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Title: Outlet Works and Stilling Basin Ririe Dam and Reservoir, Willow Creek, Idaho : Hydraulic Model Investigation
Authors: Perkins, Louis Z.
Smith, Peter M.
Keywords: Hydraulic structures
Hydraulic models
Ririe Dam (Idaho)
Publisher: United States. Army. Corps of Engineers. Walla Walla District.
Abstract: Ririe Dam is a 251-ft-high rockfill embankment on Willow Creek near Idaho Falls, Idaho. Flow regulation is provided by an outlet works consisting of an intake tower, two 3.75-ft by 7.0-ft slide valves, an 8.0-ft-wide by 11.25-ft-high conduit, a 20.0-ft-wide by 77.66-ft-long stilling basin, and a riprapped exit channel with bottom as wide as the stilling basin. A portion of the forebay, the hydraulic structures, and 300 ft of exit channel were reproduced in a 1:25-scale model. The model conduit was sloped to produce the computed specific energy gradient for the design discharge of 1900 cfs. The outlet works of original design was satisfactory when the stilling basin and exit channel were enlarged to provide a hydraulic jump for the maximum outlet flow of 3270 cfs. The original plan, as modified, was rejected because the valves were not readily accessible. Tests of the adopted design indicated that maximum unregulated discharges for minimum and maximum pool elevs 5023 and 5119 msl were 1847 and 4250 cfs, respectively. Flow conditions and pressures in the intake and at the valves were satisfactory. Standing waves generated in the curved upstream end of the conduit disappeared before they reached the downstream end. The stilling basin produced a good hydraulic jump for the design discharge of 1900 cfs and an acceptable jump for 4250 cfs. With 1900 cfs and maximum tailwater, the walls of the stilling basin were overtopped about 7 ft. No adverse effects resulted when the left side of the exit channel was steepened to reduce rock excavation and riprap along that side was eliminated. The 75- to 1200-lb rock proposed for riprap was more than adequate for a flow of 1900 cfs and inadequate for 4250 cfs when tested with the revised downstream exit channel. Erosion with two types of stilling basin end walls (curved to banks and 20-ft extensions of side walls) was approximately equal.
Description: Technical Report
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Technical Reports

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