Verification of HYDRASTAR: Analysis of hydraulic conductivity fields and dispersion

HYDRASTAR is a code for the stochastic simulation of groundwater flow. It can be used to simulate both time-dependent and steady-state groundwater flow at constant density. Realizations of the hydraulic conductivity field are generated using the Turning Bands algorithm. The realizations can be conditioned on measured values of the hydraulic conductivity using Kriging. This report describes a series of verification studies that have been carried out on the code. The first study concerns the accuracy of the implementation of the Turning Bands algorithm in HYDRASTAR. The implementation has been examined by evaluating the ensemble mean and covariance of the generated fields analytically and comparing them with their prescribed values. Three other studies were carried out in which HYDRASTAR was used to solve problems of uniform mean flow and to calculate the transport and dispersion of fluid particles. In all three cases the hydraulic conductivity fields were unconditioned. The first two were two-dimensional: one at small values of the variance of the logarithm of the hydraulic conductivity for which there exists analytical results that the code can be compared with, and one at moderate variance where the results can only be compared with those obtained by another code. The third problem was three dimensional with a small variance and again analytical results are available for comparison. 14 refs, 24 figs