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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The initial design of the stilling basin was based on a smooth dam face with a 0.65: 1.0 slope. Tailwater <br />conditions beyond the stilling basin were designed to pass flows in the subcritical regime. Tailwater <br />depths were determined to be 2.9 feet which equal an elevation of 5862.9. The spillway face velocity <br />was calculated at 51 fps and a Froude number of 12.9. The design of the stilling basin was based on a <br />Type III Bureau of Reclamation Basin. This would require a length of 23.5 feet. <br /> <br />Model studies of Upper Stillwater, Stagecoach, and Monksville indicated that the steps produce a 70 to <br />90 percent energy reduction in spillway velocities resulting in reduction or elimination spillways. The <br />final design of the stilling basin is based on a velocity reduction of 50 percent due to the tumbling action <br />caused by the steps. The resulting Froude number would be 4.3. Using the criteria for a Type III basin, <br />the required length would be 12.3 feet. Therefore, a 13-foot-long basin was used. The end sill height <br />was determined to be two feet based on Type III basin criteria. <br /> <br />During PMF, overtopping the spillway and dam would produce a downstream tailwater depth of six feet <br />at a velocity of 16 fps. Scour to downstream channel areas could be anticipated during this event. <br /> <br />The crest shape was determined from criteria established by the Bureau of Reclamation. <br /> <br />Outlet Structure <br />Outlet control for the reservoir is controlled by the gate house located on the upstream face of the dam. <br />Two 36-inch gates will be used to control flow out of the reservoir. Normal operation would be for the <br />reservoir gate to be fully open, filling the gate house. The downstream gate would be used to control <br />flow to the desired discharge rate. <br /> <br />During winter operations, the downstream gate would be fully open and control would be by the reservoir <br />gate. This would keep the gate house dry and eliminate problems with ice buildup. <br /> <br />The outlet capacity requirement to pass the top five feet of the dam in 54 days requires a capacity of 27 <br />cfs. The outlet conduit to be installed will be a 30-inch Rep encased in concrete. At maximum reservoir <br />elevation, the capacity of the outlet would be 117 cfs. The excess capacity will allow for a conduit <br />relining project in the future. <br /> <br />An impact stilling basin is designed at the outlet to dissipate the flows of 75 cfs. A riprap channel is used <br />to carry flows downstream to a 4-foot Parshall measuring flume. <br />