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Page 2 of 3 <br />FIGURE 2.05.3(3)(c)(i) (con't) <br />' Rain required to initiate runoff is P = 0.25, where <br />S = 1000 _ 10 = 1000 _ 10 = 2.5" <br />• cra g0 <br />P .2S = .2(2.5) = 0.5" <br />' From NCAA, 7.5 year - 24 hour P = 2.2". Since 0.5" is less than <br />2.2", runoff, Q, will occur. O i= determined as <br />Q P+0.8S 4.2 = 0.405 <br />' Peak discharge ("Peak Flows in Colorado", Soil Conservation <br />Service, t?arch 1980, page 12 graph) <br />Tc = 0.0078L0.77(L/H).385 (Hydrology and Sedimentology of <br />Surface I4ined Lands, page 83) <br />' L = 465 <br />H = 26' <br />' To = 2.68 = .045 hr. <br /> Peak discharge = unable to obtain from graph. <br /> Use rational formula Q = (CiA)1.008 to get maximum intensity for <br />' 25 year storm, see below <br /> To determine the greates t intensity, assum e most severe time of <br />' Type II storm will occur at t = 12 hours (Hydrology and <br /> Sedimentology of Surface N:ined Lands, 1979 ed., pages s3 and 54) <br />' TIME ORDINATE P /P DEPTH INCRED7ENT DEPTH INTENSITY <br /> (hrs) * t 24 fin) (in1 (ioh) <br />II <br />II <br /> <br />I~ <br />A <br />11.25 0.257 <br />11.50 0.290 <br />11.75 0.40 <br />12.00 0.66 <br />12.25 0.710 <br />12.50 0.735 <br />* <br />page 59 above reference <br />0.5654 <br />0.638 <br />0.88 <br />1.452 <br />1.562 <br />1.617 <br />0 <br />0.0726 <br />0.242 <br />0.572 <br />0.11 <br />0.055 <br />0.2904 <br />0.968 <br />2.288 <br />0.44 <br />0.22 <br />' REVISED D1ay 15, 1981 <br />