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<br />Rainfall runoff hydrographs produced by SWMM for the 2-, <br />5-, 10-, 50-, 100- and 500-year storms are shown in Figure 2 for <br />Lawson. A comparison of peak discharges for the 2- through <br />100-year rainfall events are shown in Table 5 for the <br />statistical analysis of stream gage records and the SWMM modeled <br />discharges. Table 6 lists the recurrence interval and <br />corresponding rainfall discharges for different locations in the <br />basin. <br /> <br />TABLE 5 <br />Results of SWMM Calibration <br />Rainfall Discharge Frequency at Lawson Gage <br /> <br />Recurrence Peak Discharge in c.t.s. <br />Interval statistical SWMM Difference <br />(years) Analysis Model c.t.s. Percent <br />2 352 390 38 10.8 <br />5 605 630 25 4.1 <br />10 817 840 23 2.8 <br />50 1430 1340 -90 -6.3 <br />100 1760 1850 90 5.1 <br /> <br />Snowmelt Discharqe Frequencv Curve <br /> <br />The snowmelt discharge frequency curves were determined <br />from an intra-basin regional analysis utilizing streamflow <br />records at the Lawson and Golden streamgages. The regional <br />analysis was developed using the mean flood logarithm and <br />standard deviation of the logarithms for annual snowmelt peak <br />discharges and were plotted versus the drainage area of 147 <br />square miles at Lawson and 399 square miles at Golden. The mean <br />logarithm and standard deviation were obtained from frequency <br />analyses derived at the two locations using annual snowmelt peak <br />flows. Snowmelt peak flows were obtained from the same USGS re- <br />port that rainfall peak flows were found. For Lawson, the mean <br />flood logarithm was 3.00 with a standard deviation of logarithms <br />of 0.16. For Golden, the mean logarithm was 3.16 with a stan- <br />dard deviation of 0.20. These values were plotted versus drain- <br />age area and are shown in Figures 3 and 4. Snowmelt frequency <br />curves were computed at various locations in the study area us- <br />ing the log Pearson Type III distribution equation, with mean <br />flood logarithms and standard deviations'of logarithms being ob- <br />tained from Figure 3 and 4, respectively. A regionalized skew <br />coefficient of -0.10 for snowmelt-runoff for the South Platte <br />River basin was used (Jarrett, 1987). Table 7 lists the <br />recurrence interval and corresponding snowmelt discharges for <br />various locations in the study reach. <br /> <br />6 <br />