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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” identifying which water bodies, including wetlands, within the project boundaries meet the definition of "waters of the United States." More information on this can be found on the Seattle District Corps' Waters and Wetlands Information web page.

Wetland delineations must be done in accordance with the currently acceptable methods. At present, this includes the:

1987 Corps of Engineers Wetlands Delineation Manual (PDF, 1.43 mb) with all applicable guidance.
Washington State Wetland Identification and Delineation Manual (Chapter 173.22.080 WAC). The state manual includes guidance that clarifies the 1987 manual published by the Corps as well as guidance on regional issues issued by the Seattle District of the Corps and EPA Region 10 office. The state manual is consistent with the Corps 1987 manual and is required by all state agencies in the application of any state laws and regulations addressing wetlands, as well as by any city or county implementing their regulations under the Growth Management Act (Chapter 36.70A.175 RCW).
Arid West Interim Regional Supplement (December 2006, PDF, 13mb) to the 1987 Wetland Delineation Manual. Use of this manual is now required for conducting wetland delineations for Clean Water Act purposes in the arid west region of WA. The interim document will be tested for a one year period prior to finalization. Effective January 17, 2007 the Supplement data forms and indicators must be used for any data collection for wetland delineations submitted to the Corps. There was limited agency training offered on the arid west manual. For details see the Corps Special Public Notice (issued December 18, 2006, revised December 26, 2006). NOTE: You should continue to use the state manual (and the included data sheets) in addition to the arid west manual when delineating wetlands in the arid west region of Washington State. See shaded box at the bottom of the page for more details on an ongoing effort by the Corps to "regionalize" the 1987 wetland delineation manual.
Western Mountains, Valleys, and Coast Supplement (April 2008, PDF, 5 mb) to the 1987 Wetland Delineation Manual. Use of this manual is now required for conducting wetland delineations for Clean Water Act purposes in the western mountains, valleys, and coast region of WA. The Supplement data forms and indicators must be used for any data collection for wetland delineations submitted to the Corps. For details see the Corps Special Public Notice (issued May 28, 2008, PDF). NOTE: You should continue to use the state manual (and the included data sheets) in addition to this manual when delineating wetlands in the western mountains, valleys, and coast region of Washington State. See shaded box at the bottom of the page for more details on an ongoing effort by the Corps to "regionalize" the 1987 wetland delineation manual.

It may be necessary to hire a qualified wetland professional to assist with identifying and delineating wetlands using the methods listed above. For recommendations to help you locate and select a qualified wetland professional, click here (PDF, 81 kb).

Wetland delineation should result in three things:

A wetland boundary clearly marked in the field.
A map that accurately represents the boundary and location of data collection points.
A report that explains how the boundary was determined. It should include:

A description of how and when the delineation was conducted.

Data sheets used to delineate the wetland area (for the Arid West region also use the new data sheets).

A map (topographic and aerial site maps are very helpful) with data plots and the boundaries of the delineated wetland areas clearly identified.

A soil survey map.

Click here for a checklist of information that should be included in a wetland delineation report as well as a sample outline for a report.

It is important to remember that it is the Corps of Engineers, not applicants or their consultants, that is responsible for determining whether or not a wetland is a water of the U.S. and thus regulated under the federal Clean Water Act (CWA). If the Corps determines that a wetland is not subject to regulation under the CWA, applicants should be aware that these wetlands may still be subject to regulation by Ecology as well as by local jurisdictions and should be delineating using the existing state delineation manual. For more information on Ecology's regulation of wetlands determined by the Corps to be non-jurisdictional due to their isolation from navigable waters, click here.

If you have any questions on implementation of the state delineation manual, email Tom Hruby at the Department of Ecology.

Regional Supplements to the 1987 Wetland Delineation Manual

There has been an ongoing effort by the Corps to "regionalize" the 1987 wetland delineation manual. The Corps has been working with states, federal agencies, and others to develop supplemental regional criteria to refine the 1987 delineation manual.

Two regions fall within the state of Washington: The Arid West (dry lands west of the Continental Divide, from Idaho and eastern Washington south to the U.S. - Mexico border) and the Western Mountains, Valleys, and Coast.

Interim documents have been completed for both regions in Washington and the appropriate Supplement should be used when conducting delineations in those regions. See the third and fourth bullets at the top of the page for more information.

For more information and a link to a map of the regions, go to the Corps web page: Regional Supplements to Corps Delineation Manual.