Some aspects of head-variance evaluation

We compare two methods of evaluating head covariance for two-dimensional st eady-state flow in mildly heterogeneous bounded rectangular aquifers. The q uasi-analytical approach, widely used in stochastic subsurface hydrology, i s based on the Green's function representation, and involves numerical four -fold integration. We compare this approach with a numerical solution of th e two-dimensional boundary-value problem for head covariance. We show that the finite differences integration of this problem is computationally less expensive than numerical four-fold integration of slowly-convergent infinit e series.