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<br />The Corps hydrograph has a longer tail \lhich is probably attributed to the <br />fact that the Corps included the upper 'part of the basin in the watershed <br />model. The times to peak Cia not coincide, but this is probably dUll to the <br />differences in the rainfall distributions that were used in the two studies. <br /> <br />r <br /> <br />As a result of these favorable comparisons, the model as presented, is <br />judged to be an acceptable representation of the rainfall-runoff process in <br />the watershed. The model input is summarized below: <br />Rainfall - as per UDFCO Drainage Manual <br />Rainfall Losses - Greel and Ampt infiltration equation with a <br />surface retention loss <br />Unit hydrograph - Buckhorn Creek S-'Jraph <br />Muskingum Routing - mean velocity of 5 to 10 ft/sec. <br /> <br />Fl.JISH FLOOD PREDICTION GRAPH <br /> <br />[ <br /> <br />The final model confiquration was used to generate flood peak discharges <br /> <br /> <br />for various rainfalls. This was performed by running the model with the <br /> <br /> <br />100-year rainfall multiplied by ratios from 50 percent to 200 percent. All <br /> <br /> <br />four assumptions of antecedent soil moisture were used. The results are shown <br /> <br /> <br />in Table 5. The maximum rainfalls for 6-hours, I-hour, and 20-minutes are <br /> <br /> <br />also shown in Table 5. <br /> <br />The results from Table 5 are plotted in Figure 4. Peak dischargf' at the <br />mouth of the canyon can be predicted as a function of the maximum I-hour <br />rainfall, averaged over a 10 square mile portion of the watershed, by using <br />Figure 4. An estimate of the antecedent soil moisture is required. Season of <br />the year can be used if an estimate of the antecedent soil moisture is not <br />available. <br /> <br />HISTORICAL STnRII RECONSTITUTION AND TRANSPOSITION <br /> <br />The historical rainfall derived for this study is based on the reconsti- <br />tution and transposition of three significant storm episodes into the Boulder <br />Creek watershed: the Big Thonpson flash flood of 31 July 1976; the Cheyenne, <br />'yoming flash flood of 1 August 1985; and the Masonville, Colorado flash flood <br /> <br />7 <br />