J. Kotze, G. van Tonder, I. Dennis, and S. Zimmermann (South Africa)
Sustainable yield, Groundwater/surface water interaction; baseflow
This study uses a phased approach to groundwater development in the Mpumalanga Province of South Africa. It is shown that the sustainable wellfield yield is easily over-estimated using short-term pump testing interpretations and simple catchment water balance calculations, not recognising surface water/groundwater interaction and riparian vegetation water use. In Phase I, a pilot wellfield and conceptual site model were established. In Phase II the wellfield was extended to fourteen boreholes with a collective yield of about 5 Ml/day, based on the preliminary wellfield exploitation potential. A long-term pump test with an extensive monitoring program was carried out. Interpretation of these data, as well as detailed water balance calculations, base flow separation and numerical modelling, indicated that the long-term sustainable yield of the aquifer is only 1.8 Ml/day, about 35% of the original exploitation potential. Minimum, moderate and maximum abstraction scenarios are proposed, with the possibility of baseflow reduction increasing with each proposed scenario. The paper also illustrates that the best way to determine aquifer sustainable yield is to stress the aquifer over a short duration, followed by detailed data analysis.
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