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3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish peak discharge- frequency relationships for each flooding source studied in detail affecting the community. Methods employed in the COE's frequency analyses (Reference 3) include streamflow records analysis and the synthetic hydrograph method. Peak discharge values were obtained by the COE from a log-Pearson Type III distribution (Reference 4). Frequency analyses for the Animas River were based on streamflow records of rain and snowmelt flood and on data from historic floods. Eleven stream-gage records, having an average length of approximately 30 years, were used; the longest record was 57 years. Frequency analyses for Junction Creek were based on streamflow records and on data developed from similar stream basins in the region. Frequency analyses for Dry gulch Creek were based on the synthetic hydrograph method because historic floodflow and precipitation data were not available. Peak discharge-drainage area relationships for the Animas River, Junction Creek, and Dry Gulch Creek are shown in Table 1. Table 1. Summary of Discharges Flooding Source and Location Drainage Area (square miles) Peak Discharges (cfs) lO-Year 50-Year lOO-Year 50D-Year Animas River At Northern Corporate Limits At Confluence With Junction Creek At Confluence With Lightner Creek 649 Dry Gulch Creek At Mouth 4 9,800 17,500 22,500 38,000 10,000 18,000 23,000 39,000 10,200 18,500 23,500 40,000 1,500 3,000 4,350 7,700 150 650 1,200 3,000 690 760 Junction Creek At Mouth 39 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of streams in the community were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIMR represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data tables in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS in conjunction with the data shown on the FIRM. Cross section data aerial photographs field measurement. elevation data and for streams in the study area were obtained from (Reference 5), the below-water sections were obtain by All bridges and culverts were measured to obtain structural geometry. 7