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 characte ristic of the Sicilian environment. Shrinkage behaviour of the two soi ls was analysed in order to verify if significant changes in soil volu me occurred during the outflow process. One-step outflow experiments w ere performed, with comparisons between different procedures analysed not only in terms of estimated average functions, but also from the po int of view of the uncertainty in the predictions, evaluated by a firs t-order analysis. Multi-step outflow experiments were then performed a nd compared to results obtained by the onestep method. The results sho wed that the theta(h) and K(theta) functions deduced by performing opt imization on the outflow volume V vs. time t obtained from multi-step experiments supplemented with three equilibrium theta(h) values were m ore reliable than the: theta(h) and K(theta) functions determined by p erforming optimization on the V(t) obtained from one-step experiments supplemented with independently determined theta(h) values.