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Concrete dam and part of the Bonneville Unit of the Central Utah Project, is located about 80 miles east of Salt Lake City, Utah (fig. 1). Upper Stillwater Reservoir will be used to regulate the flows of Rock Creek and South Fork of Rock Creek for release to the Strawberry Aqueduct. The reservoir water surface will be kept constant during the summer but will be lowered about 160 feet during fall and winter releases. The structural height of the dam is 285 feet. Its crest length is 2,800 feet at elevation 8175.5 feet with parapets to elevation 8180.0. The spillway, whose crest length is 600 feet at elevation 8172.0, must pass the design discharge of 15,000 ft3/s at maximum reservoir elevation 8175.5. The maximum tailwater elevation is 7985.0. The outlet works is controlled by a 14-inch submerged jet-flow gate. The operating head ranges from 42 to 207.5 feet with a maximum discharge of 29 IV/s. The minimum tailwater height above the end sill of the outlet works stilling basin is 3 feet (El. 7975.0). The model studies of the spillway and outlet works were conducted to study the hydraulic efficiency of the stepped spillway and to size the stilling basin for the spillway and the outlet works. The stepped spillway investigation included determining the crest shape, measuring velocities and pressures on the spillway face, and sizing the stilling basin. The outlet works study involved sizing the stilling basin, measuring wave heights and impact pressures, and testing the debris-handling capability of the basin. The spillway model testing was conducted from April 1980 to March 1982, and the outlet works study was conducted from February 1982 to June 1982.