16 questions · Technology
On the evening of 9 October 1963 a whole mountainside broke away from Monte Toc in the Italian Alps and slid into the reservoir behind the Vajont Dam. A wave surged over the crest and crashed into the valley; within minutes the town of Longarone was wiped out and almost 2,000 people died. The dam itself was left standing almost undamaged. Few disasters show so clearly that a dam is never just concrete, but the whole valley around it. The engineering behind it is surprisingly simple. A gravity dam resists the water by its mass alone, like the 285-metre Grande Dixence in the Swiss canton of Valais. An arch dam carries the pressure into the rock walls like a vault lying on its side, as Contra in Ticino does, from which James Bond jumps in “GoldenEye”, or Jinping-I in China, at 305 metres the tallest concrete dam in the world. Behind every dam lies a reservoir. Some dams are world history. The Hoover Dam on the Colorado River holds back Lake Mead, Grand Coulee on the Columbia River is the most powerful plant in the United States, Itaipú is shared by Brazil and Paraguay, and the Aswan High Dam created Lake Nasser. The Three Gorges Dam on the Yangtze has the greatest capacity of any hydropower plant, Lake Kariba on the Zambezi the largest volume, and the Atatürk Dam holds back the Euphrates. War was waged on dams too. On the night of 16 to 17 May 1943 British bombers dropped bouncing bombs on the Möhne Dam in the Sauerland during Operation Chastise. The wall broke, and the flood wave killed well over a thousand people.
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Yangtze
Completed in 2006, the wall is over two kilometres long; more than a million people had to move for the reservoir.
💡 Did you know? Its turbines together generate 22.5 gigawatts.
Hoover
It was built between 1931 and 1936 in the desert between Nevada and Arizona, in the middle of the Great Depression.
💡 Did you know? From 1933 to 1947 it was officially called Boulder Dam.
Itaipú
In service since 1984, for many years it produced more electricity per year than any other power station in the world.
💡 Did you know? The reservoir drowned the Guaíra Falls, once the most powerful waterfalls on Earth by volume.
Aswan
Built in the 1960s, the high dam was meant to tame the annual floods and generate electricity.
💡 Did you know? For the reservoir the temples of Abu Simbel were taken apart and rebuilt higher up.
Grand Coulee
Completed in 1942, it is one of the largest concrete structures in the world and also irrigates vast farmland.
💡 Did you know? Woody Guthrie wrote a song about it, commissioned by a government agency.
Kariba
It was finished in 1959; as the valley filled, rescuers saved thousands of animals in “Operation Noah”.
💡 Did you know? Tens of thousands of Tonga people had to leave their villages for the lake.
Vajont
More than 260 million cubic metres of rock slid from Monte Toc into the reservoir; the wave destroyed the town of Longarone.
💡 Did you know? The dam itself was left standing almost undamaged.
Möhne
The flood wave killed well over a thousand people in the Möhne and Ruhr valleys, many of them forced labourers.
💡 Did you know? The bouncing bombs were designed by the engineer Barnes Wallis; they skipped over the water up to the wall.
Operation Chastise
No. 617 Squadron, formed especially for the task under Guy Gibson, flew the raid on the night of 16 to 17 May 1943.
💡 Did you know? The squadron has been known as the “Dambusters” ever since, and a film of that name came out in 1955.
Gravity dam
Its cross-section is a broad triangle: very thick at the bottom, narrow at the top, so that it neither tips nor slides.
💡 Did you know? The tallest of its kind is the Grande Dixence in Valais, at 285 metres.
Arch dam
Because the rock carries the load, it needs far less concrete than a gravity dam, but it requires a narrow valley with solid sides.
💡 Did you know? The Vajont Dam is an arch dam and survived the huge flood wave of 1963.
Jinping-I
The arch dam stands on the Yalong River in China’s Sichuan province and went into service around 2013.
💡 Did you know? It tops the Eiffel Tower without mast and antennas, which measures 300 metres.
Grande Dixence
Completed in 1961, it is also the tallest gravity dam in the world.
💡 Did you know? It contains about six million cubic metres of concrete.
Contra
The 220-metre arch dam in the Verzasca valley was completed in 1965.
💡 Did you know? Today visitors make the same jump on a rope themselves.
Reservoir
It stores water for drinking, irrigation and power and catches floodwater.
💡 Did you know? Whole villages lie beneath some reservoirs; in droughts church towers reappear.
Euphrates
Completed around 1990, it is the core of a large irrigation and energy project in south-eastern Anatolia.
💡 Did you know? Syria and Iraq, which lie downstream, protested against its construction.
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