Model For Rainfall Excess Patterns on Randomly Heterogeneous Areas

A model is presented that can simulate infiltration from rainstorms on areas exhibiting random variation in saturated hydraulic conductivity KS. Heterogeneity in the capillary drive (or length scale) parameter G can be treated as well. The method is based on a point infiltration model that includes the Green-Ampt or Smith-Parlange infiltration functions. The runoff area is characterized as an ensemble of infiltrating points or flow path strips that provides runoff to a receiving channel. The model is developed by simulation of a large ensemble using Latin hypercube sampling. The infiltration expression is responsive to a changing rainfall rate r and is easily characterized using the basic infiltration parameters KS and G, plus a third parameter based only on the coefficient of variation of KS or G. Areal heterogeneity causes a rainfall-dependent change in the areal effective value for KS, called Ke(r). The infiltration expression contains rainfall rate as a variable, and observed storms with temporal rainfall patterns may easily be treated. Moreover, the new expression eliminates the explicit concept of ponding time as a separate calculation. The effect of heterogeneous infiltration parameters is demonstrated using several field cases.