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<br />Cost estimates prepared by Morrison-Knudsen compare well with ENR Index <br /> <br />updated cost estimates prepared by t:he Gorps of Engine,ers for the Castlewood <br /> <br />Project in the Interim Report on Sand and Toll Gate Creeks, Colorado, January <br /> <br />1972. Although there are differences in details of design bet",een the Corps of <br /> <br />Engineers design and Morrison-'Knudsen design, these detaIls are not significant <br /> <br /> <br />at this init:ial phase of study, <br /> <br />The dam would be a zoned earth-rDckfill :;tructure having ..a length of about <br /> <br />',,050 feet and a maximum height "bove the streambed of about 267 feet. <br /> <br />Embankment internal zones would consist of a central impE!rvious core flanked by <br /> <br />an upstream rock transition zone and 11 filter and drain 2:ones on the downstream <br /> <br />sides. Outer shells would consist of conglomE!rate cap rock excavated from the <br /> <br /> <br />left abutment channel spillway. Outer slopes would be IV on 2H for upstream <br /> <br />slopes and IV on 1.75H for downstream slopes, <br /> <br />The dam would be founded on castle Rock Conglomerate in the: abutment <br /> <br />locations and on Dawson Formation Sandstone irl the valley location. <br /> <br />A double row grout curtain would be constructed beneath the central <br /> <br />impervious core for seepage control beneath the dam, Foundation preparation <br /> <br />would consist of removal of a thin blaxtket of al.luvium and some weathered bedrock <br /> <br />beneath the impervious core and shells. Foundation cleanup would consist of <br /> <br /> <br />slush grouting after exposing the rock surfac,es beneath the embankment, <br /> <br />The outlet works would consist of a 10-foot-diameter concrete conduit, and <br /> <br /> <br />an intake to\'ler with a catwalk providing access from the dam crest to .the intake <br /> <br /> <br />tower. <br /> <br />The spDlway located in the left abutment ,J'Ould consist of a 2,000..foot-wide <br /> <br /> <br />unlined channel which would be cut abotlt 25 to 30 feet deep into the conglomerate <br /> <br /> <br />cap rock.. Flow through the spillw..ay would be discharged into the natural <br /> <br /> <br />drainage approximately 1,500 feet downstream of the: left abutment, <br /> <br />Spillway rating curves were determine:d u:;:lng the HEC-2 program assuming a <br />Mannings n-value of 0.035, <br /> <br />53 <br />