Laserfiche WebLink
Table 1. Summary of Discharges <br />Peak Discharges <br />Flooding Source Drainage Area (Cubic Feet per Second) <br />and Location (Square Miles) 10-Year 50-Year 100-Year 500-Year <br />South Platte River <br />At Fort Lupton 5,010 10,000 22,000 29,000 52,000 <br />3.2 Hydraulic Analyses <br />Analyses of the hydraulic characteristics of streams in the community <br />were carried out to provide estimates of the elevations of floods of <br />the selected recurrence intervals along each stream studied in the <br />community. <br />Water-surface profiles were computed for the 10-, 50-, 100-, and <br />500-year floods using the U.S. Army Corps of Engineers' HEC-2 <br />computer program (Reference 7). The elevations determined from <br />these computations were plotted on the Flood Profiles (Exhibit 1). <br />Cross section data for the South Platte River were obtained from <br />field surveys. All bridges and backwater-producing structures were <br />surveyed by the U.S. Army Corps of Engineers to obtain elevation <br />data and structural geometry. <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 is computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2). <br />Roughness coefficients (Manning's "n") were estimated by field <br />inspection and adjusted where necessary to match the flood elevations <br />computed by the U.S. Army Corps of Engineers (Reference 5). The <br />channel "n" value used for the South Platte River is 0.03, while the <br />overbank values ranged from 0.045 to 0.120. <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1). <br />Starting water-surface elevations for the South Platte River were <br />taken from the U.S. Army Corps of Engineers report on the South <br />Platte River (Reference 5), which used the slope-area method to <br />determine the elevations. <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in the study <br />are shown on the maps. <br />5