Water resources million cubic metres( see Table 1.11), equivalent to 66 per cent of the total mean annual runoff( DWAF, 2004). Surface water from dams and direct abstraction from rivers, accounted for 9 500 million cubic metres per annum, with a significant volume of the surface water yield( 3000 million cubic metres per annum) moved via inter-basin transfers to areas in the country where requirements exceed supply( DWAF, 2012).
Groundwater plays an important role, especially in rural water supplies. Because of the predominantly hard rock nature of the South African geology, only about 20 percent of groundwater occurs in major aquifers( DWAF, 2004). Some of the most favourable aquifers include: the Dolomites of the West and Far West Rand; Table Mountain Group Aquifers of the Western and Eastern Cape; Coastal sand aquifers in the Western and Eastern Cape, and northern KwaZulu- Natal. Other high yielding aquifers include basement granites in the Polokwane Dendron-Coetzer dam area, alluvial deposits along sections of major rivers such as the Limpopo, and parts of the Karoo Sequence associated with dolerite dykes and ring structures( DWAF 2012). The most recent estimate of sustainable potential yield of groundwater resources at high assurance is 7 500 million cubic metres per annum, while current groundwater use is estimated at around 2 000 million cubic metres per annum( DWAF, 2012).
Due to the poor spatial distribution of rainfall in the country, the natural availability of water across the country is also highly uneven. This situation is compounded by the strong seasonality of rainfall, as well as high within-season variability, over virtually the entire country. Consequently surface runoff is also highly variable. As a result, stream flow in South African rivers is at relatively low levels for most of the time. The sporadic high flows that do take place limit the proportion of stream flow that can be relied upon to be available for use( DWAF, 2004).
Four of South Africa’ s main rivers are shared with other countries. These are the Limpopo, Inkomati, Pongola( Maputo) and Orange
( Senqu) Rivers, which together drain about 60 per cent of the country’ s land area and contribute about 40 per cent of its total surface runoff( river flow). Approximately 70 per cent of its gross domestic product( GDP) and a similar percentage of the population are supported by water supplied from these rivers, making their judicious joint management of paramount importance to South Africa( DWAF, 2004).
To facilitate the management of water resources, the country has been divided into 19 catchmentbased water management areas as shown in Table 1.1. The table shows the mean annual runoff and the estimated average annual requirements for the ecological component of the Reserve per water management area, together with an estimate of the total storage capacity in large dams- full supply capacity exceeding1 million cubic metres- in each area. Of the 19 water management areas only the Mzimvubu to Keiskamma management area is currently not linked to another management area through intercatchment transfers. Eleven of the 19 water management areas share international rivers( DWAF, 2004). The catchment management areas are further mapped in Figure 4.2
1.2. Water Use Water provides economic benefits to a variety of users throughout its cycle, creating added value from both its productive use and measures to protect its quality and the integrity of the aquatic environment. More productive uses of water by industry, agriculture and energy will save costs for those businesses and release more freshwater for other beneficial uses. Withdrawing less from water systems reduces the need to expand infrastructure, and releases more water to support ecosystem services, including fisheries. Measures to mitigate water scarcity and water-related disasters will reduce economic and social losses across all sectors of society and all businesses.
Water is environmental capital that provides essential eco-system services with intrinsic value to society, apart from their impact on directly productive activities. The essential eco-system services
Figure 2.1 Rainfall and Evaporation( DWAF, 2004)
Water Management Area
Natural Mean annual runoff( 1)
Ecological Reserve( 1,2)
Storage in major dams( 3)
1. Limpopo 986 156 319 2. Luvuvhu / Letaba 1185 224 531
3. Crodile West and Marico
855 164 854
4. Olifants 2040 460 1078 5. Inkomati( 4) 3539 1008 768 6. Usuthu to Mhlatuzi( 5) 4780 1192 3692 7. Thukela 3799 859 1125 8. Upper Vaal 2423 299 5725 9. Middle Vaal 888 109 467 10. Lower Vaal 181 49 1375 11. Mvoti to Umzimkulu 4798 1160 827
12. Mzimvubu to keikamma
7241 1122 1115
13. Upper Orange( 6) 6981 1349 11711 14. Lower Orange( 7) 502 69 298 15. Fish to Tsitsikama 2154 243 739
16. Gouritz 1679 325 301 17. Olifants / Doring 1108 156 132 18. Breede 2472 384 1060 19. Berg 1429 217 295 Total for South Africa 49040 9545 32412
Table 1.1 Natural mean annual runoff and the ecological Reserve( million m ³/ a) and storage in major dams( million m ³)( DWAF 2004)
Figure 2.2 Catchment Management Areas( DWAF, 2004)
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