Deformations and the Karoo aquifers of South Africa

This paper introduces a new three-dimensional poro-elastic model for the flow of groundwater through an aquifer. The main purpose with the model was to investigate to what extent deformations are responsible for the observed physical behaviour of Karoo aquifers in South Africa, which cannot be explained with the conventional porous flow models. This applies in particular to the effect that linear and nonlinear deformations may have on the behaviour of the aquifer. The model not only showed that many of the observations can be explained by the nonlinear deformation of the aquifer, but also that the parameters specific storativity and hydraulic conductivity (and their derivatives storativity and transmissivity) are not independent parameters, as assumed in the conventional literature on groundwater motion. The real independent parameters are the rate at which a borehole in the aquifer is pumped and the mechanical properties of the aquifer. A comparison of the model results and known transmissivities of these aquifers showed that the aquifers are highly anisotropic.