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.).

Littell Bridge

This final link in the western 27 miles of the trail intersects with SR 6. The previous at-grade crossing coincided with a sharp curve in the highway, creating a risk for pedestrians and cyclists. In close coordination with WSPRC, the structural team designed this grade-separated pedestrian crossing using a 250-foot-long, sinuous bridge to provide safe, handicap-accessible passage over the highway. The unique design that satisfied a multitude of the owner's requirements has earned it recognition for engineering excellence.

Dryad Bridge

The Dryad Bridge is a replacement for an original structure that was washed out by flooding. It is a single span, 300-foot-long post-tensioned steel truss bridge with precast concrete deck panels that provides safe crossing over the Chehalis River. By utilizing a long span design that keeps piers out of the river, the structure avoids fast-moving wood debris and trees present during large flood events. Deep drilled shaft foundations were constructed at each end of the bridge.

Spooner Bridge

Along with the Dryad Bridge, the Spooner Bridge is also a replacement for an original structure that was washed out by flooding. It is the exact same bridge type and length as the Dryad bridge with minor variations of the foundations. The post-tensioning allowed control of the deflections for this long span. Both take an award-winning creative engineering approach of providing post-tensioning in a steel truss structure to provide the long span needed.

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Structural Engineering
“The best part of my job is seeing needed infrastructure (especially bridges) get designed, permitted, and built.”

Doug Sarkkinen

Director of Bridges & Structures

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Jennifer Goldsmith



Professional Registrations

Licensed Geologist: WA Project Management Professional (PMP)
Water Resources Engineering
“Otak has always provided me with the opportunity to chart my own course and surround myself with amazing, talented, and interesting people.”

Kevin Timmins

Director of Water & Natural Resources