Lower Granite Dam Snake River Washington PDF Download

Flow conditions during construction and performance of the final-design structures of Lower Granite Dam were studied in a 1:10-scale comprehensive hydraulic model and in a 1:42.47-scale sectional model of the spillway. Principle features of the project included an eight-bay, tainter-gate controlled spillway, a six-unit powerhouse, a navigation lock with a maximum single lift of 105 feet, a fish collection system including a 20-foot-wide fishladder with a floor slope of 1V on 10H, and appurtenant non-overflow sections. The purpose of this study was to check the adequacy of the original design for the project and to develop revisions, if required, to benefit fish passage, energy dissipation, and power generation. Selected discharges tested included 200,000 cfs (5-year frequency and the upper limit for fish movement), 420,000 cfs (the regulated standard project flood), and 850,000 cfs (spillway design flow). Revisions to the first-step diversion and first-step cofferdam provided satisfactory fish passage conditions and a safe design for protecting the work area for flows up to 300,000 cfs. Development of deflectors on the face of the spillway necessitated several revisions to facilitate fish migration. High velocities along the surface downstream from the deflectors produced unsatisfactory fish attraction conditions at the north fishway entrance in spite of revisions developed earlier. Use of rock groins downstream from the north fishway entrance, an extended training wall, and a non-uniform method of spillway operation made fish attraction satisfactory with flows up to 225,000 cfs.