The Zambezi (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers 1,390,000 km2 (540,000 mi2), slightly less than half of the Nile's. The 2,574 km (1,599 mi) river rises in Zambia and flows through eastern Angola, along the north-eastern border of Namibia and the northern border of Botswana, then along the border between Zambia and Zimbabwe to Mozambique, where it crosses the country to empty into the Indian Ocean. The Zambezi's most noted feature is Victoria Falls. Its other falls include Chavuma Falls and Ngonye Falls.
The two main sources of hydroelectric power on the river are 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. Additionally, two smaller power stations in Zambia are at Victoria Falls and Zengamina.
Course
Origins
The river rises in a black, marshy dambo in dense, undulating miombo woodland 50 km (31 mi) north of Mwinilunga and 20 km (12 mi) south of Ikelenge in the Ikelenge District of North-Western Province, Zambia, at about 1,524 metres (5,000 ft) above sea level. The area around the source is a national monument, forest reserve, and important bird area.
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 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 900–1,200 m high, composed in the remote interior of metamorphic beds and fringed with the igneous rocks of the Victoria Falls. At Chupanga, 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.
Upper Zambezi
The river flows to the southwest into Angola for about 240 km (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 m (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 m (1,300 ft) in elevation from its source at 1,500 m (4,900 ft) to the Chavuma Falls at 1,100 m (3,600 ft), over a distance of about 400 km (250 mi). From this point to the Victoria Falls, the level of the basin is very uniform, dropping only by another 180 m (590 ft) across a distance of around 800 km (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 flows 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.
About 30 km 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. About 80 km further down, the Luanginga, which with its tributaries drains a large area to the west, joins the Zambezi. A short distance 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 the 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 south-southeast. From the east, it continues to receive numerous small streams, but on the west, it 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. 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.
Middle Zambezi
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 km (120 mi), cutting through perpendicular walls of basalt 20 to 60 m (66 to 197 ft) apart in hills 200 to 250 m (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 that end 240 km (150 mi) below Victoria Falls. Over this distance, the river drops 250 m (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 Kafue rivers are the two largest left-hand tributaries of the Zambezi. The Kafue joins the main river in a quiet, deep stream about 180 m (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, formerly the site of dangerous rapids known as Kebrabassa; the lake was created in 1974 by the construction of the Cahora Bassa Dam.
Lower Zambezi
The lower Zambezi's 650 kilometres (400 mi) 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 kilometres (200 mi) from its mouth, is the river confined between high hills. Here, it is scarcely 200 metres (660 ft) wide. Elsewhere it is from 5 to 8 kilometres (3 to 5 mi) 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 kilometres (99 mi) 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 primary distributaries, 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 metres (6 ft 7 in) at the entrance and 4 metres (13 ft) further in, and is the branch used for navigation. About 100 kilometres (62 mi) 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.
Discharge
Average, minimum and maximum discharge of the Zambezi River at Marromeu (Lower Zambezi). Period from 1998 to 2022.
Delta
The delta of the Zambezi is today about half as broad as it was before the construction of the Kariba and Cahora Bassa dams controlled the seasonal variations in the flow rate of the river. Before the dams were built, seasonal flooding of the Zambezi had quite a different impact on the ecosystems of the delta from today, as it brought nutrient-rich fresh water down to the Indian Ocean coastal wetlands. The lower Zambezi experienced a small flood surge early in the dry season as rain in the Gwembe catchment and north-eastern Zimbabwe rushed through while rain in the upper Zambezi, Kafue, and Lake Malawi basins, and Luangwa to a lesser extent, is held back by swamps and floodplains.
The discharges of these systems contribute to a much larger flood in March or April, with a mean monthly maximum for April of 6,700 m3 (240,000 cu ft) per second at the delta. The record flood was more than three times as big, 22,500 m3 (790,000 cu ft) per second being recorded in 1958. By contrast, the discharge at the end of the dry season averaged just 500 m3 (18,000 cu ft) per second.
