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pond upstream. The city used the COE HEC-1 rainfall-runoff computer program (Reference 13) to compute the 100-year discharge. The same model was used in this Flood Insurance Study with appropriate precipitation values for the 10-, 50-, and SOO-year storms. . The HEC-l computer program utilizes as input the following data: rainfall, loss rates, unit hydrographs, base flow, and routing criteria. Rainfall computations for the 10- and 50-year storms were based on precipitation-frequency data and areal reduction factors derived from the National Oceanic and Atmospheric Administration Atlas. To obtain the precipitation value for the SOO-year flood, a frequency-precipitation curve for the stream was plotted using the 10-, 50-, and 100-year value, and the curve was extrapolated to a SOO-year value. Unit hydrographs were derived by the Snyder Method and loss rates were established by hydrologists familiar with the area. A base flow of 60 cfs was used. ,. Results of hydrologic analysis for Big Salt Wash and Little Salt Wash presented in the 1976 COE Flood Hazard Information Reports (Reference 15) were used in this study. Plateau, Grove, Buzzard and Roan Creeks, among tributaries to the Colorado River from the vicinity of DeBeque to Glenwood Springs, Colorado, are streams that flood from snowmelt as well as from summer rain. Peak di scharges for 10-, 50-, 100-, and SOO-year floods were determined using a regional floodflow frequency analysis (Reference 16) based on rainfall and snowmelt data. The results of the snowmelt and rainfall frequency analysis were combined statistically to give a maximum flow for both events. Regional curves of drainage area versus discharge were computed for the four frequency floods for Roan Creek. Streamflow data of rainfall flood events were insufficient to accomplish this, therefore the SCS TR-20 computer program was used to simulate rainfall flood peaks. The model was used on 16 watersheds of varying sizes. A regional curve of drainage area versus peak discharge and frequency was developed for rainfall flooding. The TR-20 analysis included the standard SCS Type II (24-hour) rainfall distribution and curve numbers for an average antecedent soil moisture condition (AMC-II). The discharge-versus-drainage-area data from this analysis were plotted, and a regression line computed for several frequencies. . A regional curve was developed for snowmelt flood events using streamgage data from 8 streamgages in the area. The log-Pearson Type III frequency distribution as defined in WRC Bulletin l7-B (Reference 12) was used with a regional skew weighted wi th each computed station skew. The data were plotted and frequency 1 ines were drawn. The two regional discharge frequency-drainage area curves (rainfall and snowmelt) were combined using a standard probability equation: P(comb)=P(snow)+P(rain)-(P(snow)xP(rain)) 21