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drainage area versus peak flow rate with each line representing all values of the same frequency event. For smaller basins (less than 30 square miles), the rainfall events were investigated using the Soil Conservation Service (SCS) TR-20 model. The 500-year peak flow due to rainfall was found to be much higher than the SOO-year peak flow due to snowmelt. The 50-, 100-, and SOO-year regression lines were modified to incorporate the discharge versus drainage area relationship obtained by the SCS procedure. . The Master Drainage Plan for Breckenridge (Reference 32), prepared in 1986, contains a statistical analysis of 21 individual gage stations. A regional frequency analysis, similar to the analysis described in Reference 6, was performed to determine if the peak discharge values from Reference 6 were still representative. The results from the 1986 Master Plan Study as compared to the FEMA values were in close agreement; therefore, the peak discharge values were considered still valid. Formulas were derived for the 10-, 50-, and 100-year recurrence intervals. The tributaries to the Blue River, which have drainage areas ranging from 0.8 to 11.1 square miles, were analyzed using the HEC-l computer model. The HEC-l run provided runoff rates produced by rainfall. The results indicated that the peak flow rates for the lower return periods, such as the lO-year, were dominated by snowmelt values as calculated using the regional regression analysis. For the SO- and lOO-year floods, the HEC-l results were adopted as peak flow rates. , The peak flow rates used in this study were either taken directly from previous Flood Insurance Studies or other studies, derived from other frequencies using log-probability plots, or calculated using regression equations from previously referenced studies (for small basins regression lines were adjusted to consider rainfall effects). The peak diSCharge-drainage area relationships for the Blue River, French Gulch, Jug Creek, Meadow Creek, Miners Creek, No Name Creek, North Fork Snake River, Snake River, South Barton Gulch, Swan River, and Tenmile Creek are shown in Table 4. ~ The revised hydraulic analyses of the streams studied using detailed methods were performed using the USACE HEC-2 step- backwater program (Reference 33). Starting water-surface elevations (SWSELs) for the following streams were calculated using the slope-area method: Blue River (above Dillon Reservoir), Tenmile Creek (lower portion), Meadow Creek (lower portion), Miners Creek, French Gulch, and South Barton Gulch. For the following streams, the SWSELs were chosen based on coincident peaks: Swan and North Fork Snake Rivers, Jug Creek, and No Name Creek. The SWSELs for Tenmile Creek (upper portion), Meadow Creek (upper portion), the Snake River, and the 31