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<br />Chapter II -- Project Description <br />protection on the upstream face; and a key trench tying the structure into the foundation bedrock. A <br />RCC spillway section will be constructed to the right (looking downstream) of the maximum dam <br />section. Based on the final field exploration program, the upstream and downstream slopes will be <br />3H: 1 V and 2.5H: 1 V, respectively. Figure II-2 presents a plan and profile of the dam and Figure II-3 <br />presents typical sections of the dam. <br />The earthfill materials for the dam will be borrowed from the reservoir basin. The selected <br />contractor will import the filter drain materials, riprap, and RCC materials into the site. <br /> <br />B. Hydrologic Evaluation and Spillway Design <br /> <br />Since the dam will be classified as a Class I dam by the SEO, the spillway will be required to <br />convey 100 percent of the probable maximum precipitation (PMP) storm event. In an effort to <br />reduce the spillway size, a Site-Specific PMP Study was performed for the project. The study <br />justified a 28.5 percent reduction in the PMP. The reduced PMP precipitation resulted in an inflow <br />design flood (IDF) of 11,918 cfs. The spillway will consist of a two-cycle labyrinth weir constructed <br />on a RCC section. This will result in a spillway width of 41 feet. The maximum spillway discharge <br />will be 2,266 cfs to elevation 5224.0 feet. The maximum reservoir elevation of 5224 feet will allow <br />for 1.0-foot of residual freeboard as required by the SEO. Figure II-4 shows the RCC Spillway. <br />The RCC spillway section will reduce the land acquisition requirements compared with a <br />spillway located at the right abutment as described in the original study. The final design field <br />exploration program also revealed that the rock in the right abutment was weak, fractured, and <br />erodable which would not withstand the anticipated spillway velocities. An option of lini.ng the <br />chute with riprap or concrete was considered, however this was more costly than the selected RCC <br />spillway section. <br /> <br />C. Outlet Works <br /> <br />The low-level outlet will be used to fill and drain the reservoir. For this reason, a gate tower <br />recommended in the original study is not suitable. SEO criteria requires that the low-level outlet be <br />capable of evacuating the top five feet of the reservoir in five days starting at the normal high water <br />line (spillway crest elevation). A 36-inch epoxy line steel pipe, with all losses considered, meets the <br />SEO reservoir evacuation criteria. <br /> <br />The primary features of the outlet works are the intake structure, outlet conduit, valve <br />chamber, and baffled outlet. The intake structure will be constructed at the upstream toe of the dam <br /> <br />Dry Creek Reservoir Project <br /> <br />6 <br /> <br />SOVLE <br />