The Zambezi is the fourth-longest river in Africa, and the largest flowing into the Indian Ocean from Africa. The area of its basin is 1,390,000 square kilometres (540,000 sq mi), slightly less than half that of the Nile. The 3,540-kilometre-long river (2,200 mi) has its source in Zambia and flows through eastern Angola, along the eastern border of Namibia and the northern border of Botswana, then along the border between Zambia and Zimbabwe to Mozambique, where it crosses that country to empty into the Indian Ocean.
The Zambezi's most well-known feature is Victoria Falls. Other notable falls include the Chavuma Falls at the border between Zambia and Angola, and Ngonye Falls, near Sioma in Western Zambia. There are two main sources of hydroelectric power on the river. These are the Kariba Dam, which provides power to Zambia and Zimbabwe and the Cahora Bassa Dam in Mozambique, which provides power to both Mozambique and South Africa. There is also a smaller power station at Victoria Falls.
The river rises in a black marshy dambo in north-western Zambia, in undulating miombo woodland, quite dense in parts, about 1,524 m (4,900 ft) above sea level. Eastward of the source, the watershed between the Congo and Zambezi basins is a well-marked belt of high ground, falling abruptly north and south, and running nearly east-west. This distinctly cuts off the basin of the Lualaba (the main branch of the upper Congo) from that of the Zambezi. In the neighborhood of the source the watershed is not as clearly defined, but the two river systems do not connect.
The region drained by the Zambezi is a vast broken-edged plateau 900–1200 m high, composed in the remote interior of metamorphic beds and fringed with the igneous rocks of the Victoria Falls. At Shupanga, on the lower Zambezi, thin strata of grey and yellow sandstones, with an occasional band of limestone, crop out on the bed of the river in the dry season, and these persist beyond Tete, where they are associated with extensive seams of coal. Coal is also found in the district just below Victoria Falls. Gold-bearing rocks occur in several places.
Ecology of the delta:
As well as the Zambezi this section applies to the Buzi, Pungwe, and Save rivers which also drain the Zambezi basin. Together the floodplains of these four river floodplains make up the World Wildlife Fund's Zambezian coastal flooded savanna ecoregion. They are a mixture of open grassland and freshwater swamp inland from the Indian Ocean in Mozambique. Although the dams have stemmed some of the annual flooding of the lower Zambezi and caused the area of floodplain to be greatly reduced they have not removed flooding completely.
They cannot control extreme floods, they have only made medium-level floods less frequent. When heavy rain in the lower Zambezi combines with good runoff upstream, massive floods still happen and the wetlands are still an important habitat. However, as well as the shrinking of the wetlands further severe damage to wildlife was caused by uncontrolled hunting of animals such as buffalo and waterbuck during the Mozambique Civil War and now the conflict has ceased it is likely the floodplains will become more populated, and further damming has also been discussed. The only protected area of floodplain is the Marromeu Game Reserve near the city of Beira.
The north of the Zambezi basin has mean annual rainfall of 1100 to 1400 mm which declines towards the south, reaching about half that figure in the south-west. The rain falls in a 4-to-6-month summer rainy season when the Inter-Tropical Convergence Zone moves over the basin from the north between October and March. Evaporation rates are high (1600 mm-2300 mm) and much water is lost this way in swamps and floodplains, especially in the south-west of the basin.
The river supports large populations of many animals. Hippopotamuses are abundant along most of the calm stretches of the river, and many crocodiles are also present. Monitor lizards are found in many places. Birds are abundant, with species including heron, pelican, egret and African fish eagle present in large numbers. Riverine woodland also supports many large animals, such as buffalo, zebras, giraffes, elephants.
The Zambezi also supports several hundred species of fish, some of which are endemic to the river. Important species include cichlids which are fished heavily for food, as well as catfish, tigerfish, yellowfish and other large species. The bull shark is sometimes known as the Zambezi Shark after the river but is found around the world. It normally inhabits coastal waters but has been found far inland in many large rivers including the Zambezi.
Sewage effluent is a major cause of water pollution around urban areas, as inadequate water treatment facilities in all the major cities of the region force them to release untreated sewage into the river. This has resulted in eutrophication of the river water and has facilitated the spread of diseases of poor hygiene such as cholera, typhus and dysentery. The construction of two major dams regulating the flow of the river has had a major effect on wildlife and human populations in the lower Zambezi region.
When the Cahora Bassa Dam was constructed in 1973, its managers allowed it to fill in a single flood season, going against recommendations to fill over at least two years. The drastic reduction in the flow of the river led to a 40% reduction in the coverage of mangroves, greatly increased erosion of the coastal region and a 60% reduction in the catch of prawns off the mouth due to the reduction in emplacement of silt and associate nutrients. Wetland ecosystems downstream of the dam shrank considerably. Wildlife in the delta was further threatened by uncontrolled hunting during the civil war in Mozambique.
Length: 2,574 km (1,599 mi)
Basin: 1,390,000 km2 (536,682 sq mi)