AN ITERATIVE STOCHASTIC INVERSE METHOD - CONDITIONAL EFFECTIVE TRANSMISSIVITY AND HYDRAULIC-HEAD FIELDS

An iterative stochastic approach is developed to estimate transmissivi ty and head distributions in heterogeneous aquifers. This approach is similar to the classical cokriging technique; it uses a linear estimat or that depends on the covariances of transmissivity and hydraulic hea d and their cross covariance. The linear estimator is, however, improv ed successively by solving the governing flow equation and by updating the covariances and cross-covariance function of transmissivity and h ydraulic head fields in an iterative manner. As a result the nonlinear relationship between transmissivity and head is incorporated in the e stimation, and the estimated fields are approximate conditional means. The ability of the iterative approach is tested with some determinist ic and stochastic inverse problems. The results show that the estimate d transmissivity and hydraulic head fields have smaller mean square er rors than those obtained by classical cokriging even in the aquifer wi th variance of transmissivity up to 3.