Anchorage’s Seward Highway expansion helps transport more than just trucks and cars. The construction of two culverts under the roadway also provides flood mitigation and passageways for fish.

The $6-million project twice crosses Little Campbell Creek, which encompasses 24 miles of stream habitat and is home to the Coho salmon and Dolly Varden trout. The project’s clamshell design allowed engineers to replicate the fish spawning and rearing habitat of the native riverbed within the concrete culverts. Each culvert was delivered in two pieces. The team placed the U-shaped bottom of a culvert, reconstructed the streambed inside, then placed the top half. This two-piece design also speeded the often time-consuming inspection process by the Alaska Dept. of Fish and Game.

The area’s spring thaw and rain challenged designers to predict creek water volume, so each culvert was offset from the existing ones, allowing dry construction while lowering risks and cost.