Washington State Department of Transportation (WSDOT) is responsible for over 3,000 highway bridges throughout the state. Maintenance and rehabilitation for this many structures, as well as the design of new ones, means bridge management is a continuous process.
WSDOT has contracted NHC to assist with this continuous process through various means—one example being the analysis for the SR 107 bridge. In 2018, WSDOT determined a replacement was necessary for the timber trestle section of the original bridge, while choosing to leave the concrete section in place. NHC provided a full geomorphic, hydraulic, and scour analysis for both the new bridge section and the original portions that were to remain. As part of this assessment, a geomorphic analysis was conducted along this reach of the Chehalis River that evaluated historic channel migration patterns and rates, meander radii, lateral migration potential, and limits to determine the long term risks at the bridge.
Additional elements of the project included:
- A full watershed assessment
- A channel hydrologic analysis including tidal cycles
- A SRH-2D hydraulic analysis
- A scour analysis for both the new bridge section and the original portions of the structure that were to remain.
Throughout the project, NHC worked collaboratively with WSDOT to successfully develop the final designs for the replaced bridge section and provided recommendations to monitor the erosion risks to the existing bridge piers of the remaining portions as the evolution of the Chehalis River continues.