IIHR Gives a Dam About Fish Passage

November 6, 2019

by Margot Dick

They may not know it, but millions of salmon in the Pacific Northwest have safely passed through major hydroelectric dams thanks in part to the problem-solving and modeling expertise of the engineers at IIHR—Hydroscience & Engineering (IIHR).

Gabriele and Troy in front of the Priest Rapids Sign

Villarini and Lyons pose in front of the Priest Rapids Dam sign

IIHR Director Gabriele Villarini recently led a group from IIHR to HydroVision, an annual international gathering of hydro professionals. Villarini and his team took advantage of the opportunity to drive along the Columbia River to see the results of IIHR’s efforts—in particular, several fish passage structures on dams along the river upstream of Portland, Oregon, where the conference was held. Two of the dams they saw include fish passage structures modeled and studied by IIHR, and a third includes improvements by IIHR’s numerical modeling. Lyons says that both the fish bypasses designed and tested at IIHR were in operation during the tours.

“I have known about these projects and seen photos and videos of them,” Villarini says, “but seeing them in person and the operational structures that IIHR helped design through our physical and numerical modeling expertise, as well as the dams themselves, was an amazing experience!”

IIHR’s Jacob Odgaard and former IIHR Director Larry Weber for many years spearheaded IIHR’s fish passage work. Their team, including Troy Lyons and Marcela Politano, has worked on fish passage projects for more than two decades.

“Credit is due to Marcela for her TDG [total dissolved gas] model, as it has been her blood, sweat, and tears that built the incredible computational model,” Weber says. “In addition, Troy’s remarkable experience and expertise have been invaluable to almost every aspect of our fish passage projects.” TDG models show the concentration of total dissolved gas in the water below the dam.

Four Men stand in front of a large dam

IIHR members stand with an Army Corps of Engineers employee in front of one of the dams

Salmon in the Columbia River begin their lives by hatching and swimming downriver to the ocean. Before the creation and implementation of dams along the river, most fish survived the long journey without an issue. Since about 1930, eight dams have been constructed along the river, all with turbines to harness the power of the currents and create electricity that makes up nearly all the renewable energy produced in the northwest. An unforeseen consequence of the dams was the harm that sometimes comes to the juvenile salmon that must pass through them.

“During fish passage season, the dams are required to either pass a certain percentage of the total river flow rate through their spillway or to operate an approved fish bypass,” Lyons says.

Priest Rapids Dam from above

The Priest Rapids Dam fish passageway was in action during IIHR’s tour

Fish passage systems at dams allow young fish to avoid the turbines that can cause injuries, while still allowing the power plants to generate electricity. Each passage is unique to the dam for which it is built. This is where IIHR comes in. IIHR models the dam both numerically and physically to understand flow patterns upstream and downstream of the dams and establish safe, efficient fish pathways. Coupled with field studies that determine how fish are most likely to approach the dam, IIHR’s models have proven to be a valuable tool for increasing downstream survival at the projects.

Grant County Public Utility District (Grant PUD) owns and operates the Wanapum and Priest Rapids dams. Grant PUD hired IIHR to model fish passageways at both dams; the fish passage structures there act as slides for the fish, attracting them away from the potentially dangerous turbines.

Operators at McNary Dam open spillway gates during fish passage season (from around April through the summer) to provide passage through the dam that avoids the turbines. IIHR developed computer models of McNary to calculate the total dissolved gas (TDG) created by the dam’s spillway. Elevated levels of TDG can create air bubbles that get trapped under the scales of fish and lead to injury or death. IIHR researches and models strategies to reduce the amount of air trapped in the water, focusing on flow deflectors that change the direction of the water so it stays near the surface rather than plunging to the river bottom where higher pressures increase TDG levels.

The needs of the environment evolve over time. Newly built dams create more renewable energy, but problems also crop up for the local wildlife. The salmon that use the Columbia River as a spawning ground depend on the fish passage and TDG models developed by IIHR to deliver their young to the ocean.