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Living under the imposing shadow of a large dam means entrusting your safety to the engineers who designed it. If there are flaws in their calculations, it could lead to a catastrophic disaster. When a dam collapses, the rush of water can devastate everything in its path, destroying homes, infrastructure, and claiming lives of people and animals alike. As this list highlights, errors made during dam construction can have horrific consequences. But rest assured, the majority of dams are safe and function as intended.
10. Banqiao Dam (China, 1975)
In August 1975, a violent typhoon struck the western Chinese province of Henan, causing massive destruction. Among the affected was the Banqiao Dam, which stood 387 feet (118 meters) tall across the Ru River. Built in 1952, it was designed to irrigate the farmland in the Huai River Basin. The dam’s reservoir could hold 158 billion gallons (600 billion liters) of water.
The Banqiao Dam was built to endure a flood that only occurs once every thousand years. Sadly, this once-in-a-lifetime event took place just five years after the dam’s completion, when a brutal typhoon unleashed 55 inches (140 centimeters) of rain over three days, whereas the region typically receives only 32 inches (81 centimeters) annually. This overwhelming downpour caused the dam to collapse, sending a wall of water 33 feet (10 meters) high and up to 7 miles (11.3 kilometers) wide. While exact casualty numbers are difficult to verify, estimates suggest that as many as 230,000 people lost their lives in the tragedy.
9. Machchhu Dam II (Gujarat, India, 1979)
In August 1979, the Indian state of Gujarat was hit by relentless monsoon rains. While the monsoon is a yearly occurrence, this particular year was far more intense, with rainfall that could be described as catastrophic. The Macchu River, swollen by the torrential downpour, began to flow with great force and depth.
The rain-soaked river forced the Machchhu Dam II to open its floodgates to relieve pressure on the dam. However, the sheer volume of water wasn’t enough to prevent the floodwaters from surging over the earth banks surrounding the structure. This breach led to the dam's collapse. Many people who were in the flood’s path had already moved to higher ground, undoubtedly saving themselves. But countless others did not evacuate in time. While the exact number of casualties remains uncertain, some estimates suggest that as many as 25,000 people may have perished in the disaster.
8. South Fork Dam (Pennsylvania, 1889)
The South Fork Dam, constructed using rock and packed earth, stood approximately 8 miles (13 kilometers) east of Johnstown, Pennsylvania. Originally built in 1852, the dam measured 918 feet (280 meters) in length and 72 feet (22 meters) in height. Just a decade after its completion, the first failure of the dam occurred.
In 1872, Benjamin Ruff purchased the remains of the South Fork Dam and the surrounding land with the intention of repairing the dam and establishing a luxury resort. This led to the creation of the South Fork Fishing and Hunting Club, frequented by wealthy industrialists such as Henry Frick and Andrew Carnegie. However, disaster struck on May 31, 1889, when a violent storm brought torrential rainfall, triggering the collapse of the dam. The failure was partly due to modifications made by Ruff to the dam’s original design. The collapse unleashed 20 million tons of water, causing 2,209 fatalities.
7. Vajont Dam (Italy, 1959)
When the Vajont Dam in Italy’s Alpine region was completed in 1959, it stood as one of the largest dams in the world. Although the dam itself was structurally sound and did not collapse, a catastrophic event unfolded in 1963 due to a combination of factors. A massive landslide and the reservoir being filled beyond its intended capacity triggered the tragedy, leading to flooding that destroyed both property and lives.
The situation grew dire when a huge landslide from the nearby Monte Toc released 9,200 cubic feet (260 million cubic meters) of rock into the reservoir. The resulting wave of water overflowed the dam, creating a monstrous deluge. The force of the water was so extreme that it created an air wall capable of tearing the clothes off the victims. Around 2,000 lives were claimed in the tragedy.
6. The Ruhr Valley Dams (Germany, 1943)
The failure of two of the Ruhr Valley dams in Germany and the resulting loss of life had a distinct cause compared to the other disasters on this list. This was not an accident but rather a deliberate act of destruction. In May 1943, a squadron of 19 Lancaster bombers launched from England with the mission to destroy the dams using a specially designed “bouncing” bomb.
The original plan was to destroy all three dams, but only the Eder and Möhne dams were breached. The Sorpe Dam remained intact. Yet the destruction of the two dams was enough to cause massive devastation. Of the 133 British airmen who took part in the mission, 53 were killed. The casualties from the flood were far worse. German fatalities, both dead and missing, totaled 545, while 749 workers and prisoners from the Netherlands, Ukraine, France, and Belgium also perished or vanished, bringing the total number of casualties to just under 1,300.
