Groundwater whirls in heterogeneous and anisotropic layered aquifers

Groundwater flow is affected by heterogeneity in the anisotropy. Our investigations started with some simple numerical experiments consisting of one or two homogeneous anisotropic blocks. Three-dimensional pathlines in such models have the shape of spirals; bundles of spiralling pathlines were termed 'groundwater whirls'. The present research also deals with hypothetical models of stratified aquifers. Investigations are extended to include aquifers in which all layers have a laterally heterogeneous anisotropy. All models were built with the finite element model MicroFEM. In these tests the heterogeneity of the hydraulic conductivity is not taken into account. Pathlines show complex patterns of clockwise and counter-clockwise groundwater whirls because of the heterogeneity in the anisotropy. The practical consequence of groundwater whirls is that water is exchanged between aquifer layers, even when the gradient of the hydraulic head in the aquifer as well as the general direction of flow is parallel to the layered structure of the aquifer. This may have a significant impact on contaminant spreading throughout the aquifer. Several analytic solutions have been developed that confirm the existence of groundwater whirls in anisotropic layered aquifers.