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• <br />LJ <br />Tunnel construction <br />diversion cap. <br />Outlet operating capacity <br />Stilling basin size <br />Basin design capacity <br />1945 cfs (10-year flood) <br />200 cfs project <br />90X storage volume <br />drawdown in <br />4 months <br />24 cfs minimum stream <br />flow <br />20 to 34 feet wide x 42 <br />feet long <br />390 cfs (190-foot head) <br />CONSTRUCTION OF FACILITIES <br />3.09 The proposed Sandstone Dam would be a zoned,. earthfill <br />structure. A central impervious core would extend to sound rock. <br />The more pervious soil would be placed in the outer shells. An <br />upstream free draining shell would be provided to improve <br />stability during reservoir drawdown. An impervious soil blanket <br />would extend over the left abutment ridge to reduce seepage <br />through the ridge. Internal drainage would be provided by a <br />10-foot-thick chimney drain adjacent to the downstream slope of <br />the core and connected to drainage strips under the downstream <br />shell. <br />3.10 The upstream slope would be protected from wave erosion by <br />riprap. The downstream slope would be either grassed or covered <br />by oversize rock. <br />3.11 Preliminary estimates indicate construction of the <br />embankment would require a total of approximately 6,125,000 cubic <br />yards of fill including 1,430,000 cubic yards of impervious <br />material, 1,190,000 cubic yards of granular material, 3,380,000 <br />cubic yards of random fill, and 125,000 cubic yards of riprap <br />(SWEC, 1986a). <br />3-5 <br />