5. Puentes Dam (Spain, 1802)
In 1802, the Puentes dam, located in the southeastern Murcia region of Spain, was the longest in the country, stretching 940 feet (286.5 meters). Situated just over 7 miles (11 kilometers) from Lorca, the dam stood 165 feet (50 meters) tall. Designed by Jerónimo Ortiz de Lara, construction began in 1785 and took six years to complete. The dam was built to replace a previous structure that had failed in 1648, which some might view as an ominous sign.
The new Puentes Dam began its journey under an unlucky star, as its reservoir remained almost entirely empty due to nearly a decade of severe drought in Murcia. However, in March 1802, the skies finally opened, unleashing torrential rainfall. By the end of April, the dam appeared to be on the brink of overflowing, and that’s when disaster struck. The dam failed, sending a 40-foot-high (12-meter-high) surge of water rushing towards Lorca. The flood devastated the area, destroying over 800 homes, numerous industrial and agricultural buildings, and claiming the lives of 608 people.
4. St. Francis Dam (California, 1928)
Completed in 1926, the St. Francis Dam was located about 40 miles (64 kilometers) northwest of Los Angeles, and was designed to supply water for the city’s aqueduct system. The concrete dam stood 205 feet (62.5 meters) tall and spanned 70 feet (21.3 meters). The construction was overseen by the Los Angeles Bureau of Waterworks & Supply, with chief engineer William Mulholland leading the project.
Although Mulholland was a self-taught engineer, he had gained experience building embankment dams but had never worked on a concrete dam. This inexperience proved to be a significant factor, especially considering that the dam's height had been increased by 20 feet (6 meters) during the design phase. Unfortunately, the impact of this change on the structure was not fully accounted for. Just two years after its completion, in 1928, the St. Francis Dam catastrophically failed, resulting in the deaths of around 400 Californians.
3. Dale Dyke Reservoir (England, 1864)
The Dale Dyke Reservoir was located approximately 8 miles (12.8 kilometers) from the northern English city of Sheffield. This 100-foot-high dam was built as an earth embankment structure, stretching 500 feet (152 meters) across, holding back a reservoir that was a mile (1.6 kilometers) long and a quarter-mile (0.4 kilometers) wide. As construction neared completion in March 1864, a severe storm struck the region, leading to the dam’s breach.
The failure of the dam released an enormous flood of 650 million gallons (2,954 million liters) of water, which rushed down the Loxley Valley. The floodwaters passed through several towns before finally reaching Sheffield, where the water rose to 6 feet (1.8 meters) deep. The devastation was widespread, with houses, pubs, factories, and various buildings flattened. At least 240 people lost their lives in the disaster.
2. Brumadinho Dam (Brazil, 2019)
The Brumadinho dam in Brazil was not designed for storing water for drinking or irrigation. Instead, its primary purpose was to contain the toxic runoff from mining operations that extracted iron ore. Essentially, it held millions of tons of poisonous sludge. When the dam collapsed in January 2019, it unleashed a torrent of toxic waste that engulfed surrounding villages and farms, resulting in the deaths of 270 people.
The mining company Vale, which operated the mine, was ordered in 2021 to pay $7 billion in compensation for the disaster. This amount could rise even further. The Brumadinho dam failure is considered the worst industrial accident in Brazil's history.
The flood completely obliterated the village of Córrego do Feijão. Although an alarm system had been set up to alert residents of any potential danger, it failed to function that day. Sirley Gonçalves, a survivor who lost her husband, a mine worker, during the disaster, shared her thoughts with the BBC: 'Vale destroyed our lives. They must have known the dam would collapse, but they don’t care about their workers; they care only about their profits.'
1. Malpasset Dam (France, 1959)
Nestled on the French Riviera near Cannes, the Malpasset dam crossed the Reyran River. Construction began in 1952, and by the time the dam was completed a few years later, it stood 218 feet (66.5 meters) tall and measured just over 22 feet (6.7 meters) in thickness. A single spillway was placed at the center of its 736-foot (224-meter) span. It wasn’t until December 1957 that the reservoir was filled to its full capacity, which ultimately led to its failure.
The collapse occurred after days of heavy rainfall and strong winds, factors that likely contributed to the disaster. The flood claimed the lives of 421 people, with the death toll being even higher than expected due to blocked access roads preventing timely rescue efforts. An investigation later revealed that the Malpasset Dam had significant design flaws, made worse by a lack of comprehensive geological assessments during its construction.
