Culverts are structures that, when well designed, pass water, sediment, suspended debris (wood, etc.), and fish under roadways at stream-road intersections.
Some culverts allow water to pass downstream, but are too narrow, too long, too steep, or installed too high above the water surface for a salmon to be able to travel upstream. Culverts that were not designed or installed correctly, or that have been intentionally or unintentionally altered, often prevent upstream and/or downstream fish passage. A single culvert can block fish from utilizing miles of stream habitat. Eliminating fish passage barriers is a very cost-effective approach to increasing habitat for fish. These same fish-blocking culverts often present maintenance, erosion, and flooding concerns because of their inability to transport flood water, sediment and other suspended debris downstream.
In 2003 the City of Bellingham began to systematically assess all culverts on fish-bearing streams inside Bellingham’s city limits. This project helps meet the goals and objectives of the City of Bellingham Comprehensive Stormwater Plan (PDF).
The Salmon Screening, Habitat Enhancement and Restoration Protocol used in the study was designed by the Washington State Department of Fish and Wildlife to identify fish barriers and prioritize remedies. This protocol can be used to assess culverts, dams, and fishways (defined as any in-stream structure installed to facilitate fish passage).
The goal of the project was to assess each culvert’s ability to either block or allow fish passage. The study assessed 85 structures. Of those, forty were classified as fish barriers. The SSHEAR protocol assigns different levels of blockage to each structure. Additional information enabled the city to determine that many of the 40 structures deemed as fish barriers were only partial blockages. Thus far the city has replaced or retrofit over 20 culverts to facilitate fish passage. The data collected in the study will continue to guide the city’s efforts to prioritize replacement and improvement of fish-blocking culverts in the city.