Wetland reconnaissance & assessment

Wetland reconnaissance and assessment allow project designers to avoid wetlands, and when that is not practicable, to minimize impacts to the wetlands. Assessments of impacted wetlands are used to design compensatory mitigation and provide information for permit applications. This page contains technical information used by qualified wetland biologists (pdf 40 kb) for completing wetland reconnaissance and assessments on your project site.

  • Wetland reconnaissance identifies potential wetlands and other waters and approximates their locations during early planning and scoping stages of projects.
  • Wetland assessments determine the location and area of wetlands and aquatic resources, their classification, rating, and functions.

Read Chapter 431: Wetlands in the Washington State Department of Transportation (WSDOT) Environmental Manual for the policies regarding wetlands.

Information on this page is organized in order of typical activities:

Wetland reconnaissance (determining presence or absence of wetlands and waters)

The planning and scoping phase generally includes wetland reconnaissance level documentation, leaving more involved wetland delineation and assessment tasks to the environmental review and permitting phase of a project, as documented below.

A Wetland and Stream Inventory memo is the product of the wetland reconnaissance and includes approximated wetland boundary, size, and category as well as estimated locations of other aquatic resources.

If your project is in the planning or scoping phase, determine if wetlands or other waters are present in the project vicinity by following Procedure and Task 300-a: Determining presence or absence of wetlands for planning and scoping (pdf 103 kb).

WSDOT staff may use the WSDOT GIS Workbench to estimate if sensitive resources are present in the project vicinity and aid in background research.

Determining presence of wetlands and other waters is required for an Environmental Classification Summary (ECS) and, in some cases, may also apply to the Environmental Review Summary (ERS). Find more information about completing the ECS and ERS on our Categorical Exclusion process page. 

Wetland assessment

Environmental review and permitting processes require a wetland assessment including a delineation, rating, and classification of each wetland the project might impact. A wetland assessment is also conducted on future mitigation sites to determine the boundary between preservation or enhancement and new wetland establishment.

Review Procedure and Task 431-a: Assessing Waters and Wetlands (NEPA) to learn how to coordinate a wetland assessment and obtain a wetland assessment report.

Refer to the Generic Scope of Work for Delineation (docx 33 kb) for an overview of the scope of work for consultant contracts for wetland and stream delineation and assessment.

For the latest information on the Clean Water Act: Waters of the United States (WOTUS) Rulemaking, visit the U.S. Environmental Protection Agency’s WOTUS rulemaking page.

Delineation methods

Read the Corps of Engineers Wetlands Delineation Manual (pdf 1.44 mb) for delineation guidance outlined by the US Army Corps of Engineers (the Corps).

Use the Major Land Use Resource Areas map (Natural Resources Conservation Service (NRCS) Agriculture Handbook 296) (pdf 626 kb) to determine which Land Resource Region (LRR) your project is located in.

Delineation tools

Below are tools, forms, guidance, and links for collecting vegetation, soil, and hydrology data for wetland delineation.

Wetland determination data forms

WSDOT created automated electronic versions of the Corps Wetland Determination Data Forms for both the Arid West and the Western Mountains, Valleys, and Coast Regions.

  • Disclaimer: These electronic wetland determination data forms were created for WSDOT employees. WSDOT wants to share these useful tools with the understanding that they are not approved or endorsed by the Corps. They are provided “as is”, with no guarantees as to accuracy, appropriateness, completeness, or legal effect for any purpose. Usage is “at your own risk”. For non-WSDOT users, additional support is not provided.
  • System requirements: A full Windows operating system and Excel. (Note: these data forms will not function in mobile versions of Excel which do not support macros.).
  • What is included: There are two Excel template files for each Corps regional supplement: one file name begins with “Field” and the other with “Office”. The “Field” file is designed for field use and is optimized for tablets as small as 7 inches. The “Office” file is designed to produce report-quality electronic forms in the Corps format. The “Office” file can either be used to import data from the field forms or to transcribe data collected on paper datasheets. User notes are provided in the “Office” file.
  • Built-in features of the WSDOT forms include tools for inserting scientific plant names with their associated wetland indicator statuses, automated calculations, and dropdown menus for common responses.


For plants commonly found in Washington, use the Plant Code List (pdf 271 kb) to record field data. This list provides the scientific and common names, origin, and wetland indicator status (WIS) of a subset of commonly encountered plants based on the 2016 National Wetland Plant List (NWPL).

We have developed a corresponding auto-text macro for Microsoft Word that inserts information when plant codes are entered, including scientific name, common name, and WIS. Find installation instructions, plant codes, and the macro file “Autotext_Plants.dotm” on the public FTP server.

