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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The Runoff Curve Number was determined by inspection of the soils <br />and hydrologic condition of the watershed, as well as an analysis of <br />the basin using soils information provided by the S.C.S. The soils in <br />the basin are classified as 20 percent hydrologic group A, 58 percent <br />group B, and 22 percent group C. The hydrologic cover condition was <br />considered to range from fair to good. The Runoff Curve Number (RCN) <br />for the entire basin, assuming antecedent moisture condition II <br />(AMC II), was calculated as 55. For the runoff analysis, the curve <br />number was converted to antecedent moisture condition III, which <br />resulted in an RCN of 74. <br /> <br />The total, 6-hour point precipitation value of 2.BO inches for <br />the 100-year storm event was determined from the NOAA Atlas 2 National <br />Weather Service Isopluvials for Colorado (Reference 4). The 6-hour <br />precipitation was obtained for the annual period. The 6-hour precipi- <br />tat i on was rea rranged accordi ng to the procedures in "Small Dams" <br />(Reference 1). Also, the 6-hour precipitation was extended to <br />18-hours and rearranged according to the procedures in "Small Dams". <br />The runoff hydrographs at the dam site for the 6-hour and 1B-hour <br />100-year general rainstorm and the freeboard hydrograph were computed <br />using the data presented in Tables A-I and A-2 in Appendix A. The <br />100-year 6-hour and 18-hour peak flows were determined to be 542 cfs <br />(volume = 9B acre-feet) and 997 cfs (volume = 197 acre-feet), <br />respectively. The freeboard hydrograph peak flow is 516 cfs (volume = <br />110 acre-feet). <br /> <br />- V-5 - <br />