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<br />where. <br /> <br />L = Loss rate in inches per hour <br />a = Infiltralion capacity <br />S = Available Storage in inclles <br />e = Exponent of storage <br />c = constant rate of infiltration <br /> <br />Estimates of "c" can be based on the hyclrologic soil group given in tilll SCS <br />handbook as shown in the section discussing Ille initial and uniform methocl. <br /> <br />5. HORTON'S METHOD. <br /> <br />In the 1930's Robert E. Horton. a consultinq Hyclraulic Engineer, founcl tllat <br />infiltration capacity curves approximate the form: <br /> <br />F"F'(F' Flak' <br />p - (; 0 c. '-, <br /> <br />(119) <br /> <br />where. <br /> <br />F p = Infiltration rate in inches per hour <br />Fe = Minimum constant infiltrat'on rate <br />Fp = Maximum infiltration rate <br />e = Napierian base <br />k = empirical constant <br />t = time from beginning of rainfall <br /> <br />In the Storm Water Management Model (SWMM), tile Horton equation is used tor <br />pervious areaS. Additional parameters can be specified f'Jr initial abstractions for bot II <br />pervious and impervious areas. If the Maximum and min' mum infiltration rates are set <br />equal in Horton's equation, a uniform infiltration rate is achieved. <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />DRAFT <br /> <br />7.24 <br />