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