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<br />< <br /> <br />! <br /> <br />Q = q p * (tp + tr) / 2 <br /> <br />(15) <br /> <br />where: <br /> <br />Q = runoff volume <br />q = peak discharge <br />tp = time to peak <br />tr = recession time equal to time base of hydrograph - time to peak <br /> <br />with three-eights of the volume under the rising limb, tr = 1.67 fp and equation <br />(15) reduces to: <br /> <br />q p = .75 * Q / tp <br /> <br />(16) <br /> <br />When tp is hours and Q is inches, equation (16) is multiplied by the <br />drainage area (A) in square miles and the factor 645.3 to get Q p in cfs. <br /> <br />q p = (484 * A * Q) / tp <br /> <br />(17) <br /> <br />SUGGESTED FURTHER READING <br /> <br />1. U.S. Army Corps of Engineers, 1991. "Flood Runoff Analysis". EM 1110-2- <br />9021, Draft pp. 7-1 to 7-14. <br /> <br />2. Linsley, R. K.; Kohler, M.A.; and Paulhus,J. L., 1975. "Hydrology for Engineers". <br />pp. 235-252. McGraw Hill Book Company, New York. <br /> <br />3. U.S. Army Corps of Engineers, 1959. "Flood Hydrograph Analyses and <br />Computations", EM 1110-2-1405. <br /> <br />4. U.S. Army Corps of Engineers, 1963. "Unit Hydrographs - Part 1 Principles and <br />Determinations", Civil Works Investigations, Project 152, Baltimore District. <br /> <br />5. U.S. Army Corps of Engineers, 1973, "Hydrograph Analysis", IHD Volume 4, <br />Hydrologic Engineering Center. <br /> <br />6. Snyder, Franklin F., 1938. "Synthetic Unit Graphs". Trans. Am. Geography <br />Union, Part I. pp 447-454. <br /> <br />7-35 <br />