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<br />SUMMARY <br /> <br />This study was prepared to evaluate in specific detail the <br />hydrologic characteristics of the Dry Creek basin and to <br />utilize new, more detailed contour information to establish <br />water surface elevations and flood plain boundaries. The <br />limits of study extended from the Dry Creek confluence with <br />the poudre River approximately 6.5 miles upstream to a point <br />north of U. S. Highway 287 and east of Terry Lake (Figure 2). <br /> <br />Benefit:cost ratios and net benefits were determined for each of <br />the improvements plans (Tables XII and XIV), a:'1.d other benefits or <br />drawbacks of the plans were discussed. Based on this info~ation, <br />a recommended plan of improvement was selected. <br /> <br />The Storm Water Management Model (SWMM), a hydrologic computer <br />model developed by the U. S. Environmental Protection Agency, <br />was utilized to determine magnitude of the 2-year, la-year, <br />50-year and 50 a-year frequency flood events within the study <br />reach (Table III). <br /> <br />The major components of this improvement plan are a channel to <br />divert lOa-year flood flows to the poudre River from an area <br />just above Willox Lane (Sheet 10) and channel improvements to <br />contain lOa-year residual flows through developed areas at Alta <br />Vista and the Valley Airpark (Sheets 8 and 9). <br /> <br />The cost estimates for these improvements and a plan of <br />implementation are presented in Table XV. <br /> <br />A hydraulic analysis was completed using the HEC-II computer <br />model to determine water surface elevations for the lO-y~ar, <br />50-year, lOa-year and SO a-year events. The water surface <br />profiles are presented on Sheets P-l to P-S. These water <br />surface elevations were used to delineate flood plain boundaries <br />for the lOa-year and SOD-year events shown on figures 2 through 7. <br />A floodway or high hazard area was defined and is also presented <br />on these figures. floodway data and water surface elevations <br />for the lOa-year event are presented in Table VI. <br /> <br />Potential flood damage in the basin was determined by considering <br />depthS of flooding at structures located in the floodplain during <br />the variouS frequency flood events. Prop~rty valuation was <br />provided by the City of Fort Collins and Larimer County. These <br />potential damages are displayed in Figure 6. <br /> <br />Improvement alternatives to allevii'\tf' or mitigate these flood <br />damages were prepared. Cost estimates were prepared using these <br />preliminary designs. These alternatives are described in the <br />section, "Improvement Alternatives". <br /> <br />-48- <br /> <br />-49- <br />