Wetland delineation resources

Federal manual and supplements

Delineations should be done using the current approved federal manual and supplements, as well as all applicable guidance:

• 1987 Corps of Engineers Wetlands Delineation Manual
• Regional Supplements to the 1987 Wetland Delineation Manual — The Corps developed supplemental regional criteria for the 1987 Wetland Delineation Manual. Two regions fall within Washington (see the map of the regions):
  • Arid west (dry lands west of the Continental Divide, from Idaho and Eastern Washington south to the U.S.-Mexico border)
  • Western mountains, valleys, and coast
• User Guide for Automated Wetland Determination data sheets - Excel automated data sheets are available for each regional supplement.  They can be found under "General Information" on the Corps regional supplements webpage.

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, not solely on map location.

Vegetation resources

• National Wetland Plant List (NWPL) — The current list should be used in any wetland delineation or determination. Make sure you are using the most current list and reference it in your documentation. (2020 NWPL for historical reference.)

Soil resources

• Field Indicators of Hydric Soils in the United States (Version 9.0, 2024)
  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 NTCHS field indicators represents a change to the subset of indicators for the regions. Check the NRCS field indicators of hydric soils web page for updates to these indicators.

Hydrology resources

• Guidelines for Conducting and Reporting Hydrologic Assessments of Potential Wetland Sites
• Installing Monitoring Wells/Piezometers in Wetlands
• Technical Standard for Water-Table Monitoring of Potential Wetland Sites
• Water Table Monitoring Project Design
• Accessing and Using Meteorological Data to Evaluate Wetland Hydrology
• Hydrology Tools for Wetland Determination (NRDC, Part 650 Engineering Field Handbook, Chapter 19)

NOTE: You may need to hire a qualified wetland professional to help you identify and delineate wetlands and prepare a delineation report. See our tips on hiring a qualified wetland professional.

Generally, any delineation done more than 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 five years" (page 41, Step 5).

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

Consult with the agencies to discuss your specific wetland delineation.

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.

For a list of what a complete wetlands delineation report should include, see the Components of a Complete Wetland Delineation Report (U.S. Army Corps of Engineers, January 20, 2011).

For a wetlands delineation report sample outline, refer to Wetland Mitigation in Washington State, Part 2, Version 1, Appendix H.

Chapter 5 of the regional delineation supplements addresses the following difficult wetland situations:

• Periods of below-normal rainfall
• Drought years (find drought monitoring resources on our water supply monitoring web page)
• Years with unusually low winter snowpack

Delineations done when these situations are present should be conducted using the methods in Chapter 5. You may be asked to provide supplemental information if a delineation is not conducted using appropriate methods.