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Environment and health
Overall, water quality is comparatively high (OECD, 2015). However, only one third of the mainstream rivers are in good condition and one quarter of the river ecosystems are critically endangered. This last ratio reaches almost half of the river ecosystems when considering only the main rivers without the tributaries (OECD, 2015). Water monitoring since 2006 shows a decline of biological and chemical water quality of surface water and groundwater due to various factors:
- Wastewater: the wastewater treatment capacity is not sufficient in South Africa to treat all wastewater (DWA, 2013), resulting in pollution both from untreated wastewater and from treated effluents not meeting the standards and causing microbial contamination, in particular due to rapid urbanization in informal shanty towns that rise near cities.
- Acid Mine Drainage (AMD): water flowing from closed mines contains high concentrations of metals, sulphides and salts contaminating both surface water and groundwater. This occurs particularly in Gauteng province, as well as in the Witbank and Vryheid areas. AMD also originates from runoff from open pits, stockpiles and mine tailings (OECD, 2013). The Olifants and Vaal rivers, located in highly concentrated mining activity areas, are rich in sulphates, alkalinity and magnesium among others (DWA, 2012). It is considered as the most pressing issue in water management in South Africa.
- Salinization: it is widespread in the country, both naturally by leaching from geological features or groundwater discharge, or due to human activity. Natural salinization from sodium and chloride affects mostly the Sout and Berg rivers in the Western Cape, but it is coupled with seawater intrusion and intensive agricultural activities such as citrus and grapes cultivation using extensive fertilization. Rise in salinity in groundwater reflects local land-based activities such as in the Lower Vaal and the Upper Orange. The Nossob and Auob rivers flowing from Namibiaľnorthern sub-catchment of the Lower Orangeľexperience rapidly increasing salinity. On the contrary, improvement of the salinity levels occurs in the Limpopo and Olifants basins and small aquifers of the western Crocodile, Marico and northern Lower Vaal basins (DWA, 2012). An estimated 260 000 ha of irrigated land in South Africa is affected by waterlogging and/or salinization.
- Eutrophication: this is a serious problem in Haartebeespoort, Rietvlei and Roodekoppies dams, where efforts to control it are in place (DWA, 2012).
Water contamination also occurs through toxicants, altered flow regime, suspended solid, radioactivity and agrichemicals (DWA, 2013). As agriculture mostly uses water that was not previously treated, except for the small portion using treated wastewater, there is thus a concern on its impact when irrigating agricultural products (DAFF, 2012b).
The National Water Act 1998 specifies that a specific amount of water be kept earmarked to satisfy ecological requirements. All water balance calculations must include a provision for this ecological reserve to remain in the river, although the application of this principle has not been practically described. However, it has a positive impact by stopping unbridled development. It is nonetheless, difficult to meet environmental needs in fully developed rivers, such as the Vaal, Mgeni and Crocodile East, without reallocation of water licences. For partially developed rivers, such as the Olifants and Mkuze rivers in particular, ecological reserve will help to avoid any further degradation. For the few rivers that have not been developed, the Mzimvubu and Mkomazi in particular but small coastal rivers also, applying the ecological reserve will be easier but should not be overlooked (DWAF, 2009).
Sedimentation of dams is a problem, especially in the dams that impound parts of the Central Plateau that are covered by the very old rock of the Karoo (Karroo) System and its sediments. As a general rule the soils that develop from this material are prone to erosion and hence some dams in the central parts of the country have lost a substantial amount of their capacity. The exact dimensions of this problem have not been determined but some exceptional cases are known where dams have lost more than 25 percent of their capacity over the last 90 years.