed or local plan as important for
maintaining water quality?
To answer this question you will need to seek information from the planning department of
the local jurisdiction where the site is located. Information on regional or local plans can often
be found on the website of the city or county in which the site is found. Useful search phrases
include: “watershed plan”, “water quality”, or “wetland protection”.
If the basin in which the wetland is found has a Total Maximum Daily Loads (TMDL) plan (also
called a Water Cleanup Plan) developed for it, then you should answer YES for this question.
It is assumed that all wetlands are valuable in a basin where water quality is poor enough to
require a TMDL. The Department of Ecology’s website lists all the bodies of water that have
TMDLs: http://www.ecy.wa.gov/programs/wq/tmdl/TMDLsbyWria/TMDLbyWria.html.
NOTE: Total Maximum Daily Loads (TMDL) or Water Cleanup Plans describe the type,
amount, and sources of water pollution in a particular water body. They analyze how much
the pollution needs to be reduced or eliminated to meet water quality standards, and then
provide targets and strategies to control the pollution. Wetlands that discharge directly to
these polluted waters are judged to be more valuable because they function at a landscape
scale to mitigate discharges of pollutants. TMDLs are based on models that estimate the
natural decay and adsorption of pollutants under current conditions. Wetlands are an
important part of that natural decay; their destruction would require a recalibration of the
TMDL models and force reductions in current levels of discharge.
D 4.0 Does the site have the potential to reduce flooding and erosion?
D 4.1 Characteristics of surface water outflows from the wetland:
See the description for question D 1.1. This question is answered the same way as question D
1.1. The difference between D 1.1 and D 4.1, however, is in the scores assigned to each type of
Rationale for indicator: Wetlands with no outflow are more likely to reduce flooding
than those with outlets, and those with a constricted outlet will more likely reduce flooding
than those with an unconstricted outlet (review in Adamus et al., 1991). In wetlands with
no outflow, all waters coming in are permanently stored and do not enter any streams or
rivers. Constricted outlets will hold back flood waters and release them slowly to reduce
flooding downstream. Wetlands with intermittent flow also provide a higher level of
protection than those with unconstricted permanently flowing discharges because they
can hold back flash floods that can occur during storms when there is no outflow.
Rationale for indicator: Not all pollution and water quality problems are identified by
Ecology’s water quality monitoring program. Local and watershed planning efforts
sometimes identify wetlands that are important in maintaining existing water quality.
These wetlands provide a value to society at the local level that needs to be replaced if
they are impacted.
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outflow. Differences in scores are based on the difference in importance of the outflow
characteristics to the two functions.
D 4.2 Depth of storage during wet periods (estimating live storage):
The depth of the water stored during wet periods can be estimated as the difference in
elevation between the upper edge of seasonal ponding and the low point of the wetland or
surface of permanent ponding (see Figure 24).
For wetlands that have areas of permanent ponding, the lowest point is the surface of the
permanent ponding (as measured at its lowest point, typically in late summer and fall). See
Figure 25 for an example. You should estimate the height of seasonal ponding above that. For
wetlands that have no areas of permanent ponding, locate the lowest point in the wetland and
measure the depth of the ponding above that.
Level of seasonal ponding
Depth above lowest point
Rationale for indicator: The amount of water a Depressional wetland stores is an
important indicator of how well it functions to reduce flooding and erosion. Retention time
of flood waters is increased as the volume of storage is increased for any given inflow
(Fennessey et al., 1994). It is too difficult to estimate the actual amount of water stored for
a rapid method such as this one, and we use an estimate of the maximum depth of storage
as a surrogate. This is only an approximation because depressional wetlands may have
slightly different shapes and therefore the volume of water they can store is not exactly
correlated to the maximum depth of storage.
Bottom of wetland, or surface of permanent ponding
Figure 24. Measuring maximum depth of seasonal ponding.
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Figure 25. A Depressional wetland with permanent water present. This is the maximum extent of summer
drawdown in the wetland. The difference between this level and the seasonal high water mark is more
than 3 ft.
NOTE: During the winter and spring it may be difficult to identify the level to which the water
drops during the summer. In general, the level will usually be at the edge of the area
dominated by large, obligate, emergent plants such as bulrushes or cattails (Figure 26). Use
the lower edge of this vegetation as the bottom from which to estimate the depth of seasonal
ponding. Estimate the difference in elevation between the bottom of the plants and any
marks of ponding along the shore to estimate the depth of seasonal ponding.
Figure 26. A Depressional wetland with water level close to its seasonal maximum. This is the same
wetland as shown in Figure 25 but photographed in March rather than late September.
There are five thresholds used to score this characteristic: 3 ft or more of storage, 2 ft to <3 ft
of storage, 1 ft to <2 ft, 6 in to <1ft, and less than 6 in. Your measurements, therefore, do not
There are marks on the shore
left behind by the high water
during the seasonal
maximum.
The difference in elevation
between the mark on the shore
and the level of the permanent
ponding is the depth of seasonal
storage.
Use the depth of water along
the inward edge of emergent
plants (bulrushes in this case)
to estimate the depth of
seasonal ponding. In this case,
the depth of water is about 3.5
ft at the edge of the plants.
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need to be exact. These thresholds can usually be estimated with a yard stick or tape measure
without needing to use special equipment.
Headwater wetlands: Question D4.2 also asks if the wetland being rated is a headwater
wetland. Depressional wetlands found in the headwaters of streams often do not store
surface water to any great depth. However, they can be important in reducing peak flows
because they slow down and desynchronize the initial peak flows from a storm (Brassard et
al., 2000). A review of 169 scientific articles worldwide of the role of wetlands in the
hydrologic cycle concluded that about ½ of the relevant studies showed that headwater
wetlands have an important role in desynchronizing flood flows (Bullock & Acreman, 2003).
The depth of seasonal storage in headwater wetlands was judged to be an inadequate
representation of the importance of these wetlands in the hydrologic functions. For this
reason, headwater wetlands are scored 4 points, out of 8 possible, even if their storage is less
than 2 ft.
To identify if the wetland is a headwater wetland, use the information collected in question D
1.1. If the wetland has a permanent or seasonal outflow through a defined channel but NO
inflow from a permanent or seasonal channel, it is a headwater wetland for the purposes of
this rating. NOTE: One exception to this criterion is wetlands whose water regime is
dominated by groundwater coming from water storage facilities. Depressional wetlands at
the base of irrigation reservoirs, dams, or the edge of irrigation canals are not headwater
wetlands, even if they have surface water that flows out of them without an inflow.
D 5.0 Does the landscape have the potential to support the hydrologic functions
of the site?
Human changes in land use tend to de-stabilize the flows of water in a watershed. Generally,
human activities reduce infiltration and increase the run-off during storm events and thus
increase flooding problems (reviewed in Sheldon et al., 2005). A wetland located in areas
where run-off has increased can provide more flood protection than one located in an
undeveloped area. Thus, the Landscape Potential for the function is related to the increased
amounts of water coming into the wetland from human sources. Qualitatively, the increase is
modeled as the number of different new sources of water coming into the wetland.
D 5.1 Does the wetland receive stormwater discharges?
This question is the same as D 2.1. Answer YES to the question if you see any pipes coming
into the wetland from the surrounding land. These are usually stormwater discharges. Also,
look on the aerial photograph of the wetland and its surroundings for stormwater ponds. If
you see any ponds, determine if their discharges can get into the wetland. Stormwater may
come into the wetland by way of a stream, road runoff, or ditch, as well as a pipe.
Rationale for indicator: A depressional wetland that receives stormwater directly has a
higher potential for providing hydrologic functions. It will receive more water during a
rain event than under normal (no stormwater discharges) conditions.
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D 5.2 Is more than 10% of the area within 150 ft of wetland in land uses that generate
excess runoff (agricultural, pasture, residential, commercial, or urban)?
Use your aerial photo and draw a line that is 150 ft from the edge of the wetland you have
mapped for rating. Answer YES to this question if you find the listed uses within 150 ft of the
wetland and they cover more than 10% of the area within the 150 ft perimeter around the
wetland. Use a graphic aid, such as an acetate overlay with a grid or dots, to estimate area.
Visual estimates are not accurate enough and may result in significant errors.
D 5.3 Is more than 25% of the contributing basin of the wetland covered with intensive
human land uses (residential at >1 residence/ac, urban, commercial, agriculture,
etc.)?
This question asks you first to estimate the geographic area that contributes surface water to
the wetland you are rating. This is called the “contributing basin” of the wetland. You will
then need to estimate the area of the wetland and calculate the ratio of the two. You do not
need to estimate these areas exactly because the scoring is based on thresholds for the ratio.
If the contributing basin is less than 10 times the size of the wetland itself, the wetland will
score the most points. On the other hand, if the area of the contributing basin is more than
100 times the area of the wetland, the score is 0, and you will not need to make any further
estimates. If the wetland is large relative to its contributing basin, you will need to add the
area of the wetland to the total since rain also falls within the wetland.
