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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 dis- charge-frequency relationships for each flooding source studied in detail affecting the community. Hydrologic analyses for the detailed-study areas on the Roaring Fork River below its confluence with the Fryingpan River and on the Fryingpan River were carried out by the COE, Sacramento Dis- trict (Reference 7), using the methodology detailed below. The hydrologic techniques used are fully documented in a separate report, Hydrology Report For ~ity of Aspen and Pitkin Coun~y (Unincorporated Areas) (Reference 8). Data from a large number of stream gaging stations located within the homogenous watershed area similar to Pitkin County area were analyzed. These gages are located within Pitkin County and nearby Summit, Eagle, Garfield, Mesa, Delta, and Gunnison Counties. The streamflow data were separated into snowmelt and rainfall peaks and analyzed separately. Snowmelt peaks from a total of 40 gages and rainfall peaks from 25 gages were analyzed to obtain individual and regional statistical parameters of mean, standard deviation, and skew for the two types of flow peaks. In numerous instances, the rainfall peaks were of very small magnitude. Several stream gages did not show any sig- nificant peaks caused by rainfall. Using log-Pearson Type III distribution as described in U.S. Water Resources Council Bulletin 17A (Reference 9), the discharge-fre- quency information was developed separately for the snowmelt peaks and the rainfall peaks for the 10-, 50-, 100-, and SOO-year recur- rence intervals. These two distributions were combined to obtain the overall peak discharge-frequency relationship for each stream. For ungaged streams, the values of regional statistical parameters were used and the discharge-drainage area curves were developed for the 10-, 50-, 100-, SOO-year recurrence intervals. 7