Runoff-infiltration partitioning using an upscaled Green-Ampt solution

A new set of formulae for calculating regionally averaged infiltration rates into heterogeneous soils is presented. The solutions are based upon an upscaled approximation of the explicit Green-Ampt (GA) infiltration solution, and require specification of the spatial distribution of saturated hydraulic conductivity and/or initial soil water deficit in the sub-basin. The resultant areal averaged infiltration formulae, which ignore the impacts of run on or spatial correlation, are easily integrated into existing distributed surface water schemes, and can also be used to calculate saturated soil surface area. The impacts of preferential flow may be investigated through the use of a bimodal conductivity distribution. The solutions are tested against Monte Carlo simulations and assessed for accuracy. Interesting results are obtained regarding the impacts of upscaling on GA infiltration, most notably that the cumulative infiltration is most impacted by low-conductivity soils and that calibration of the standard (point-scale) GA equation to basin-scale hydrographs will lead to an underestimation of average system hydraulic conductivity. Copyright © 2010 John Wiley & Sons, Ltd.