DAMSDeadly Dam Failures: Cause, Effect, and Prevention
No dam is flood-proof. Thousands are at alert level. But dam failure needn’t be deadly the way it was in Libya’s devastating floods. Here’s what you need to know.
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 are thought to be dead and many more are missing.
The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) has expressed concerns about two further Libyan dams — the Jaza Dam, between Derna and Benghazi, and the Qattara Dam near Benghazi — but cited “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, TÜV SÜD, had certified the dam to be safe.
What Is a Dam and Why Do We Build Them?
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.
How Are Dams Made and How Do They Resist Water Pressure?
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.
Gravity dams are the most common concrete dams. They are made of vertical concrete blocks and sealed with flexible joints. The pressure of the water hits the dam wall and is forced downwards.
