Determining Soil Hydraulic Properties by Inverse Method in One-Dimensional Unsaturated Flow

For physically based models, the hydraulic conductivity function and the effective fluid saturation function are the most important parameters affecting water and solute movements in the vadose zone. Direct parameter measurements in heterogeneous soils are very difficult and scale-dependent. The inverse approach is an indirect and interesting way to estimate hydrodynamic parameters. In-situ soil water retention and hydraulic conductivity relations were determined for a layered soil from knowledge of initial and boundary conditions and observed pressure heads during infiltration, evaporation, and redistribution. We will present efficient algorithms for inverse problems applied to both synthetic and real test cases. The location and the number of observation points are very important ; the number of observations must be sufficient, i.e., the variables have to be measured for each layer of the soil. Large differences in sensitivity are observed among the various model parameters.