Dealing with deadly dam failures
Dams are built to hold back water and put it to use for irrigation or creating electricity. But around the world, thousands of dams are in need of repair. Many have been too weak to protect local communities amid sustained heavy rains. More than 300,000 people in Brazil’s Rio Grande do Sul region, for example, were left without electricity when a dam at a hydroelectric power plant burst May 2, 2024. In late April 2024, a dam collapsed north of the Kenyan capital Nairobi after heavy rains and flooding. Water levels had been described as a “historic high”.
It’s becoming a regular occurrence. When the Abu Mansour and Derna dams collapsed during Storm Daniel’s attack on Libya, the cries came fast: We’ve been warning about this for years, said the experts. If there’s a flood, they said, it will be catastrophic for the residents living below. And so it was: Thousands were thought to be dead in the immediate aftermath.
The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) expressed concerns about two further Libyan dams — the Jaza Dam, between Derna and Benghazi, and the Qattara Dam near Benghazi — citing “contradictory reports” over the dams’ stability. Contrary reports about the stability of dams is not unique to Libya. There were allegations of contrary reports in Brazil after a mining dam at Minas Gerais failed. It collapsed in January 2019, causing a toxic mudslide that killed 270 people — one year after a Brazilian subsidiary of a German risk assessment firm, TUV SUD, had certified the dam to be safe.
A dam is a way to gather and store water. That can be natural water or wastewater from a nearby mine — if it’s water from a mine, people talk of dams containing “mine tailings”. Mine tailings can be a mix of materials, metals, chemicals and liquid waste leftover when ore is mined. Dams can also be used to store up water for irrigation and as a supply of water for livestock, pollution control, energy generation and, if the water is safe, for recreation.
There are two main types of constructed, human-made dams: embankment and concrete dams. Embankment dams are the most common and can be made with waste from mining or milling operations. But they are also made of natural soil and rock that is compacted to create a containment area, or reservoir, for the water.
Its ability to contain the water — or resist pressure from the water — depends on the mass weight, strength and type of materials used to build the dam. Concrete dams are divided into three subtypes: gravity, buttress and arch dams.
One of the most common causes for dam failure — that’s when the dam breaks in an uncontrolled way — is their age. In 2021, the United Nations University published a report indicating that “tens of thousands of existing large dams have reached or exceeded an ‘alert’ age threshold of 50 years, and many others will soon approach 100 years.” The Brumadinho dam at Minas Gerais was built in 1976, which means it was approaching the end of its lifespan. And Libya’s Abu Mansour and Derna dams were also built in the 1970s — so, while Storm Daniel triggered their failure, they may have been ready to fail, anyway. But dams also fail due to poor design and irregular maintenance.
Over-topping can occur if a spillway design is inadequate and can’t cope when there’s heavy rainfall. The spillway may get blocked over time, too. The older a dam gets, the more its foundation can experience a natural process called settling. Slopes surrounding the dam can become unstable, and if the original construction materials start to erode, it can cause seepage.