NOTE: You can use whatever means available to estimate the area of the upstream basin
contributing surface water to a wetland. A topographic map works well if the landscape is not
too confusing. If you have GIS with basin boundaries, you will have to be careful to include
only the areas up-gradient of the wetland. If you are unfamiliar with the methods for mapping
contributing basins, the procedure is described in a fact sheet by the NRCS, How to Read a
Topographic Map and Delineate a Watershed:
http://www.nycswcd.net/files/NRCS%20Reading%20Topo%20Maps%20to%20Delineate%
20Watersheds1.pdf . NOTE: If this link is no longer valid, search for the title of the focus sheet
using your web search engine.
Rationale for indicator: Human changes in land use tend to de-stabilize the flows of
water in a watershed. Generally, human activities reduce infiltration and increase the run-
off during storm events and thus increase flooding problems (reviewed in Sheldon et al.,
2005). Research in the Puget Sound area by the University of Washington has found that
there are significant increases in water flows when intensive land uses represent more
than 25- 35% of the contributing basin (Azous & Horner, 1997).
Rationale for indicator: Water can also flow into the depression directly from
surrounding land uses that prevent some or all water from infiltrating. For example, a
lawn can reduce infiltration by as much as 65% relative to a forest (Kelling & Peterson,
1975).
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NOTE: It is sometimes difficult to map the contributing basins of Depressional wetlands on
the Columbia Plateau in the areas that were eroded by the ice-age floods. In general, the
contributing basin for surface waters of wetlands on the top of the plateau is very small and
may extend only a few feet beyond the wetland boundary. However, the contributing basin
for the Depressional wetlands in the major coulees and channels will usually be much larger.
D 6.0 Are the hydrologic functions provided by the site valuable to society?
D 6.1 Is the wetland in a landscape that has flooding problems?
You will need to do some fact finding if you do not know whether floods have caused damage
downstream of the wetland. Your best sources of information on flooding problems are the
emergency planning office in your local government, the local Federal Emergency
Management Agency (FEMA), or the United State Geological Survey (USGS) for groundwater
issues. You can search the web using the name of the location, town, or watershed and
“flooding” or “flooding problems”.
Choose the descriptions that best match conditions for the wetland being rated; then choose
the description that generates the highest score on the rating form.
The wetland captures surface water that would otherwise flow down-gradient into areas
where flooding has damaged human or natural resources (e.g., houses or salmon redds).
o Flooding occurs in a sub-basin that is immediately down-gradient of wetland.
o Surface flooding problems are in a sub-basin farther down-gradient.
Flooding from groundwater is an issue in the sub-basin where the wetland is found.
The existing or potential outflow from the wetland is so constrained by human or natural
conditions that the water stored by the wetland cannot reach areas that flood.
NOTE 1: Many Depressional wetlands with no surface water outflow can protect natural or
human resources from flooding. They are performing the hydrologic functions at the highest
levels possible. No surface water leaves the wetland to cause flooding or erosion. The water
either infiltrates to groundwater or it evaporates. To answer the Value question for a wetland
with no outflow, try to picture the wetland as filled with a parking lot. Where would the
surface water it normally stores flow? If it would flow into a swale, channel, or stream, there
is a possibility that the flow would increase flooding or erosion.
Rationale for indicator: The value of wetlands in reducing the impacts of flooding and
erosion is based on the presence of human or natural resources that can be damaged by
these disturbances. In general, the value of a wetland in reducing flood damage is judged
to decrease with the distance downstream because the amount of water stored by the
wetland relative to the overall flows decreases.
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NOTE 2 (a landscape constraint on function): When a Depressional wetland is situated
upslope of a road where water movement through the road is limited by ineffective culverts,
the roadway typically acts as a levee, de-coupling upslope wetlands from downstream
flooding. The roadway, rather than the wetland, delays storm flows, and acts like a flood-
control dam. This indicates that the hydrologic connection between the floodway and the
upslope area is impaired. If, however, the water impounded on the upslope side of the road
recedes at the same rate as the water on the downslope side, you can assume the connections
through the road are not constrained. In this case, the storage provided by the wetland on the
upslope side is important, and the wetland should be scored accordingly.
NOTE 3 (a landscape constraint on function): Depressional wetlands situated at the base of a
hillside typically receive water inputs from groundwater. Generally, you can conclude that
wetlands receiving less than 10% of their water from surface flows do not provide much
protection from flooding because they are not connected to the major patterns of surface
flows. If the dominant water inputs are from a spring or seep emerging from a hillslope, then
the wetland likely does not provide much value in reducing surface flooding. If, however,
there are indicators that the wetland receives surface runoff from farther up the slope (e.g.,
small gullies, washes, etc.) as well as groundwater, then the wetland may be valuable if there
are flooding problems farther downstream. A wetland can be considered to have more than a
90% groundwater influence if there is no seasonal or permanent surface water inflow and a
very small contributing basin.
NOTE 4 (a landscape constraint on function): A Depressional wetland that receives only
return flow from irrigation is not in a landscape position to perform the hydrologic functions.
Since the inflow is controlled, there is little chance that the water coming into the wetland will
cause downstream flooding or erosion.
D 6.2 Has the site has been identified as important for flood storage or flood
conveyance in a regional flood control plan?
To answer this question contact the jurisdiction in which the site is found to determine
whether any regional flood control plans exist. A search of websites for flood prone areas will
probably also list flood control plans for the watershed in question. If plans exist, determine if
the site is listed as important or valuable for flood storage. To answer YES to this question,
the flood control district needs to have developed a flood control or flood hazard mitigation
plan that identifies the site as one that needs to be preserved or enhanced to improve flood
protection.
Rationale for indicator: The values of flood storage and flood conveyance provided by
wetlands are often recognized in regional flood control plans, and specific sites are
mentioned in these plans. If the value of a wetland for flood attenuation has already been
recognized, it is assigned a High rating for value.
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5.4 Water quality and hydrologic functions in Riverine
wetlands (questions starting with ‘R’)
R 1.0 Does the site have the potential to improve water quality?
R 1.1 Total area of surface depressions within the wetland that can trap sediments and
associated pollutants during a flooding event:
For this question you will need to estimate the fraction of the wetland that is covered by
depressions. Using your map or photo of the site, sketch the areas where depressions are
found. From this you can make a rough estimate of the total area that has depressions.
Determine if this area is more than 1/3 or more than 1/10 of the total area of the wetland.
Standing or open water present in the wetland when the river is not flooding are good
indicators of depressions. Figure 27 shows a Riverine wetland that has a large depression
filled with water.
NOTE: Generally you should count only depressions that hold water for more than a week
after a flood recedes. If a depression is not flooded at the time of your site visit, look for the
deposition of fine or mucky sediments in the bottom of the depression. Sediments in the
depression usually have a finer texture than those in the immediate area and indicate the
water was present in the depression for longer periods of time.
Rationale for indicator: Depressions in Riverine wetlands will tend to accumulate
sediment and the pollutants associated with sediment (phosphorus and some toxics)
because they reduce water velocities (Fennessey et al., 1994) when the river floods.
Wetlands where a larger part of the total area has depressions are relatively better at
removing pollutants associated with sediments than those that have no such depressions.
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Figure 27. A Riverine wetland with two depressions. In this wetland the depressions cover between 1/10
and 1/3 the area of the wetland.
R 1.2 Structure of the plants in the wetland:
For this question you will need to group the plants found within the wetland into three
categories: 1) forest or shrub, 2) ungrazed or unmowed emergent plants (> 6 in high), and 3)
neither forest, shrub, nor ungrazed emergent plants.
NOTE: This question about plant cover is NOT based on the Cowardin classification. The
polygons you draw for this question must have a 90% cover of the ground when you look
down from a person’s height (~5 ft).
Rationale for indicator: Plants in a Riverine wetland will improve water quality by acting
as a filter to trap sediments and associated pollutants. The plants also slow the velocity of
water which results in the deposition of sediments. Persistent, multi-stemmed plants
enhance sedimentation by offering frictional resistance to water flow (review in Adamus et
al., 1991). Shrubs and trees are considered to be better at resisting water velocities in
riverine systems than emergent plants during flooding and are scored higher. Aquatic bed
species or grazed, herbaceous (non-woody) plants are not judged to provide much
resistance to water flows and are not counted as filters.
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NOTE: You will need to judge if the plants in the wetland are 6 in high or more at the time
when the stream floods and is actually transporting sediment. If grazing or mowing occurs in
summer but the plants have time to grow again before the time when the Riverine wetland
gets flooded, then the system is ungrazed. If, however, the grazing pressure is intense enough
that the grass does not have time to recover during the flood season, then it should be
considered grazed.
There are two size thresholds used to score this characteristic: 1) more than 2/3 of the
wetland area is covered (>66% cover) with either herbaceous, forest, or shrubby plants, and
2) more than 1/3 is covered with these plants. These thresholds should be measured from
aerial photographs of the site.
