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4-32 <br />• latitude in deriving the required parameters and, therefore, <br />results are less likely to reflect individual bias than when <br />using other methods usch as the U.S. Soil Conservation <br />Service Unit Hydrograph Method. Also, the regression method <br />provides<-in estimate of the range of error which can be <br />expected while other methods do not. The SCS method was <br />used in the West-Central Colorado Coal EIS to predict flood <br />peaks for East Salt Creek near Mack, the only site for which <br />floods were estimated in these studies. A 10-year flood <br />of 5,999 cfs and a 100-year flood of 13,700 cfs were predicted <br />by the Bureau of Land Management compared with 2,222 cfs for <br />a 10-year recurrence interval and 3,850 cfs for a 100-year <br />recurrence interval projected in this report. In our <br />• judgement, the lower discharges reflect more reliable values <br />because they are based on local flood-flow characteristics. <br />4.5.3.2.4 Flood °lows and Watershed Size <br />Peak discharges per unit are have been calculated for several <br />watersheds in East Salt Creek Basin. They are plotted for <br />various recurrence intervals in Fire 4.5-5. <br />Estimated discharges range f~m 11 cfs/sq. mi. (CSM), 10-year <br />and 26.5 CSM, 500-year floods for the 197 square miles of East <br />Salt Creek Drainage Basin to 105 CSM, 10-year and 230 CSM, <br />500-year floods on a 96 acre catchment. As expected, the <br />smaller basin deliver more runoff per unit aiea than do larger <br />. basins. <br />The graph can be used to estimate peak flows from any area <br />