Chehalis River Basin Flood Hazard Mitigation Alternatives Analysis

WSE was selected as part of the Anchor QEA study team to evaluate a broad range of options for flood hazard reduction in the Chehalis River basin.

Role / Services: WSE had primary responsibility for all hydrologic and hydraulic related tasks in the current project. Specific work completed by WSE includes: 1) peer review of USGS Hydrologic data for the basin, 2) new statistical analysis and development of updated hydrology for the watershed, 3) refinement of a basin wide HEC-RAS hydraulic model of the entire Chehalis River and key tributaries, 4) development of a structure survey database to facilitate flood damage assessments, 5) mapping and analysis of flooding throughout the watershed to support economic evaluation of floods, 6) evaluation of a suite of small scale flood damage reduction projects, and 7) hydraulic design of a range of options to protect Interstate 5 and other critical transportation routes from flooding. In all, over 500 scenarios were modeled using HEC-RAS and relevant data on flooding was summarized and reported. WSE's work on this project was completed within a 2 year timeframe and the work involved significant participation by every member of WSE's staff.

Outcome: WSE provided support to other members of the consultant team and to the State Work Group that is responsible for identifying options for flood relief in the Chehalis Basin. WSE has presented technical information at more than a dozen public and policy workshops and responded to numerous requests for hydrologic and hydraulic data related to flooding or aquatic resources in the basin. WSE consistently delivered quality work products in a timely manner facilitating stakeholder involvement and a better understanding of flood issues in the basin. WSE developed a reputation for excellence in presenting technical data to the public, which allowed the State team to keep stakeholders well informed.