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f' ') ~ 31 DESCRIPTION OF ALTERNATIVES ate a reservoir with a total storage capacity of 109,250 acre-feet (70,700 active and 38.550 inactive). At max- imum capacity elevation, 5.017 feet (1.528 m), the reservoir would produce a body of water approximate- ly 11.7 miles (19 km) long (13,5 river miles) with a maximum width of 0.7 miles (1,13 km) (Figure 2-6). About 1.980 surface acres (801 ha) would be inun- dated when the reservoir was filled to capacity. At the minimum water surface elevation of 4,970 feet (1.514 m). the reservoir surface would inundate approximate- ly 1.128 acres (456 ha) and would extend 6.5 miles (10,5 km) upstream from the dam, Maximum depth of the reservoir from streambed to service spillway crest would be 127 feet (39 m), The area-capacity curves for the reservoir are shown in Figure 2-7. As discussed in Chapter 1. Purpose and Need sec- tion, the applicant has projected that the project would deplete up to 75.000 acre-feet (104 cfs) plus approx- imately 5.500 acre-feet of evaporation. The 75.000 acre-foot figure is slightly higher than the active stor- age of 70.700 acre-feet. This would not present a probiem because the present inflow to the reservoir (1931-1980 record at Watson) is 479,500 acre-feet. Also with the present flows and the proposed run-of- the-river operation. the surface level would remain high. averaging 5.5 feet of drawdown during normal years, Under these conditions. a large percent of the fiows entering the reservoir would be released. Only in periods of extreme drought would the reservoir be drawn down to or near the inactive storage level. Vegetation in the fluctuation zone (47 feet) (14 m)of the reservoir would be removed and burned or buried, as would dead falls below the dead storage level. Outlet Works The outlet works would consist of a 1 O-foot diameter (3 m) penstock (water supply pipe to the power gener- ating turbines). a 36-inch diameter (91.4 cm) bypass pipe, and an intake structure. The penstock and bypass pipe would be encased in reinforced concrete. as shown in Figure 2-8, and would be supported on undisturbed bedrock. The intake for the outlet pipes would consist of a tower and three gated openings located at various levels and an ungated inlet box located at the base of the dam, These outlets are designed to release water at various temperatures, The gates would provide for emergency closure to enable inspection and maintenance of the pipes. The bypass outlet would be used to maintain downstream releases if the power plant were to be shut down. Spillways SERVICE SPILLWAY The service spillway would be a reinforced concrete structure on the left (south) abutment (Figure 2-4) with an uncontrolled overflow crest elevation of 5.017 feet (1.528 m) and a capacity of 9.300 cfs. This capacity would be sufficient to pass a 1 OO-year flood. The ser- vice spillway would discharge into a stilling basin ener- gy dissipator near stream level below the dam. During May and June there would be up to 1.500 cfs offlow in the spillway 4 out of 10 years and no flow in the remaining months. AUXILIARY SPILLWAY An auxiliary spillway located south of the dam abut- ment would be designed to accommodate flows to 86.000 cfs. The crest of the auxiliary spillway would be at an elevation of 5.019 feet (1.529 m) and would have a length of 1.500 feet (457 m). A road would be located across the crest of the spillway as shown in Figure 2-4, The existing natural draw (into which flood flows from the auxiliary spillway would discharge) would be en- larged and graded, This spillway would be used in an extreme flood emergency to provide for the structural safety of the dam. Material Sources Approximately 2.600.000 cubic yards (1.987,960 m') of material would be needed to construct the var- ious zones of the dam embankment. Most of the mate- rial would be obtained from the excavation for the auxiliary spillway, shown in Figure 2-4. The rock excavated for the access road, outlet works. and power house would also be incorporated into the embankment as rockfill and riprap. It is antici- pated that as much as 925.000 cubic yards (707,255 m') of rockfill would be excavated. In addition to the above on-site borrow material areas, two off-site borrow areas have been identified as potential sources for material for the embankment and inner core. The areas are shown in Figure 2-9. Site 1 . located east of Utah State Highway 45. north of Bonanza. has a surface area of approximately 450 acres (182 halo Site 2. on the west side of Utah State Highway 45. adjacent to Site 1, has a surface area of approximately 432 acres (175 halo A total of approx- imately 120,000 cubic yards (91.752 m3) of material could be required from these sites for construction of the dam, Two sources are being considered for sand and gravel required for concrete aggregate: terrace de- posits upstream from the dam and a commercial source near Jensen, Utah. In either case, the material would have to be processed to satisfy concrete aggre- gate requirements. Construction Dam construction would require about 2 years and 15 to 50 workers on schedule. Figure 2-10 shows the 21