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<br />where, <br /> <br />L = Loss rate in inches per hour <br />a = Infiitration capacity <br />S = Available Storage in inches <br />e = Exponent of storage <br />c = constant rate of infiltration <br /> <br />Estimates of 'c' can be based on the hydrologic soil group given in the SCS <br />handbeok as shown in the section discussing the initial and uniform method. <br /> <br />5. HORTON'S METHOD. <br /> <br />In the 1930's Robert E. Horton, a consuiting Hydraulic Engineer, found that <br />intiitration capacity curves approximate the form: <br /> <br />F =F +(F -F) e-kf <br />p c 0 C <br /> <br />(11-9) <br /> <br />where, <br /> <br />Fp = Infiitration rate in inches per hour <br />F,= Minimum constant infiltration rate <br />Fo = 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), the Horton equation is used for <br />pervious areas. Additional parameters can be specified for initial abstractions for beth <br />pervious and impervious areas. If the Maximum and minimum infiitration rates are set <br />equal in Horton's equation, a uniform infiitration rate is achieved. <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />DRAFT <br /> <br />7.24 <br />