Kariba Dam is a double-curvature concrete arch dam in the Kariba Gorge of the Zambezi River, on the border between Zambia and Zimbabwe. It stands 128 metres tall and 579 metres long, and it holds back Lake Kariba, which at 185 cubic kilometres of storage is the largest artificial reservoir in the world by volume. Built between 1955 and 1959 and officially opened on 17 May 1960, the dam feeds two power stations with a combined capacity of 2,010 MW, generating about 6,400 GWh a year for Zimbabwe and for Zambia’s Copperbelt, and it is now owned and run jointly by the two countries through the Zambezi River Authority.
A Rock Called the Trap in the Middle Zambezi
Everything about Kariba begins with the shape of the river. The Zambezi runs 2,574 km from a marshy source in north-western Zambia to the Indian Ocean, and for most of its upper course it wanders across a plateau 900 to 1,200 metres high. Below Victoria Falls that changes. For about 200 km the river is squeezed between basalt walls in the Batoka Gorge, then it drops through a run of rapids that ends some 240 km below the falls, losing about 250 metres of height on the way. Beyond that point the middle Zambezi enters a broad trough and then pinches again into a narrow cut through the hills: the Kariba Gorge, about 1,300 km upstream from the river’s mouth.
A gorge like that is what dam engineers look for. A wide, flat valley upstream can store an enormous volume of water, while a tight rock throat downstream lets a relatively small wall close it off. Kariba had both. The name itself is said to come from kariva or karinga, meaning trap, a reference to a rock that jutted out from the gorge where the wall was eventually built. The BaTonga, who had farmed the valley floor for generations, believed that rock was the home of Nyami Nyami, the river spirit usually shown with a snake’s body and a fish’s head.
The choice of site was political as well as geological. The dam was ordered by the Federation of Rhodesia and Nyasaland, a British federal colony that existed from 1953 to 1963. Northern Rhodesia (now Zambia) had already decided in 1953 to dam the Kafue River, a Zambezi tributary much closer to its Copperbelt mines, which would have been cheaper and smaller. Southern Rhodesia (now Zimbabwe), the richest member of the federation, objected and insisted on Kariba. A dam at Kariba also offered far more storage and generating capacity than the Kafue scheme could. Zambia got its Kafue dams only after independence: Kafue Gorge Upper, Kafue Gorge Lower and Itezhi-Tezhi.
Building an Arch Across Kariba Gorge, 1955 to 1960
The design suited the gorge. A double-curvature arch curves both across the valley and from crest to base, so the push of the reservoir is carried sideways into the rock walls rather than resisted by sheer weight. The consulting engineers were a joint venture, Gibb, Coyne, Sogei (Kariba), bringing together Sir Alexander Gibb & Partners, whose team was led by Sir Angus Paton, and the French firm Coyne et Bellier under André Coyne. The Italian contractor Cogefar-Impresit built the wall between 1955 and 1959 for about US$135 million, a first stage that included only the south bank power cavern.
The gorge fought back. Floods on the Zambezi damaged the works while the wall was rising, and 86 construction workers died during the project. Many Tonga saw the floods and deaths as Nyami Nyami’s anger at being separated from his wife, who in the story lived downstream of the rock, and some held that the river spirit withdrew from the world of people once the wall was finished. To house the workforce, the contractor Costain built a new town on the hills above the gorge. Kariba town, in Zimbabwe’s Mashonaland West province, had about 27,600 people at the 2022 census and is still laid out around three suburbs: lakeside Mahombekombe, newer Nyamhunga, and Kariba Heights on the hilltop.
Queen Elizabeth the Queen Mother formally opened the dam on 17 May 1960. The job was not finished, though. The north bank power station, on the Zambian side, was delayed for years, largely for political reasons as the federation broke up in 1963 and its members went separate ways. Mitchell Construction completed it only in 1977, bringing the total cost of the scheme to about US$480 million.
How Lake Kariba Swallowed the Valley, 1958 to 1963
Water began backing up behind the wall in 1958, and the lake took until 1963 to fill. What it covered was a long stretch of valley floor upstream of the gorge. Today Lake Kariba is more than 220 km long and up to 40 km wide, with a surface of 5,580 km² (2,150 sq mi). Its mean depth is only 29 metres and its deepest point 97 metres, which shows how much of the storage comes from area rather than depth: a shallow sheet of water spread over the old valley, held by a comparatively short wall at the one narrow point.
