US Army Corps of Engineers
Seattle District

Chehalis Basin Ecosystem Restoration

The Chehalis River Basin covers over 2,600 square miles in southwestern Washington and is the largest river basin in the state. Much of the natural aquatic ecosystem has been degraded over time as a result of development and logging activities mostly occurring between 1920 and 1950. Many fish and wildlife species, including Endangered Species Act list bull trout, have seen sharp decline in population and spawning habitat. This study will identify potential alternatives for restoring wetlands and riparian habitat on a basin-wide scale. The study may be expanded to include flood risk management as a second project purpose after major floods in 2007 and 2009 renewed local interest.

The study is currently in the feasibility phase and the non-federal sponsor is Grays Harbor County, Wash. The current study is focused on ecosystem restoration within the entire Chehalis River Basin. Basin-wide hydraulic modeling to define baseline conditions was initiated in Fiscal Year 2011 and will continue in FY12. As a result of significant flooding in the basin in 2007 and 2009 there has been renewed interest from local governmental agencies in pursuing basin-wide flood risk management solutions as part of this study.