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<br />in May was assumed to increase by about IS inches. <br /> <br />d. Methodology <br /> <br />The runoff from snowmelt in two basins were estimated - S par Gulch and Vallejo Gulch. <br />Spar Gulch consists of Sub-basins 14,22,23, and 24 as defined in the CUHP/SWMM <br />analysis, and Vallejo Gulch is Sub-basin 16, In the CUHP/SWMM analysis the runoff <br />from the Sub-basins was routed down to Original Street. To simplify the analysis, the <br />HEC-I model combines the four basins comprising Spar Gulch into one basin and there <br />is no routing analysis. The outflow from Vallejo Gulch is calculated at Durant Street. <br /> <br />HEC-I also can model the infiltration of water into the ground by several different <br /> <br /> <br />methods. This study used a uniform infiltration rate to estimate the amount of in filtration <br /> <br /> <br />from snowmelt. It was assumed that snowmelt would have been occurring previously and <br /> <br /> <br />the ground would already be saturated, Infiltration would then occur at a constant rate, <br /> <br /> <br />and there would also be no initial loss due to depression storage, etc, The model also <br /> <br /> <br />ignored the possible effect of base flow due to previous ground water infiltration <br /> <br /> <br />reentering the runoff further down-gradient <br /> <br />e. Results <br /> <br />Tables 12 and 13 provide the results of snowmelt analysis for Spar Gulch .and Vallejo <br />Gulch, respectively. The peak flow expected from snowmelt for these size watersheds <br />should vary little from year to year and from day to day. The magnitude of the peak <br />snowmeltrunoffis also very small in comparison to rainfall runoff, although it will occur <br />over a much.longer period of time <br /> <br />0, SNOW11EL T ANALYSIS - NATURAL AND MANMADE <br /> <br />1. Introduction <br /> <br />The effect that manrnade snow would have on the peak runoff from the watershed was also <br />estimated. It was assume that an additional IS inches ofmanrnade snow would be applied on the <br />Spar Guich basin and the Vallejo Gulch basin between an elevation ofS,OOO feet and 9,000 feet. <br />All other factors and were identical to those previously discussed for natural snow runoff, <br /> <br />20 <br /> <br />, <br />:'1 <br />