North Creek Trail Snohomish County, Washington

Including five boardwalks, a bridge, and 20 retaining walls, North Creek Trail extends 2.5 miles outside Bothell, Washington to traverse sensitive wetlands and a canyon that holds North Creek itself. In leading the project, Otak provided trail and roadway, stormwater, and structural design as well as construction support services for the first phase of construction as the design of phases two and three were completed. That effort included review and responses to RFIs and close coordination with the County project manager and construction inspection staff.

An Urban Trail and Structural Design to Minimize Impact to Sensitive Wetlands

This urban trail segment connects an existing segment near SR 524 with North Creek Park. To minimize environmental impacts and simplify permitting, micropiles support the boardwalks that carry the regional trail over sensitive areas. A 1,383-foot, 14-span prestressed concrete girder bridge crosses the canyon where North Creek runs, including 800 feet of surrounding wetlands. In accommodating ADA grades along the crossing, several portions of the bridge are 30 to 40 feet in the air. Because of the difficulty and sensitivity of constructing a long bridge through the wetlands, a detailed alternative analysis was performed evaluating varying span lengths, foundation types, construction methodologies, access, along with pier and superstructure types. The pedestrian bridge over North Creek would be constructed as part of phase three.