Zambezi River

Physiography

The Zambezi rises out of a marshy bog near Kalene Hill, Zambia, about 4,800 feet (1,460 metres) above sea level, and flows some 20 miles before entering Angola, through which it runs for more than 175 miles. In this first section of its course, the river is met by more than a dozen tributaries of varying sizes. Shortly after reentering Zambia, the river flows over the Chavuma Falls and enters a broad region of hummocky, sand-covered floodplains, the largest of which is the Barotse, or Zambezi, Plain. The region is inundated during the summer floods, when it receives fertile alluvial soils. The main tributaries intersecting the river along the plains are the Kabompo River from the east and the larger Lungué-Bungo (Lungwebungo) River from the west.

The Zambezi then enters a stretch of rapids that extends from Ngonye (Sioma) Falls south to the Katima Mulilo Rapids, after which for about 80 miles it forms the border between Zambia to the north and the eastern Caprivi Strip—an extension of Namibia—to the south. In this stretch the river meanders through the broad grasslands of the Sesheke Plain until it is joined by the Cuando (Kwando) River. Near Kazungula, Zambia, the river, after flowing past Botswana territory to the south, turns almost due east and forms the frontier between Zambia and Zimbabwe. From the Cuando confluence to the Victoria Falls, the Zambezi varies considerably in width, from open reaches with sand islands to stretches of rapids through narrow channels separated by numerous rock islands.

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The Victoria Falls mark the end of the upper course of the Zambezi, as its waters tumble with a thunderous roar and an enormous cloud of spray. The area around the falls was once covered by a thick layer of lava, which as it cooled formed wide cracks, or joints, that became filled with softer sediments. As the Zambezi cut its present valley it encountered one of these joints, eroded the sediment, and created a trench, eventually forcing a gap at the lower end of the trench that quickly widened into a gorge. The force of the water also created a second gap at the upper end of the trench that gradually diverted the river until the trench itself was left dry. As the river cut backward it repeated the process, scouring eight successive waterfalls in the past half million years.

The Zambezi’s middle course extends about 600 miles from Victoria Falls to the eastern end of Lake Cahora Bassa in Mozambique. It continues to form the boundary between Zambia and Zimbabwe until it crosses the Mozambique border at Luangwa. Below the falls a gorge some 60 miles long has been formed by the trench-scouring process, through which the river descends in a series of rapids. Just upstream of Lake Kariba the river valley widens and is contained by escarpments nearly 2,000 feet high. The middle Zambezi is notable for the two man-made lakes, Kariba and Cahora Bassa (see below), that constitute much of this stretch of the river. Between the two lakes the Zambezi trends northeast for nearly 40 miles before it turns east below the confluence with the Kafue River, the Zambezi’s largest tributary. In this section the river rushes through two rocky, narrow gorges, the first just below the Kariba Dam and the other above the confluence with the Luangwa River.

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At the dam at the eastern end of Lake Cahora Bassa, the Zambezi begins its lower course, during which it descends from the Central African Plateau to the coastal plain. At first the hilly country is replaced by flat areas at the head of the Tete Basin, and the river becomes more placid. About 40 miles downstream the river has cut the Lupata Gorge through a range of hills, where it emerges onto the Mozambique Plain and occupies a broad valley that spreads out in places to a width of three to five miles. Near Vila Fontes the river receives its last great tributary, the Shire River, which drains Lake Nyasa (Malaŵi) some 210 miles to the north.

At its mouth the Zambezi splits into a wide, flat, and marshy delta obstructed by sandbars. There are two main channels, each again divided into two. The wider, eastern channel splits into the Muselo River to the north and the main mouth of the Zambezi to the south. The western channel forms both the Inhamissengo River and the smaller Melambe River. North of the main delta the Chinde River separates from the Zambezi’s main stream to form a navigable channel leading to a shallow harbour.

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Hydrology

The Zambezi, according to measurements taken at Maramba (formerly Livingstone), Zambia, experiences its maximum flow in March or April. In October or November the discharge diminishes to less than 10 percent of the maximum. The annual average flow reaches about 247,000 cubic feet (7,000 cubic metres) per second. Measurements taken at Kariba Dam reflect the same seasonal pattern; the highest flood recorded there was in March 1958, when the flow reached 565,000 cubic feet per second.