That volume is about four times the reservoir behind China’s Three Gorges Dam. Its weight has had effects of its own. The Kariba area is seismically active, and the filling of the lake is believed to have triggered induced seismicity, including more than 20 earthquakes above magnitude 5. The drowned bush also changed the water: rotting vegetation released nutrients that made the new lake unusually productive. Kapenta, a small sardine-like fish brought in from Lake Tanganyika, now supports a commercial fishery, and native tigerfish feed on it and draw anglers. Hippos and Nile crocodiles live along the shore, and Matusadona National Park lines part of the southern side.
The people of the valley paid for this. Around 57,000 Tonga were moved off the land along both banks. Settlements such as Binga and Mlibizi in Zimbabwe and Siavonga and Sinazongwe in Zambia grew to house them. Anthropologist Thayer Scudder, who has followed these communities since the late 1950s, described many as still being “development refugees”, and in 2002 displaced families founded the Basilwizi Trust to push for development in the Zambezi Valley.
Animals were caught by the rising water too. From 1958 to 1961 game rangers ran Operation Noah, capturing and moving about 6,000 large animals, and many smaller ones, off islands that were shrinking as the lake rose. A monument to the operation stands at Kariba Heights.
Kariba South and Kariba North: Two Countries, Two Power Stations
Because the dam straddles a border, each country has its own power station, one on each bank. Kariba South, on the Zimbabwean side, has run since 1960. It began with six 125 MW generators, 750 MW in all. Work on a 300 MW expansion started in 2014 with a loan from China, and President Emmerson Mnangagwa commissioned the two new units in March 2018. The work, carried out by Sinohydro for US$533 million, took the station to 1,050 MW. Kariba North, on the Zambian side, came into service in 1976 with four 150 MW units (600 MW), and two 180 MW generators added by December 2013 raised it to 960 MW.
The dam controls about 90 per cent of the Zambezi’s total runoff, so how it is operated shapes the river all the way downstream. The lower Zambezi’s seasonal floods, which once spread nutrient-rich water over the delta, are now much reduced by Kariba and by Mozambique’s Cahora Bassa Dam further down. The delta is roughly half as broad as it was before the two dams were built.
The Plunge Pool, the Drought and the Kariba Dam Rehabilitation Project
The dam’s biggest weakness sits at its foot. Kariba was built on what looked like solid basalt, but in the decades since, water shooting from the spillway gates has carved a deep crater into the riverbed below the wall. That scour pool has been cutting back towards the dam’s foundations along a weak fault zone. In March 2014 engineers at a Zambezi River Authority conference warned that the foundations had weakened, and in October that year the BBC reported the authority’s estimate that 3.5 million people’s lives would be at risk if the wall failed, with a flood reaching the Mozambique border within about eight hours and overwhelming Cahora Bassa.
The response is the Kariba Dam Rehabilitation Project, under way since 2017 and funded by the European Union, the World Bank, the Swedish government and the African Development Bank, with Zambia and Zimbabwe also contributing. It has two parts. Crews behind a temporary watertight cofferdam are excavating and reshaping the plunge pool so the spillway water no longer eats towards the foundation, and the spillway gates are being rebuilt. In 2022 the authority said the work was scheduled to be finished in 2025.
Too little water has become as serious a problem as too much. In January 2016 the reservoir fell to 12 per cent of capacity. By November 2020 it had recovered to around 25 per cent, with the water line at about 478.3 metres above sea level, just above the 475.5-metre minimum for generating power. In January 2023, after further drought, the level fell to about 1 per cent of capacity and output was held to 800 MW for only part of each day. Industrial power users have since proposed a 250 MW floating solar plant on the lake.
Those shortages show what the gorge site gave and what it cannot: Kariba stores a huge volume, but it depends on rain over the Zambezi’s upper basin, including the stretch above Victoria Falls. For the rest of the river’s course, from its source to the delta, see our Zambezi River guide, and for the next great wall downstream, the story of Mozambique’s Cahora Bassa Dam picks up where Kariba’s water leaves off.