Imaging Smolt Behavior on Extended-Length Traveling Screens, McNary Dam: 1991 Pilot Survey

Abstract : Extensive bypass facilities have been installed at Corps of Engineers dams on the Columbia River system to intercept and bypass out-migrating salmon smolts before they enter the turbines. However, the performance of different screen designs and deployment configurations is incompletely known because the deep water, high turbidity, and rigorous hydraulic environment in the intakes prevent direct observation. Underwater video imaging was used to characterize the behavior of smolts as they approach and are influenced by the bypass screens. The objectives of this pilot study were to design and deploy an underwater video camera system to (a) assess smolt screen contact and impingement rates on extended-length slanted traveling screens (ESTSs) at different screen locations and different turbine loadings and (b) and describe the response of smolts as they approach and are intercepted by ESTSs. Significant differences between contact rates on different parts of the screens were observed. The conclusion was that screen contact and impingement rates are highly dependent on local hydraulic conditions on the screens. In addition, the bottom third of the ESTS exhibits significantly higher impingement than the upper third or middle of the screen. Thus, comparison of screen design or deployment alternatives must be made by looking at impingement and approach behavior for similar areas of the screens and integrating effects across areas to obtain an overall effect for a particular screen design or deployment alternative.