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Table 1. Summary of Discharges Flooding Source and Location Drainage Area (Square Miles) Peak Discharges (Cubic Feet per Second) 10-Year 50-Year 100-Year 500-Year River 1,890 3,100 7,100 9,400 17,000 6,000* * N/A 3,500 : 6,800 8,500 1,875 3,500 8,000 10,700 19,000 1,825 .2,600 6,000 8,100 14,500 1,810 3,400 7,200 9,600 17,000 *Flow loss due to overflow 3.2 Hydraulic Analyses REVISED DATA Analyses of the hydraulic characteristics of streams in the commu- nity were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each stream studied in the community. Cross sections for the Cache La Poudre River were taken from topo- graphic maps supplied by the U.S. Army Corps of Engineers for a Flood Plain Information report (Reference 4). All bridges were field surveyed to obtain elevation data and structural geometry. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (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 Floo~way Map (Exhibit 2). water-surface profiles were computed by the U.S. Army Corps of Engineers for the lOa-year flood. Profiles for the 10-, 50-, and 500-year floods were computed by the study contractor with informa- tion provided by the U.S. Army Corps of Engineers. 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 for the Cache La Poudre River were determined by employing the standard step method. Roughness coefficients (Manning's "n") were selected by the U.S. Army Corps of Engineers. Roughness values for the Cache La Poudre River are 0.040 for the channel and ranged from 0.060 to..o .100 for the overbank ardas. 5 REVISED TO REFLECT LOMR DATED NOV 2 3 1994