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We're not that fishy, or are we? Stabilizing streambeds

Culverts and simulated streambeds

About the project

Culverts are one of the main barriers to fish passage that people can actually do something about. Road crossings become fish passage barriers when the velocity is too high for fish, when there is no natural stream bed in the culvert, or if the inlet to the culvert is too high for the fish to jump into. Adding natural material to culverts to create “simulated streambeds” has a lot of benefits that reduce the formation of fish passage barriers, but there are minimal guidelines for engineers about how to keep the material in the culvert. The most common strategy for low slope channels (<4%) is to add “coarse bands” and the purpose of this project was to help determine how to place bands of coarse material in the stream bed to help the channel keep its shape and retain sediment, while still allowing some natural movement. The 2.5 year long project sponsored by the Washington State Department of Transportation wrapped up in December 2020, but more work in this area is expected in the future.

The team

The coarse band project team next to a simulated streamed with coarse bands installed (they’re the light colored strips of cobbles you can see along the sides of the channel): Prof. Engdahl, Bailee Kelty, Tyler Fouty, and Ben Kuffour (front to back)

A day in the life on the streambed project

This time lapse shows the complete construction, test, and measurement suite for a single trial of one coarse band layout (it may take a while to load on some internet connections)

Building streambeds in the flume

We start with a flat bed, carve the target channel shape, add coarse bands, then slam it with water and try to destroy it. If we do things right, everything stays put!