In the past two years, Uganda has witnessed an influx of nearly one million refugees who have settled in the sparsely populated northwestern region of the country. This rapid population growth has created high demand for clean water resources. Water supply has been unable to keep pace with demand because the fractured rock aquifers underlying the region often produce low yielding wells. To facilitate management of groundwater resources it is necessary to quantify the spatial distribution of groundwater.
In fractured rock aquifers, there is significant spatial variability in water storage because fractures must be both connected and abundant for water to be extracted in usable quantities. Two conceptual models were evaluated to determine the groundwater storage mechanism in the fractured crystalline bedrock aquifers of northwestern Uganda: permeability is controlled by faulting which opens up fractures in the bedrock, and permeability is controlled by weathering, which occurs when water dissolves components of rock. The conceptual models were evaluated using four inverse groundwater MODFLOW models based on known head and estimated flux targets. The first model was based on the underlying bedrock units, the second model incorporated both bedrock units and known fault zones, the third model incorporated bedrock units and land surface slopes (thought to be a predictor of deep weathering), and the fourth model combined slope, faults and bedrock units. Predicting permeable zones is vital for water well drilling in much of East Africa and South America where there is an abundance of both fractured rock and tectonic activity.
Given that the population of these developing regions is growing, the demand for sufficient clean water is likely to increase significantly in the next few decades. Thus, it is necessary to improve our ability to predict locations of permeable zones in fractured rock aquifers.
Department of Geology