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insurance premium rates. These events, commonly termed the 10-, 50- 100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equalled 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 occurrence) in any 50-year period is approxi- mately 40 percent (4 in 10), and, for any 90-year period, the risk in- creases to approximately 60 percent (6 in 10). The analyses reported here reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood eleva- tions 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 floods of the selected recurrence intervals for each flooding source studied in detail affecting the community. Peak discharges of the selected recurrence intervals were calculated for Bear Creek using a log-Pearson Type III frequency analysis (Reference 5). Frequency analyses were calculated using streamflow data from a U.S. Geological Survey stream gaging station located at the western edge of Morrison (Gage No. 067105 with continuous records since 1922), and historical records for the flood of 1896. As is typical in Colorado, flood events in the study area comprise two distinct and generally independent populations (i.e., rain and snowmelt floods). For this reason, it is necessary to analyze the rain and snowmelt events separately. Each type of flood event is assumed to follow log-Pearson Type III distribution, which has been widely adopted for flood frequency analyses. These two flood-frequency curves, one for rain events and the other for snowmelt events, are then statistically combined to give a composite flood-frequency curve that defines the flood-frequency curve for the gaged site in question. The results of this stream gage analysis were used as the discharges for the reach of Bear Creek upstream of the confluence with Mount Vernon Creek. The reach of Bear Creek downstream of the confluence with Mount Vernon Creek required adjustment of the gage records because of the intervening drainage area. For this reach and others along Bear Creek, regression equations were derived. The final regression equations, including only significant independent variables for the mean coefficient of variation (and hence the standard deviation) , and skew for each type of event, were used to compute the flood- frequency curve at any ungaged site with given drainage area and mean watershed elevation. 8