Abstract
The Grootfontein Aquifer, part of the important North West dolomite aquifers, supplies about 20% of Mahikeng’s domestic water needs. Over-abstraction caused the large natural spring draining the aquifer to disappear in 1981, and groundwater levels have since fallen nearly 30 m in the vicinity of the former spring. Analysis of water levels and a water balance using recent assessments of groundwater abstractions confirm past work describing the hydrogeological functioning of the aquifer, and suggest that current abstractions need to fall by between 19 and 36 ML/day (7 and 13 Mm3/a) to bring the aquifer back into longterm balance. Continued over-abstraction at Grootfontein implies increasing risk to Mahikeng’s water supply, and illuminates the larger challenge of ensuring groundwater use in the North West dolomites that is sustainable and in the public interest.
Highlights
The Grootfontein aquifer is of particular interest because it is well studied hydrogeologically, and it is part of the domestic water supply of Mahikeng, the capital of North West Province
The discrepancy between long-term estimates based on water-level changes, and estimates based on current irrigation abstractions, is partly due to increasing irrigation
Recent sampling confirms that the groundwater quality is good
Summary
The Grootfontein aquifer is of particular interest because it is well studied hydrogeologically, and it is part of the domestic water supply of Mahikeng, the capital of North West Province. Some of the springs draining North West dolomite compartments are large and important – for example, the Molopo Eye near Mahikeng and the Maloney’s Eye near Mogale City are the sources of the Molopo and Magalies Rivers, respectively. Both have long-term average flow rates exceeding 30 ML/day or 11 Mm3/a (DWS NGA data; Vahrmeijer et al, 2013). Today the water table in the vicinity of the old Grootfontein Eye is more than 28 m below ground level This fall in groundwater level has led to some of the municipal boreholes failing, and it threatens some of the irrigation boreholes. The dewatered state of the Grootfontein aquifer means that it cannot be used as a backup supply during a prolonged drought, a temporary breakdown at the Setumo Dam, or another crisis
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