R 2.0 Does the landscape have the potential to support the water quality function
of the site?
Wetlands will remove many pollutants from water coming into them, and it is the removal of
these pollutants that is considered to be a valuable function for society. The landscape
surrounding the wetland will, to some degree, determine how well a wetland improves water
quality. If the wetland receives a heavy load of pollutants from the surrounding areas it will
function to its maximum capacity. If, however, there are no pollutants coming in, the wetland
cannot remove them, even if it has the necessary physical and chemical characteristics. Thus,
the Landscape Potential for the function is related to the amount of pollutants that come into
the wetland from the surrounding areas. Qualitatively, the level of pollutants can be
correlated with the level of disturbance, development, and intensity of agriculture in the
landscape. For example, relatively undisturbed watersheds will carry much lower sediment
and nutrient loads than those that have been impacted by development, agriculture, or
logging practices (Hartman et al., 1996; Reinelt & Horner, 1995).
R 2.1 Is the wetland within an incorporated city or within its Urban Growth Area (UGA)?
R 2.2 Does the contributing basin to the wetland include an UGA or incorporated area?
To begin, trace the stream or river to its source and determine if there are any urban or
suburban areas adjacent to the stream that floods the wetland. Answer YES to R 2.1 if the site
is in a city or Urban Growth Area (UGA) and YES to question R 2.2 if there are any
incorporated cities and towns or their UGAs upstream of the wetland, but the wetland is not
within the boundaries. Maps of UGAs and urban areas can be found at:
http://www.ecy.wa.gov/programs/air/aginfo/ugamaps.htm.
Rationale for indicators: Urban and suburban areas are a major source of pollutants to
streams (reviewed in Sheldon et al., 2005). The presence of development adjacent and
upstream of the wetland is a good indicator that there are pollutants in the water reaching
the Riverine unit from the stream.
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For questions R 2.2 and R 2.3, you will need to identify the contributing basin to the stream
that floods the wetland you are rating. This can be done using topographic maps or through
websites such as the USGS: http://water.usgs.gov/wsc/map_index.html.
NOTE: A wetland can have a YES answer for both questions if it is within a UGA and there are
other cities or UGAs farther upstream.
R 2.3 Does at least 10% of the contributing basin contain tilled fields, pastures, or
forests that have been clearcut within the last 5 years?
Define the boundaries of the contributing basin to the stream that floods the wetland as in
question R 2.2. Answer YES to this question if at least 10% of the total area of the upstream
contributing basin has at least one or a combination of pasture, tilled fields, or clearcut
logging. Land uses can be determined from aerial photographs of the area or by downloading
land use maps from the USGS: http://www.mrlc.gov/nlcd06_data.php
R 2.4 Is more than 10% of the area within 150 ft of the wetland in land uses that
generate pollutants in surface runoff (agricultural, pasture, residential, urban,
commercial)?
Use your aerial photo and draw a line around the wetland that is 150 ft from the edge of the
wetland you have mapped for rating. Answer YES to this question if you find the listed uses
that generate pollutants within 150 ft of the wetland and they cover more than 10% of the
area within the 150 ft perimeter around the wetland. Use a graphic aid, such as an acetate
overlay with a grid or dots, to estimate area. Visual estimates are not accurate enough and
may result in significant errors.
Rationale for indicator: Farming, grazing, golf courses, residential areas, commercial
areas, and urban areas, in general, are major sources of pollutants (reviewed in Sheldon et
al., 2005). The review also found that a well-vegetated buffer of 150 ft will only remove
60-80% of some pollutants from surface runoff into a wetland. Thus, pollutants from such
land uses will probably reach the wetland unit if they are within 150 ft of the wetland.
Rationale for indicator: Tilled fields are a source of nutrients, pesticides, and sediment.
Pastures are a source of nutrients and pathogenic bacteria, and clearcut areas are a source
of sediment (reviewed in Sheldon et al., 2005). The presence of these conditions upstream
of the wetland unit is a good indicator that there are pollutants in the river waters
reaching the unit.
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R 2.5 Are there other sources of pollutants coming into the wetland that are not listed
in questions R 2.1-R 2.4?
Answer YES to the question if you can identify any source of pollutants in the groundwater or
surface water coming into the wetland caused by human land uses. Identify the source of the
pollution on the rating form. Wetlands can receive polluted waters even if they have large,
well-vegetated buffers. For example, a stream that drains areas where pollutants are released
far from the wetland can pass through the wetland. Also, silt fences often do not prevent all
the sediment from reaching the wetland during construction. Other sources of pollutants may
be pesticide spraying on golf courses, particulates in exhausts from airplanes or motor
vehicles, and pesticides used in mosquito control.
Activities that generate pollutants within the wetland itself, such as grazing, also count for a
YES for this question. Cattle, sheep, or large native herbivores such as elk grazing within the
wetland are a source of pollutants. Also answer yes to this question if the wetland has a pond
that is commonly used by migrating waterfowl. Waterfowl droppings are a source of both
excess nutrients and bacteria.
R 3.0 Is the water quality improvement provided by the site valuable to society?
R 3.1 Is the wetland along a stream or river that is on the 303(d) list or on a tributary
that drains to a stream on the 303(d) list?
To answer this question you will need to access the Department of Ecology’s website that lists
the bodies of water that do not meet water quality standards:
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html . Determine if the
Riverine wetland lies on a stream or river mapped as a Category 5 water, or is on a tributary
to one. The map tool on the Ecology website provides a quick way to identify Category 5
waters. Answer YES to this question if the wetland is along a stream or river that is on the
303(d) list or on a tributary that drains to one within 1 mi.
Rationale for indicator: The phrase, "303(d) list," is short for the list of impaired waters
(stream segments, lakes) that the Clean Water Act requires all states to submit to the
Environmental Protection Agency (EPA) every two years. In Washington, we identify all
waters where required pollution controls are not sufficient to attain or maintain water
quality standards. Wetlands that discharge directly to these polluted waters are judged to
be more valuable than those that discharge to unpolluted bodies of water because their
role at cleaning up the pollution is critical for reducing further degradation of water
quality.
Rationale for indicator: The sources of pollutants listed in questions
R 2.1-R 2.4 may not be the only sources coming into the wetland unit from the
surrounding landscape. In addition, sources of pollutants can be within the wetland unit
itself. For example, pollutants are discharged within the wetland if it is used for grazing.
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R 3.2 Is the wetland along a stream or river that has TMDL limits for nutrients, toxics,
or pathogens?
To answer this question you will need to access the Department of Ecology’s website that lists
all the bodies of water that have TMDLs:
http://www.ecy.wa.gov/programs/wq/tmdl/TMDLsbyWria/TMDLbyWria.html. Determine
if the wetland you are rating is flooded by a stream or river in a drainage for which TMDLs
have been developed or are being developed.
R 3.3 Has the site been identified in a watershed or local plan as important for
maintaining water quality?
To answer this question you will need to seek information from the planning department of
the local jurisdiction where the site is located. Information on regional or local plans can often
be found on the website of the city or county in which the wetland is found. Useful search
phrases include: “watershed plan”, “water quality”, or “wetland protection”.
If the river or stream along which the wetland is found has a TMDL plan developed for it, then
answer YES on this question. It is assumed that all wetlands are valuable in a basin where
water quality is poor enough to require a TMDL. The Department of Ecology’s website lists all
the bodies of water that have TMDLs (see above).
NOTE: The fact that a TMDL has been developed for the river or basin in which the wetland is
found is scored twice for Riverine wetlands: once in question R 3.2 and also in R 3.3.
Rationale for indicator: Not all pollution and water quality problems are identified by
Ecology’s water quality monitoring program. Local and watershed planning efforts
sometimes identify wetlands that are important in maintaining existing water quality.
These wetlands provide a value to society that needs to be replaced if they are impacted.
Rationale for indicator: Total Maximum Daily Loads (TMDL) or Water Cleanup Plans
describe the type, amount, and sources of water pollution in a particular water body. They
analyze how much the pollution needs to be reduced or eliminated to meet water quality
standards, and then provide targets and strategies to control the pollution. Wetlands that
discharge directly to these polluted waters are judged to be more valuable because they
function at a landscape scale to mitigate discharges of pollutants. TMDLs are based on
models that estimate the natural decay and adsorption of pollutants under current
conditions. Wetlands are an important part of that natural decay; their destruction would
require a recalibration of the TMDL models and force reductions in current levels of
discharge.
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R 4.0 Does the site have the potential to reduce flooding and stream erosion?
R 4.1 Characteristics of the overbank flood storage the wetland provides, based on the
ratio between the channel width and the width of the wetland perpendicular to
the flow:
You will need to estimate the average distance of the wetland perpendicular to the direction
of the flow, and the width of the stream or river channel (distance between the top of the
banks of the stream). Calculate this ratio by taking the width of the wetland and dividing by
the width of the stream. There are five thresholds for scoring: a ratio more than 2, a ratio
between 1- 2, a ratio between ½- 1, a ratio between ¼- ½, and a ratio < ¼.
