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<br />The risk of experiencing a rare flood increases when periods greater <br />than one year are considered. For example, the risk of having a flood <br />which equals or exceeds the 100-year flood (l-percent chance of annual <br />exceedence) in any 50-year period is approximately 40 percent (4 in <br />10), and, for any 90-year period, the risk increases to approximately <br />60 percerit (6 in 10). The analyses reported herein reflect flooding <br />potentials based on conditions existing in the community at the time of <br />completion of this study. Maps and flood elevations will be amended <br />periodically to reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak <br />discharge-frequency relationships for each flooding source studied <br />by detailed methods affecting the community. <br /> <br />The City of Edgewater is immediately west of Sloans Lake. The area <br />between Sheridan Boulevard and Depew Street has a major drainageway <br />resulting from a 2.07-square-mile tributary drainage basin flowing <br />3.4 miles easterly through it. The total basin area, including the <br />2.07-square-mile area, is 5.48 square miles. There is a stormwater <br />channel from Ingalls Street and 20th Avenue to Depew Street. <br /> <br />Peak discharges of 1,070 cubic feet per second (cfs) for the 25- <br />year flood were originally used to check "as-built" design <br />conditions for the drainageway between Depew Street and Sheridan <br />Boulevard. This flow revealed similarities and differences between <br />pa'st and present conditions in the area (Reference n. The <br />regulatory 'lOO-year discharge was applied to establish floodplain <br />delineations.' Findings indicate the 100-year flood is contained <br />within the improved channel between Depew Street and Sheridan <br />Boulevard. The UD&FCD hydrologic design point is located at the <br />intersection of the West 18th Avenue extension and Sheridan <br />Boulevard, and hydrographs of various frequencies have been <br />generalized at this point. <br /> <br />The improved stormwater channel upstream of Depew Street, storm <br />sewers, and the detention pond at 20th Avenue and Wadsworth Street <br />reduce peak flows through conveyance and detention of stormwater. <br />This is reflected in lower 100-year discharge values than those <br />published in earlier reports (Reference 1). <br /> <br />Peak discharge-drainage area relationships for the Sloans Lake <br />Basin Drainage are shown in Table 1. <br /> <br />5 <br />