Mega-fans are inland riverine deltas occuring in endorheic basins. Their potential as hosts of major aquifer systems has only been recognized rather lately.
The Cubango Mega-fan in Northern Namibia contains three aquifer systems, of which the deep one was only found at the end of the 1990s. Due to its thickness of up to 100 m, its large size and good water quality it is a game changer for the arid North of Namibia. Its spatial distribution and sedimentological background was investigated through core drilling and both geophysical and hydrogeological techniques. Due to the large size of the system, data scarcity is a constant issue affecting the exploration and management of this resource.
Core drilling revealed that the system comprises two major formations of Tertiary age, originating from different source Areas. The cores also contain an archive of the development of the climate of southwestern Africa. The sedimentary background defines the hydrogeological structures.
Groundwater modeling was applied to investigate the rate and location of groundwater recharge. Recharge rates are as low as 2-3 mm/a and limit potential extraction. This needs to be considered in management plans. Remote sensing (satellite radar altimetry) was applied to confirm the recharge areas. They are found in Southern Angola, making it a transboundary aquifer system.
Similar mega-fan systems can be found in other parts of Africa and worldwide. Their hydrogeological potential is high but needs to be investigated in the future. The Namibian case can serve as a blueprint.