Riverine wetlands are found in different positions in the floodplain and it may sometimes be
difficult to estimate this indicator. The following bullets describe some common types of
Riverine wetlands and how to estimate this indicator.
If the vegetated wetland lies within the banks of the stream or river, the ratio is
estimated as: the average width of the wetland ÷ average distance between banks.
Figure 28 shows a wetland where vegetation fills the entire distance between the banks.
In this case the ratio is 1. Figure 29 shows a small vegetated wetland on a gravel bar
where the distance between banks is much greater than the width of the wetland. In this
case the ratio is < ¼.
If the wetland lies outside the existing banks of the river, you may need to estimate the
distances using a map or aerial photograph. Riverine wetlands in old oxbows may be
some distance away from the river banks. Instead of trying to estimate a width for the
wetland and the distance between banks in feet or yards, it may be easier to estimate the
ratio directly from an aerial photo using a ruler. Ask yourself if the average width of the
wetland is more or less than the distance between banks. If it is more, is it more than
twice as wide? If not, the ratio is between 1-2. If the width of the wetland is less than the
distance between banks, use the same process: is it less than ¼, or is it less than ½?
Figure 30 shows a Riverine wetland in an old oxbow where the ratio was estimated to be
between 1-2.
Rationale for indicator: The ratio of the width of the channel to the width of the wetland
perpendicular to the flow is an indicator of the relative volume of storage available within
the wetland. The width of the stream between banks is an indicator of the relative flows at
that point in the watershed. Wider streams will usually have higher volumes of water than
narrower streams. More storage is therefore needed in larger systems to lessen the
impact of peak flows. The width of the wetland perpendicular to the stream is used as an
indicator of the amount of short-term storage available during a flood event. A wetland
that is wide relative to the width of the stream is assumed to provide more storage during
a flood event than a narrow one. The ratio of the two values provides an estimate that
makes it possible to rank wetlands relative to each other in terms of their overall potential
for storage.
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If you are including the river or stream as part of the wetland, then the width of the
stream is also included in the estimate of the width of the wetland.
Braided channels: If the wetland is associated with only some of the braids, you should
use the cumulative width of all channels to calculate the average width of the channel.
Figure 28. A riverine wetland where the width of the wetland is the same as the distance between banks.
Figure 29. A riverine wetland where the ratio of the width of the wetland to the distance between banks is
less than ¼ (30 ft / 150 ft = 0.2).
Distance between banks is the
same as the width of the wetland
perpendicular to stream flow. The
ratio is 1.
Distance between banks is approximately 150
ft. The width of the river seems smaller in the
photograph because it is farther away.
Average width of wetland perpendicular to
river flow is approximately 30 ft.
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Figure 30. A Riverine wetland in an old oxbow of the Colville River where the ratio of width of wetland to
distance between banks is between 1-2.
R 4.2 Characteristics of plants that slow down water velocities during floods:
For this question you will need to group the plants found within the wetland into two
categories: 1) emergent, and 2) forest and scrub-shrub.
There are four size thresholds used to score this characteristic: 1) forest or shrub > 1/3 the
area of the wetland, 2) emergent plants > 2/3 area, 3) forest or shrub > 1/10 area, and 4)
emergent plants > 1/3 area. Figure 30 shows an aerial photograph of a Riverine wetland that
has dense shrub plants over most of its area.
NOTE: This plant cover is NOT based on the Cowardin classification. The polygons you draw
of emergent and shrub plants must have a 90% cover of the ground when you look down from
a person’s height (5ft).
NOTE: If the wetland is covered with downed trees, you can treat large woody debris as
forest or shrub.
Rationale for indicator: Riverine wetlands play an important role during floods because
the plants act to slow water velocities and thereby erosive flows. This reduction in velocity
also spreads out the time of peak flows, thereby reducing the maximum flows. The
potential for reducing flows will be greatest where the density of wetland plants and other
obstructions is greatest and where the obstructions are rigid enough to resist water
velocities during floods (Adamus et al., 1991). The indicator combines both characteristics
for the scoring. Shrubs and trees are considered to be better at resisting water velocities
than emergent plants. Aquatic bed species are judged not to provide much resistance and
are not counted. Wetlands with a dense cover of trees and shrubs are scored higher than
those with a cover of only emergent species.
Current location of riverbanks
The average width of the old oxbow is
about ½ the maximum width. When
compared to the distance between banks
of the river in the background of the
photograph, the ratio of width of wetland
to width of river is between 1-2. Note:
The photograph is not to scale because of
differences in the distance from the
camera.
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R 5.0 Does the landscape have the potential to support the hydrologic functions of
the site?
R 5.1 Is the stream or river adjacent to the wetland downcut?
To answer this question you will need to view the section of the stream that provides the
overbank flows to the wetland. Generally, downcutting becomes visible when its watershed
contains more than 10% impervious surface (Donaldson & Hefner, 2005). Figures 31, 32, 33
and 34 show a progression of different levels of downcutting that result from development.
For the purposes of this rating, Figures 33 and 34 show streams for which the answer to R 5.1
would be YES. Figures 31 and 32 are streams for which the answer would be NO because the
floodplain is still somewhat connected to the stream. Figures 31-34 are from Donaldson &
Hefner (2005).
Rationale for indicator: Streams in developed areas are often downcut because of the
increased flows from impermeable surfaces (reviewed in Sheldon et al., 2005). As a result,
the streams can become disconnected from the surrounding floodplain and floodwaters go
overbank less frequently. A Riverine wetland that is directly adjacent to a downcut stream
will not provide the same level of flood attenuation as one that is adjacent to a stream with
no downcutting.
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Figure 31. Stream in a watershed with less than 5 percent impervious surface cover, showing no
downcutting.
Figure 32. A stream in a watershed with 8-10% impervious surface cover. Streambed is still relatively
stable, but signs of stream erosion are more apparent. Not much downcutting is evident.
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Figure 33. A stream in a watershed with approximately 20% impervious surface cover showing
downcutting. You would answer YES to question R 5.1 for this stream.
Figure 34. This stream has a surrounding area of approximately 30% impervious surface cover. The
manhole in the middle of the picture was originally in the floodplain and is an indicator of the degree
to which the channel has been downcut.
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R 5.2 Does the up-gradient watershed include an UGA or incorporated area? (This
question is the same as R 2.2.)
To begin, trace the stream or river to its source and determine whether there are any urban or
suburban areas adjacent to the stream. Answer YES to this question if there are any
incorporated cities and towns or their Urban Growth Areas (UGA) upstream of the wetland.
The wetland may be within the UGA as long as some of the UGA is upstream. Maps of UGAs
and urban areas can be found at:
http://www.ecy.wa.gov/programs/air/aginfo/ugamaps.htm.
If there are no developed areas adjacent to the stream, you will need to identify the
contributing basin to the stream that floods the wetland you are rating. This can be done
using topographic maps or through websites such as the USGS:
http://water.usgs.gov/wsc/map_index.html. Answer YES to this question if there are any
incorporated cities and towns or UGAs within the contributing basin.
R 5.3 Is the up-gradient stream or river controlled by dams?
To answer this question you will have to trace on a map or aerial photo the stream or river
adjacent to the wetland you are rating. Answer YES to this question if there is a dam within
10 miles upstream of the wetland. Look only for dams on the main channel of the stream
adjacent to the wetland. Dams on tributaries to the main stream do not count.
Rationale for indicator: Dams will buffer the flood waters that a wetland receives by
holding much of the waters back upstream of the unit. This can reduce the flood storage
and attenuation that the wetland itself performs. The landscape potential for a wetland
performing hydrologic functions is therefore reduced when dams are present upstream.
Rationale for indicator: Urban and suburban areas are a major source of impervious
surface. These areas increase both intensity of peak flows and the amount of water
flowing during a storm event (reviewed in Sheldon et al., 2005). The presence of
development upstream of the wetland is a good indicator that the landscape is increasing
the flood flows to the wetland unit, thereby increasing the wetland’s level of functioning in
attenuating floods.
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R 6.0 Are the hydrologic functions provided by the site valuable to society?
R 6.1 Distance to the nearest areas downstream that have flooding problems:
If you do not know whether floods have caused damage downstream of the wetland, you will
need to do some research. Your best sources of information on flooding problems are the
emergency planning office in your local government and the local Federal Emergency
Management Agency (FEMA). You may also find useful information using search engines on
the web. Search using the name of a downstream city or the “watershed name” + “flooding”
(or :flood problems”, “flood history”).
Determine whether flooding occurs that damages resources in:
The sub-basin that is immediately down-gradient of the wetland.
A sub-basin farther down-gradient.
R 6.2 Has the site has been identified as important for flood storage or flood
conveyance in a regional flood control plan?
