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Description
The dam, which was a doubly-curved equal angle arch type with variable radius, began construction in April 1952 and finished in 1954 to supply water and irrigation for the region. Delays haunted construction, due to lack of funding and labor strikes. Construction was halted a few times. Another source reports that construction began as early as 1941. Construction costs (by 1955 prices) were 580 million francs, and was lead by a well-known French engineer André Coyne. The project was funded and owned by Var département. Concurrent with the dam construction, A8 highway was also being built 200 meters away from the dam location.
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Disaster
The dam was breached on December 2, 1959, at 21:13 o'clock. Entire wall collapsed, and only a few blocks remained on the right bank. Even today, there are still pieces of the dam scattered in the area. The breach created a water flood wall 40 meters high and moving at 70 km/h, destroying two small villages - Malpasset and Bozon, the highway construction site, and in 20 minutes reaching Fréjus, still standing 3 meters high. Various small roads and railroad tracks were destroyed as well, water flooding western half of Fréjus and finally reaching the sea.
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Cause
Geological and hydrologic studies were done in 1946 and the dam location was considered suitable, however due to lack of proper funding, the geological study of the region was not thorough. Under the dam consisted of gneiss rock which was waterproof. On the right side (looking down the river), was also rock, and a concrete wing wall was constructed to connect the wall to the ground.
Weeks before the breach, some cracking noises were observed, but they were not examined. It's hard to determine when the cracking noises started. Right side of the dam had some leaks in November 1959.
A tectonic fault was later found as a most likely cause of the disaster. The water collected under a wall, unable to escape through the rocks. The water pressure was aimed diagonally towards the dam wall, and was not found initially. According to a source, exposions during building of highway might have caused shifting of rock base of the dam.
Between November 19th and December 2nd, there was 50cm of rainfall, and 13cm in 24 hours before the breach. The water level in the dam was only 28cm away from the edge. Rain continued, and dam guardian wanted to open discharge valves, but the authorities refused, claiming highway construction site was in danger of flooding water. 5 hours before the breach, at 18:00 o'clock, water release valves were opened, but with discharge rate of 40 m³/s, it was not enough to empty the dam in time.
Until the Malpasset incident, only 4 other incidents of arch-type dams breaches were recorded:
Manitou, Colorado, 1924
Moyie, Idaho, 1926
Lake Lanier, North Carolina, 1926
Purisima, California, 1930
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Trivia
Malpasset is pronounced the same in French as mal passer, which means "go badly" or "go wrong".
In August 2005, demoscene group Farbrausch released a demo titled Malpasset (fr-047), which featured a slideshow of Malpasset dam photographs and a chilling soundtrack
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