This project (known locally as "Twin Cities") is located on the Chehalis River in Lewis County, southwest Washington. It includes the cities of Centralia and Chehalis as well as the Interstate 5 (I-5) corridor. The project is designed to reduce flood risks in urban areas and to reduce the risk of flooding to the I-5 corridor. The Water Resources Development Act (WRDA) 2007 authorized construction of 13 miles of setback levees along the Chehalis and Skookumchuck Rivers, and modification of the Skookumchuck Dam to regulate flow during flood conditions.
After the devastating flood of 2007 in the Chehalis Basin, the State of Washington stepped forward as the non-federal project sponsor and signed a Design Agreement in June 2008. Significant floods occurred again in January 2009 closing I-5 for six days. The project is currently in pre-engineering and design phase. Fiscal Yar 2011 activities included updating the hydraulic information, cost estimates, economics, and re-analysis of required mitigation. These updates included the effects of the 2007 and 2009 floods. Results from this update determined the benefit cost ratio (BCR) for the project to be less than 1. The project as currently designed does not offer 100 year level of protection based on updated hydraulic data from recent floods.