People working in the field should be aware of poisonous and harmful plants to avoid. Our online (pdf 7.7 mb) and print-friendly (pdf 7.8 mb) booklet provide information on common plants to avoid (if printing, from print settings select “print on both sides of paper” AND “Flip on short edge”).


Reference the most recent versions of the USDA NRCS publications to describe soils on your project site:


The following tools support the collection and analysis of hydrologic characteristics of your site:

WSDOT installs shallow groundwater monitoring wells in accordance with the following documents available in the Wetlands Regulatory Assistance Program Technical Notes developed by the Corps:

Assessment Guidance for WSDOT Projects

Find information related to unique scenarios sometimes encountered on WSDOT projects below:

  • Road prisms (pdf 71 kb) – This document should be used when projects include wetlands located adjacent to road prisms.
  • Cut slopes (pdf 54 kb) – Follow this guidance when projects involve wetlands on cut slopes.
  • Buffers across roadways (pdf 24 kb) – Refer to this information when wetland buffers are adjacent to or extend across roadways.
  • Isolated wetlands (pdf 41 kb) – Refer to these guidelines to determine if a wetland is isolated.
  • Cultural resources & wetlands (pdf 31 kb) – If archaeological materials or human remains are discovered during wetland delineation or other wetland-related fieldwork, use this document to comply with federal and state cultural resource laws and regulation

Rating forms

Before rating your wetland, use the map of the boundary between Eastern and Western Washington (pdf 59 kb) to determine what geographic area your project is located in. Refer to Washington State Department of Ecology’s (Ecology) most recent version of the Washington State Rating System appropriate for your region.

Use the following WSDOT adapted data forms to rate wetlands in your study area (Microsoft Excel 2010 format for use in Windows 7).

Western Washington forms:

Eastern Washington forms:

Classification methods

WSDOT uses two different classification methods for wetland assessment:

Functions assessment

Conduct a functions assessment on your project’s wetlands to identify the hydrologic, biological, and social functions they provide.

Refer to Wetland Functions Characterization Tool for Linear Projects (pdf 96 kb) to learn how to use the Best Professional Judgement (BPJ) tool.

The Credit/Debit method is a tool used for calculating if a proposed wetland mitigation project adequately replaces the functions and values lost when wetlands are impacted. This method is commonly used on projects using in-lieu fee mitigation. Visit Ecology’s webpage on the Credit/Debit method for guidance documents, Excel worksheets, and training information.

Wetland assessment report

A wetland and stream assessment report supports National Environmental Policy Act (NEPA) documentation, permit applications, and potential mitigation. Reports are valid for five years from the date of the field work.

Follow Procedure and Task 431-a: Assessing Wetlands Waters and Wetlands (NEPA) (pdf 55 kb) and use the template Wetland and Stream Assessment Report (doc 354 kb). This report documents the exact boundaries of all wetlands and wetland buffers. It includes wetland rating, classification, and functional assessment to inform permitting and guide development of wetland mitigation. The report may also include stream locations, identified by ordinary high water mark (OHWM), stream buffers, and other aquatic resources in the study area.

Ditch Assessments

If a project has potential impacts to ditches, the project engineer’s office will request that a biologist perform a field visit to determine if the potential ditch impacts occur to ditches regulated by the Corps. Refer to Procedure and Task 431-c: Assessing Jurisdictional Ditches (pdf 47 kb). WSDOT does not make jurisdictional calls, but can recommend a jurisdictional determination. The Corps is responsible for the final decision. See our Determining jurisdiction of wetlands and other waters page for more information.

Identifying jurisdictional ditches

When completing field assessments of jurisdictional ditches, only sections of ditches with potential impacts need evaluation. Assess ditches by walking ditch lines up gradient from a traditionally navigable waterway (TNW) until there is no evidence of relatively permanent flow as indicated by flowing water, OHWM, scour marks, or the ditch no longer connects to downstream wetlands or TNWs.

The OHWM is determined by defined bed and banks or other physical indicators of flow such as lack of vegetation, scour marks, shelving, wracking, sediment sorting, and water staining. In some circumstances, such as on a steep slope or highly erodible soils, a scour mark may not accurately indicate the presence of an OHWM and the other indicators, listed above, should be considered. Information on breaks in connection should be noted in the submittal package to the Corps.

Lack of scour marks or OHWM suggests that water is infiltrating, evaporating, being taken up by vegetation, or being dispersed. However, the absence of these features does not necessarily mean that flow is insufficient to create a connection with TNWs. 

Use the WSDOT created jurisdictional ditch field data form to document ditch sections that will be impacted. Include a Jurisdictional Ditch Memo in the submittal package to the Corps when jurisdictional ditches will be impacted by your project.

See the following figures for examples of jurisdictional boundaries for common circumstances: