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<br />No.7. The SOD-year flood discharges were estimated by linear <br />extrapolation of the flood-frequency curves based on the 10-, <br />50-, and 100-year discharges. A detailed description of the CUHP <br />is qiven in Volume I of the Urban Storm Drainage Criteria Manual <br />(Reference 6). <br /> <br />Peak discharges at selected locations in the study reaches were <br />obtained by routing the flood hydrographs for each subbasin computed <br />by the CUHP. <br /> <br />The U.S. Army Corps of Engineers, Omaha District completed a Flood <br />Plain Information report on Bear Creek and Mount Vernon Creek <br />for the Town of Morrison in 1971 (Reference 7). The 100-year <br />discharge or 27,000 cfs was estimated for Bear Creek at Morrison <br />using a procedure called expected probability. Because discharges <br />determined using this procedure are not accepted by the Federal <br />Emergency Management Agency, no consideration was given to using <br />this value in this study. Present study of the Morrison gage <br />data resulted in a discharge of 13,500 cfs and a 90 percent con- <br />fidence interval between 7,730 and 28,300 cfs for the 100-year <br />flood. <br /> <br />Different methodologies and computed discharges determined in <br />studies prepared by the U.S. Army Corps of Engineers (Reference 7), <br />the U.S. Geological Survey, and the study contractor are presented <br />in Table 1. <br /> <br />Peak discharge-drainage area relationships for Bear Creek, Mount <br />Vernon Creek, and Bear Creek Tributary No. 7 are shown in Table 2. <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 />Water-surrace elevations of floods of the selected recurrence <br />intervals were computed through the use of the U.S. Army Corps <br />of Engineers HEC-2 computer program (Reference 8). <br /> <br />The cross sections used in the hydraulic analysis of the Bear <br />and Mount Vernon Creek study areas were taken primarily from the <br />U.S. Army Corps of Engineers report (Reference 7) after field <br />checking at several locations for channel invert accuracy and <br />addition of new structures. The topography from this report was <br />used to determine the cross sections for the channel area of Bear <br /> <br />11 <br />