An approximate analytical solution for well flow in anisotropic layered aquifer systems

The mathematical problem of steady groundwater flow toward a pumping well in an aquifer system consisting of layers (or aquifers) with anisotropy of the horizontal conductivity is solved analytically for the first time. The solution is an approximation for relatively weak anisotropy. If more than one layer is horizontally anisotropic, the method requires that the principal directions of anisotropy are the same in all layers. The presented solution is based on a first order perturbation technique. Comparison with numerical calculations shows a good agreement as long as Tmin is nowhere less than 0.6Tmax. Layers with stronger anisotropy are also allowed, provided these are embedded in a system with layers of weaker anisotropy.