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<br />Peak discharge-drainage area relationships <br />in detail, Cherry Creek, Sulphur Gulch, <br />shown on Table 1. <br /> <br />for the streams studied <br />and Tallman Gulch, are <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the <br />elevations of floods of the selected recurrence intervals. <br /> <br />For Sulphur and Tallman Gulches, the water-surface profiles for the <br />10-, 50-, 100-, and 500-year floods were developed using the SCS <br />WSP-2 computer program (Reference 15). These profiles and <br />elevations were compared with historic floods and the flood stages <br />then determined. <br /> <br />Water-surface profiles for floods along Cherry Creek were obtained <br />from the 1975 caE Floodplain Information report (Reference 12). <br /> <br />The water-surface profiles for 10-, 50-, 100-, and 500-year floods <br />on Cherry Creek were developed using the CaE HEC-2 step-backwater <br />computer program (Reference 16). The computations were based on <br />channel and floodplain conditions as represented by survey data <br />gathered in April 1975 and as supplemented by later field <br />insvetigations. <br /> <br />Except for portions of Sulphur and Tallman Gulches, cross section <br />data were obtained by field measurements. <br /> <br />All bridges, culverts, and other structures were surveyed to obtain <br />elevation data and structural geometry. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway was computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Insurance Rate Map <br />(FIRM) (Exhibit 2). <br /> <br />Roughness coefficients (Manning's Itnlt were estimated by field <br />investigation and from pictures of the stream and its floodplain <br />using Roughness Characteristics of Natural Channels (Reference 17), <br />aDen-Channel Hvdraulics (Reference 18), and Handbook of ADDlied <br />Hvdraulics (Reference 19). The Itnlt values for Cherry Creek ranged <br />from 0.04 to 0.055 for the channel and from 0.061 to 0.095 for the <br />overbanks. For Sulphur and Tallman Gulches, the Itn" values ranged <br />from 0.03 to 0.05 for the main channels and from 0.03 to 0.12 for <br />the overbanks. <br /> <br />For Cherry Creek. the CaE used critical depth to detrmine the <br />starting water-surface elevation. For Sulphur and Tallman Gulches, <br />the starting water-surface elevation was determined using the <br />stream slope at a starting valley cross section. <br /> <br />8 <br />