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<br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />of' <br /> <br /> <br />, Work Plan", da'0ed Sep'0e...be.' 1961. The slo:;?e of this freq,uency <br /> <br />CI" used to cOfol::?ute ratios of desired frequency events to the SPS <br /> <br />ov~ ....le. <br /> <br />Loss rates for the cloudburst storms varied from 0.14 inch per hour <br /> <br />infiltration, with 0.40 inch :;?onding loss for the 10-year storm to <br /> <br />0.11 inch per hour i.r.filtration with 0.35 inch ponding loss for the <br /> <br />500-year storm. Lo8s rates used by the U.S. Bureuu of Reclamation in <br /> <br />their inflow spillway d.esign computations for Rifle Gap Dam are 0.40 inch <br /> <br />initial loss and. O.:~7 inch per hour infiltration. The Soil Conservation <br /> <br />Service used rates that appeared to be about the same or a little higher <br /> <br />than the Bureau's rates for their Indian Wash study (lower area stream " <br /> <br />near Grand Junction). Soils in the Government Creek basin and lower <br /> <br />areas are derived mainly from the mancos shale with some influence <br /> <br />from sandstones of the Mesaverde group. /I.ancos shale is predominantly <br /> <br />a uniform silty clay shale. It weathers on the surface to a friable <br /> <br />semipowdery material that forms a sticky clay when wet. Soils in the <br />valley are clay loam and silty clay. <br /> <br />A unit hydrograph for Rifle Creek above the dam was developed by using <br /> <br />Cla.rks time-area curve procedure. No la.rge rainflood hydrographs are <br />available on Rifle Creek. The tQo cloudburst peak flows mentioned earlier <br />-...- <br /> <br />were estimated from high water marks so no hydrograph da~a is available. <br /> <br />The unit hydrograph thus developed was used with estimated 10-, 50-, <br /> <br />100-, 500-year ahd standard project storms in an effort to arrive at <br /> <br />4 <br />