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<br />Table 1. summary of Discharges <br /> <br />Flooding Source <br />and Location <br /> <br />Drainage Area <br />(Square Miles) <br /> <br />Peak Discharges <br />(Cubic Feet per Second) <br />la-Year 50-Year laO-Year SOO-Year <br /> <br />Cache La Poudre River <br />At Mouth 1,890 3,100 7,100 9,400 17,000 <br />Downstream of Eaton <br />Draw 1,87S 3,SOO 8,000 10,700 19,000 <br />Upstream of Eaton <br />Draw 1,825 2,600 6,000 8,100 14,500 <br />At 25th Avenue 1,810 3,400 7,200 9,600 17,000 <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of streams in the commu- <br />nity were carried out to provide estimates of the elevations of <br />floods of the selected recurrence intervals along each stream <br />studied in the community. <br /> <br />Cross sections for the Cache La poudre River were taken from topo- <br />graphic maps supplied by the u.s. Army Corps of Engineers for a <br />Flood Plain Information report (Reference 4). All bridges were <br />field surveyed to obtain 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 is computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2). <br /> <br />Water-surface profiles were computed by the U.s. Army Corps of <br />Engineers for the IOO-year flood. Profiles for the 10-, 50-, and <br />SOD-year floods were computed by the study contractor with informa- <br />tion provided by the U.S. Army Corps of Engineers. <br /> <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 /> <br />Starting water-surface elevations for the Cache La Poudre River were <br />determined by employing the standard step method. <br /> <br />Roughness coefficients (Manning's "n") were selected by the u.s. <br />Army Corps of Engineers. Roughness values for the Cache La poudre <br />River are 0.040 for the channel and ranged from 0.060 to 0.100 for <br />the overbank ar~as. <br /> <br />5 <br />