Coincidence of well fields and the tectonic basins in the precambrian shield area of Southeast Botswana

A compilation of ground-water exploration data in southeastern Botswana reveals that the occurrence of ground water is not primarily controlled by large-scale fracture systems and lithologies, but by folds in the Precambrian basement. Two sets of superimposed synforms and antiforms generate a “chess-board” pattern of dome and basin structures. Successful boreholes and well fields appear to be preferentially situated in the areas where synforms intersect, suggesting that tectonic basins coincide with ground-water basins. Small-scale fractures and favorable lithologies doubtless improve the permeability within a ground-water basin, but appear to be subordinate in determining the distribution of large-scale aquifer characteristics.