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3 II. HYDRAULIC ANALYSIS General The hydraulic analysis focused on establishing the existing flood plain elevations, and developing several alternative designs to reduce the impact of flooding from Fountain Creek on the Red Rock Canyon Shopping Center and the proposed additional retail improvements contemplated by Wester and Company, Inc. For the purpose of this analysis, the peak discharges for Fountain Creek were obtained from the FEMA Flood Insurance Study for Colorado Springs. This hydrologic information corresponds to the data contained in the 1974 U.S. Army Corps of Engineers' report, and the 1975 Fountain Creek Master Planning Study. The design frequencies used in the hydraulic analysis were the 100-year for channel crossings, and the 50-year for channel improvements, because the channel improvements associated with the 100-year frequency are not feasible with respect to existing right-of-way. Peak flow rates associated with the 10-, 50- and 100-year frequencies are 4,150, 13,000 and 19,600 cubic feet per second, respectively. Water surface profile data was developed using the U.S. Army Corps of Engineers HEC-2, Water Surface Profile Program (1984 version). Cross- sectional data was obtained from the Preliminary Flood Insurance Study for tile City of Colorado Springs, and supplemented with aerial topographic mapping contained in the Fountain Creek Master Plan and site inspection. A correlation was obtained between the 10-, 50-, 100- and 500-year water surface profile determined, herein, and the hydraulic analysis contained in the FEMA Flood Insurance Study, for existing flood plain and channel conditions. The computer output is contained in the Appendix. Existing Flood Plain Oescription The reach of flood plain adjacent to the Red Rock Canyon Shopping area can be characterized by deep, high velocity flows within the banks of Fountain Creek, with moderately deep (five to seven feet), flooding on the north over- bank. The overbank flooding is the result of the flow constrictions caused by the 31st Bridge. These constrictions, combined with debris blockage, will cause overtopping of 31st Street, which acts as a control for upstream water surface profile.