Represas En Africa

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FAO AQUASTAT Dams Africa – 070524

DAMS AND AGRICULTURE IN AFRICA
Prepared by the

AQUASTAT Programme
May 2007 Water Development and Management Unit (NRLW) Land and Water Division (NRL) Food and Agriculture Organization of the United Nations (FAO)

Dams
According to ICOLD (International Commission on Large Dams), a large dam is a dam with the height of 15 m or more from the foundation.If dams are 5-15 metres high and have a reservoir volume of more than three million m3, they are also classified as large dams. Using this definition, there are more than 45 000 large dams around the world, almost half of them in China. Most of them were built in the 20th century to meet the constantly growing demand for water and electricity. Hydropower supplies 2.2% of the world’s energy and 19%of the world’s electricity needs and in 24 countries, including Brazil, Zambia and Norway, hydropower covers more than 90% of national electricity supply. Half of the world’s large dams were built exclusively or primarily for irrigation, and an estimated 30-40% of the 277 million hectares of irrigated lands worldwide rely on dams. As such, dams are estimated to contribute to 12-16% of world foodproduction. Regional inventories include almost 1 300 large and medium-size dams in Africa, 40% of which are located in South Africa (517) (Figure 1). Most of these were constructed during the past 30 years, coinciding with rising demands for water from growing populations. Information on dam height is only available for about 600 dams and of these 550 dams have a height of more than 15 m.Information on reservoir capacity is available for all inventoried dams and more than half have a capacity of more than three million m3. Less than 5% of the dams has a reservoir capacity of more than 1 billion m3, 10% between 0.1 – 1 billion m3, 20% between 0.01 – 0.1 billion m3, and 35% between 0.001 – 0.01 billion m3. The majority of dams in Africa have been constructed to facilitate irrigation (52%)and to supply water to municipalities (20%). Almost 20% of dams have multiple purposes, of which irrigation is almost always one of the purposes. Although only 6% of dams were built primarily for electricity generation, hydroelectric power accounts for more than 80% of total power generation in 18 African countries, and for more than 50% in 25 countries. Only 1% of African dams have beenconstructed to provide flooding control, according to the World Commission on Dams. Considering dams with a reservoir capacity of over 1 billion m3, Africa counts 54 of such dams with a total reservoir capacity of about 726 billion m3, or almost 90% of the capacity of all dams in the inventory (Annex 1). Of these dams, 20 are multipurpose dams, mainly used for both hydroelectricity and irrigation, 22 areused mainly for hydroelectricity and 12 mainly for irrigation. Eight of these large dams have a reservoir capacity of over 10 billion m3 each and three of over 100 billion m3 each (Kariba on the Zambezi River with 188 billion m3, Aswan on the Nile River with 162 billion m3 and Akosombo on the Volta River with 148 billion m3). The reservoir capacity of these three dams represents almost 70% of thetotal capacity of the 54 dams. While the Kariba Dam and the Akosombo dam have been built for hydroelectricity, the Aswan Dam was built for irrigation in Egypt. The distribution of the large dams within the different river basins is given in Table 1. Figure 2 shows the major river basins in Africa.

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FAO AQUASTAT Dams Africa – 070524

Large-scale irrigation schemes
The most recentsurvey indicates that the total area under irrigation in Africa is about 13.4 million ha, of which almost 70 percent are located in five countries only (Egypt, Madagascar, Morocco, South Africa and Sudan) (Annex 2). The total area under irrigation in ten large international river basins is about 7 million ha, which is just over half of the total area under irrigation in Africa (Table 2). The...
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