The Forgotten and the Dammed: The Hidden Risks Behind the World's Water and Waste Reservoirs

Article by Fiona Macleod CEng FIChemE

Fiona Macleod stands in front of the reconstructed Banqiao dam

Fifty years after the Banqiao dam collapse killed hundreds of thousands in China, Fiona Macleod says deadly failures continue to expose the global threat of ageing infrastructure, climate extremes and toxic waste

ON 8 August 1975, the "unbreakable" Banqiao Dam in China's Henan province failed catastrophically. Within hours, a wall of water surged through the Zhumadian region, wiping out entire villages. It remains the deadliest structural failure in human history. Yet half a century later, the world continues to underestimate the dangers posed by dams – both for clean water and toxic mining waste.

From Libya to Brazil, and Ukraine to the US, dam failures – due to poor maintenance, extreme weather or conflict – have caused catastrophic loss of life, environmental destruction and public health crises. Despite advances in engineering, a global reckoning on dam safety remains long overdue.

Banqiao, China, 1975

The Banqiao dam in the Zhumadian region of Henan province was completed in 1952, strengthened in 1956, and hailed as the iron dam; it was considered unbreakable.

Then, in 1975, Typhoon Nina struck. A year’s worth of rain fell in a day. Just after midnight on 8 August, the Banqiao dam collapsed, releasing 700m m³ of water in just six hours.

The initial breach was 300 m wide. By the time the water reached Suiping, 16 km from the dam, it resembled a tidal wave: 10 km wide, 7 m high, travelling at up to 50 km/hr. Racing across the flat land, it demolished everything in its wake. Whole villages were swept away, taking families as they slept. Thirty dams failed downstream, one after another like dominoes.

Those who survived the deluge might have wished they hadn’t.

At least 26,000 people drowned that night. The flood water was now full of bloated, rotting corpses. Communication with the outside world was lost; road and rail access destroyed. The relief effort was too little and too late. Estimates put the final death toll at no less than 240,000 and probably closer to one million fatalities. By any reckoning, it remains the deadliest structural failure of all time.

Wadi Derna, Libya, 2023

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In the early hours of 11 September, 2023, two dams collapsed above the Mediterranean city of Derna in Libya. A wall of muddy water swept entire neighbourhoods out to sea, killing thousands of people.

Two clay-filled embankments, 45 m and 75 m tall were built in the 1970s to control flooding and provide water to agricultural communities. After Colonel Gaddafi was overthrown and killed in 2011 political chaos reigned. Attention was called to the lack of maintenance of the dams, but Derna was a battleground during the civil war and control of the city repeatedly changed hands.

On the night of 10-11 September, Storm Daniel hit. The upper dam, 13 km from the city, probably collapsed first. The lower dam, 1 km from the city could not hold back the increased flow and collapsed in turn. The floodwaters reached the city at about 3am local time with devastating consequences. Between 11,300 and 24,000 people died.

According to a report by the American Society of Civil Engineers in August 2024, over 60,000 dams in the US are more than 50 years old and were never designed to withstand increasingly heavy and frequent rain events. Most alarmingly, there are 2,500 high hazard–potential dams (those where failure would likely result in loss of life) in the US alone assessed to be in poor or unsatisfactory condition.

Worldwide, tens of thousands of water reservoir dams are at a high risk of failure.

But it is not only clean water that poses a risk.

Tailings are the collected waste products from mining. Excavated rock is ground into a fine sand and slurried with water to extract the minerals of interest. The rest, along with all the water and chemicals used for separation, is waste.

The mine tailings can contain high concentrations of substances harmful to health: cyanide, mercury, arsenic and even radioactive elements. In many countries, tailings dams are designed to contain the waste. Lakes of toxic sludge develop over time, held back by ever growing embankments which can reach hundreds of metres in height.

So, what happens when they fail?

Mariana and Brumadinho, Brazil, 2015 & 2019

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The Paraopeba River polluted by tailings after the collapse of the dam of the Córrego do Feijão mine

The collapse of the Fundão Dam at an iron mine in Mariana, Brazil 2015 killed 20 people. Risk expert Lindsay Newland Bowker warned that all 144 of Brazil’s large tailings dams were at significant risk of failure. Her warning proved prophetic.

On 25 January 2019, a tailings dam at the Córrego do Feijão iron mine, near Brumadinho in Minas Gerais, Brazil, failed catastrophically. The sludge swept through the mine offices and canteen during lunchtime and 270 people were killed.

What happens after the mine is exhausted? Who is going to monitor and maintain tailings dams when economic operations cease?

A global industry standard was developed in 2020, but compliance remains voluntary.

It is not only too much water that poses danger. Too little can also be fatal.

A reliable cooling water supply is essential for the safety of nuclear power plant operation. Active cooling is required in nuclear reactors, running or idle, to remove the heat generated by radioactive decay. The 1986 Chernobyl disaster was triggered by a misguided “safety test” which deliberately interrupted the cooling water supply.

Kakhovka dam, Ukraine, 2023

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The city of Kherson, Ukraine after the collaspe of the Kakhovka dam

The Kakhovka dam was built in 1956 and collapsed (probably deliberately destroyed as a tactic of war) on 6 June 2023, leading to over 50 immediate deaths, followed by a devastating outbreak of cholera.

Located approximately 160 km upstream, the largest nuclear power plant in Europe was starved of essential cooling water as the Kakhovka reservoir emptied through the dam breach. The Zaporizhzhia Nuclear Power Station has been under Russian occupation since 2022. Even when shut down, water is needed for residual heat removal from the reactors and fuel ponds. Groundwater is now used instead.

Summary

Reservoirs of clean water and mine tailings hold huge amounts of stored energy.

The dams that contain the stored energy can fail due to:

lack of maintenance
extreme weather
geological instability
acts of war

Loss of containment – the sudden release of stored energy – can lead to:

immediate death by impact of collapsing structures or drowning
lingering death from injury, famine, disease and destitution
environmental damage
loss of (or contamination of) clean water supply used for:
- drinking – leading to dehydration
- sewerage – leading to outbreaks of disease
- agriculture – leading to starvation
- industry – leading to poverty and destitution
- cooling of nuclear power plants – leading to further catastrophe

Conclusion

Understanding what can go wrong is the first step in all risk management. Understanding and monitoring what must go right to stop the bad things happening is critical. For existing dams this includes programmes of inspection and maintenance, responsible decommissioning of old assets, early-warning systems and emergency planning. For new assets, the principles of inherent safety should be used to build in resilience: to political instability and population growth, to armed conflict and cyber-attack, to geological conditions and extreme weather events.

Fifty years ago, in a village downstream of the Banqiao dam, only three children survived from a primary school class of 300.

The 50th anniversary of the worst structural failure in history should serve as a stark reminder that dam safety is a global problem which merits global attention.