Idaho Power contracted with IIHR to provide hydraulic modeling and analysis to improve the design of fish passage structures for its hydroelectric dams, including Brownlee Dam. Since 1983, IIHR researchers have worked to reduce the number of salmon harmed by the harsh environment in the hydroelectric turbines or to the high levels of nitrogen absorbed by the river as water mixes with air after passing through the spillway. IIHR constructed several large-scale physical models of major dams, including the Brownlee Dam, to build and test proposed fish-passage structures before construction. The laboratory models complement IIHR’s advanced CFD capabilities to simulate performance of fish passage facilities.

IIHR researchers experimentally and numerically studied the effect of spillway deflectors on the flow field in the tailrace of Brownlee Dam. They analyzed several flow rates and spillway designs and observed dramatic changes in the flow field with and without the deflectors. The deflectors caused surface jets that attracted most of the powerhouse flow into the spillway region.

IIHR’s fish passage program has led to the construction of better-designed structures and a remarkable decrease in fish mortality.