Flow at Low Water Contents: A Simple Approach for Inverse Estimation of van Genuchten-Mualem Soil Hydraulic Parameters

The unsaturated soil hydraulic properties (the soil water characteristic and relative permeability curves) are key hydrodynamic parameters in the fields of soil science and civil engineering. Because of the strong dependency of these properties on water content, their determination is subject to considerable experimental and numerical problems. Difficulties increase when the soil approaches oven-dry conditions, a situation often encountered in arid and semi-arid areas. Moreover, computational costs of estimating the hydrodynamic properties can be relatively high also. After a short review of alternative modeling approaches for the hydraulic functions from saturation to oven-dryness, we present a theoreticalnumerical approach, along with a relatively simple, robust and inexpensive experimental method for inverse determination of van Genuchten/Mualem soil hydraulic parameters. For gravimetric water contents greater than 0.04, numeral results agreed well with experimental data, while some discrepancies were observed at very low water contents.