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Design of Deflectors for Little Goose Spillway, Snake River, Oregon: A Physical Model Study


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Based on the results of the Dissolved Gas Abatement Studies, spillway deflectors were recommended for the exterior bays of the Little Goose Spillway to reduce total dissolved gas production during spill operations. The design of the deflectors was developed by examining their hydraulic performance in a 1:40-scale section model of the spillway. Four different deflector designs were compared relative to flow conditions in the stilling basin and tailrace area of the section model. The authors recommend the design of the existing deflector, designated Type I, which is 8 feet (ft) long at elevation 532.0 (National Geodetic Vertical Datum) with no transition radius for the exterior bays at Little Goose Spillway. There was essentially no difference in the performance character of the Type I deflector and the Type II deflector (12 ft long without transition radius) over the design discharge range of 7,000-10,000 cubic feet per second per spill bay. Velocities, as high as 17 ft/second, were measured along the tailrace channel bottom. Detailed hydrographic survey data should be taken in the stilling basin and tailrace to assess changes in bathymetry caused by potential scour or ball-mill grinding.



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