Wetlands during construction

Wetlands need to be protected during construction of both transportation projects and wetland mitigation sites. Wetland considerations during these two types of construction projects are outlined below:

Find additional information about construction compliance on our Environmental commitments and compliance page.

Read Chapter 620: During Construction (620.11 and 620.12) of our  Environmental Manual for an overview of Washington State Department of Transportation (WSDOT) policy regarding protecting wetlands and enforcing contracts during construction.

Read Chapter 630: Closeout of Environmental Commitments of our Environmental Manual for an overview of how to transition out of the construction phase of a project.  

Compliance during construction

Construction of transportation projects may involve work in or around existing wetlands, streams, lakes, or other sensitive environmental areas. Ensuring compliance with permit conditions during construction is critical to avoiding permit violations and negative impacts to these sensitive areas. During project design, WSDOT develops plans and specifications that follow environmental policies and incorporate the specific requirements of a project’s permits. We include these documents in project construction contracts.

One of the first project activities is installation of high visibility fencing to protect wetlands that are not permitted for impacts. Follow Procedure 610-d: Marking Clearing Limits and Protect Sensitive Areas (pdf 100 kb) to make sure all sensitive areas are properly marked with high visibility fence.

Construction inspectors should seek assistance from technical experts as needed to evaluate wetland issues that arise during construction. The environmental coordinator should secure approval from permitting agencies before deviating from mitigation plans and permits. If a deviation occurs before approval is received, work with your regional environmental coordinator to report the deviation to permitting agencies.

Construction inspector training

WSDOT provides environmental training for project inspectors tasked with overseeing compliance on project sites. Contact the Wetland Program Manager for more information. More information about training is also available on our main Wetlands page

Construction of wetland mitigation sites

WSDOT constructs wetland sites as mitigation for unavoidable wetland impact caused by our transportation projects. The following considerations are important during wetland mitigation site construction.

Compacted soils

Compacted soils can decrease the success of wetland mitigation sites by changing surface hydrology and increasing competition pressure on native plants. Use the following measures to minimize soil compaction:

  • Use low ground pressure equipment
  • Restrict access points on the mitigation site
  • Limit paths or roadways within the site
  • Rip or till compacted soils
  • Use mats such as steel or plastic plates or hog fuel to reduce compaction caused by equipment

Mitigation site construction completion

As construction of a mitigation site nears completion, the Project Engineer must request the required mitigation site monitoring. Notify the Wetland Program by submitting the monitoring start-up form (docx 39 kb) by January of the first year monitoring is required. Visit our Wetland monitoring page for more information about initiating wetland monitoring.

Most US Army Corps of Engineers (Corps) 404 permits and Washington State Department of Ecology (Ecology) 401 permits require us to submit evidence of permanent mitigation site protection. WSDOT provides this protection by identifying mitigation sites on our right-of-way (ROW) plans. To learn how to submit updates to the ROW plan, refer to Procedure 490-f: Coordinate the Wetland/Stream Mitigation Right-of-Way Plan Submittal (pdf 150 kb). The submittal due date for ROW plans is identified in the permits.

When construction of the mitigation site is complete, prepare mitigation site as-built plans to comply with Corps 404 permits and Ecology 401 permits. See Procedure 630-c: Coordinate the Wetland/Stream Mitigation As-Built Submittal (pdf 130 kb) for instructions. As-Built plans are the basis for mitigation site monitoring.