SR 520 Bridge Replacement and HOV Program - Grass Creek mitigation

Vicinity map of the Grass Creek mitigation site

Through the environmental review process, WSDOT works to avoid, minimize and mitigate for the environmental effects of our construction projects. Construction of the pontoon casting basin and launch channel in Aberdeen resulted in the loss of approximately one acre of wetlands, as well as impacts to shorelines and fish habitat. To mitigate this, WSDOT provided improvements in the Grass Creek watershed in Grays Harbor County.


Project overview

WSDOT awarded a contract to Rognlin's Inc. of Aberdeen to remove portions of an earthen dike on the 68-acre Grass Creek site. Work started in summer 2011, reconnecting tidal channels and restoring the natural tidal influence to the site. The work at Grass Creek restores and protects a variety of wetlands and shoreline habitats to mitigate for the environmental effects of the Pontoon Construction Project.


Ecological benefits of the mitigation project

The Grass Creek mitigation site supports a variety of plants and wildlife that thrive in wetlands, salt marshes and mudflats. Native fish include staghorn sculpin, bull trout, longfin smelt and shiner perch. Wildfowl include great blue heron, mallard, song sparrow and bald eagle.

The restored tidal channels provide habitat for migrating salmon. Native plants and organic soils will improve water quality and benefit the on-land and in-water environments.

This mitigation directly and indirectly benefits the environmental health of the larger Grays Harbor watershed area. The Grass Creek site's restored wetlands, saltwater marshes, tidal channels and mudflats are a good ecological complement to the harbor wetlands lost by the construction of the pontoon casting basin in Aberdeen. We selected the Grass Creek site because its location and characteristics provided the highest likelihood of successful wetland and estuary restoration.


Project timeline

Work started in summer 2011 and was substantially complete in late 2013. WSDOT will maintain and monitor the site until 2022. With 23 acres of Grass Creek lands restored as mitigation for the Pontoon Construction Project, the site provides approximately another 45 acres that potentially could be used for future WSDOT mitigation projects.