Idaho Power contracted with IIHR to provide hydraulic modeling and analysis to improve the design of fish passage structures for its hydroelectric dams, including Hells Canyon Dam.

Elevated total dissolved gas (TDG) can be a serious threat to migrating fish downstream of a dam. Deflectors installed at the spillway face transport bubbles to a thin surface layer, minimizing TDG.

Researchers used IIHR’s fully 3-D computational model for total dissolved gas (TDG) to predict the hydrodynamics and TDG distribution within the Hells Canyon tailrace and the river downstream. The study area for the simulation included a seven-mile reach of the Snake River, beginning at the dam and extending downstream to just below to Wild Sheep rapids.

Researchers designed spillway deflectors at Hells Canyon Dam using a 1:48 scale laboratory model and a two-phase flow model capable of predicting TDG production, dilution, and downstream mixing. They validated the numerical model laboratory observations and TDG field data. After a deflector was selected, they estimated possible fish injury due to pressure and acceleration changes near the deflector with a particle tracking technique.

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