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Peak discharge-drainage area relationships for the South Platte River are shown in Table 1. Table 1. Summary of Discharges Drainage Area (Square 11iles) Peak Discharges (Cubic Feet per Second) la-Year 50-Year 100-Year 500-Year Flooding Source and Location South Platte River 37th Avenue U.S. Highway 85 7,500 7,500 11,000 11,000 24,000 24,500 32,500 32,500 57,000 57,500 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of streams in the community were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each stream studied in the community. Cross section data for the South Platte River in Evans were obtained by field survey and from previous field surveys done by the U.S. Army Corps of Engineers (Reference 5). Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Pro- files (Exhibit 1). For stream segments for which a floodway is computed (Section 4.2), selected cross section locations are also shown on the Flood Boundary and Floodway Map (Exhibit 2) . All bridges were surveyed by the u.S. Army Corps of Engineers to obtain elevation data and structural geometry. Roughness coefficients (Manning's "n") were estimated by field inspection. The values used ranged from 0.035 to 0.044 for the channel and from 0.035 to 0.100 for the overbank areas. The water-surface profiles for the 10-, 50-, 100-, and SOD-year floods were computed using the U. S. Army Corps of Engineers HEC-2 computer program (Reference 7). Flood profiles were drawn showing computed water-surface elevations to an accuracy of 0.5 foot for floods of the selected recurrence intervals (Exhibit 1). Starting water-surface elevations were taken from the u.s. Army Corps of Engineers study (Reference 5). All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD). Elevation reference marks used in the study are shown on the maps. 8