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South Africa drains into four major systems:
- The Orange river, rising in the Lesotho Highlands and draining approximately 48 percent of the country (606 000 km²) to the Atlantic Ocean together with its tributaries, in particular the Caledon and the Vaal rivers. Total mean annual runoff is 11 100 million m³.
- The Limpopo river basin, draining the plateau north of the Witwatersrand ridge, i.e. approximately 14 percent of the country, to the Indian Ocean with its major tributaries such as the Crocodile and the Olifants river. This basin has a mean annual runoff of 5 100 million m³.
- All other rivers draining into the Indian Ocean, the largest of which is the Tugela river. They cover in total approximately 29 percent of the country with a mean annual runoff of 28 000 million m³.
- Rivers draining the Fold mountains of the south-western Cape into the Atlantic and Indian Oceans. They cover in total approximately 9 percent of the country, with a mean annual runoff of 5 000 million m³. The most important rivers in this area are the Olifants and the Breede rivers.
River flows reflect the rainfall pattern. Rivers that have their origin on the eastern great escarpment and in the Fold mountains of Western Cape normally have perennial flows. Rivers that originate in the immediate adjoining areas have periodic flows, whereas rivers that originate on the western great plateau have highly episodic flows.
The 19 Water Management Areas (WMAs) that were defined according hydrological catchments by the first National Water Resources Strategy (NWRS), have been merged into 9 WMAs corresponding to the 9 regional offices of the Department of Water and Sanitation (DWS) in the second NWRS. These 9 WMAs are: Berg Olifants, Breede Gouritz, Inkomati Usuthu, Limpopo, Mzimvubu Tsitsikamma, Olifants, Orange, Pongola Mtamvuna and Vaal (DWS, 2014).
Although groundwater is limited due to the geology of the country and large porous aquifers occur only in a few areas, it is often the primary source in the rural and more arid areas, as well as for many towns. It also supplies water to large irrigated areas, livestock and many mines and industries (DWA, 2013). It is expected that groundwater use for human consumption will further increase, especially in the western part of the country which lacks perennial rivers.
Internal renewable surface water resources are estimated at 43 000 million m³/year and renewable groundwater resources at around 4 800 million m³/year, but 3 000 million m³/year is considered to overlap between surface water and groundwater, which gives a value of total internal renewable water resources (IRWR) of 44 800 million m³/year (Table 2). Surface water entering the country is estimated at 6 600 million m³/year, which is the inflow from Lesotho through the Orange river (5 200 million m³/year), from Swaziland through the Maputo and Komati rivers (1 100 million m³/year) and from Botswana through the bordering Limpopo river (300 million m³/year). South Africa receives from the Orange river an increasing, guaranteed amount of water, from 57 in 1995 to 2 208 million m³/year in 2020 through the Lesotho Highlands Water Project. Surface water leaving the country to other countries is estimated at 10 850 million m³/year of which 50 million m³/year according to an agreement through the Orange river to Namibia, resulting in 6 550 million m³/year of external renewable water resources, as no groundwater enter the country. This brings the total renewable water resources to 51 350 million m³/year, or 942 m³/year per capita in 2015, and the dependency ratio is thus around 13 percent.
Wetlands mapped in South Africa cover a total area of 2.9 million hectares in 2012. About 35 to 60 percent of the wetlands have been lost or severely degraded (DWA, 2013b) from the initial 4 million ha cumulated by about 115 000 wetlands (DAFF, 2015). Degradation originates from pollution and unsustainable developments of various activities, in particular mining. In 2013, South Africa had listed 21 Ramsar sites extending over 554 136 ha, including the Natal Drakensberg Park and the Saint Lucia system (Ramsar, 2013).
South Africa's inland water area covers 600 000 ha, including its main natural lakes Lake St Lucia and Lake Sibaya in the iSimangaliso Wetland Park and artificial lakes or reservoirs created by dams. The total dam capacity is estimated at 31 020 million m³ stored in over 5 100 dams of which 320 are managed by the Department of Water Affairs (DWA), including 756 large dams, i.e. dams with wall height over 15m and capacity exceeding 3 million m³ (DWA, 2013c). The new De Hoop dam in the Mpumalanga province on the Steelpoort river, an important tributary of the Olifants river in the Limpopo river basin, was completed in 2014. Some existing dams, the Hazelmere and Clanwilliam dams, are planned to be heightened and several new dams are under construction (SANCID, 2015):
- Spring Grove dam on the Mooi River (KwaZulu Natal province)
- Nwamitwa dam on the Groot Letaba river (Limpopo province)
- Mzimvubu dam (East Cape provinve)
- Nwamithwa dam on the Great Letaba (Mpumalanga province)
Because of uneven temporal and spatial distribution of rainfall (43 percent of the rain falls on 13 percent of the land), and major cities being located far from the largest rivers, large transfers of water are made between catchments: 28 inter-basin transfer schemes have a total discharge exceeding 7 000 million m³/year (DWA, 2013c).