The Importance of Fish Friendly Culverts

Culvert at Lake Orbin. Kayla Desroches/KMXT
Culvert at Lake Orbin. Kayla Desroches/KMXT

Kayla Desroches/KMXT

Culvert replacement is an ongoing project in Kodiak and it encourages the continued health of the salmon population on the road system.

Alaska Department of Fish and Game habitat biologist Will Frost explains making the salmon passage an easy one starts with the culvert design stage. Installers need to fit the size of the pipe to the natural surroundings.

“Say a stream is 10 feet wide. Well, that culvert’s gonna be at least maybe 15 feet wide. We try to oversize the culvert, and that also helps move the water through during a flood event and keeps the culvert from backing up maybe and flooding the road. But also that culvert’s usually at the gradient of the stream. If the stream gradient’s like 3 percent, the culvert should be about 3 percent.”

The culvert also needs to fit in with the environment in regard to grasses and silt that would naturally show up in a stream bed.

To make the culvert even more fish-friendly, installers cover its bottom with rocks, plant grasses and other vegetation around the structure, and scatter bulky objects like rocks and branches in the water.

Kodiak Soil & Water Conservation District Project Coordinator, Blythe Brown, has organized the installation of many of the culverts and says the natural barriers are vital to a comfortable trip for the salmon and other anadromous fish.

“There was some comment from some of the public in the past about ‘look at all that brush in the creek, look at all those logs that are in the creek, why can’t we clean that out?’ But some of that brush and those logs are actually pretty important for a healthy riparian system. The creeks need the woody material. The fish need the cover that the brush and the logs provide.”

Brown says there are other future replacement projects in the works that will go forward once partners can secure funding.

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