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<br />Peak discharge-drainage area relationships for the North Fork <br />Republican River are shown in Table 2. <br /> <br />There are two gaging stations maintained by the U.s. Geological <br />Survey on the North Fork Republican River near Wray. The Colorado- <br />Nebraska State line station, located approximately 10 miles east <br />of Wray, was established in March 1931 and has been in continous <br />operation. The station is situated on the right bank, 100 feet <br />east of the Colorado-Nebraska State line and approximately one- <br />half mile north of U.S. Highway 34. Intermittent records are <br />also available for the Wray gaging station, located approximately <br />5 miles east of Wray. This station was established in March 1937 <br />and operated until October 1946. In October 1951, the station <br />was reestablished at a location three-quarters mile downstream <br />of the original location and operated until October 1957. Reestab- <br />lishment of the station was again made for a two-year period from <br />October 1962 to October 1964. Station USe has again been discon- <br />tinued. <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 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 step-backwater <br />computer program (Reference 7). <br /> <br />Cross sections for the backwater analysis of the North Fork Republican <br />River were obtained from 2-foot contour topographic mapping (Refer- <br />ence 8) developed from aerial photographs at a scale of 1:2,400 <br />(Reference 9). <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1) and on the Flood Boundary <br />and Floodway Map (Exhibit 2). <br /> <br />Channel and overbank roughness factors (Manning's "n") were assigned <br />on the basis of field inspection of the flood plain areas. Typical <br />values for channel roughness factors were 0.055 and 0.07 for overbank <br />coefficients. A detailed description of the hydraulic analysis <br />is included in the Technical Addendum of the COE Flood Plain Informa- <br />tion Report (Reference 6). <br /> <br />Starting water-surface elevations for all floods on the North <br />Fork Republican River were calculated using normal-depth analysis. <br /> <br />Obstructions to floodflows within the study reach include natural <br />obstructions, such as brush and other vegetation growing along <br />the stream bank, and manmade obstructions, such as bridges, buildings, <br /> <br />9 <br />