Experience of Inverse Modeling for Estimating Hydraulic Parameters of Unsaturated Soils

Soil column experiments were carried out to inversely estimate the hydraulic parameters of the unsaturated zone. This study analyzes clay soil taken from an irrigated area of the Mnasra province in northwestern Morocco which includes large agricultural areas. Fully drained and controlled laboratory model tests and their numerical simulations are presented. The inverse modeling method was applied to estimate the hydraulic properties of unsaturated soil based on the Levenberg-Marquardt algorithm. A non linear estimation method tied up with the finite difference method and inversion analysis was used to minimize the cost function defined by the difference between the predicted and observed values of the model. Unsaturated hydraulic parameters of the Van Genuchten and Mualem models were estimated using water content measurements at five clay depths (10, 20, 30, 40, and 60cm) and/or the cumulative water flux at the column bottom. The ex peri men tal hydraulic parameters and the predicted results were in good agreement with the measurements from the single and multicost function experiments. Also the results showed that the multicost function experiment was more appropriate in determining the hydraulic properties of unsaturated soils than the single-objective function experiment. The comparison between measured values and predicted results showed that the in verse analysis based on the 1D soil column experiment was efficient and useful to establish the hydraulic properties of unsaturated soils.