Kittitas Highway Fish Passage Culvert and Bridge Hydraulic Design

The Kittitas County Department of Public Works plans to widen 4.5 miles of the Kittitas Highway between the City limits of Ellensburg and Kittitas. This stretch of the highway crosses eleven streams or irrigation channels and nearly all of these crossings will be replaced. The County developed preliminary concepts for each crossing and WSE was retained to provide technical assistance on the design of three fish passage culverts and two bridges.

Role / Services: WSE conducted a detailed hydrologic and hydraulic investigation for each site and recommended design refinements to ensure that the proposed crossings adhere to WDFW and WSDOT requirements. At each crossing, WSE estimated design flood discharges, developed and utilized a HEC-RAS model to evaluate hydraulic conditions, assessed channel morphology and stability, and developed recommendations for crossing dimensions and scour/erosion countermeasures.

Outcome: Design refinements have been provided for the three fish passage culverts and investigations for the two bridge sites are on-going.