Willapa Hills Trail Bridges Lewis County, Washington

Three long-span bridges were needed for Willapa Hills Trail. The first two were replacements for the Dryad and Spooner bridges over the Chehalis River after the existing structures were washed out during an extreme weather event. The third structure, Littell Bridge, eliminates a dangerous at-grade crossing over a very busy State Highway. Together, with an Otak-led environmental assessment and structural design, all three structures provide safer, accessible, and more complete crossings as part of the local trail system in this Washington State Park.

Designing Multiple Structures to Create Safe and Resilient Trail Crossings

During the weather event that compromised the two existing structures, floodwaters swept the truss spans downstream and removed most, if not all, of the approach span structure. The resulting bridge debris removal occurred two years later. The Dryad and Spooner bridge structures are single span 300-foot-long post-tensioned steel trusses with precast concrete deck panels. Adding the Littell bridge near the Adna trailhead provides users a safe overhead crossing over SR 6. Previously trail-goers had to cross the road to continue their journey along the 56-mile Willapa Hills Trail that connects Chehalis in Lewis County with South Bend in Pacific County. In designing the structures for each crossing, this multidisciplinary effort also provided information on baseline river, geomorphic, and riparian habitat conditions and facilitated the permitting processes necessary for the project. This included SEPA documentation and compliance, impacts analysis, and aquatic permitting applications and support documentation (HPA, Lewis County critical areas compliance, etc.).