To answer this question contact the jurisdiction in which the site is found to determine
whether any regional flood control plans exist. A search of websites for flood prone areas will
probably also list flood control plans for the watershed in question. If plans exist, determine if
the site is listed as important or valuable for flood storage. To answer YES to this question,
the flood control district needs to have developed a flood control or flood hazard mitigation
plan that identifies the site as one that needs to be preserved or enhanced to improve flood
protection.
Rationale for indicator: The values of flood storage and flood conveyance provided by
wetlands are often recognized in regional flood control plans, and specific sites are
mentioned in these plans. If the value of a wetland for flood attenuation has already been
recognized, it is assigned a High rating for value.
Rationale for indicator: The value of wetlands in reducing the impacts of flooding and
erosion is based on the presence of human or natural resources that can be damaged by
these processes. The indicator characterizes whether the wetland’s position in the
landscape protects downgradient resources from flooding. In general, the value of a
wetland in reducing flood damage is judged to decrease with increasing distance from
downstream flood-prone areas because the amount of water stored by the wetland relative
to the overall flows decreases. Distance is characterized qualitatively in terms of
hydrologic basins.
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5.5 Water quality and hydrologic functions in Lake
Fringe w etlands (questions starting with “L”)
L 1.0 Does the site have the potential to improve water quality?
NOTE: Lake Fringe wetlands have a maximum score for site potential of 12 points instead of
16 for the site potential. The technical review team developing the 2004 Wetland Rating
System (Hruby, 2004a; b) concluded that Lake Fringe wetlands do not improve water quality
to the same extent as Riverine or Depressional wetlands because any pollutants taken up in
plant material will be more easily released into the water column and dispersed when the
plants die off.
L 1.1 Average width of plants along the lakeshore:
It is often difficult to map the outside edge of a wetland when it is along the shores of a lake
where open water can extend out for large distances. For this reason, the question is phrased
in terms of width of the zone of plants perpendicular to the shore rather than the area of
plants. There are three thresholds for scoring the average width of the zone of plants:
33 ft or more (10 m)
16 ft-< 33 ft (5-10 m)
6 ft-<16 ft (2-5 m)
Sketch the zone of plants on a map or aerial photo, and average the width by segment. Then,
calculate an overall average width for the wetland. Figure 35 gives an example of such a
sketch. Figure 36 shows an actual Lake Fringe wetland where the average width of plants is
greater than 33 ft.
Rationale for indicator: The intent of this question is to characterize the width of the
zone of plants that provides a vertical structure to filter out pollutants or absorb them.
Wetlands in which the average width of plants is large are more likely to retain sediment
and toxic compounds than wetlands where plants are in a narrow band (Adamus et al.,
1991). Even aquatic bed species that die back every year are considered to play a role in
improving water quality. These plants take up nutrients in the spring and summer that
would otherwise be available to stimulate algal blooms in the lake. In addition, aquatic bed
species change the chemistry of the lake bottom to facilitate the binding of phosphorus
(Moore et al., 1994).
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Figure 35. Estimating width of the plant zone along the shores of a lake. The average width for the entire
area is: (20 ft x 0.5) + (35 ft x 0.5) = 27.5 ft.
Figure 36. A Lake Fringe wetland where the zone of plants is wider than 33 ft. The plants along the shores
of this lake consist of a zone of shrubs and a zone of aquatic bed and emergent species.
L 1.2 Characteristics of the plants in the wetland:
Rationale for indicator: The intent of this question is to characterize how much of the
wetland is covered with plants that are more effective at improving water quality in a lake
environment. Herbaceous emergent species have, in general, been found to sequester
metals and remove oils and other organics better than other plant species (Hammer, 1989;
Horner, 1992).
Average width = 20 ft for ½ of
the wetland
Average width = 35 ft for ½ of
the wetland
Vegetated
area
Lakeshore
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For this question you will need to group the plants found within the wetland into three
categories: 1) herbaceous, 2) aquatic bed, and 3) any other plants. The herbaceous plants can
be either the dominant plant form (in this case it would be called emergent class) or as an
understory in a shrub or forest community. These groupings are not the Cowardin classes
for plants.
There are several size thresholds used to score this characteristic: More than 90%, more than
2/3, or more than 1/3, of the vegetated area is covered in herbaceous plants or other types.
You will need to draw the areas of plant types on a map or aerial photo before you can be
confident that your estimates are accurate.
NOTE: In Lake Fringe wetlands, the area of the wetland used as the basis for determining
thresholds is only the area that is vegetated. Do not include open water beyond the outer
edge of the wetland in determining the area of the wetland covered by a specific type of
plants. Small patches of open water within the vegetated zone, however, are included in the
estimate for total area.
L 2.0 Does the landscape have the potential to support the water quality function
of the site?
L 2.1 Is the lake used by power boats?
To answer this question you will need to know if the lake has any restrictions on use by power
boats. The local planning department or parks department should have this information. The
answer to this question is NO if there is a complete ban on gasoline or diesel motors on the
lake. Many lakes are limited to small outboards of less than 5 or 10 hp, but these are still
sources of pollutants and the answer would be YES. Other lakes are limited to electric motors
only. In this latter case, the answer would also be NO.
The answer to this question should be YES unless you can provide evidence that a ban on
power boats exists.
Rationale for indicator: The presence of power boats on a lake will increase the
pollutants entering a Lake Fringe wetland. Toxic chemicals, oils, cleaners, and paint
scrapings from boat maintenance can make their way into the water (reviewed in Asplund,
2000). In addition, older two stroke engines still found on many recreational boats and jet
skis were purposely designed to discharge their exhaust, which often contains gasoline and
oil, into the water. The landscape potential of a wetland along the shores of a lake to
improve water quality is higher if the lake itself is directly receiving pollutants from power
boats.
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L 2.2 Is more than 10% of the area within 150 ft of the wetland on the upland side in
land uses that generate pollutants in surface runoff (agricultural, pasture,
residential, commercial, urban)?
Use your aerial photo and draw a line around the wetland that is 150 ft from the upland edge
of the wetland. The line should be 150 ft on the landward side of the wetland boundary.
Answer YES to this question if you find the listed uses within 150 ft of the wetland and they
cover more than 10% of the area within this 150 ft perimeter upslope of the wetland.
L 2.3 Does the lake have problems with algal blooms or excessive plant growth such as
milfoil?
To answer this question you will need to visit the lake in the summer, or examine aerial
photographs taken in the summer, to determine whether there is excessive plant growth
(Figures 37, 38). If you are rating the wetland in the winter, you will need to inquire locally
(residents, board of health officials, or parks departments) to determine whether blooms
occur in the summer.
Rationale for indicator: Algal blooms and blooms of larger plants such as milfoil are an
indication of excessive nutrients in the lake water (Schindler & Fee, 1974; Smith et al.,
1999). The increased levels of nutrients in the lake increase the amount of nutrients that
the wetland plants absorb (Venterink et al., 2002) and thus also increase the level of
function within the wetland unit.
Rationale for indicator: Farming, grazing, golf courses, residential areas, commercial
areas, and urban areas, in general, are major sources of pollutants (reviewed in Sheldon et
al., 2005). The review also found that a well-vegetated buffer of 150 ft will remove only
60-80% of some pollutants from surface runoff into a wetland. Thus, pollutants from such
land uses will probably reach the wetland unit along the lake if they are within 150 ft of it.
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Figure 37. Algal blooms in a lake in the Puget Sound area.
Figure 38. A lake infested with milfoil indicating the presence of excess nutrients (photo courtesy of New
Hampshire Department of Environmental Protection).
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L 3.0 Is the water quality improvement provided by the site valuable to society?
L 3.1 Is the lake on the 303(d) list of degraded aquatic resources?
To answer this question you will need to access the Department of Ecology’s website that lists
the bodies of water that do not meet water quality standards:
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html. Determine if the
wetland is along the shores of a lake on the 303(d) list.
L 3.2 Is the lake in a sub-basin where another aquatic resource is on the 303(d) list?
To answer this question you will need to access the Department of Ecology’s website that lists
all the bodies of water that do not meet water quality standards (see above). Determine if the
wetland is in a basin or sub-basin where any body of water is on the 303(d) list.
L 3.3 Has the site been identified in a watershed or local plan as important for
maintaining water quality?
To answer this question you will need to seek information from the planning department of
the local jurisdiction where the site is located. Information on regional or local plans can often
be found on the website of the city or county in which the site is found. Useful search phrases
include: “watershed plan”, “water quality” , or “wetland protection”.
Rationale for indicator: Not all pollution and water quality problems are identified by
Ecology’s water quality monitoring program. Local and watershed planning efforts
sometimes identify wetlands that are important in maintaining existing water quality.
These wetlands provide a value to society that needs to be replaced if they are impacted.
