Abstract

Groundwater resources in crystalline rock are typically associated with the weathered and fractured zones that are well connected to the surface. However, these zones are highly-productive aquifers. In this paper, numerical simulations of a conceptual hydrogeological model show that the flow to such strongly transmissive fractured zones is controlled by their Transmissivity or by their structure. While leakage through the regolith unit is generally the major factor of recharge that sometimes occurs at least close to the outcrop of the fractured zone where the overlying rock is thinner and guarantees the availability of some groundwater. This is precisely the case of the Pallisa aquifer (eastern Uganda) located in a crystalline rock geologic setting, where groundwater in a shallowly fractured zone is used as the source of water supply for the rural poor. Even though the model was constructed as a simplified conceptual model, it constitutes the first attempt to simulate the entire Pallisa aquifer. The hypothesis of a continuous porous medium unit was sustainable as a first approximation to construct a numerical Model muse model covering the full extent of the aquifer. The model was calibrated for a steady-state condition. Simulation results show that the weathered and fractured zones represent potential aquifers under a large variety of hydrogeological conditions. The leakage through the regolith to the basement complex fractured rock unit enhances water availability.

Keywords: Modeling; Fractured-basement-aquifer; Pallisa district;  Hydrogeology; Model muse