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. 'J '.~ .. .' Combined-Population Discharqe Freauencv . The rainfall and snowmelt discharge frequency curves were plotted for each location. The combined-population curve at each location was calculated using the following equation for combining two independent frequency curves: Pcomp = Psnow + Prain - (psnow) (prain) To verify the combined-population discharge frequency curve that was developed, a mixed-population frequency analysis of streamflow records at Lawson was conducted using HECWRC. All-season annual peak flow records were available at Lawson from 1946 to 1986. A mixed-population regional skew coefficient of 0.18 for the South Platte River basin was used. This regional skew coefficient was also obtained from (Jarrett, 1987). Results of this analysis indicated a mean flood logarithm of 2.99, a standard deyiation of logarithms of 0.16 and an adopted skew of 0.18. ~I.trhe computed 100-year mixed-population discharge at Lawson w:~s 2480 cfs. This compares to a combined-population 100~year discharge of 2600 cfs. The final mixed-population frequency curve, along with the combined-population frequency values are shown in Figure 5. Table 8 lists the recurrence interval and corresponding combined-population discharges in key areas of the upper Clear _______ Creek drainage basin . Figures 6 through 9 show the rainfall, snowmelt and composite curves for Lawson, Silver Plume, Georgetown, and Idaho springs, respectively. COMPARISON WITH PREVIOUS STUDIES Results of this analysis were compared to previous studies within the basin. Discharges for the previous studies were obtained from the Colorado Water Conservation Board. Table 9 presents a comparison of the results of this study with those of previous studies at various locations throughout the basin. 7