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3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for floods of the selected recurrence inter- vals for each stream segment studied in detail in the county. ~ Data used in these analyses include synthetically developed storm runoff records, and information from the U.S. Army Corps of Engineers study of the South Platte River (Reference 10). The discharge profiles used in this study were provided by the u.S. Army Corps of Engineers, Omaha District, on June 17, 1975, and July 18, 1975 (Reference 10). These discharge profiles were keyed to the 100-year flood values computed from the Denver and Henderson gaging records, which were adjusted for the regulating effects of Chatfield, Mt. Carbon, and Cherry Creek Reservoirs. The Den~er gage operated from May to October 1889, from June to October 1890, and from July 1895 to the present. The Henderson gage has been in operation since 1926. Values above and below these gaging stations were based on the u.S. Army Corps of Engineers analysis using their hydrologic computer model for the South Platte River (Reference 10). This study was revised to use the final versions of the discharge pro- files, covering the segment downstream of the Henderson Gaging station (Reference 11). For Little Dry Creek, Big Dry Creek, Hidden Lake, Niver Creek, and Northfield Creek, synthetically developed hydrographs were computed to determine potential flood magnitudes. Rainfall data used in the development of these hydrographs was taken from the Denver Regional Council of Governments' Urban Storm Drainage Criteria Manual (USDCM) (Reference 12). Synthetic hydrograph procedures used in the study include the Colorado Urban Hydrograph Procedure (CUHP), outlined in the USDCM and the U.S. Army Corps of Engineers' HEC-l Computer Hydrograph Package (Reference 13). Discharges were also computed on Big Dry Creek, prior to the start of this study, by the Denver area Urban Drainage and Flood Control District (Reference 4). The discharges computed for this stream varied only slightly from those computed in the previous study. Therefore, the original information was used. For the larger drainage basins east of the Denver metropolitan area, discharge versus drainage area relationships were developed. These determinations were based on the standard log-Pearson Type III statistical analysis (Reference 14) of flood discharge records from several streams adjacent to the study area as well as in eastern Colorado. The discharge records for the streams considered covered periods from 10 to 74 years. The data used in making these deter- minations were recorded at 18 gaging stations by the U.S. Geological ~ 14