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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 lOa-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 discharge values on the Crystal River were adopted from a regional analysis performed by the COE, Sacramento District, (Reference 3). Both snowmelt and rainfall flood peaks were analyzed to define flood flow frequency. Regional drainage-area, mean peak flow relationships, regional standard elevations, and regional skew coefficients were developed for both flood types. This information was adjusted using statistics developed from Crystal River USGS gage records. Floodflow-frequency curves for rainfall and snowmelt floods were developed at selected sites using the adjusted information. These curves were then combined statistically to generate composite flow-frequency curves. A separate review by the study contractor (Reference 4) of existing methods recommended using the COE regional analysis. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the eleva- tions of floods of the selected recurrence intervals. Water-surface elevations for floods of the selected recurrence intervals were computed using the COE HEC-2 step-backwater computer program (Reference 5). Cross section data for the backwater analyses were digitized from 1982 aerial photography at a scale of 1:2,400 (Reference 6). Because the cross sections for the Crystal River did not include any belaw-water geometry, adjusted discharge values were used in the HEC-2 analysis for this stream. The adjusted discharge values were determined by reducing the peak discharges, as shown in Table 1, by the flaw in the Crystal River at the time of the 5