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and SOa-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood which equals or exceeds the 100-year flood (1 percent chance of annual exceedence) in any 50-year period is approximately 40 percent (4 in 10), and, for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge-frequency relationships for each flooding source studied in detail affecting the community. Peak discharges for floods of the 10-, 50-, 100-, and SOO-year recurrence intervals for the Mancos River were based on a flow- frequency analysis prepared by the COE (Reference 3). In this analysis, the flood peak estimates were determined from a regional analysis of peak-flow data from stream-gaging stations in the area. Peak discharges for floods of the 10-, 50-, 100-, and SOO-year recurrence intervals for Chicken Creek were computed using region- alized basin parameters determined by the COE for the Mancos River. COmparative hydrologic calculations were also made for the Chicken Creek basin using the Manual for Estimating Flood Characteristics of Natural-Flow Streams in Colorado (Reference 4) as well as unit area discharges. Peak discharge-drainage area relationships for the Mancos River and Chicken Creek are shown in Table 1. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Water-surface elevations for floods of the selected recurrence intervals were computed using the COE HEC-2 computer program (Reference 5). The cross sections used in the hydraulic analysis were obtained by both photogrammetric and field survey methods. All bridges and 6