Vadose Zone Composite Hydraulic Conductivity

Abstract

Grid networks, consisting of nodes and line elements, are often used in porous media flow simulation. An important step in the simulation process is the quantification of the line element conductivity when the pressure or capillary potential at both end nodes is given. Under saturated condition, when the porous medium is layered, the variation of conductivity along the line element is treated by calculating a composite conductivity as the line element conductivity. The composite conductivity under saturated condition can be derived analytically and is the harmonic mean of the saturated conductivity of the layers. For the unsaturated flow in the vadose zone, analytically derived composite conductivity is not available. Heuristic rules, including weighted, geometric, and harmonic means, have been used to estimate line element conductivity in practice. The lack of agreement in estimating composite conductivity indicates that the simulation technique for the vadose zone has not reached its maturity, and that improvements are needed. The purpose of this paper is to derive an analytical method to estimate vadose zone composite conductivity to be used in porous media flow simulation.