Jensen Provides Precast Culvert for WSDOT Fish Passage Project

Sometimes the same problem calls for two very different solutions.

When two undersized pipes carrying streams connected to Hylebos Creek beneath SR 161 needed to be replaced to improve fish passage, they became part of a larger WSDOT effort to restore access to upstream habitat for salmon, steelhead, and trout.

Jensen Infrastructure supplied precast concrete culvert for two crossings on the project.

While the goal was the same at each location, differences below ground and plans for future use ultimately required two very different designs.

Replacing the existing 24″ pipes meant creating significantly more room beneath SR 161 for reconstructed stream channels while continuing to safely support the highway above.

WSDOT and its Tribal partners generally prefer Type 3 structures supported by footings because the design helps address concerns about stream scour potentially exposing concrete within the center of the channel.

That approach worked for one crossing, but poor soil conditions at the second site created a different challenge. The soil could not provide the bearing capacity required for the Type 3 design, so the structure needed a larger surface area to distribute its load and meet geotechnical and structural requirements.

Also, the second crossing had to account for more than fish.

Plans called for the culvert to accommodate a future extension of the Interurban Trail, so the structure needed to create a dedicated undercrossing where pedestrians, bicyclists, and fish could eventually travel safely beneath SR 161.

Working with Guy F. Atkinson Construction and Pretek Group, Jensen manufactured two precast culvert engineered around the conditions and long-term needs of each site.

For the smaller crossing, a Type 3 design placed the 14-foot-wide culvert on precast footings, leaving the streambed open between them. This configuration provides room for a reconstructed channel while minimizing concrete within the center of the stream.

But poor soils at the second location required a different approach. Jensen manufactured an 82-foot-long Type 2 precast culvert with a 30-foot span. The Type 2 design increased the structure’s surface area, spreading its weight across more of the soil below.

The wider structure solved more than the soil challenge. Its 30-foot span also provides the space necessary for the crossing to serve a second purpose as a future Interurban Trail undercrossing.

Once the structures were installed, crews placed streambed material within them to create more natural, fish-passable channels. And these two culvert are just part of a much larger effort. The overall fish passage project will improve nine crossings, opening access to approximately 7,150 linear feet of fish habitat.

Two nearby crossings ultimately required two very different solutions, each designed around the conditions below ground and the needs above it.