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<br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic char~cteristics of flooding from the <br />sources studied were carried o~t to provide estimates of the eleva- <br />tions of floods of the selected recurrence intervals. <br /> <br />Water-surface elevations of floods of the selected recurrence <br />intervals were computed through use of the COE HEC-2 water-surface <br />profile computer program (Reference 5). <br /> <br />Cross sections for Fountain Cr,ek were compiled from aerial topo- <br />graphic mapping prepared for the COE by VTN, Inc., in 1976 (Refer- <br />ence 6). <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 was computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2). <br /> <br />Channel roughness factors (Manning's On") used in the hydraulic <br />computations were chosen, by engineering judgment, based on field <br />observations of the streams an~ flood plains. A roughness value <br />of 0.030 was used in the chann,l, while overbank values ranged <br />from 0.020 to 0.035. <br /> <br />Starting water-surface elevations were based on water-surface <br />elevations computed for the El'Paso County, COlorado, Flood Insur- <br />ance Study (Reference 1). <br /> <br />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations sh9wn on the profiles are thus considered <br />valid only if hydraulic structures remain unobstructed, operate <br />properly, and do not fail. <br /> <br />Flood elevations for streams studied by approximate methods were <br />determined from drainage-area flood depth relationships (Reference 7) <br />and topographic maps (Referenc~ 8). <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). <br /> <br />4.0 E~OOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local ~overnments to adopt sound flood <br />plain management programs. Therefore, each Flood Insurance Study produces <br />maps designed to assist communities ~n developing flood plain management <br />measures. <br /> <br />8 <br />