Rationale for indicator: Lake Fringe wetlands can mitigate the impacts of pollution even
if they are not located directly on a polluted body of water. At a watershed scale, Lake
Fringe wetlands can remove pollutants that might otherwise cause problems farther
downstream. They can also trap airborne pollutants. Thus, wetlands can provide an
ecosystem service and value to our society in any basin and sub-basin that has pollution
problems. The removal of pollutants by wetlands is judged to be more valuable in basins
where other aquatic resources are already polluted. The 303(d) list is used as an indicator
of pollution problems in a basin.
Rationale for indicator: The phrase "303(d) list" is short for the list of impaired waters
(stream segments, lakes) that the Clean Water Act requires all states to submit to the
Environmental Protection Agency (EPA) every two years. In Washington, we identify all
waters where pollution controls are not sufficient to attain or maintain applicable water
quality standards. Wetlands along the shores of lakes on the 303(d) list are judged to be
more valuable because their role in cleaning up the pollution is critical for reducing further
degradation of water quality.
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If the basin in which the wetland is found has a Total Maximum Daily Loads (TMDL) plan (also
called a Water Cleanup Plan) developed for it, then answer YES for this question. It is
assumed that all wetlands are valuable in a basin where water quality is poor enough to
require a TMDL. The Department of Ecology’s website lists all the bodies of water that have
TMDLs: http://www.ecy.wa.gov/programs/wq/tmdl/TMDLsbyWria/TMDLbyWria.html.
NOTE: Total Maximum Daily Loads (TMDL) or Water Cleanup Plans describe the type,
amount, and sources of water pollution in a particular water body. They analyze how much
the pollution needs to be reduced or eliminated to meet water quality standards, and then
provide targets and strategies to control the pollution. Wetlands in these basins are judged to
be more valuable because they function at a landscape scale to mitigate discharges of
pollutants. TMDLs are based on models that estimate the natural decay and adsorption of
pollutants under current conditions. Wetlands are an important part of that natural decay;
their destruction would require a recalibration of the TMDL models and force reductions in
current levels of discharge.
L 4.0 Does the site have the potential to reduce shoreline erosion?
The site potential for Lake Fringe wetlands has a maximum score of only 6 points for the
hydrologic functions instead of 16. The technical review team developing the 2004 wetland
rating system concluded that Lake Fringe wetlands do not provide hydrologic functions to the
same extent as Riverine or Depressional wetlands. The function of reducing shoreline erosion
at the local scale was not judged to be as important as reducing peak flows and reducing
erosion at the watershed scale, and should not be scored as highly. Lake Fringe wetlands,
however, do provide a hydrologic function by dissipating wave energy before it reaches the
shore. Waves can erode shorelines and cause damage to resources along the shore.
L 4.1 Average width and characteristics of plants along the lakeshore (do not include
aquatic bed species):
This characteristic is similar to that used in L 1.1 and L 1.2, but the grouping of plant types and
thresholds for scoring are different. You are looking for the areas that would be classified as
Forested, Scrub-shrub, or Emergent. This indicator is based on the Cowardin plant
classes.
It is difficult to map the outside edge of a wetland when it is along the shores of a lake where
open water can extend out for large distances. For this reason the question is phrased in
terms of the width and type of plants found only within the area of trees, shrubs, and
Rationale for indicator: The intent of this question is to characterize how much of the
wetland is covered with plants that provide a physical barrier to waves and protect the
shore from erosion. This protection consists of both shoreline anchoring and the
dissipation of erosive forces (Adamus et al., 1991). Wetlands that have extensive,
persistent (especially woody) plants provide protection from waves and currents
associated with large storms that would otherwise penetrate deep into the shoreline
(Adamus et al., 1991). Emergent plants provide some protection but not as much as the
stiffer shrubs and trees.
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emergents. There are two thresholds for measuring the average width of plant zones [33 ft
(10 m) and 6 ft (2 m)], and two thresholds based on length of the wetland along the shore (¾
and ¼ of the length along the shore). Figure 39 gives an example of such a sketch.
L 5.0 Does the landscape have the potential to support the hydrologic functions of
the site?
L 5.1 Is the lake used by power boats with more than 10 hp?
To answer this question you will need to know whether the lake has any restrictions on
power boats. The local planning department or parks department should have this
information. The answer to this question is NO if there is a complete ban on gasoline or diesel
motors on the lake. Many lakes are limited to small outboards of less than 5 or 10 hp. Other
lakes are limited to electric motors only. In both cases the answer would also be NO because
the speed of these smaller boats is limited, and correspondingly, their wakes will be smaller.
The answer to this question should be YES unless you can provide evidence that the bans on
power boats are present.
Rationale for indicator: Boat wakes can be a major source of shoreline erosion (Maynord
et al., 2008; review in Asplund, 2000). Lakes with boat traffic will have larger waves than
lakes without. Wetlands along the shores of the latter will provide a higher level of
function by reducing the impact of the larger waves.
Average width = 20 ft for ½ of
the distance along the shore Average width = 35 ft for ½ of
the distance along the shore
Area of shrubs Area of emergents
Figure 39. Estimating width of plant types along the shores of a lake. The average width of shrubs is
35 ft for ½ the distance along the shore and the width of emergents is 20 ft for ½ of the distance. This
wetland would score 4 points because more than ¼ distance consists of shrubs wider than 33 ft.
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L 5.2 Is the fetch on the lake side of the wetland at least 1 mile in distance?
Use a topographic map or scaled aerial photograph to measure the farthest distance to
another shore or obstruction. This is the maximum fetch over which a wind can blow.
Answer YES to this question if the length is 1 mi or more.
L 6.0 Are the hydrologic functions provided by the site valuable to society?
L 6.1 Are there resources, both human and natural, along the shore that can be
impacted by erosion?
Users of this method must make a qualitative judgment on the value of the Lake Fringe
wetland in protecting resources from shoreline erosion. Generally, a Lake Fringe wetland
does have value if:
There are human structures or old growth/mature forests within 25 ft of the Ordinary
High Water Mark (OHWM) of the shore in the wetland.
There are nature trails or other paths and recreational activities within 25 ft of the
OHWM.
The rating form has space to note observations of resources along the shore that do not meet
the criteria above. If you observe or know of other resources, note this on the form and score
it.
Rationale for indicator: Lake Fringe wetlands provide value by protecting a shoreline
from erosion if there is some resource that could be damaged by this erosion. For
example, houses are often built along a shoreline, and these can be damaged by shoreline
erosion, especially if the house is on a bluff. Buildings, however, are not the only resource
that can be impacted. A mature forest along the shores of a lake is a valuable natural
resource that provides important habitat. Shoreline erosion, especially erosion from boat
wakes, may topple trees into the lake and reduce the overall area of this valuable resource.
Rationale for indicator: The size of wind-generated waves on lakes depends on the
fetch. The fetch is the uninterrupted distance over which the wind blows without a
significant change in direction. Lakes with larger fetches will have larger waves. Wetlands
along the shores of lakes with longer fetches will provide a higher level of function by
reducing the impact of the larger waves. The threshold of 1 mi was chosen because in
many lakes such a fetch will generate a wave of approximately 1 ft in a 20 mph wind. See
the following website for more information:
http://woodshole.er.usgs.gov/staffpages/csherwood/sedx_equations/RunSPMWave.html
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5.6 Water quality and hydrologic functions in Slope
wetlands (questions starting with “S”)
S 1.0 Does the site have the potential to improve water quality?
The site potential for Slope wetlands has a maximum score of 12 points for the water quality
functions instead of 16. The technical review team that developed the 2004 Wetland Rating
System (Hruby, 2004a; b) concluded that Slope wetlands do not improve water quality to the
same extent as Riverine or Depressional wetlands because Slope wetlands tend to release
surface water fairly quickly. They are usually less effective at trapping sediment and all the
pollutants associated with sediment because of their topography and the way water moves
through them.
S 1.1 Characteristics of the average slope of the wetland:
For this question you will need to estimate the average slope of the wetland. Slope is
measured either in degrees (°) or as a percent (%). In this method, we use the latter
measurement, percent, which is calculated as the ratio of the vertical change between two
points and the horizontal distance between the same two points [vertical drop in feet (or
meters) ÷ horizontal distance in feet (or meters)]. For example, a 1-ft drop in elevation
between two points that are 100 ft apart is a 1% slope, and a 2-ft drop across the same
distance is a 2% slope.
For large wetlands, the slope can be estimated from topographic maps of the area. The change
in contour lines can be used to calculate the vertical drop between the top and bottom edges
of the wetland. The horizontal distance can be estimated using the appropriate scale (which
should be at the bottom of the map). Local jurisdictions sometimes have assessor’s maps that
are contoured at 2-ft intervals. These can be very useful in estimating the slope.
For small wetlands, it will be necessary to estimate the vertical drop visually and the
horizontal distance by pacing or using a tape measure. Visual estimates of the vertical drop
are more accurate if you can find a point of reference near the bottom edge of the wetland.
