Townley, L.R. (1988), Modelling flow in heterogeneous aquifers : Identification of the important scales of variability, VII International Conference on Computational Methods in Water Resources, Boston, USA, June 1988, 197-202.

Although the spatial distribution of transmissivity in real aquifers is highly variable, adequate simulation is often achieved using spatially averaged transmissivity for model input. A fundamental question concerns the choice of the largest suitable averaging scale at which adequate simulation is achieved, but above which, prediction accuracy deteriorates. Prediction accuracy for a hypothetical aquifer is evaluated numerically using first-order calculations of the co-variance of predicted heads. Uncertainty in transmissivity is represented by spatial covariance functions which take into account the length scales of averaging. The prediction accuracy is found to deteriorate when the averaging scale exceeds the correlation length of the underlying log transmissivity field.