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Wetland Delineation

Wetland delineations during a drought year

Delineations done during a drought year should be done using the methods in Chapter 5 of the regional delineation supplements (you can download them below), which address the following "Difficult Wetland Situations:"

  • Periods of below-normal rainfall
  • Drought years
  • Years with unusually low winter snowpack.

For delineations done during a drought year, Ecology may request supplemental information if it was not conducted using appropriate methods.

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' of Engineers (Corps) Regulatory Guidance Letter 08-02, Jurisdictional Determinations.

Remember that the 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

Does a wetland delineation expire?

Generally, any delineation done over five years ago needs to be revisited.  This is due to several factors:

  • Wetlands can change significantly in a five-year period, due to changes in hydrology, land uses, and plant species composition.
  • Approved jurisdictional determinations by the Corps expire after five years (see the Corps' Regulatory Guidance Letter 05-02, Expiration of Geographic Jurisdictional Determinations).
  • The Corps' 1987 wetland delineation manual has a requirement for comprehensive determinations to "quantitatively describe the vegetation in the past 5 years" (page 41, Step 5).

Revisiting a wetland delineation that is five or more years old does not necessarily mean that a new wetland delineation needs to be done. It means that it may be necessary to revisit the site to determine whether the delineation is still accurate or whether it needs to be redone based on current conditions. Consult with the agencies to discuss your specific wetland delineation.

How do I delineate wetlands?

According to a 2011 amendment to state rules (WAC 173-22-035), delineations should be done using the current approved federal manual and supplements. > More about the rule amendment       

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

  • National Wetland Plant List (NWPL).  The current NWPL should be used in any wetland delineations or determinations. The Corps plans to update the NWPL annually, so make sure you are using the most current list and reference which list you used in your documentation.
  • Field Indicators of Hydric Soils in the United States (Version 8.1, 2017, PDF; 16.6 MB).  The soil field indicators presented in the Corps' 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, which should include:
  • A description of how and when the delineation was done.
  • Data forms used to delineate the wetland area:
  • The map described in #2 above.
  • A soil survey map.

See Ecology's delineation checklist (PDF) for a detailed list 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.  See Hiring a Qualified Wetland Professional for tips to help you find and select a qualified wetland professional.


If you have any questions about wetland delineation, contact the regional wetland specialist for your area. 


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