Pacific Highway Emergency Culvert Replacement at Wellman Road

Otak, Inc. and Clark County Public Works

Clark County, Washington


Pacific Highway Sinkhole

This project won an American Public Works Association (APWA) Washington State Chapter 2020 Public Works Project of the Year Award in the category of disaster or emergency construction repair.

Heavy snow and rain clogged a Pacific Highway culvert with debris, which impounded water upstream. The roadway base was severely undermined, creating a 20-foot wide by 17-foot deep sinkhole. The reinforced concrete panels of the old highway failed.

The route became impassible, creating a severe problem for Clark County. First, it is an alternate route for truck traffic bypassing the load-limited I-5 Woodland East Fork Bridge. WSDOT had to re-route traffic through Highway 30 to St. Helens, Oregon and Longview, Washington. Second, local residents had to detour 7-10 miles from standard routes. Last but not least, emergency response took longer and services had to be shifted to alternate fire stations for support.

Hart Crowser joined the team to help reopen the highway as soon as possible. We provided the county and the project team with a description of surface and subsurface conditions, developed geotechnical design recommendations and construction guidelines, and evaluated potential earthwork constructability issues. The replacement was designed and constructed within 6 weeks of the initial culvert and roadway failure, shaving months off the of the typical contracting, investigation, and design schedule.

The East Fork Lewis River 2,000 feet away is listed as critical habitat for Chinook, chum, coho, and steelhead. Replacing the crossing with a fish passable structure allowed resident trout as well as anadromous fish access to upstream habitat. The new 13-foot by 8.5-foot-tall steel plate arch culvert is suitable for hydraulic flows and fish passage.

Pacific Highway after repair

Pacific Highway Culvert