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<br />Flood frequency determinations were based on the standard <br />log-Pearson Type III statistical analysis of flood dis- <br />charge records of several streams adjacent to the study <br />area, as well as in eastern Colorado. The discharge <br />records for the streams considered covered periods of <br />from 10 to 74 years. The records and flood frequency <br />determinations were generated at various gaging stations <br />by the U. S. Geological Survey and published as regional <br />100-year flood data (Reference 2). In addition, the <br />analyses were correlated with the Colorado State Univer- <br />sity study on flood magnitudes in the area (References 8 <br />and 9). <br /> <br />In order to assure consistency ipthe hydrology, the <br />recorded data analyzed, as discussed above, were plotted <br />on a graph of 100-year discharge (QIOO) versus drainage <br />area (A). This plot is shown in Figures 6 and 7. The <br />dashed line depicts a characteristic 100-year flood <br />magnitude for any area, based on the U. S. Geological <br />Survey's regional data. This curve was used as a com- <br />parison for synthetically generated hydrograph flows for <br />each stream in the study. Figure 6 provides the dis- <br />charge data for the South Platte River, while Figure 7 <br />gives the discharge data for the tributary streams. <br /> <br />The South Platte River peak discharges for the 100- and <br />SOO-year frequency floods below the dam were computed to <br />reflect the U. S. Army Corps of Engineers' information <br />on the operation of Chatfield Dam. For that reason, the <br />South Platte River does not match the regional data of <br />the U. S. Geological Survey. <br /> <br />Rainfall data for the synthetic analysis were taken from <br />the Denver Regional Council of Governments' Urban Storm <br />Drainage criteria Manual (USDCM) (Reference 10). Syn- <br />thetic hydrograph procedures used in the study included <br />the Colorado Urban Hydrograph Procedure (CUHP), outlined <br />in the Denver Regional Council of Governments' USDCM <br />(Reference 10), and the U. S. Army Corps of Engineers' <br />HEC-l, computer hydrograph package (Reference 11). <br /> <br />Peak-discharge, drainage area curves for the streams <br />studied in detail are shown in Table 1. <br /> <br />. <br /> <br />11 <br />