Severe structural faults have been identified in the Kariba Dam, located in the Kariba Gorge of the Zambezi River basin, which experts warn could lead to a catastrophic humanitarian disaster.

A failure in the dam could unleash 180 billion tonnes of water from the continent’s largest man-made lake, engulfing Zambia’s capital city of Lusaka, flooding the neighbouring Mozambique and Malawi and threatening the lives of more than 3.5 million people.

The dam serves two power stations – the northern plant which belongs to Zambia, and the southern plant which is controlled by Zimbabwe – and generates more than 1,300 megawatts of hydro-power. A collapse would cause electricity blackouts across southern Africa.

The facility was built in two phases (1955-59 and 1977), and was last inspected in 2010. In its five-year strategic plan (2010-2014), the Zambezi River Authority identified one of its main objectives as “undertaking critical dam maintenance work,” including plunge pool re-shaping and spillway refurbishment

Christopher Yaluma, Zambia’s energy and water development minister, said the dam, which is 128 metres high, needs to be repaired within three years.

“We need at least $220 million to resolve this issue,” he said on state radio. “It’s quite serious but we are determined to resolve it.”

Defects at the dam have also led to concerns about the risk of earthquakes, because the structure sits at the southern end of the Rift Valley, a tectonically active area where there have been at least 20 tremors of a magnitude greater than five.

Construction of the dam wall began in the late 1950s. Well over a million cubic metres of concrete was poured into the 36.6-metre high wall with a thickness of over 24 metres to sustain the pressure of nearly 10 million litres of water passing through the spillway each second. At the end of 1958 the sluice gates were closed, and in 1963 the maximum level was reached.

Kariba Dam was designed by the French engineer and inventor Andre Coyne, a specialist in “arch dams,” who designed over 55 dams.

The design of his Marèges Dam, a concrete arch dam on the Dordogne River, incorporated several features never seen before including a ski-jump spillway, the right abutment anchored with a pre-stressed cable and monitored with audible signals and a new cofferdam design.

Coyne also designed the Malpasset Dam in Southern France, the scene of a major disaster in 1959 when the dam abruptly swung open releasing a 50-metre high wall of water that hit the nearby town of Frejus and killed more than 400 people.

Although almost immediately after construction was completed cracks were noticed at the base, a study later found that the design of the dam was probably not the reason for its failure. Other factors such as the location of the dam, the stability of the rock material, a geological fault on the site, and heavy rain were all cited as possible causes.

As for the fears at Kariba Dam Elizabeth Karonga, a spokeswoman for the Zambia-based Zambezi River Authority, which is jointly owned by Zambia and Zimbabwe, said “[w]hile the situation at the Kariba Dam wall is cause for grave concern, the engineers on the ground have the situation under control. This does not translate to an immediate calamity.”

Zimbabwe’s energy and power development minister Dzikamai Mavhaire also sought to allay fears of a potential catastrophe, insisting that the dam is in a “stable state.”