Stand at the upper edge of the wetland and visualize a horizontal line to a tree, telephone pole,
or another person at the lower edge of the Slope wetland. The point at which the horizontal
line intersects the object at the lower edge can be used to estimate the vertical drop between
the upper and lower edges of the wetland (see Figure 40).
NOTE: If you are standing at the upper edge of the wetland looking for a visual marker at the
lower edge using a level, do not forget to subtract your height from the total. If you are at the
bottom edge, you will need to add your height.
Rationale for indicator: Water velocity decreases with decreasing slope. This increases
the retention time of surface water in the wetland and the potential for retaining sediments
and associated toxic pollutants. The potential for sediment deposition and the retention of
toxics by burial increases as the slope decreases (reviewed in Adamus et al., 1991).
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NOTE: If the slope of a wetland changes, the best way to estimate the average is to calculate
the slope between the uppermost wetland boundary and the lowest point on the boundary.
This will average out all the variations unless the wetland has a much higher slope for a short
distance on the borders of the wetland.
NOTE: If the Slope wetland has a ditch along its bottom side DO NOT use the bottom of the
ditch for calculating the slope. Use the elevation of the top of the ditch for calculating the
slope.
Figure 40. Estimating the slope of a small Slope wetland. The top of a 6-ft tall person is about level with
the upper edge of the wetland. The average slope is approximately 6/200 = 0.03 or 3%.
S 1.2 The soil 2 in below the surface is a true clay or true organic soil.
If the wetland lies within an area that is mapped as an organic or clay soil by the National
Resource Conservation Service (NRCS) in their county soil maps, you do not need to
Rationale for indicator: Clay soils and organic soils are both good indicators that a
wetland can remove a wide range of pollutants from surface water. The uptake of
dissolved phosphorus and toxic compounds through adsorption to soil particles is highest
when soils are high in clay or organic content (Mitsch & Gosselink, 1993).
Upper edge
of wetland
Lower edge of wetland
200 ft
6 ft - The approximate
height of a person
standing here
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investigate further. Consider the wetland to have clay or organic soils. If it is not mapped as
an organic or clay soil, you will need to take at least one sample at the site.
To look at the soil: Dig a small hole within the wetland boundary and pick a sample from the
area that is about 2 in below the duff layer. Usually it is best to sample the soil toward the
middle of the wetland rather than at the edge. Avoid picking up any of the duff or recent plant
material that lies on the surface. Determine if the soil is organic or clay. If you are not familiar
with procedures for identifying clay soils, a key is provided in Appendix C.
NOTE: The presence of organic or clay soils anywhere within the wetland counts. There is no
scaling for this question based on the size of the patch of soil. This simplification is necessary
because it is not possible to develop a reproducible map of different soils in a wetland within
the time frame for doing the field work.
See the NRCS web page for more descriptions on how to identify organic soils:
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/?cid=nrcs142p2_053
580.
S 1.3 Characteristics of the plants that trap sediments and pollutants:
For this question you will need to group the plants found within the wetland into two groups:
1) dense, ungrazed or unmowed, herbaceous plants, and 2) all other types (Figure 41). NOTE:
The Cowardin plant classes are NOT used for this question. For this question the area of
herbaceous plants can include the areas of emergent plants as classified by Cowardin as well
as the herbaceous understory in a shrub or forest. To qualify as “dense”, the herbaceous
plants must cover at least ¾ (75%) of the ground (as opposed to the 30% requirement in the
Cowardin plant classes).
NOTE: The best information on reducing surface flows in a slope is provided by the basal
cross-section of the plants. However, this is not easy to measure. The best indicator we were
able to find is an estimate of the cover from a person's height. Generally, if less than 25% of
the ground is visible at 5-6 ft, then there will be a fairly high stem density and basal cross
section to trap sediments and reduce flows.
Rationale for indicator: The intent of this question is to characterize how much of the
wetland is covered with plants that are more effective at improving water quality in a
slope environment. Herbaceous species have, in general, been found to sequester metals
and remove oils and other organics better than other plant species (Hammer, 1989;
Horner, 1992). Furthermore, dense herbaceous plants present the greatest resistance to
the surface flow often found on slope wetlands. Water in this environment tends to flow
very close to the surface and be shallow (not more than a few inches). Trees and shrubs
tend to be widely spaced relative to herbaceous plants and don’t provide as much
resistance to this type of surface flow.
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Figure 41. A Slope wetland where dense, unmowed plants are between ¼ and ½ the area of
the wetland.
S 2.0 Does the landscape have the potential to support the water quality function
of the site?
S 2.1 Is more than 10% of the area within 150 ft of the wetland on the uphill side in
land uses that generate pollutants in surface runoff (agricultural, pasture,
residential, commercial, or urban)?
Use your aerial photo and draw a line around the wetland that is 150 ft from the edge of the
wetland. The line should be 150 ft upslope of the wetland boundary. Answer YES to this
question if you find the listed uses within 150 ft of the wetland and they cover more than 10%
within this perimeter upslope of the wetland. Use a graphic aid, such as an acetate overlay
with a grid or dots, to estimate area. Visual estimates are not accurate enough and may result
in significant errors.
Rationale for indicator: Farming, grazing, golf courses, residential areas, commercial
areas, and urban areas, in general, are major sources of pollutants (review in Sheldon et al.,
2005). The review also found that a well-vegetated buffer of 150 ft will only remove 60-
80% of some pollutants from surface runoff into a wetland. Thus, pollutants from such
land uses will probably reach the wetland unit if they are within 150 ft of the unit and
upslope of it.
Unmowed part of the
wetland covered by Juncus
spp.
Mowed part of wetland.
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S 2.2 Are there other sources of pollutants coming into the wetland that are not listed
in questions S 2.1?
Answer YES to the question if you can identify any source of pollutants in the groundwater or
surface water coming into the wetland caused by human activities. Identify the source of the
pollution on the rating form. Other sources of pollutants may be spraying of pesticides on
golf courses, particulates in exhausts from airplanes or motor vehicles, and pesticides used in
mosquito control.
Activities that generate pollutants within the wetland itself, such as grazing, also count for a
YES for this question. Cattle, sheep, or large native herbivores such as elk grazing within the
wetland are a source of pollutants. Also, answer YES to this question if the wetland has a pond
that is commonly used by migrating waterfowl. Waterfowl droppings are a source of both
excess nutrients and bacteria.
S 3.0 Is the water quality improvement provided by the site valuable to society?
S 3.1 Does the wetland discharge directly to a stream, river, or lake that is on the
303(d) list?
To answer this question you will need to access the Department of Ecology’s website that lists
all the bodies of water that do not meet water quality standards:
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html. Use the Map Tool to
locate your site. Determine from the aerial photograph or the map on the Ecology website if
the wetland you are rating is within at least 1 mi up-gradient of any aquatic resource mapped
as not meeting water quality standards and has a surface water channel, ditch, or other
discharge leading to it (red lines or polygons on the map).
Rationale for indicator: The phrase "303(d) list" is short for the list of impaired waters
(stream segments, lakes) that the Clean Water Act requires all states to submit to the
Environmental Protection Agency (EPA) every 2 years. In Washington, we identify all
waters where pollution controls are not sufficient to attain or maintain applicable water
quality standards. Wetlands that discharge directly to these polluted waters are judged to
be more valuable than those that discharge to unpolluted bodies of water because their
role in cleaning up the pollution is critical for reducing further degradation of water
quality.
Rationale for indicator: The sources of pollutants listed in question S 2.1 may not be the
only sources coming into the wetland unit from the surrounding landscape. In addition,
sources of pollutants can be within the wetland unit itself. For example, pollutants are
discharged within the wetland if it is used for grazing.
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S 3.2 Is the wetland in a basin or sub-basin where another aquatic resource is on the
303(d) list?
To answer this question you will need to access the Department of Ecology’s website that lists
the bodies of water that do not meet water quality standards:
http://www.ecy.wa.gov/programs/wq/303d/currentassessmt.html. To find the boundaries
of basins and sub-basins (called hydrologic units) in the area, consult with the planning
department of the local jurisdiction, or use the map of hydrologic units developed by the
USGS: http://water.usgs.gov/GIS/huc.html.
S 3.3 Has the site been identified in a watershed or local plan as important for
maintaining water quality?
To answer this question you will need to seek information from the planning department of
the local jurisdiction where the site is located. Information on regional or local plans can often
be found on the website of the city or county in which the site is found. Useful search phrases
include: “watershed plan”, “water quality” , or “wetland protection” .
If the basin in which the wetland is found has a Total Maximum Daily Loads (TMDL) plan (also
called a Water Cleanup Plan) developed for it, then answer YES for this question. It is
assumed that all wetlands are valuable in a basin where water quality is poor enough to
require a TMDL. The Department of Ecology’s website lists all the bodies of water that have
TMDLs: http://www.ecy.wa.gov/programs/wq/tmdl/TMDLsbyWria/TMDLbyWria.html.
