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  • Robert Dickinson September 12, 2013 at 5:03am

    A source for Green Ampt Parameters is the SWMM 5 Help file or this site

    http://www.dynsystem.com/NetSTORM/docs/GreenAmptParameters.html

    This is how the Suction head is used in the Green Ampt code


    double grnampt_getInfil(TGrnAmpt *infil, double tstep, double irate,
    double depth)
    //
    // Input: infil = ptr. to Green-Ampt infiltration object
    // tstep = runoff time step (sec),
    // irate = net "rainfall" rate to upper zone (ft/sec);
    // = rainfall + snowmelt + runon, //(5.0.022 - LR)
    // does not include ponded water (added on below)
    // depth = depth of ponded water (ft).
    // Output: returns infiltration rate (ft/sec)
    // Purpose: computes Green-Ampt infiltration for a subcatchment.
    //
    // Definition of variables:
    // IMD = initial soil moisture deficit at start of current rain event
    // (void volume / total volume)
    // IMDmax = max. IMD available (ft/ft)
    // Ks = saturated hyd. conductivity (ft/sec)
    // S = capillary suction head (ft)
    // F = cumulative event infiltration at start of time interval (ft)
    // F2 = cumulative infiltration at end of time interval (ft)
    // Fs = infiltration volume needed to saturate surface (ft)
    // T = cumulative event duration (sec)
    // Tmax = max. discrete event duration (sec)
    // L = depth of upper soil zone (ft)
    // FU = current moisture content of upper zone (ft)
    // FUmax = saturated moisture content of upper zone (ft)
    // DF = upper zone moisture depeletion factor (1/sec)
    // DV = moisture depletion in upper zone (ft)
    //
    // f = infiltration rate (ft/sec)
    // ivol = total volume of water on surface (ft)
    // ts = remainder of time step after surface becomes saturated (sec)
    // iv2 = available surface water volume over time step (ft) //(5.0.021 - LR)
    // c1, c2 = terms of the implicit Green-Ampt equation
    {
    double F = infil->F;
    double F2;
    double DF;
    double DV;
    double Fs;
    double f;
    double ivol, iv2;
    double ts, c1, c2;

    // --- add ponded water onto potential infiltration
    irate += depth / tstep;
    if ( irate < ZERO ) irate = 0.0; //(5.0.021 - LR)
    ivol = irate * tstep;

    // --- add ponded water head to suction head //(5.0.019 - LR)
    c1 = (infil->S + depth) * infil->IMD; //(5.0.019 - LR)

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