Fish passage barriers can be any natural or anthropogenic feature that prevents the movement of salmonids up or down a stream. These barriers include waterfalls, cascades, dikes/levees, ditches, culverts, weirs, flood/tide gates, dams, and other human made structures. These structures can affect fish passage throughout the watershed, and one project that removes a fish passage barrier can open miles of spawning habitat.
Although all of these structures block fish passage, our service area has a largest presence of culverts.
Fish Passage Barrier Projects
Culverts were installed years before the needs of fish were recognized or even understood. They were widely used to pass water under a road way. Improperly installed culverts can be a barrier to fish passage if one or more of the following occur.
- The outlet of the culvert is too high, exceeding the jumping capacity of fish.
- Water velocity through the culvert is too fast, exceeding the swimming ability of fish. This can happen if the culvert is too small for the stream.
- Depth of the water inside the culvert is to shallow for fish to swim through.
- Debris can block access or create turbulence that exceeds the swimming abilities of fish.
Fish friendly culverts are constructed wider than the existing streambed, sloped at a similar gradient to the existing natural stream, and usually consist of a bottomless culvert placed over a natural streambed.
Washington Department of Transportation (WSDOT) fixes barrier culverts using a few approaches. They include fixing culverts as a general highway construction project, where culverts are fixed at the same time as roads. The Environmental Retrofit program (I-4) funds standalone fish barrier removal. It targets high priority culverts that would not otherwise be fixed through road construction. WSDOT works with WDFW to identify, fix, and monitor culverts that fall under I-4. Prioritizing factors include the amount of spawning/rearing habitat gained, quality of the habitat, the number of species that would benefit from the habitat, and the cost of the project.
Other barriers include abandoned structures such as old culverts, bridge structures, and dams. These obstructions may partially restrict fish passage or represent complete blockage to fish migration.
SPSSEG works along side many partners to identify and replace fish passage barriers. One project can open miles of spawning and rearing habitat.
For further information regarding properly/improperly designed culverts, please see: