Abstract
In a previous study, we showed that the cumulative infiltration rate measured with a tension disc infiltrometer at one particular tension does not provide enough information to estimate van Genuchten's soil-hydraulic 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 estimating soil hydraulic parameters. We also investigate whether additional, easily obtainable information improves identifiability of the unknown 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 estimation procedure combines the Levenberg-Marquardt nonlinear parameter optimization method with a quasi three-dimensional numerical model, HYDRUS-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 unique solutions of the inverse problem for the unknown parameters.
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