IDENTIFICATION OF HYDRAULIC PARAMETERS IN LAYERED SOILS BASED ON A QUASI-NEWTON METHOD

In models for one-dimensional unsaturated flow in layered soils based on the general flow equation, non-linear coefficient functions appear. The inverse problem consists of the identification of parameters in m odels for these coefficients. In this study, parameters are identified for layered soils. The general flow equation is solved iteratively, a djusting the values of the parameters until the solution matches a set of in situ water content data. The optimization method is based on a quasi-Newton method with Richardson extrapolation. Data sets of differ ent size and with various degrees of perturbation are used to investig ate existence, uniqueness and accuracy of parameter estimates. To stab ilize parameter estimates, a weighting procedure is proposed based on the values of the water content data. The correspondence of parameter estimates, based on relatively small sets of unperturbed data, to the true parameter values indicates a high degree of numerical accuracy of the method. Parameter estimates based on perturbed data sets suggest that ill-posedness of the estimation problem is a matter of data insuf ficiency and modeling errors, rather than of data error alone.