Groundwater in SADC
Groundwater is a critical source of water for people living in the SADC region, with approximately 37 % of the population of the region relying on formal or improved groundwater sources, 23 % from formal surface water supplies and 40 % relying on unimproved groundwater and surface water sources. This level of dependence is combined with the fact that approximately one third of the population of the region live in drought-prone conditions, making groundwater an even more precious resource (SADC 2011).
Groundwater is used extensively throughout the southern African region, including the Limpopo River basin, supplying a large percentage of water for irrigation and rural water supply schemes (FAO 2004). This is especially true in rural areas, located away from surface water resources. Groundwater is also used extensively by the mining industry in the basin (CGIAR 2003).
Groundwater plays an important role in water supply in rural areas of the South African portion of the Limpopo River basin, providing domestic and irrigation water in the order of approximately 850 Mm³/year. Many of the rural communities of this region are located on or near marginal aquifers with potential yields of 2 l/s (FAO 2004). Groundwater quality is relatively poor due to high salinity. Groundwater resources in the Dendron area of the Limpopo Province of South Africa have been severely overexploited.
Groundwater Resources in southern Zimbabwe are not very productive, with many of the domestic wells and boreholes supplying individual households and small communities drying up before the end of the dry season (FAO 2004). Land degradation resulting from poor land use management have meant that the remaining dambo wetlands of the Matabeleland south province have long dried up.
To date, no basin-wide groundwater recharge assessment has been performed, but localised data scattered across the basin does provide a certain insight into the recharge situation in the basin.
Groundwater recharge in the Limpopo river basin in Botswana is thought to be very low, with rates of approximately 1 to 3 mm/yr in the Kalahari and central regions, with 5 to 9 mm/yr in the eastern regions, excluding the Tuli block. Total water abstraction in Botswana in 1990 was 76 x more than annual recharge, with abstraction predicted to rise by almost 100 % by 2020.
In addition to the local aquifer systems, the Limpopo River basin includes a series of transboundary aquifers. These aquifers are particularly important as they are shared by two or more countries, requiring cooperative management of water use/abstraction and sources of pollution that may affect them.
Exploitation of Groundwater
Groundwater is primarily abstracted through boreholes (groundwater wells), drilled from the surface by a groundwater drilling rig. The actual number of boreholes may vary significantly as many boreholes are not registered when drilled or were drilled prior to the creation of national inventories.
Overall the potential yields of boreholes in the Limpopo River basin is relatively low, limiting the extent to which groundwater can be used for large scale water supply. The exceptions to this are areas accessing the alluvial aquifers along the Limpopo River.
Over-Exploitation of Groundwater
The Dendron area is one of the prime examples in South Africa where uncontrolled extraction of groundwater on private farms for irrigation purposes greatly exceeded recharge, leading to unsustainable development. In the 1970s and 1980s, on a cluster of farms on which boreholes supplied copious volumes of groundwater, a flourishing potato production industry developed in this semi-arid area. The area receives 440 mm mean annual summer rainfall, and the seasonal recharge varies between 3 and 35 mm (1-8 percent of the MAP). After a number of years and great expenditure, the granite aquifer became depleted and potato production ground to a permanent halt.
There were two issues in this case. The first was a lack of recognition of the fossil nature of the groundwater body, and the second was the way safe delivery was estimated. Borehole yield information was based on the initial drilling-rig blow test of the borehole. This test was later shown to be overgenerous. In recent years, DWAF has been recommending 30-50 percent of the blow yield for long-term use (Bang and Stimie, 1999).
Source: FAO 2004
The majority of groundwater information available in the region is at a country-level, with very little information aggregated at a basin or regional scale. SADC, supported by international financial and technical agencies, is currently leading an initiative to develop regional groundwater information resources to support transboundary water resources management and cooperation.
While much of the detailed information available on groundwater at a country-level such as borehole data use different protocols for naming and storing information, making integration problematic; general geological and hydrogeological information is to a large extent compatible (LBPTC 2010). As a result regional geology and hydrogeology maps are becoming available for the region.
Limpopo River Awareness Kit