PULLMAN, Wash. — Washington State University engineers are seeking ways to aid fish migration in Washington’s mountain streams. But to do that, they need to find ways to improve the interior design and alter the flow in the state’s existing road culverts.
When new construction or development disturbs natural streambeds, replacing them with culverts, fish can’t easily make a return to their natural spawning grounds. The thousands of culverts already alongside Washington roads constrict water flow and produce higher velocities than fish can handle.
Engineer researchers Thanos Papanicolaou, Mike Barber, Ken Campbell and Rollin Hotchkiss are helping the Washington State Department of Transportation simulate natural gravel streambed conditions inside culverts. With a $72,300 grant from WSDOT, they test ways to maintain stable bed conditions in culverts and examine the role of relative roughness to successful fish passage.
WSU’s Albrook Hydraulic Laboratory contains several experimental runs to examine the resistance to the flowing water in beds of varied gravel roughness. One of these is a 75-foot re-circulating flume that can change its slope from 2-15 degrees, create a flow of 40 cubic feet of water per second, and simulate gravel beds with 2-8-inch rocks. Thus, it tests a wide range of slope variation and flow conditions, channel roughness, and depths. It is the only flume of its kind in the U.S.
By October, the team will make preliminary recommendations to the WSDOT about the hydraulics of culvert design allowing fish passages in stable beds on steep rivers, charting variable flow regimes for different slopes, relative roughness and channel profiles.
Phase two of the study, beginning in January, will involve measuring the velocity of the flow on fish — first using mock plastic models of fish, until refined. Then the researchers will build holding pens for live fish testing.
Campbell, a biosystems engineer who also is on the veterinary medicine faculty, has developed a computer model to measure the effects of the turbulence on fish muscle.
WSDOT has documented problems with adult salmon passage in the state’s 7,000 miles of roads. Of 1,585 culverts important to fish passage inventoried between 1992-95, 32 percent were partially or completely impassable to adult salmon. Applying this percentage to the 42,000 miles of county roads and 11,000 miles of city roads, an estimated 19,000 problem-culverts lie along Washington’s paved roads. State and federal forest roads total another 21,000 miles, along which thousands more impassable culverts may exist.
In addition to the plight of adult fish, it is clear that juvenile salmon and trout are also affected. They use off-channel wetlands and ponds for feeding and rearing, for protection during high flows and to move between habitats. Therefore, their need for access to different parts of the watershed during their freshwater rearing period also will be factored into the study.
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