A small culvert beneath U.S. Route 101 near Shelton, Washington was obstructing flow and blocking critical fish species from accessing more than 13 miles of upstream spawning habitat in Coffee Creek. The Washington State Department of Transportation (WSDOT) hired GeoEngineers and partner firms to design and build a new culvert and sustainable stream alignment that would restore fish access while causing minimal disruption to traffic.

Initial plans called for a new bridge and stream passage under U.S. 101 along the existing alignment of Coffee Creek. This approach meant expensive construction and long-term road closures to the busy highway. By stepping back and considering the client’s needs and larger geographic context of the site, GeoEngineers’ project team discovered an alternative concept that would resolve these challenges.

GeoEngineers’ interdisciplinary design-build team collaborated with the client and partner firms closely throughout the process, and eventually recommended rerouting Coffee Creek through more than a mile of carefully designed habitat toward a new confluence with nearby Goldsborough Creek—a tactic that avoided expensive and time-consuming cuts into busy U.S. 101. Instead of as many as three culverts, GeoEngineers’ concept required only one new culvert to carry Coffee Creek beneath the much smaller Shelton Matlock Road.

In addition to developing this alternative concept for the project, GeoEngineers provided a suite of complementary environmental, biological and geotechnical services. The finished project also replaced existing southbound U.S. 101 ramps with a diamond interchange, relocated a park-and-ride facility and installed new stormwater management and treatment systems.


  • Alternative Technical Concept: Instead of following Coffee Creek’s existing alignment, GeoEngineers recommended rerouting Coffee Creek north through 3,000 feet of new stream habitat, using existing WSDOT right-of-way on the west side of U.S. 101. This new alignment would take Coffee Creek under Shelton Matlock Road via a new culvert to merge with Goldsborough Creek farther to the west, where it could then cross U.S. 101 beneath a large, previously existing bridge. Instead of requiring as many as three new culverts, this creative approach needed only one culvert to be constructed beneath the smaller and less-trafficked Shelton Matlock Road.
  • Hydraulic/Hydrologic Modeling and Geomorphic Assessments: Flow redirection was the most challenging technical aspect of the project. Finding a channel design that was environmentally sustainable and fit within the congested project area was difficult. Because Goldsborough Creek supports fish species, there were concerns about diverting too much flow into the new channel. GeoEngineers performed a hydrologic flow comparison of Goldsborough and Coffee Creeks to analyze potential effects of additional flows in Goldsborough creek.
  • Environmental Impacts and Permitting: WSDOT typically handles permitting in-house but leaned on our experienced natural resources staff for this project. They secured necessary NEPA permits in coordination with WSDOT officials and Parsons, our client. GeoEngineers created a detailed Interim Environmental Compliance Plan and took additional steps to reduce environmental impacts during geotechnical investigation, for instance by drilling outside of sensitive wetland areas. Because GeoEngineers’ alternative technical concept expanded the project area, the team also performed a supplemental wetland assessment to study habitat along the new stream alignment.
  • Geotechnical Evaluation and Recommendations: In addition to environmental and biological services, GeoEngineers’ interdisciplinary team led geotechnical work for the stream redesign and new culvert. Services included geotechnical drilling investigations to characterize soil and groundwater conditions, recommendations for reuse of excavated material, specifications for temporary and permanent cut/fill slopes, embankment settlement, foundation design, seismic hazards, excavation dewatering and a geotechnical instrumentation plan to monitor settlement and groundwater levels during construction.
  • Stream Design: GeoEngineers assisted with design for the new mile of channel connecting Coffee Creek with Goldsborough Creek by identifying fish passage and habitat requirements like channel gradient, grade control, alignment, substrate supplementation and bridge/culvert size and alignment. The team also recommended including large woody material (logs, root wads, etc.) bioengineered bank stabilization, native vegetation and pools and riffles in the channel to create additional fish habitat.


GeoEngineers avoided complications and saved WSDOT more than $3 million by recommending an alternative technical concept that rerouted Coffee Creek through more than a mile of new stream alignment and restored fish access to upstream spawning and rearing habitat.

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