A parameterized model for local infiltration in two-layered soils with a more permeable upper layer

A simple conceptual model for local infiltration into a two-layered soil profile with the upper layer much more permeable than the subsoil is proposed. It is a reformulation of a conceptual model of Corradini et al. (2000) U. Hydrol. 273,58-73] involving coupled ordinary differential equations that was developed for infiltration and soil water content distribution in a two-layered soil under any rainfall pattern. The simpler model framework proposed here is restricted to the estimate of infiltration rate alone in cases where the upper layer is more permeable than the lower one. First, the maximum value, K(1h), of the saturated hydraulic conductivity of the upper soil, K(1s), that yields the time to ponding while the dynamic wetting front is entirely within this homogeneous layer is defined by a conceptual approach. Then, parameterized forms for the time when the wetting front reaches the interface, for time to ponding associated with K(1s) >= K(1h), and for the suction head at the interface as a function of time are determined. With these functional forms, the current model utilizes algebraic equations for ponding time and soil infiltration capacity, thus providing substantial savings in computational effort for describing infiltration in two-layered soils. When compared to the detailed conceptual model, the proposed model represents the infiltration rate accurately, with less than 10% average error on the dynamic cumulative infiltration depth. This simplified model offers potential for upscaling to field-scale infiltration over layered soils exhibiting spatial heterogeneity. (C) 2010 Elsevier By. All rights reserved.