DUVALL – Replacing old culverts that block fish passage is common in western Washington, but a project that begins July 26 on State Route 203 just south of Duvall is decidedly uncommon.

This bridge will be the first of its kind on the West Coast. It will replace the culvert that carries Loutsis Creek. Contractor crews working for the Washington State Department of Transportation will use carbon fiber forms to build the concrete structure. The process has been used for a few years in the northeastern United States.

The work will require a month-long closure in both directions of SR 203 just south of Big Rock Road from July 27 to August 26. By using this new method, crews expect to shave several weeks off the work.

“Often building a bridge requires bringing in a large crane to place concrete girders, but these carbon fiber forms are light enough that people can handle them,” said Shawn Wendt, WSDOT’s engineer for the project. “We know this is a long time to close a highway thousands of people depend on each day, but traditional construction would take much longer.”

Building with carbon fiber
The carbon fiber forms are hollow arched tubes with an opening to pump concrete. They also have small holes to allow air to escape. They are relatively light – a 50-foot-long, 1-foot diameter pipe weighs about 200 pounds, light enough to be handled by two or three people. Once the arches are in place, carbon fiber panels are inserted between them and the concrete is poured inside. After it cures, crews will put fill over the top and repave the highway.

Plan ahead for travel on SR 203
People who use SR 203 between Duvall and Carnation need to plan for a detour via Northeast Woodinville-Duvall Road, West Snoqualmie Valley Road Northeast and Northeast 124th Street. This adds about 2 miles to a trip. To allow WSDOT to complete the Loutsis Creek project, King County offered to delay its work on West Snoqualmie Valley Road so that road could remain open as a detour. That King County project now will begin Aug. 27.

Local traffic will be able to travel as far as Northeast 138th Street from the north and Duvall Park from the south. No one will be able to cross through the work zone once construction starts.

Travel information on this and other projects on the @wsdot_traffic Twitter feed, the weekly King County construction update and through WSDOT’s mobile app.

Improving conditions for salmon and other species
The existing Loutsis Creek culvert under SR 203 blocks fish from traveling upstream because the water flow is too swift during spawning season. The new culvert will create a more natural streambed, letting migratory and resident fish travel up and downstream more easily. It will open additional habitat and salmon spawning grounds to support growing fish populations in the Salish Sea.