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<br />Flood discharges for the lO-, 50-, 100-, and SOO-year floods on <br />all the streams except Gore Creek were calculated using the regression <br />equations directly. The 10- and 100-year discharges for Gore <br />Creek were taken from a Flood Plain Information report (Reference 4). <br />The SO- and 500-year discharges were extrapolated from frequency- <br />discharge relationships in that report. <br /> <br />Peak discharge-drainage area relationships for each stream studied <br />in detail are shown in Table 1. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of the flooding sources <br />studied in the community were carried out to provide estimates <br />of the elevations of floods of the selected recurrence intervals <br />along each of these flooding sources. <br /> <br />Cross sections for the backwater analyses of all the streams in <br />this study were obtained either by field surveyor from topographic <br />maps at a scale of 1:2400, with contour intervals of 2, lO, and <br />20 feet (Reference 6), obtained from the Town of Vail. <br /> <br />All bridges and culverts were field checked to gather elevation <br />data and structural geometry. In the case of the Spraddle Creek <br />culverts running under Interstate Highway 70, no information could <br />be located showing the actual profile. Therefore, slopes were <br />designed by assuming a 2-foot minimum of cover over the pipes. <br />However, actual analyses showed that even with a large variation <br />of slope, culvert capacity to handle flows varied slightly. It <br />was determined that the culverts could not handle SOO-year floodflows. <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 />Roughness factors (Manning's "nil) used in the hydraulic computations <br />were chosen by engineering judgment and were based on field observations <br />of the streams and flood plain areas. For all the streams in <br />this study, roughness values for the channel ranged from 0.040 <br />to 0.060. The overbank "n" values varied from O.OSO to 0.080. <br /> <br />Water-surface elevations of floods of the selected recurrence <br />intervals were computed through use of the U.S. Army Corps of <br />Engineers HEC-2 step-backwater computer program (Reference 7). <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 />8 <br />