Dramatic water supply problems in southern Africa: BGR hydrogeologists call for new exploration strategy for semi-fossil aquifers

Long-lasting periods of drought due to climate change are causing significant water supply problems also in southern Africa - with increasingly serious consequences for agriculture as well as directly for the people. In large cities such as Cape Town, drinking water has already to be rationed. Current projects of the Federal Institute for Geosciences and Natural Resources (BGR), Germany indicate that water resources in deeper rock formations can provide additional sources and offer an important contribution to solving the water supply problems in southern Africa.

Cattle watering hole in the dry savanna of northern Namibia Source: BGR

In South Africa, Namibia and Botswana, precipitation rates have lately been well below the long-term average. The result: Most of the larger reservoirs are currently filled to only 10 to 30% of their capacity. Water levels in many rivers are either very low or rivers have dried up completely. Groundwater has also been regularly overused. More water is abstracted from aquifers than is replenished by natural infiltration. This has dramatic consequences. “At some point, certain regions in southern Africa are literally left high and dry,” explains Prof. Dr. Thomas Himmelsbach, Director of the Department “Groundwater and Soil Science” at BGR.

Through projects in research and development cooperation, BGR hydrogeologists and geophysicists have demonstrated alternative options, how southern Africa could address the continuous problems with its water supply. BGR scientists carried out a targeted exploration of previously unknown semi-fossil aquifers. One of these aquifers is located at several hundred meters depth as a transboundary resource between Namibia and Angola. The Ohangwena II Aquifer, which was discovered only in the late 1990s, is now considered by the Namibian government as a new strategic water resource for the arid north of the country and is already being developed.

The results of numerical groundwater modeling, based on extensive geophysical surveys, groundwater age dating and satellite-based remote sensing, confirm that this semi-fossil aquifer is slowly replenishing by nature. Even if the groundwater recharge is only very small compared to Germany, due to the enormous extent of the aquifer the quantities of water are nevertheless large enough, to plan for a sustainable management of these groundwater resources. Himmelsbach: “In phases of prolonged droughts, the Ohangwena groundwater reserves can at least temporarily support the water supply in northern Namibia.”

New scientific findings of the BGR scientists suggest the existence of further, large groundwater resources that are related to large tectonic trough faults within the continent, as well as intra-continental and coastal river deltas. “To develop these aquifers a paradigm shift is required in hydrogeological exploration. Groundwater development in semi-arid areas, most notably in southern and eastern Africa, will therefore need to move away from coincidental findings to an exploration strategy that is largely based on methods of oil and gas exploration,” stresses Himmelsbach.

For the BGR expert, a combination of structural geological analyses, targeted geophysical investigations as well as an assessment of satellite images would be necessary for the exploration. Such an exploration need to be supported by drilling and the analysis of sediment properties. Subsequent investigations of water samples with regard to their isotopic signature and hydro-chemical nature could clarify questions about the age and origin of the groundwater. Himmelsbach: “On the basis of numerical models the prerequisites for a sustainable utilisation and long-term protection of these groundwater resources could be generated.”