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<br />A = area, square miles <br /> <br />(csm) = runoff factor from Figure 111-4 or 111-5 in cfs <br />per inch of runoff per square mile, based on <br />calculated time of concentration <br /> <br />If further information on flood volume as well as peak flow <br />is required, i.e., for sizing of detention facilities, an approxi- <br />mation of the flood hydrograph can be made using the following <br />relationships: <br /> <br />Tp = ~D + 0.6 Tc = 0.67 Tc where 6D = 0.133 Tc <br /> <br />Tb = 2.67 Tp = 1.78 Tc <br /> <br />where: <br /> <br />Tp = time to peak flow rate from start of rise, hours <br />Tb = time base of hydrograph, hours <br />6D = rainfall excess period, hours <br />Tc = time of concentration, hours <br /> <br />--- ! <br /> <br />~J <br />~ <br />! <br />! <br />- <br />.... <br /> <br />! <br /> <br />These relationships will define a triangular hydrogtAph --~-- <br />which can be refined to a curvilinear hydrograph with the infor- <br />mation presented in Table 111-6. The development of a hydrograph <br />should be accomplished with the procedures outlined in the SCS <br />National Engineering Handbook, Section 4, Hydrology. The use <br />of the "CSM" procedure utilizing Figures 111-4, -5, and -6 should I' <br />not be incorporated with hydrograph development. <br /> <br />_ _ ~- ----"-- <br /> <br />30 <br /> <br /> <br /> <br />I <br /> <br />i <br /> <br />'1 <br />II <br />~ <br />