Culverts are structures that, when well
designed, pass water, sediment, suspended debris (wood, etc.), and fish
under roadways at stream-road intersections.
Affects on Salmon
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.
Culvert Projects in Bellingham
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).
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 fish-ways (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.