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 2,574-kilometre-long river (1,599 mi) rises 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 noted 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, the Kariba Dam, which provides power to Zambia and Zimbabwe, and the Cahora Bassa Dam in Mozambique, which provides power to Mozambique and South Africa. There is also a smaller power station at Victoria Falls.
Course of the river
The Zambezi and its river basinThe river rises in a black marshy dambo in north-west Zambia, in dense undulating miombo woodland, 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, running nearly east-west and falling abruptly to the north and south. 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.
The river flows to the south-west into Angola for about 240 kilometres (150 mi), then is joined by sizeable tributaries such as the Luena and the Chifumage flowing from highlands to the north-west. It turns south and develops a floodplain, with extreme width variation between the dry and rainy seasons. It enters dense evergreen Cryptosepalum dry forest, though on its western side, Western Zambezian grasslands also occur. Where it re-enters Zambia it is nearly 400 metres (1,300 ft) wide in the rainy season and flows rapidly, with rapids ending in the Chavuma Falls, where the river flows through a rocky fissure. The river drops about 400 metres (1,300 ft) in elevation from its source at 1,500 metres (4,900 ft) to the Chavuma Falls at 1,100 metres (3,600 ft), in a distance of about 400 kilometres (250 mi). From this point to the Victoria Falls, the level of the basin is very uniform, dropping only by another 180 metres (590 ft) in a distance of around 800 kilometres (500 mi).
The first of its large tributaries to enter the Zambezi is the Kabompo River in the north-western province of Zambia. The savanna through which the river has flowed gives way to a wide floodplain, studded with Borassus fan palms. A little farther south is the confluence with the Lungwebungu River. This is the beginning of the Barotse Floodplain, the most notable feature of the upper Zambezi, but this northern part does not flood so much and includes islands of higher land in the middle.
Thirty kilometres below the confluence of the Lungwebungu the country becomes very flat, and the typical Barotse Floodplain landscape unfolds, with the flood reaching a width of 25 km in the rainy season. For more than 200 km downstream the annual flood cycle dominates the natural environment and human life, society and culture.
Eighty kilometres further down, the Luanginga, which with its tributaries drains a large area to the west, joins the Zambezi. A few kilometres higher up on the east the main stream is joined in the rainy season by overflow of the Luampa/Luena system.
A short distance downstream of the confluence with the Luanginga is Lealui, one of the capitals of the Lozi people who populate the Zambian region of Barotseland in Western Province. The chief of the Lozi maintains one of his two compounds at Lealui; the other is at Limulunga, which is on high ground and serves as the capital during the rainy season. The annual move from Lealui to Limulunga is a major event, celebrated as one of Zambia’s best known festivals, the Kuomboka.
After Lealui, the river turns to south-south-east. From the east it continues to receive numerous small streams, but on the west is without major tributaries for 240 km. Before this, the Ngonye Falls and subsequent rapids interrupt navigation. South of Ngonye Falls, the river briefly borders Namibia’s Caprivi Strip. The strip projects from the main body of Namibia, and results from the colonial era: it was added to German South-West Africa expressly to give Germany access to the Zambezi.
Below the junction of the Cuando River and the Zambezi the river bends almost due east. Here, the river is broad and shallow, and flows slowly, but as it flows eastward towards the border of the great central plateau of Africa it reaches a chasm into which the Victoria Falls plunge.
The Victoria Falls are considered the boundary between the upper and middle Zambezi. Below them the river continues to flow due east for about 200 kilometres (120 mi), cutting through perpendicular walls of basalt 20 to 60 metres (66 to 200 ft) apart in hills 200 to 250 metres (660 to 820 ft) high. The river flows swiftly through the Batoka Gorge, the current being continually interrupted by reefs. It has been described as one of the world’s most spectacular whitewater trips, a tremendous challenge for kayakers and rafters alike. Beyond the gorge are a succession of rapids which end 240 km (150 mi) below Victoria Falls. Over this distance, the river drops 250 metres (820 ft).
At this point, the river enters Lake Kariba, created in 1959 following the completion of the Kariba Dam. The lake is one of the largest man-made lakes in the world, and the hydroelectric power-generating facilities at the dam provide electricity to much of Zambia and Zimbabwe.
The Luangwa and the Kafue are the two largest left-hand tributaries of the Zambezi. The Kafue joins the main river in a quiet deep stream about 180 metres (590 ft) wide. From this point the northward bend of the Zambezi is checked and the stream continues due east. At the confluence of the Luangwa (15°37′ S) it enters Mozambique.
The middle Zambezi ends where the river enters Lake Cahora Bassa (also spelled Cabora Bassa). Formerly the site of dangerous rapids known as Kebrabassa, the lake was created in 1974 by the construction of the Cahora Bassa Dam.
The lower Zambezi’s 650 km from Cahora Bassa to the Indian Ocean is navigable, although the river is shallow in many places during the dry season. This shallowness arises as the river enters a broad valley and spreads out over a large area. Only at one point, the Lupata Gorge, 320 km from its mouth, is the river confined between high hills. Here it is scarcely 200 m wide. Elsewhere it is from 5 to 8 km wide, flowing gently in many streams. The river bed is sandy, and the banks are low and reed-fringed. At places, however, and especially in the rainy season, the streams unite into one broad fast-flowing river.
About 160 km from the sea the Zambezi receives the drainage of Lake Malawi through the Shire River. On approaching the Indian Ocean, the river splits up into a delta. Each of the four prime tributaries, Kongone, Luabo and Timbwe, is obstructed by a sand bar. A more northerly branch, called the Chinde mouth, has a minimum depth at low water of 2 m at the entrance and 4 m further in, and is the branch used for navigation. 100 km further north is a river called the Quelimane, after the town at its mouth. This stream, which is silting up, receives the overflow of the Zambezi in the rainy season.
Geological changes to the course
More than two million years ago, the Upper Zambezi river used to flow south through what is now the Makgadikgadi Pan to the Limpopo River. The land around the pan experienced tectonic uplift (perhaps as part of the African superswell) and a large lake formed, and extended east.
Meanwhile, 1,000 kilometres (620 mi) east, a western tributary of the Shire River in the East African Rift’s southern extension through Malawi eroded a deep valley on its western escarpment. At the rate of a few cm per year, this river, the Middle Zambezi, started cutting back the bed of its river towards the west, aided by grabens (rift valleys) forming along its course in an east-west axis. As it did so it captured a number of south-flowing rivers such as the Luangwa and Kafue.
Eventually the large lake trapped at Makgadikgadi (or a tributary of it) was captured by the Middle Zambezi cutting back towards it, and emptied eastwards. The Upper Zambezi was captured as well. The Middle Zambezi was about 300 metres (980 ft) lower than the Upper Zambezi, and a high waterfall formed at the edge of the basalt plateau across which the upper river flows. This was the first Victoria Falls, somewhere down the Batoka Gorge near where Lake Kariba is now.
Note : The above story is based on materials provided by Wikipedia