Using an inverse method to estimate the hydraulic properties of crusted soils from tension-disc infiltrometer data

b ( Laboratoire d'etude des Transferts en Hydrologie et En˝ironment LTHE, CNRS URA 1512, ´ ) Abstract An inverse procedure was used to estimate the soil hydraulic characteristics of a two-layered soil system—soil surface crust and subsoil—from data obtained during a tension-disc infiltration experiment. The inverse procedure combined the Levenberg-Marquardt nonlinear parameter optimization method with a numerical solution of the axisymmetric variably-saturated flow equation. The objective function was defined in terms of the cumulative infiltration curve and the final water content measured directly below the tension-disc infiltrometer at the end of the experiment; this final water content was assumed to correspond to the final supply pressure head. We analyzed two infiltration experiments carried out with a 25-cm diameter tension-disc infiltrom- eter. One experiment was carried out on a two-layered system, and a second after removal of the surface crust covering the sandy subsoil. Both experiments were performed with six consecutive supply tensions. We first analyzed the infiltration experiment for the subsoil only, thus yielding its hydraulic characteristics. Subsequent analysis of the infiltration experiment for the two-layered system with known hydraulic properties of the subsoil provided estimates of the hydraulic properties of the surface crust. We further compared the estimated hydraulic parameters of the w subsoil with those obtained using Wooding's analytical method Wooding, R.A., 1968. Steady x

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