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<br />exceeds the 100-year flood (I Percent chance of annual exceedence) in <br />any 50-year period is approximately 40 percent (4 in 10), and, for any <br />90-year period, the risk increases to approximately 60 percent (6 in <br />10). The analyses reported herein reflect flooding potentials based on <br />conditions existing in the comm4nity at the time of completion of this <br />study. Maps and flood elevations will be amended periodically to <br />reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were qarried out to establish the peak <br />discharge-frequency relat~onships for each flooding source studied <br />by detailed methods affec~ing the community. <br /> <br />No stream gaging stations !were available for analysis. To develop <br />a rainfall-runoff relationship, the U.S. Soil Conservation Service <br />(SCS) TR-20 computer progtam was used (Reference 8). To account <br />for the differences in the Arkansas River Basin, represented by <br />Fountain Creek, and the South Platte River Basin, represented by <br />Trout Creek, two different rainfall distributions were used. The <br />more intense Type IIA sto~m was used on Fountain Creek, whereas <br />the Type II storm was use4 on Trout Creek. The basins were <br />developed into hydrologic~lly homogenous areas for which required <br />parameters were estimated !using available information, including <br />field observations. Both!the 6-hour and 24-hour storms were used. <br />The 24-hour storm was sel~cted, as it resulted in higher <br />discharges. <br /> <br />The results on Fountain Creek were compared to those in the <br />previous COE study (Reference 1), as shown in Table 1. <br /> <br />The comparison at the 50-iand 100-year flood values is acceptable <br />and has resulted in accep~ance of all of the COE figures for use <br />in this study. <br /> <br />The 100-year flood dischatge at State Highway 67, computed using <br />the SCS TR-20 computer prdgram, was 810 cfs, compared with a 100- <br />year flood discharge of 841 cfs developed using the graphical SCS <br />methods (Reference 4). Tqe 100-year floodflow at the upstream <br />limit of study for Paint ~ony was taken as 120 cfs, compared with <br />113 cfs from an earlier dqainage report (Reference 7). The <br />hydrologic analyses have heen reported in more detail in a <br />separate document (Refereqce 10). <br /> <br />Peak discharge-drainage area relationships for the streams studied <br />by detailed methods are shown in Table 2. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic :characteristics of flooding from the <br />sources studied were carr~ed out to provide estimates of the <br />elevations of floods of tqe selected recurrence intervals. <br /> <br />8 <br />