ESTIMATING UNSATURATED SOIL HYDRAULIC-PROPERTIES FROM MULTIPLE TENSION DISC INFILTROMETER DATA

In a previous study, we showed that the cumulative infiltration rate m easured with a tension disc infiltrometer at one particular tension do es not provide enough information to estimate van Genuchten's soil-hyd raulic parameters by numerical inversion of the Richards equation. In this paper we analyze the possibility of using cumulative infiltration rates obtained at several consecutive tensions for the purpose of est imating soil hydraulic parameters, We also investigate whether additio nal, easily obtainable information improves identifiability of the unk nown parameters, The study is carried out using numerically generated data, The uniqueness problem was analyzed by studying the behavior of response surfaces in the optimized parameter planes, Our parameter est imation procedure combines the Levenberg-Marquardt nonlinear parameter optimization method with a quasi three-dimensional numerical model, H YDRUS-2D, which solves the variably-saturated flow equation, We found that the combination of multiple tension cumulative infiltration data with measured values of the initial and final water contents yielded u nique solutions of the inverse problem for the unknown parameters.