PARAMETER-ESTIMATION BY INVERSE METHOD BASED ON ONE-STEP AND MULTISTEP OUTFLOW EXPERIMENTS

The applicability of the inverse method for determining the soil water characteristic theta(h) and the hydraulic conductivity/water content K(theta) functions was investigated on two Typic Haploxererts characteristic of the Sicilian environment. Shrinkage behaviour of the two soils was analysed in order to verify if significant changes in soil volume occurred during the outflow process. One-step outflow experiments were performed, with comparisons between different procedures analysed not only in terms of estimated average functions, but also from the point of view of the uncertainty in the predictions, evaluated by a first-order analysis. Multi-step outflow experiments were then performed and compared to results obtained by the onestep method. The results showed that the theta(h) and K(theta) functions deduced by performing optimization on the outflow volume V vs. time t obtained from multi-step experiments supplemented with three equilibrium theta(h) values were more reliable than the: theta(h) and K(theta) functions determined by performing optimization on the V(t) obtained from one-step experiments supplemented with independently determined theta(h) values.