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<br />mately 40 percent (4 in 10), and, for any 90-year period, thp risk in- <br />creases to approximately 60 percent (6 in 10). The analyses reported <br />here reflect flooding potentials based on conditions existing in the <br />community at the time of completion of this study. Maps and flood eleva- <br />tions will be amended periodically to reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for floods of the selected recurrence <br />intervals for each flooding source studied in detail affecting <br />the community. <br /> <br />For Minnesota Creek peak discharges for the 10-, 50-, 100-, and <br />SOO-year floods were determined using a regional flood flow frequency <br />analysis (Reference 3). For the regional study, the U.S. Geological <br />Survey stream gage records for 15 gaging stations in hydrologically <br />similar watersheds were analyzed (References 3, 4, and 5). The <br />length of record at these gaging stations ranges from 9 to 53 <br />years. The station data were separated into rainfall and snowmelt <br />peaks. Frequency analyses were conducted on the rainfall and <br />snowmelt data (Reference 7). The results of the snowmelt and <br />rainfall frequency analyses were combined statistically to give <br />a maximum flow for both events. Regional curves of drainage area <br />versus discharge were computed for the four frequency floods. <br /> <br />For the North Fork Gunnison River the peak discharges for the <br />10-, 50-, 100-, and SOO-year floods were computed by the U.S. <br />Army Corps of Engineers (Reference 6). For the U.S. Army Corps <br />of Engineers determination, a flood flow frequency analysis of <br />gaging station records was the basis for the computation. Included <br />in the computations were the effects of regulation of paonia Reser- <br />voir on flood flows at paonia. <br /> <br />Peak discharge-drainage area relationships for Minnesota Creek <br />and North Fork Gunnison River are shown in Table 1. <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 />For the streams studied, the water surface elevations of floods <br />of the selected recurrence intervals were computed through use <br />of the U.S. Army Corps of Engineers HEC-2 step-backwater computer <br />program (Reference 8). <br /> <br />Cross-sections used in the backwater analyses for Minnesota Creek <br />were developed by aerial photogrammetry (Reference 9). Digitized <br /> <br />8 <br />