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The four main river systems in the country are:
- The Komati and Lomati systems, in the north of the country, both originate in South Africa and flow out of Swaziland back into South Africa, before entering Mozambique;
- The Mbuluzi River rises in Swaziland and flows into Mozambique;
- The Usuthu River, together with a number of major tributaries, originates in South Africa and flows out into Mozambique, forming the border between Mozambique and South Africa;
- The Ngwavuma, in the south of the country, rises in Swaziland and flows into South Africa before entering Mozambique.
The fifth river system contributing to the surface water resources of Swaziland is the Pongola River, which is found in South Africa, south of Swaziland. The Jozini dam, built on the South African side, floods some land on the Swaziland side and the water is available for use in Swaziland.
The total renewable water resources of the country are 4.51 km3/year, with 1.87 km3/year or 42 percent originating from South Africa (Table 4). A quantitative assessment of groundwater resources of the country has not been undertaken. It is estimated that the groundwater resource potential is about 21 m3/s countrywide, which is equal to 0.66 km3/year, while the bulk of the groundwater resources occurs in the Highveld and Middleveld regions. With the exception of the post-Karoo igneous intrusive formation and the recent thin alluvia along the major river valleys, the strongly consolidated rocks of the Archean Basement Complex and the Karoo system underlie practically all of Swaziland and limit the groundwater development potential of the country.
There are nine major dams with a height of more than 10 metres and with a total storage capacity of about 585 million m3. Seven are used for irrigation purposes, one for hydroelectric purposes and one for water supply (Table 5).