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<br />TABLE 4 <br />RESERVOIR INFORMATION <br /> <br />River <br /> <br />size at <br />Normal Pool <br />(Acres) <br /> <br />spillway' <br />capacity <br />(cfs) <br /> <br />Use <br /> <br />Reservoir <br /> <br />S Clear Cr <br />Clear Lake <br />Green Lake <br />G'Town Res <br />Clear Cr Res <br /> <br />S Clear Cr <br />S Clear Cr <br />S Clear Cr <br />S Clear Cr <br />Clear Cr <br /> <br />36.6 <br />26.9 <br />10.3 <br />2.3 <br />51.5 <br /> <br />31,300 <br />190 <br />1,200 <br />770 <br />12,500 <br /> <br />Hydropower <br />Water Supply <br />Water Supply <br />Water Supply <br />Water Supply <br /> <br />Model Calibration <br /> <br />The SWMM was calibrated to the rainfall discharge frequency <br />relationship at the Lawson gage. A frequency analysis of <br />streamflow records for exclusively rainfall events at the Lawson <br />gage was conducted using the flood flow frequency analysis <br />computer program, HECWRC (USACE, 1982). Annual rainfall peak <br />flow records for Lawson were taken from the United States' <br />Geological Survey (USGS) report, "Annual Snowmelt and Rainfall <br />Peak-Flow Data on Selected Foothills Region Streams, South <br />Platte River, Arkansas River, and Colorado River Basins, <br />Colorado", Open-File Report 82-426 (USDOI, 1982). Records were <br />available from 1946 through 1977. Appendix A contains the <br />annual peak discharge values obtained from that report. A gen- <br />eralized skew coefficient 0.22, for rainfall discharge frequency <br />data in the South Platte River basin, was obtained from "Flood <br />Hydrology of Foothill and Mountain Streams in Colorado <br />"(Jarrett, 1987). The pervious surface storage, infiltration <br />rates, impervious area, channel roughness coefficient and <br />overland roughness coefficient were varied in order to calibrate <br />the model. <br /> <br />Results <br /> <br />Results of the calibration indicated that a value of 4 <br />percent should be used for impervious area. The Manning "nil <br />coefficient used for the channel and overbank conditions was <br />0.50. The resistance factors used for overland flow were 0.013 <br />for impervious areas and 0.8 for pervious areas. Surface <br />storage values used for impervious and pervious areas were 0.06 <br />and 0.18 inches, respectively. A uniform infiltration rate of <br />0.95 inches per hour was used. <br /> <br />5 <br />