Shannon & Wilson's Lower Dungeness Project Wins ACEC WA 2024 Engineering Excellence Gold Award
Congratulations to Clallam County and the entire Shannon & Wilson project team for their recognition at the ACEC Washington Engineering Excellence Awards.
Our project, Lower Dungeness River Floodplain Restoration and Levee Realignments, was a Gold medalist and will advance to the National ACEC Engineering Excellence Awards later this year.
The Lower Dungeness River Floodplain Restoration and Levee Realignment is located on the Dungeness River of the Olympic Peninsula in Washington state. The Dungeness River is home to nine salmonoid species, including Chinook, Chum, Steelhead, and Bull Trout, all of which are listed as threatened under the Endangered Species Act. Pacific salmon habitat recovery efforts are underway in Washington state and the Dungeness River has been identified as a key area for meeting salmon recovery goals.
A challenge with floodplain restoration along the Lower Dungeness River corridor is addressing the social-political stress points of community versus environment. A functional floodplain would provide fish with spawning and rearing habitat, an abundance of food, and refuge from predators and floods. However, restoration efforts also need to incorporate protection for existing agricultural farmland, neighborhood communities, and public infrastructure from flooding and inadequate drainage.
The design elements Shannon & Wilson developed created a balance between long-term flood protection, interior drainage, and fish and wildlife habitat interests. The project team removed 4,430 feet of existing levee, 2,950 feet of roadway, and approximately 6,785 tons of contaminated road base from the site. The team installed side and return channels, woody material, and native vegetation to encourage riparian ecosystem development and reconnect 110 acres of floodplain. The team incorporated flood protection, including wood complexes, to discourage immediate river migration, and 6,000 feet of new setback levee to retain up to, and including, the 500-year flood event.
The design improved interior drainage for the existing creek behind the levee with larger fish passable culverts. We developed local, state, and federal partnerships along the way to facilitate project development, permitting, and construction, which resulted in the completion of this highly successful, large-scale, $19M floodplain restoration and levee realignment.
