Wetland reconnaissance & assessment

This page contains technical information used by qualified wetland biologists (pdf 566 kb) for completing wetland reconnaissance and assessments on Washington State Department of Transportation (WSDOT) projects. Wetland reconnaissance and assessment allow project engineers and designers to avoid and minimize impacts to wetlands and other waters. Staff use assessments of impacted wetlands to design compensatory mitigation and provide information for permit applications. 

  • 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, boundary, and area of wetlands and their classification, rating, and functions. Other waters such as streams and ditches are also documented during wetland assessment.

Read Chapter 431: Wetlands in the WSDOT Environmental Manual for the policies regarding wetlands. See the Determining jurisdiction of wetlands and other waters page for more on law and policy regulating waters of the US and waters of the State.

Information on this page follows the order of typical activities:

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

The planning and scoping phase of a project generally includes wetland-reconnaissance-level documentation. To determine presence of wetlands or other waters in the project vicinity, follow Procedure and Task 300-a: Determining presence or absence of wetlands, streams, and other waters for planning and scoping (pdf 254 kb).

Biologists write a Wetland and Stream Inventory memo after completing the wetland reconnaissance. This memo includes approximated wetland boundary, area, category, and estimated locations of other waters.

Staff may use the WSDOT GIS Workbench to check for presence of sensitive resources in the project vicinity and aid in background research.

Documenting the wetland reconnaissance in the Environmental Review Summary (ERS) informs project costs, and provides an early understanding of wetland and other waters to consider during project design. Find more information about completing the ERS on our Categorical Exclusion process page.

Wetland assessment

Wetland assessment includes a delineation, rating, classification, and functions characterization of each wetland. It also includes evaluation of each stream reach occurring in the project area of potential effect (APE) and any ditch section the project might impact. Future mitigation sites also require an assessment to determine the boundary between existing wetland areas, such as preservation or enhancement, and new wetland establishment areas.

Review Procedure and Task 431-a: Assessing Waters and Wetlands (NEPA) (pdf 271 kb) to learn how to coordinate a wetland assessment and obtain a wetland and stream assessment report.

Biologists delineate and assess wetlands during the environmental review and permitting phase of a project. The Environmental Classification Summary (ECS) requires staff to determine the presence of wetlands and other waters. Find more information about completing the ECS on our Categorical Exclusion process page.

The Generic Scope of Work for Delineation (docx 33 kb) provides an overview for consultant contracts for wetland and stream delineation and assessment.

Delineation methods

Use the Corps of Engineers Wetlands Delineation Manual  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, including WSDOT-specific guidance on assessments around transportation infrastructure. Also find information on documenting streams and ditches.

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 (WMVC) Regions. A full Windows operating system and Excel is required for use (note: macros used in the forms are not supported in mobile versions).

Built-in features of the WSDOT forms include tools for inserting scientific plant names with their associated wetland indicator status (WIS), also referred to as “FAC status”, 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 WIS of a subset of commonly encountered plants based on the 2016 National Wetland Plant List (NWPL).

A corresponding WSDOT auto-text macro for Microsoft Word inserts information when you enter plant codes, including scientific name, common name, and WIS. Find installation instructions, plant codes, and the macro file “Autotext_Plants.dotm” on the WSDOT public FTP server.

Poisonous and harmful plants to avoid

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 provides 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 U.S. Department of Agriculture (USDA) National Resource Conservation Service (NRCS) publications to describe soils on your project site:


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

WSDOT may install shallow groundwater monitoring wells or piezometers.  These tools are primarily installed during mitigation site selection, site design, or on mitigation sites during monitoring to gather groundwater information. These tools are less commonly used for wetland assessment, but may be used to gather additional hydrology information or in problematic situations. Wells and piezometers are installed 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) – Use this document 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 and wetlands (pdf 2.2 mb) – If archeological materials or human remains are discovered during fieldwork, use this document to comply with federal and state cultural resource laws and regulations.

Rating forms

Before rating your wetland, use the boundary between Eastern and Western Washington (pdf 59 kb) map 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 calculates if a proposed wetland mitigation project adequately replaces the functions and values lost when impacting wetlands. This method is commonly used on projects using in-lieu fee mitigation.

Stream assessment

Environmental review and permitting processes require streams be identified within a project’s APE. This includes an ordinary high water mark (OHWM) delineation in non-tidal areas and mean higher high water mark (MHHW) delineation in tidal areas. Stream information gathered from background information and field visits should include:

Biologists document streams in the WSAR.

OHWM and MHHW delineation methods

Read the Corp’s regulatory guidance letter 05-05 for OHWM identification methods in non-tidal areas.

Use MHHW to delineate tidally influenced waters. MHHW is the average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch, a 19-year period of data collection that informs mean values of tidal datums. Find MHHW datums from specific monitoring stations on the NOAA Tides and Currents website and help interpreting the data on their Tidal Datums page

Ditch assessments

If a project proposes potential impacts to ditches, the project engineer’s office (PEO) requests that a qualified wetland biologist identify potentially impacted ditch sections during the wetland assessment field work. The PEO will provide the biologist with plan sheets identifying potentially impacted ditch sections, known flow directions, and relevant infrastructure such as culverts and stormwater features. The biologist will document regulated ditch sections in the WSAR. Review Procedure and Task 431-a: Assessing Waters and Wetlands (NEPA) (pdf 271 kb) for more details. WSDOT does not make jurisdictional calls, but can recommend a jurisdictional determination. The Corps is responsible for the final decision. See our US Army Corps of Engineers jurisdiction over 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 the nearest downstream WOTUS. Background information, such as topographic maps, USGS StreamStats, and aerial photos may be used to help identify where the ditch flows and if it drains to a WOTUS, when physical access is inaccessible or impractical. Use the WSDOT created jurisdictional ditch recommendation field form (doc 132 kb) during field work to document ditch sections with proposed impacts. Document jurisdictional ditches including ditches containing wetlands and tributaries in the WSAR.

Tributaries include:

  • Perennial flowing ditches, flowing directly or indirectly into a WOTUS.
  • Intermittent flowing ditches, draining wetlands, and flowing directly or indirectly into a WOTUS.
  • Ditches, which receive water from upstream features that have bed and bank and OHWM, and which flow directly or indirectly into a WOTUS.

Ditches regulated as wetlands are documented in the wetland section of the WSAR. Ditches regulated as tributaries occur in the stream section of the WSAR. Biologists document ditches exempted form Corps jurisdiction on the field data form. They save it in the project file as internal documentation showing the ditch was evaluated and recommended as a ditch exempt from Corps jurisdiction. Consider if features exempt from Corps jurisdiction are waters of the state and regulated by Ecology or local jurisdictions. Use the chart below to help determine which kind of ditch you have.

Use this flow chart to determine whether your ditch is non-jurisdictional or a tributary.

Wetland and stream assessment report

A Wetland and Stream Assessment Report (WSAR) 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 271 kb) and use the Wetland and Stream Assessment Report (doc 354 kb) template. This report documents the exact boundaries of all wetlands and wetland buffers. It includes wetland rating, classification, and functional assessment to avoid and minimize impacts, inform permitting, and guide development of compensatory wetland mitigation when impacts are unavoidable. The report may also include stream locations identified by OHWM or MHHW, ditched tributaries identified by a tributary center line, stream buffers, and other aquatic resources in the study area.