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<br />TABLE 1. SUMMARY OF DISCHARGES (cont'd) <br /> <br />Flooding Source <br />and Location <br /> <br />Drainage Area <br />(Sauare Miles) <br /> <br />Peak Discharges (cfs) <br />10-Year SO-Year lOa-Year SOO-Year <br /> <br />Elk River <br />At downstream end of <br />the study reach <br /> <br />lData Not Available <br /> <br />221 <br /> <br />1 <br /> <br />1 <br /> <br />4,220 <br /> <br />__1 <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the <br />elevations of floods of the selected recurrence intervals. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For streani segments <br />for which a floodway was computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Insurance Rate Map <br />(FIRM) (Exhibit 2). <br /> <br />A total of 81 cross sections were used in the backwater analyses <br />for the Yampa River. Forty-seven cross sections were obtained from <br />field surveys and 13 were synthesized. Eight cross sections, R <br />through Y, were obtained from the U. S. Army Corps of Engineers <br />(COE) Flood Hazard Information Study and 13 cross section were <br />obtained from the Town of Steamboat Springs Flood Insurance Study <br />(References 3 and 4). A total of of 39 cross sections were used in <br />the backwater analyses for the Elk River. Twelve cross sections <br />were obtained from field surveys and 27 were synthesized. The <br />synthesized cross sections were estimated from adjacent surveyed <br />cross sections and topographic maps. Three field-surveyed cross <br />sections defined the structural geometry and elevations for one <br />railroad bridge and one private road bridge along the downstream <br />portion of the Yampa River. The structural geometry and elevations <br />for the two bridges and road sections were also obtained from the <br />field survey along the Elk River. The locations of the cross <br />sections used in the backwater analysis are shown on the flood <br />profiles and maps. The lengths between cross sections R to Y along <br />the downstream portion of the Yampa River are unknown and are only <br />shown to the limits of the flood boundary. Cross sections were <br />located upstream and downstream from bridges in order to compute <br />the backwater effects of the structures. <br /> <br />Parts of the Yampa River floodplain are relatively wide shallow- <br />flow areas or are bisected by the Denver and Rio Grande Western <br />Railroad embankment, U.S. Highway 40, or State Highway 131 <br />culverts, and hence would be ineffective flow areas of relatively <br />shallow ponding during the laO-year flood. The ineffective flow <br />areas were not considered in the hydraulic analysis, but the flood <br />boundaries do reflect the flooding in these areas. There are areas <br /> <br />6 <br />