The Yakima River levee system is bustling with activity these days as the U.S. Army Corps of Engineers works to construct a setback levee measuring nearly 3,900 linear feet on the left bank of the Yakima River near Sportsman State Park.
Construction commenced Monday on the approximately $2.9 million federally-funded project which is expected to be complete by early February.
High flows during a May 2011 flood event damaged approximately 500 feet of the Yakima Authorized Levee at Sportsman Park and reduced flood defense to a 2-year flood protection level. While a plan to repair and restore the damaged levee to its original condition was considered, it was ruled out. Repairing the levee to restore flood protection prior to the spring flood season, would have required in-water work outside of the fish window, potentially harming or harassing Endangered Species Act listed fish. By setting back the levee, flood protection could be restored with only out-of-water construction.
Working closely with Yakima County, the Corps developed the setback design alternative which would minimize environmental impacts and was in-line with the County’s long term, basin-wide realignment plan, according to Brian Nelson, Yakima Authorized Levee Rehabilitation project manager for the Army Corps of Engineers, Seattle District.
The setback segment will start upstream of West Birchfield Road and extend downstream to the Washington State Highway 24 bridge abutment. Riprap armor protection on the setback levee will extend up to the 100-year flood protection level and the levee crown will provide an additional three feet of freeboard height.
The downstream end of the existing levee will be removed to ground level, to include removing 200 linear feet from the center line of the old State Route 24 bridge approach. In order for the setback levee to function correctly within the Yakima River levee system, the remainder of the old bridge embankment will be armored with a four-foot-thick blanket of riprap.
“The project will reconnect 20 acres of floodplain at the setback site, providing an opportunity for high flow events to establish side channels and natural depressions that will increase flood storage, limit hardened banks along the river, improve riparian corridors, and increase habitat function for endangered salmonids,” Nelson said.
Throughout the planning process the Corps coordinated and worked with a number of state and federal agencies, including: Yakima County, U.S. Bureau of Reclamation, Washington State Parks and Reclamation, Washington State Department of Transportation, U.S. Fish and Wildlife, Washington Department of Fish and Wildlife, Washington Department of Ecology, and the National Marine Fisheries Service.
Dredging Today Staff, January 13, 2012; Image: usace