The dam at Malpasset was completed in 1954 to protect the adjacent villages and lands from the Reyran river, which is completely dry during summer, but a raging torrent during winter and spring.

Malpasset means “going wrong” and that was what happened in December of 1959. Earlier that autumn, small cracks had been discovered along the bank of the dam. The cracks grew rapidly, but the population was not notified.

There was nearly 50 cm of rainfall from the 19 November to the 2 December, with 13 cm in the last 24 hours. The dam was filled to the brim.

The guardian of the dam wanted to warn the authorities and as the phones were not working because of a telephone-company strike, he set out on his scooter. The authorities refused his request to open the valves, because the released water might ruin the new pylons for a highway.

Finally, at 6 p.m. the valve was opened, but it was too late. At 9 p.m. the dam burst and sent a 40 meter wall of water down the valley at 70 kph.

The small villages lying beneath the dam, Malpasset and Bozon, were annihilated as was the highway construction site. Most of the inhabitants and construction workers were killed. The waters roared down the valley, destroying houses, roads and railways on its way, leaving many victims behind, many of whom were never found.

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Links and references:

Chanson, Hubert: The Hydraulics of Open Channel Flows:
http://www.structurae.de/en/refs/items/ref00235.ph...

Pictures of the dam:
http://www.ulg.ac.be/hach/fr/malpasset.html

The course of events:
http://www.beyond.fr/sites/malpasset.html