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<br />Hydrologic information for the streams studied by approximate methods <br />was obtained from various sources. A 1975 UDFeD report ,was used <br />directly for McMurdo Gulch (Reference 15), a procedure developed <br />by the SCS was used for the 6400 Tributaries (Reference 16), Sec- <br />tion 34 Tributary was studied using the TR-20 computer program <br />(Reference 13), and Technical Manual No.1 was used for Mitchell <br />Gulch and Tributary D (Reference 14). <br /> <br />Peak discharge-drainage area relationships for the streams studied <br />by detailed methods are shown in Table 1. <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 eleva- <br />tions of floods of the selected recurrence intervals. <br /> <br />Cross section data were obtained by field measurements. All bridges, <br />culverts, and other structures were surveyed to obtain elevation <br />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 />(Exhibit 2). <br /> <br />Roughness coefficients (Manning's On") were estimated by field <br />investigation and from pictures of the stream and its flood plain <br />using USGS Water-Supply Paper 1849 (Reference 17), Open-Channel <br />Hydraulics (Reference 18), and Handbook of Applied Hydraulics <br />(Reference 19). The "n" values for East Plum Creek, Hangmans Gulch, <br />Sellers Gulch, and Unnamed Tributary to Sellers Gulch ranged from <br />0.03 to 0.06 in the main channels and from 0.04 to 0.12 for the <br />overbanks. The "n" values for Cherry Creek ranged from 0.04 to <br />0.055 for the channel and from 0.061 to 0.095 for the overbanks. <br /> <br />For Cherry Creek, the COE used critical depth to determine the <br />starting water-surface elevation. For every other stream studied <br />by detailed methods, the starting water-surface elevation was <br />determined using the stream slope at a starting valley cross <br />section. <br /> <br />For East Plum Creek, Hangmans Gulch, Sellers Gulch, and Unnamed <br />Tributary to Sellers Gulch, 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 19). These profiles and eleva- <br />tions were compared with historic floods and the flood stages then <br />determined. <br /> <br />11 <br />