PNNL

Abstract

At The Dalles Dam, located between Oregon and Washington on the Columbia River, juvenile salmon passing over the spillway have a survival rate that is below acceptable levels. An important factor affecting survival is the egress route fish take through the immediate tailrace of the dam. Passage through the high-energy spillway and stilling basin environment can leave fish disoriented and vulnerable to predators. Egress conditions can be improved through structural and operational modifications that provide flow paths that move fish more rapidly into the thalweg of the river hence reducing their exposure to predators. We used the results from free-surface computational fluid dynamics (CFD) modeling combined with Lagrangian particle tracking to evaluate the tailrace egress conditions at The Dalles Dam for different alignments of a proposed guidance wall and for different spillway discharge scenarios.