It was at precisely 9.13pm on the rainy night of 2nd December, 1959 when the arched dam at Malpasset on the Reyran river collapsed, releasing 50 million cubic metres of water which roared down the valley towards Fréjus, obliterating everything and everyone in its path. Arched dams or barrages voûtés are reputed for their exceptional strength and solidity. What went wrong?
The idea of a dam at Malpasset was first put forward as early as 1865, as a potential means of capturing the heavy winter rains which regularly caused the river Reyran to burst its banks, and storing them for use in the summer, when water was scarce. The idea did not come to fruition, however, until after the Second World War, when the region experienced a boom in tourism and agriculture and the problem of supplying the Frejus area with a regular water supply became the most pressing problem.
In October 1945 the issue was raised during a local government meeting of Conseillers Généraux and André Coyne, who had designed dams all over the world and was the undisputed expert on the construction of arched dams, was brought in. Geological surveys were carried out and the Malpasset site in the Reyran valley was chosen.
The hydro-electric dam took two and half years to buid and delays caused by lack of funding and labour disputes plagued the construction. The dam was finally inaugurated and partially-filled in 1954, but a lack of rain for the next few years and further disputes meant that it was not filled completely.
The autumn of 1959 brought heavy rain which poured the dam. As water levels rose, leaks were spotted in the wall of the structure but the local population was not informed of any potential danger.
The rain continued unabated and by the 2nd December, 1959, water levels behind the dam had risen so high that the on site guardian became concerned and tried to phone the authorities, but the telephone company was on strike and he couldn't get through, so he jumped on his motor scooter and drove to see them in Fréjus. His request to open the valves was denied. The A8 autoroute was under construction nearby and it was feared that water released from the dam would damage the freshly-poured concrete supports of a new bridge. By 6pm that evening, however, the dam was filled to overflowing and the decision was taken to release some of the water, but by this time it was too late.
At exactly 9.13pm the guardian of the dam heard a cracking sound and took refuge on the roof of his house. Seconds later a 40 metre high wall of water, travelling at 70kms per hour came crashing down the Reyran valley, destroying everything in its path. It hit Fréjus 20 minutes later.
It's possible the exact number of people killed that night will never be known for sure. It was at least 420, but it has been rumoured that undeclared workers were in the area at the time the dam ruptured, and that their deaths were not included in the official death toll. Many bodies were never recovered and it is thought they were washed out to sea.
Apart from the fatalities, around 1,850 families were made homeless, dozens of farms and vast stretches of agricultural land were lost and thousands of animals drowned. Not to mention damage caused to surrounding railway lines, roads and vehicles.
Initial hypotheses into the cause of the disaster ranged from seismic activity to explosives damage from the nearby construction of the autoroute. The construction delays at the dam which had resulted in certain areas of concrete being left to stand for long periods before fresh concrete was poured on top, perhaps compromising the integrity of the structure, were also cited as possible causes.
The results of the official investigation, published in 1967, concluded that the problem lay with previously undetected geological faults in the rock beneath the left bank of the dam which had, the report claimed, allowed water to seep down and collect underneath one section of the wall. This had caused a pocket of pressure, creating an unsuspected weak point at the base of the wall which eventually gave way under the weight and pressure of the water above it.
Most constructions are only as strong as their foundations, and, in the words of André Coyne, the expert, who suffered a fatal illness 6 months after the disaster, “Of all man-made inventions, dams are the deadliest”.
From The Riviera Reporter Var Supplement, issue April/May 2007