Orange–Senqu River Basin Transboundary Diagnostic Analysis
Aquifers
These largely hidden resources deserve special mention. They cannot be regarded separately from the river and other aquatic ecosystems because they are linked, and degradation of one contributes to the degradation of the other. In addition, many rural areas of the basin and the drier western areas of the basin are almost wholly dependent on groundwater sources to meet their supply needs.
Š UNOPS/Christoph Mor
This artesian groundwater well in Stampriet, Namibia, supports the irrigation of fruit and vegetable cultivation.
Although groundwater resources are limited in comparison to surface water, the extent, quality and contribution they possibly make to the water balance is not well understood. There are insufficient data regarding this hidden resource. The concern is that in some areas abstraction is not sustainable and that it is impacting water levels. Lowering of groundwater levels hampers the ability of plants to take up water and leads to the desiccation of springs and, consequently, destruction of habitats. Invasions by the alien plant Prosopis is considered a significant threat to groundwater sources in the western areas of the basin. Salinity is often naturally high in groundwater, especially in the Nama Karoo biome. Salinisation as a result of increasing total dissolved solids (TDS), nitrates and fluorides is another concern. In extreme cases, over-abstraction can also reduce fluid pressure in confined and artesian aquifers and cause aquifer deformations through the compaction of geological material. Heavy metals can also leach out into the groundwater and find their way into surface water courses. Groundwater sources are also highly susceptible to pollution from land-use activities through seepage and runoff, even in sparsely populated rural settings. Reversing pollution problems in groundwater is much more difficult than dealing with similar issues in surface sources. In the region as a whole, the transboundary implications of groundwater use are not particularly significant. A major factor, however, is that reduced flows in the lower Orange River will inevitably lead to a significant reduction in aquifer resources close to the river.
Groundwater is used for stock watering in the lower Orange sub-basin.
Improving understanding of groundwater sources through monitoring and implementing regulations on the abstraction and protection of groundwater resources would go a long way to addressing these concerns.
Š UNOPS/Leonie Marinovich
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