Department of Transportation crews have begun surveying an old section of Highway 169 north of Black Diamond this week to prepare for a new bridge and culvert removal over the next year.
Crews will work on the bridge and other improvements in chunks, with the goal of keeping traffic in both directions open the entire time. To do that, they’ll start by building a single-lane bypass on a nearby old section of the highway.
Ravensdale creek currently flows under SR 169 through an 82-foot long culvert at milepost 10. But the culvert is narrow, and during spawning season, the water moves too quickly for salmon and other fish to swim upstream.
So crews plan to replace that culvert with a bridge, opening up the creek and surrounding wetlands. They’ll also remove another culvert about 200 feet downstream, leaving an open channel behind, and correct a fish barrier about 350 feet downstream. All told, the work should open 2.4 miles of spawning and rearing habitat for fish, WSDOT said, and give the creatures a more natural stream bed to work with.
Crews plan to build the bridge first and have it finished by summer next year. That will tee them up to actually remove the culverts and bypass road, as well as rebuild the creek bed, in the late summer and early fall, when migratory fish traffic through the area is lower, WSDOT spokesperson Tom Pearce said. The bypass road will “go back to nature,” Pearce said.
The timing of the project is dependent on the weather, Pearce said, but if all goes as planned, the work will be wrapped up in time for the fall 2022 spawning season. The work will also involve the construction of a footbridge over another of the culverts.
Trail users will also be affected by the construction. About a quarter-mile of trails will be closed temporarily in the Black Diamond Natural Area, and about one-tenth of the trails – or 0.5 percent of trail space in the park – will be cut off by the construction and closed permanently.
The $11.4 million project is funded primarily through the Connecting Washington funding package, passed by the state legislature in 2015.
Rough project timeline
The week of Aug. 19, 2021: Contractors for WSDOT begin surveying the old SR 169 roadway to create a temporary bypass for southbound traffic on the highway.
Late August / early September: Crews begin building the bypass. Trail closures begin.
Late September / early October 2021: Southbound traffic is diverted to the completed bypass, likely requiring a brief closure for a few hours, and workers begin building the southbound lane of a new bridge over Ravensdale creek.
Late winter 2022: Southbound portion of the bridge is complete. Northbound traffic shifts onto the completed southbound bridge portion so crews can begin building the northbound section of the bridge. Temporary trail closures end.
Mid-summer 2022: Construction on northbound side of the bridge is complete. Regular traffic resumes, and crews start removing culverts and pulling out the temporary bypass road.
Fall 2022: Culverts removed, project finished.