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were computed using the USGS regional analysis outlined in Water Supply Paper 1680 (Reference 36) for Region B, Area 10. The relationship between flood magnitude and frequency, as portrayed in the composite frequency curve in Water-Supply Paper 1680, was extrapolated to give a ratio of lOa-year flood discharge to mean annual discharge as the basis for the regional curve in Figures 4, 5, 6, and 7. The streams whose hydrology was derived from this regional analysis were the upper reaches of Piney Creek and Coal Creek, Lone Tree Creek, Senac Creek, 1-05-4412 Creek, West Box Elder creek, Box Elder Creek, Kiowa Creek, Wolf Creek, Comanche Creek, Little Comanche Creek, West Bijou Creek, Middle Bijou Creek, and Deer Trail Creek. This curve was used as a comparison for synthetically generated hydrograph flows for each stream in the study. For some streams, the lOa-year flood discharge generated by hydrograph methods is higher than the curve would indicate due to the effects of recent urbanization. The South Platte River peak discharges for the 100- and sOO-year floods below the dam were computed to reflect information on the operation of Chatfield Dam. For that reason, the South Platte River does not match the USGS regional data. Rainfall data for the synthetic hydrologic analyses was taken from the UDFCD Urban Storm Drainage Criteria Manual (Reference 37). Synthetic hydrograph procedures used in the study included the Colorado Urban Hydrograph Procedure (CUHP), outlined in the UDFCD Manual (Reference 37), and the COE HEC-l Flood Hydrograph Package (Reference 38). The sOO-year flood discharges for all detailed-study streams were checked by straight-line extrapolation of frequencies previously determined using the procedure of the USGS (References 27 and 36), and compared to the COE Standard Project Flood data when available. Hydrologic analyses included in the Flood Insurance Studies for the incorporated communities of Aurora, Cherry Hills Village, Littleton, and Sheridan were incorporated into the restudy in their entirety with the exception of streams or portions of streams which were superseded by more up-to-date information (References 2, 3, and 5 through 9). In addition, hydrologic data from various engineering reports (discussed in Section 7.0) were used extensively in the restudy of Arapahoe County. The methods used in these report s include CUHP, MITCAT, and Stormwater Management Model (References 10, 11, 12, 13, 14, IS, and 16). Peak discharge-drainage area relationships for the streams studied by detailed methods within Arapahoe County, except Spring Creek and SJCD 6100, are shown in Table 1 and Figures 4, 5, 6, and 7. 12