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<br />the White River did not include any below-water geometry, adjusted <br />discharge values were used in the HEC-2 analysis for this portion of <br />the White River. The adjusted discharge values were determined by <br />reducing the peak di scharge by the flow in the White River at the <br />time of the aerial photography. The flow in the White River at the <br />time of the photography was obtained from records at the USGS gaging <br />station No. 0906300. <br /> <br />The State Highway 64 and South whi te Avenue bridges over the Whi te <br />River and all culverts along College Canyon Draw and Coal Mine Draw <br />were field surveyed to obtain elevation data and structural <br />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 />where a floodway was computed (Section 4.2), selected cross section <br />locations are also shown on the Flood Insurance Rate Map <br />(Exhibit 2). <br /> <br />Channel roughness factors (Manning I s "n" values) for these computa- <br />tions were assigned on the basis of field inspection of the flood- <br />plain areas. The values for Manning's "n" range as follows (Refer- <br />ence 2): Main channel - White River, .04 to .05; clear overbank <br />areas, .04 to .06; obstructed overbank areas, .06 to .1; and main <br />channel overbank areas of Coal Mine Draw, .04; and main channel and <br />overbank areas of College Canyon Draw, .04 to .045. <br /> <br />Flood profiles were drawn showing the computed water-surface eleva- <br />tions for floods of the selected recurrence intervals. <br /> <br />The hydraulic analyses for this study are based on unobstructed <br />flow. The flood elevations shown on the profiles are thus <br />considered valid only if hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum (NGVO) of 1929. Elevation reference marks used in this study <br />are shown on the maps; the descriptions of the marks are presented <br />in Elevation Reference Marks (Exhibit 3). <br /> <br />4.0 FLOODPLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound <br />management programs. Therefore, each Flood Insurance Study <br />floodplain boundary map designed to assist communities in <br />sound floodplain management measures. <br /> <br />floodplain <br />includes a <br />developing <br /> <br />9 <br />