Analysis of interfacial error in saturated–unsaturated flow models

Interfacial error results from estimation of interblock conductivities related to the saturated–unsaturated interface. Both interfacial conductivity error (IE_K) and interfacial pressure error (IE_h) were analyzed under the arithmetic mean scheme while IE_K was numerically investigated under the averaging schemes arithmetic, geometric and harmonic. IE_K, dependent on the media pore size, is regularly less than zero while IE_h, associated with the height of capillary fringe, may be greater than zero. An interfacial discretization technique was developed to add two complementary equations into the saturated–unsaturated model with respect to the interface. The proposed interfacial approach may eliminate interfacial error from the approximations of interblock conductivities. Underestimation of the water-table response to infiltration is related to the negative IE_K. The water-table response error reaches −5.13% in our investigation, which is an accumulated result from IE_K.