Survival of Coho Salmon Fingerlings Passing Through a Perforated Bulkhead in an Empty Turbine Bay and Through Flow Deflectors (With and Without Dentates) on Spillway at Lower Monumental Dam, Snake River, April - May 1973




Contract No. DACW-68-72-C-0101


Army Corps of Engineers, bulkhead, chinook, coho, deflectors, fingerlings, flow deflectors, injuries, intake, Lower Monumental Dam, Lower Snake River, migration, mortality, perforated plates, salmon, Snake River, spillway, structures, survival, turbines


To reduce high levels of dissolved nitrogen and other gases in the Snake River, the U.S. Army Corps of Engineers has designed and tested the mechanical and hydraulic performance of perforated bulkheads in the intakes of skeleton turbine units and of experimental flow deflectors on spillways at dams in lower Snake River. At Lower Monumental Dam, a flow detector with dentates was installed in spillway bay No. 2 and a plain deflector in spillway bay No. 4. Although these hydraulic structures allow the passage of significant volumes of water through the dam with little, if any, increase in dissolved atmospheric gases, they may cause death or injury to young fish that pass through the structures on their migration to the sea. The National Marine Fisheries Service, under contract to the Corps of Engineers, is evaluating fingerling passage and survival through the bulkhead and flow deflector. Studies in 1972 showed that perforated bulkheads caused high mortality to young fall chinook salmon, but flow deflectors with dentates were less harmful. Similar tests were run in 1973 to compare the effects of flow deflectors (with and without dentates) and to examine the effects of the perforated bulkhead on passage and survival of yearling coho salmon. This report summarizes the results of the latter tests.

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