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Wetland Delineation

What is wetland delineation?

Wetland delineation establishes the existence (location) and physical limits (size) of a wetland for the purposes of federal, state, and local regulations.

Wetland delineation is also an element of a “jurisdictional determination.” This process identifies which water bodies within a project's boundaries meet the definition of "waters of the United States." For more information on this, see the Corps' Regulatory Guidance Letter 08-02, Jurisdictional Determinations (issued June 26, 2008, PDF 118 kb).

Remember that the Corps of Engineers (Corps), not applicants or their consultants, determines whether or not a wetland is a "water of the United States" and thus regulated under the federal Clean Water Act (CWA). If the Corps determines that a wetland is not subject to the CWA, the wetland may still be a "water of the State" and subject to regulation by Ecology as well as by local jurisdictions. Ecology regulates wetlands determined by the Corps to be non-jurisdictional due to their isolation from navigable waters.  > More on Isolated Wetlands

How do I delineate wetlands? 

Wetland delineations must be done using the methods outlined in the following:

• 1987 Corps of Engineers Wetlands Delineation Manual (PDF, 1.25 MB) and all applicable guidance that is not superseded by the new regional Supplements (see below).
• Regional Supplements to the 1987 Wetland Delineation Manual. The Corps has developed supplemental regional criteria for the 1987 Wetland Delineation Manual. Two regions fall within Washington:  the Arid West (dry lands west of the Continental Divide, from Idaho and eastern Washington south to the U.S.-Mexico border) and Western Mountains, Valleys, and Coast. >Map of the regions (PDF, 1.5 MB). The decision to use the Western Mountains, Valleys, and Coast Regional Supplement or the Arid West Regional Supplement on a particular field site should be based on landscape and site conditions, and not solely on map location.

  The Corps now requires you to use the appropriate regional Supplement when delineating wetlands:

  • Arid West Final Regional Supplement (September 2008, PDF, 4.7 MB).
  • Western Mountains, Valleys, and Coast Interim Regional Supplement (May 2010, PDF, 5.87 MB).

• Updated 2012 National Wetland Plant List (NWPL).  The 2012 NWPL will be used in any wetland delineations or determinations performed after June 1, 2012. The 2012 NWPL may be used in delineation/determination forms prior to that date, and should be referenced on any data forms used in the wetland delineation/determination if used.
• Field Indicators of Hydric Soils in the United States.  The indicators presented in the regional supplements are a subset of the National Technical Committee for Hydric Soils (NTCHS) Field Indicators of Hydric Soils in the United States that are commonly found in the region. Any change to the NTCHS Field Indicators represents a change to the subset of indicators for the regions. Check the NRCS hydric soils web site for updates to these indicators.

Wetland delineation should result in three things:

1. A wetland boundary clearly marked in the field.
2. A map that clearly identifies data collection points and the boundaries of the delineated wetland. (Topographic and aerial site maps are very helpful.)

3. A report that explains how the boundary was determined. It should include:

• A description of how and when the delineation was done

• Data forms used to delineate the wetland area

  • Arid West (PDF) data forms
  • Western Mountains, Valleys, and Coast (PDF) data forms.

• The map described in #2 above

• A soil survey map.

Delineation checklist (PDF) -a checklist of information that should be in your wetland delineation report, as well as a sample report outline.

NOTE:  You may need to hire a qualified wetland professional to help you identify and delineate wetlands (using the manuals listed above) and prepare a delineation report. 
> Hiring a Qualified Wetland Professional (PDF) -tips to help you find and select a qualified wetland professional.

Questions?

If you have any questions about wetland delineation, contact:

Tom Hruby, PhD
Senior Ecologist
Washington State Department of Ecology
P.O. Box 47600
Olympia WA 98504
(360) 407-7274
 

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