In the 1960s and 1970s, the building of dams changed that pattern completely. Downstream, the mean monthly minimum–maximum was 500 to 6,000 m3 (18,000 to 212,000 cu ft) per second; now it is 1,000 to 3,900 m3 (35,000 to 138,000 cu ft) per second. Medium-level floods especially, of the kind to which the ecology of the lower Zambezi was adapted, happen less often and have a shorter duration. As with the Itezhi-Tezhi Dam's deleterious effects on the Kafue Flats, this has these effects:
Fish, bird, and other wildlife feeding and breeding patterns were disrupted.
Less grassland remains after flooding for grazing wildlife and cattle.
Traditional farming and fishing patterns were disrupted.
Ecology
The Zambezi delta has extensive seasonally and permanently flooded grasslands, savannas, and swamp forests. Together with the floodplains of the Buzi, Pungwe, and Save Rivers, the Zambezi's floodplains make up the World Wildlife Fund's Zambezian coastal flooded savanna ecoregion in Mozambique. The flooded savannas lie close to the Indian Ocean coast. Mangroves fringe the delta's shoreline.
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, and they have only made medium-level floods less frequent. When heavy rain in the lower Zambezi combines with significant runoff upstream, massive floods still happen, and the wetlands are still an important habitat. The shrinking of the wetlands, though, resulted in uncontrolled hunting of animals such as buffalo and waterbuck during the Mozambican Civil War.
Although the region has had a reduction in the populations of the large mammals, it is still home to some, including the reedbuck and migrating eland. Carnivores found here include lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), spotted hyena (Crocuta crocuta), and side-striped jackal (Canis adustus). The floodplains are a haven for migratory waterbirds, including pintails, garganey, African openbill (Anastomus lamelligerus), saddle-billed stork (Ephippiorhynchus senegalensis), wattled crane (Bugeranus carunculatus), and great white pelican (Pelecanus onocrotalus).
Reptiles include Nile crocodile (Crocodylus niloticus), Nile monitor lizard (Varanus niloticus), African rock python (Python sebae), the endemic Pungwe worm snake (Leptotyphlops pungwensis), and three other snakes that are nearly endemic: floodplain water snake (Lycodonomorphus whytei obscuriventris), dwarf wolf snake (Lycophidion nanus), and swamp viper (Proatheris).
Several butterfly species are endemic.
Climate
The north of the Zambezi basin has a 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 Intertropical 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.
Wildlife
The river supports large populations of many animals. Hippopotamuses are abundant along most of the calm stretches of the river, as well as Nile crocodiles. Monitor lizards are found in many places. Birds are abundant, with species including heron, pelican, egret, lesser flamingo, and African fish eagle present in large numbers. Riverine woodland also supports many large animals, such as buffalo, zebras, giraffes, and 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, not to be mistaken with Glyphis freshwater shark genus that inhabit the river, as well.
Tributaries
Upper Zambezi: 507,200 km2, discharges 1044 m3/s at Victoria Falls, comprising:
Northern Highlands catchment, 222,570 km2, 850 m3/s at Lukulu:
Chifumage River: Angolan central plateau
Luena River: Angolan central plateau
Kabompo River: 72,200 km2, NW highlands of Zambia
Lungwebungu River: 47,400 km2, Angolan central plateau
Central Plains catchment, 284,630 km2, 196 m3/s (Victoria Falls–Lukulu):
Luanginga River: 34,600 km2, Angolan central plateau
Luampa River/Luena River, Zambia: 20,500 km2, eastern side of Zambezi
Cuando /Linyanti/Chobe River: 133,200 km2, Angolan S plateau & Caprivi
Middle Zambezi cumulatively 1,050,000 km2, 2442 m3/s, measured at Cahora Bassa Gorge
(Middle section by itself: 542,800 km2, discharges 1398 m3/s (C. Bassa–Victoria Falls)
Gwembe Catchment, 156,600 km2, 232 m3/s (Kariba Gorge–Vic Falls):
Gwayi River: 54,610 km2, NW Zimbabwe
Sengwa River: 25,000 km2, North-central Zimbabwe
Sanyati River: 43,500 km2, North-central Zimbabwe
Kariba Gorge to C. Bassa catchment, 386200 km2, 1166 m3/s (C. Bassa–Kariba Gorge):
Kafue River: 154,200 km2, 285 m3/s, West-central Zambia & Copperbelt