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Wetland Mitigation

Weeping Willow at SR 16 Wetland Site
Wetland Mitigation is the process used by WSDOT to compensate for adverse effects transportation projects may have on wetlands, streams, lakes, and other aquatic resources. The mitigation process follows a specific sequence of actions required to comply with state and federal regulations and WSDOT's policy for protecting wetlands (pdf 58 KB). 

The required sequence of mitigation is:

  • avoid impacts,
  • minimize impacts,
  • rectify impacts,
  • reduce the impact over time,
  • compensate for impacts, and
  • monitor the impact.

This means that if after avoiding and minimizing impacts by alignment and design, the project still has adverse effects on wetland resources, then WSDOT is required to monitor the construction project to be sure the impacts were as permitted, and provide compensatory mitigation to offset those impacts.

Project teams should start evaluating available compensatory mitigation options during the Planning phase, continue in the Scoping phase, and should make a firm decision in the Environmental Review phase.  WSDOT’s approach to mitigation will vary depending on local circumstances, but in general, seeks to produce the greatest environmental benefits for their investment and efforts.  Compensatory mitigation may involve restoration, establishment, enhancement, or preservation (pdf 26 kb) of aquatic resources.