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<br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carri~d out to establish the peak <br />discharge-frequency relationsh~ps for each flooding source studied <br />by detailed methods affecting qhe community. <br /> <br />Peak discharges for the 10- and 100-year floods for the City Park, <br />Nissen Reservoir, Gay Reservoir, and West Lake Basins were <br />obtained from a 1979 UD~CD report (Reference 2). In the UD~CD <br />report, the 10- and 100-year flood discharges were computed using <br />the Storm Water Management computer model (Reference 3), The <br />rainfall figure used was based ion Volume III of the <br />Precipitation-~reQuency Atlas of the Western United States <br />(Reference 4). <br /> <br />. <br /> <br />The study contractor determine4 the 50- and 500-year flood <br />discharges by plotting the 10-iand 100-year flood discharges on <br />log-probability paper and interpolating or extrapolating as <br />appropriate. The 50-year flood discharge was determined by <br />interpolation; the 500-year flood discharge was determined from <br />extrapolation. <br /> <br />Peak discharge-drainage area r~lationships for all flpoding <br />sources are shown in Table 2. ' <br /> <br /> Table 2. Summary of Discharges <br />~looding Source Drainage Area Peak Discharges (Cubic ~eet per Second) <br />and Location (Square Miles) 10-llear 50-Year 100-Year 500-Year <br />Airport Creek <br />At Confluence With <br />Big Dry Creek 2.51 550 1,300 1,640. 3,040 <br />At Confluence With <br />Tributary 1 1.22 370 760 920 1,540 <br />At Upstream Limit of <br />Detailed Study 0.43 390 690 810 1,220 <br />North Branch Airport <br />Creek <br />At Confluence With i <br />Airport Creek 0.30 100 230 280 510 <br />At Upstream Limit of <br />Detailed Study 0,03 30 50 60 90 <br />Rock Creek <br />Confluence With Coal 1 <br />Creek 1 5,~20 8,740 10,640 15,920 <br />At Dillon Road 2,~20 5,240 6,500 9,840 <br />At Denver-Boulder 1 <br />Turnpike 3,630 5,820 6,B10 9,350 <br /> <br />10 <br />