NOTE: Total Maximum Daily Loads (TMDL) or Water Cleanup Plans describe the type,
amount, and sources of water pollution in a particular water body. They analyze how much
the pollution needs to be reduced or eliminated to meet water quality standards, and then
provide targets and strategies to control the pollution. Wetlands that discharge directly to
these polluted waters are judged to be more valuable because they function at a landscape
scale to mitigate discharges of pollutants. TMDLs are based on models that estimate the
natural decay and adsorption of pollutants under current conditions. Wetlands are an
important part of that natural decay; their destruction would require a recalibration of the
TMDL models and force reductions in current levels of discharge.
Rationale for indicator: Not all pollution and water quality problems are identified by
Ecology’s water quality monitoring program. Local and watershed planning efforts
sometimes identify wetlands that are important in maintaining existing water quality.
These wetlands provide a value to society that needs to be replaced if they are impacted.
Rationale for indicator: Wetlands can mitigate the impacts of pollution even if they do
not discharge directly to a polluted body of water. Wetlands can remove nitrogen from
groundwater as well as surface water. They can also trap airborne pollutants. Thus,
wetlands can provide an ecosystem service and value to our society in any basin and sub-
basin that has pollution problems. The removal of pollutants by wetlands is judged to be
more valuable in basins where other aquatic resources are already polluted.
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S 4.0 Does the site have the potential to reduce flooding and erosion?
The site potential for Slope wetlands can only rate low or moderate for the hydrologic
functions . The technical review teams that developed the 2004 Wetland Rating Systems
(Hruby, 2004a; b) concluded that Slope wetlands may provide some velocity reduction but do
not provide flood storage. Thus, they should be rated lower than wetlands that can perform
both aspects of the function.
S 4.1 Characteristics of plants that reduce the velocity of surface flows:
For this question you will need to estimate the area of two categories of plants found within
the wetland: 1) dense, uncut, rigid plants, and 2) all other plants. This indicator for plants is
not related to any of the Cowardin classes. Dense means that individual plants are spaced
closely enough that the soil is barely, if at all, visible (> 75% cover of plants) when looking at it
from the height of an average person. Uncut means that the height of the plants has not been
significantly reduced by grazing or mowing. “Significantly reduced” means that the height is
less than 6 in. Rigid is defined as having stems thick enough (usually > 1/8 in) to remain erect
during surface flows.
There is only one threshold used to score this characteristic: dense, ungrazed, rigid plants for
more than 90% of the area of the wetland (Figure 42), The wetland in Figure 41 was mowed
over much of its area, except where the Juncus spp. was growing. The mowed plants were less
than 6 in high, so the only plants that were included for this indicator were the Juncus.
NOTE: This is a simpler version of the questions in the 2004 Wetland Rating System (Hruby,
2004a). Only one answer resulted in a Moderate rating of 6 or more points. As a result, the
other questions were dropped since their scores did not change the rating.
NOTE: This description is not species specific because a species may be rigid in one
environment and not rigid in another. For example, reed canarygrass (Phalaris arundinacea)
can grow very thick and rigid stems in areas with high nutrients. In other situations (e.g.,
shady environment), however, it can be very thin and would easily be bent to the ground by
runoff.
Rationale for indicator: The intent of this question is to characterize how much of the
wetland is covered with plants that provide a physical barrier to sheetflow coming down
the slope. Plants on slopes will reduce peak flows and the velocity of water during a storm
event (U.S. Geological Service, http://ga.water.usgs.gov/edu/urbaneffects.html, accessed
July 31, 2003). The importance of plants on slopes in reducing flows has been well
documented in studies of logging (Lewis et al., 2001), though not specifically for Slope
wetlands. The assumption is that plants in Slope wetlands play the same role as plants in
forested areas in reducing peak flows.
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Figure 42. A Slope wetland with dense erect, ungrazed plants over more than 90% of its area. The
direction of the slope is from the bottom of the photograph toward the center.
S 5.0 Does the landscape have the potential to support the hydrologic functions of
the site?
S 5.1 Is more than 25% of the area within 150 ft upslope of wetland in land uses that
generate excess surface runoff (agricultural, pasture, residential, commercial, or
urban)?
Use your aerial photo and draw a line around the wetland that is 150 ft from the edge of the
wetland. Estimate the land uses in the area 150 ft upslope of the wetland boundary. Answer
YES to this question if you find the listed land uses within 150 ft of the wetland and they cover
more than 25% of the area upslope within this perimeter.
Rationale for indicator: Human land uses tend to de-stabilize the flows of water in a
watershed. Generally, human activities reduce infiltration and increase the run-off during
storm events (review in Sheldon et al., 2005). For example, a lawn can reduce infiltration
by as much as 65% (Kelling & Peterson, 1975). Thus, a slope unit located in areas where
run-off has increased can provide more velocity reduction of surface flows than one
located in an undeveloped area.
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S 6.0 Are the hydrologic functions provided by the site valuable to society?
S 6.1 Distance to the nearest areas downstream that have flooding problems:
If you do not know whether floods have caused damage in the sub-basin farther downstream,
you will need to do some research. Your best sources of information on flooding problems are
the emergency planning office in your local government and the local Federal Emergency
Management Agency (FEMA).
Choose the description that best matches conditions around the wetland being rated.
The wetland reduces velocities that would otherwise impact down-gradient areas where
flooding has damaged human or natural resources (e.g., houses or salmon redds):
In the sub-basin that is immediately down-gradient of the wetland.
In a sub-basin farther down-gradient.
NOTE 1 (a landscape constraint on function): A Slope wetland that receives only return flow
from irrigation is not in a landscape position to perform the hydrologic functions. Since the
inflow is controlled, there is little chance that the water coming into the wetland will cause
downstream flooding or erosion. Answer NO to the question if you can document that more
than 90% of the flow through the wetland is a result of irrigation.
NOTE 2 (a landscape constraint on function): When a Slope wetland is situated upslope of a
road where water movement through the road is limited by ineffective culverts, the roadway
typically acts as a levee, de-coupling upslope wetlands from downstream flooding. The
roadway, rather than the wetland, delays storm flows, and acts like a flood-control dam. This
indicates that the hydrologic connection between the floodway and the upslope area is
impaired. If, however, the water impounded on the upslope side of the road recedes at the
same rate as the water on the downslope side, you can assume the connections through the
road are not constrained. In this case, the velocity reduction provided by the wetland on the
upslope side is important, and the wetland should be scored accordingly.
Rationale for indicator: The value of wetlands in reducing the impacts of flooding and
erosion is based on the presence of human or natural resources that can be damaged by
these processes. The indicator used characterizes whether the wetland’s position in the
landscape protects downgradient resources from flooding. In general, the value of a
wetland in reducing flood damage is judged to decrease with increased distance to
downstream areas with flooding problems because the amount of water flowing through
the unit relative to the overall flows decreases.
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S 6.2 Has the site been identified as important for flood storage or flood conveyance in
a regional flood control plan?
To answer this question contact the jurisdiction in which the site is found to determine
whether any regional flood control plans exist. A search of websites for flood prone areas will
probably also list flood control plans for the watershed in question. If plans exist, determine if
the site is listed as important or valuable for flood storage. To answer YES to this question,
the flood control district needs to have developed a flood control or flood hazard mitigation
plan that identifies the site as one that needs to be preserved or enhanced to improve flood
protection.
5.7 Habitat functions for all HGM classes (questions
starting with ‘H’)
A rapid method such as this one relies on indicators of function that are fixed and present
throughout most of the year (see Appendix D). As a result, it is not possible to actually
monitor the species that use a wetland, or determine their abundance. The one aspect of
habitat that we can determine is the number of habitat niches present. The questions below
describe indicators that represent different habitat niches. The basic assumption is that
wetlands with more niches can provide a higher level of habitat functions than one with
fewer. The rating of the site potential for this function is based on the number of species for
which a site can potentially provide habitat.
H 1.0 Does the site have the potential to provide habitat?
H 1.1 Structure of the plant community:
Rationale for indicator: This indicator addresses two types of vegetation structure, the
Cowardin vegetation classes and several size ranges within the Emergent class of
vegetation. First, more habitat niches are provided within a wetland as the number of
vegetation classes increases. The increased structural complexity provided by different
plants optimizes potential breeding areas, escape, cover, and food production for the
greatest number of species (Hruby et al., 2000). Secondly, the team developing the
methods for assessing wetland functions in the Columbia Basin judged that different
guilds of species may partition the habitat based primarily on differences in height in the
emergent plants. The assessment team determined that the varying heights of emergent
vegetation played a significant role in providing structural complexity that might
otherwise, in wetter environments, be provided by scrub-shrub and forested vegetation.
This increased species richness arising from the increased structural diversity also
supports a greater number of terrestrial species in the overall wetland food web (Hruby et
al., 2000).
Rationale for indicator: The values of flood storage and flood conveyance provided by
wetlands are often recognized in regional flood control plans, and specific sites are
mentioned in these plans.
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