Intro

It is the 2nd December 1959, and a photographer is preparing their camera, today they aren't documenting a wedding or baptism but a disaster. The city of Frejus has been battered by a wave of flood water, the culprit? the dam that towered above it, the Name? Malpasset. My name is John and welcome to plainly difficult.

Background

Background Our story starts and will ultimately end in the French Riviera, and the need for a dam just north of the city of Fréjus in the early 1950s. Frey Juice Although a new project, the need for a dam in the region had been frequently brought up over several decades. A number of previous projects had failed to get off the ground as early as 1865, you see the area had an issue with the Reyran river, where it is mostly dry in the summer but conversely bursting at the banks in the winter. This is where a dam would be beneficial as it could attempt to regulate the flow of water and even out the Jekyll and Hyde like behavior of the river. A Dam would have a number of other benefits providing water for agriculture, domestic use, as well as creating a lake for use in the tourism sector. Before any concrete could be poured for the dam, geological surveys had to be undertaken, with each preceding project surveys had been completed, but these were not particularly useful, as each proposed dam was a completely different design from the other. Well in preparation for the 1950s project surveys of the valley at the potential building site took place in 1946 where a fault line was discovered, by the science department in Marseille, who were undertaking the initial site investigations. They advised that further investigation was required by excavating sections of the river banks to check their internal composition and identify any unweathered rock; they also suggested that other sites should also be considered. Another survey took place in November 1949 but the company in charge of the project decided to move the foundation site 200 m downstream without any additional geological study at the new placement. The dam was going to be an Arch dam; these had a number of advantages, most notably cost, as it uses a thin dam curved structure, which spreads the weight of the reservoir into the presumably solid banks. The 1800s design was going to be a gravity type which is very large and expensive in comparison. So the new malpasset dam was penned by renowned french civil engineer André Coyne, and the project would be funded and owned by Département Var. The dam was 222 meters wide and was a doubly curved equal angle arch type with variable radius. It was to be made out of concrete It was 6.78 meters wide at the base, 1.5 meters thick at the top and 66 meters tall with an aimed reservoir capacity of 50 million m3 of water. On the right bank looking upstream a 10 meter high concrete abutment was also planned due to the topography of the valley. Level control was rather simple at Malpasset with a spillway in the Center of the dam, which would allow water to, well spill over the top. There was also a draw-off made from a metal pipe of 1.5 m diameter cutting across the foot of the arch at a height of + 45.5 m and shut by valves. If the level exceeded 99 meters then a fixed wheel gate would automatically open allowing water to flow down the draw off, this system was also able to be manually controlled. Construction began in April 1952 and after 2 years was completed in October 1954. Upon completion it was said to be the thinnest dam at its height. But although the structure was complete, the filling of the lake behind the dam would be a long, long task, taking several more years. Filling the reservoir at an even pace is vital. Over stress too quickly and structural failure is guaranteed, but filling too slowly can cause issues as well, but we will come back to this later. This was the reason why Malpasset, although built in 1954, wouldn't be even close to full capacity until 1959. As the water level increased cracks appeared on the right side of the dam. By mid November 1959 the reservoir was roughly 7 meters below the crest, and the cracks had turned into clear streams of water running down the right hand side of the dam. Somehow reservoir water was escaping, now if things were looking a little bit Ropey imagine what a torrential downpour would add to the mix, well imagine no more....

Disaster

The disaster So the malpasset dam wasn’t looking too great towards the end of november, the dams right side was still leaking, and now a downpour of rain wasn’t helping. One of the dam guardians André Ferro requested permission to open the gate for the draw off to reduce the reservoir level on the 2nd of December. Sensible idea however this would have encroached upon the construction of the Marseille-Nice motorway about 1 km downstream from the dam. The reservoir would be allowed to fill up, remember how it had taken years to fill so far, well it would increase the water depth by 4 meters in just 24 hours. Ferro was finally given the ok to open the gate at 6pm, but by then it was too little too late over 3 hours of the gate being open only a few centimeters of depth was removed, the dam was now groaning under the weight of the water. The dam breached at 21:13 releasing a torrent of water 40 m (44 yd; 130 ft) high moving at 70 km/h (38 kn; 43 mph) downstream. It destroyed everything in its wake including two small villages the motorway building site reaching 20 minutes later frejus, flooding the western half of the town. By the time it hit the town the wall of water was still 3 meters tall and littered with concrete debris. Eventually the torrent reached the Mediterranean Sea. Complete destruction had hit the region, all road and rail connections were severed, hindering residents from escaping and rescue workers reaching the disaster site. 155 buildings were destroyed with a further 796 buildings damaged, cars were washed away, shops were decimated. And an estimated 423 lost their lives in the tragedy, with many more injured. Hundreds were made homeless with 79 children orphaned. Sadly dam failures cause incomprehensible tragedy to an area, but as the community began to clean up and try to heal the wounds the cause had to be found..

Aftermath

The Aftermath. Well it would become quite clear that the interrupted and incomplete surveys of the dam site would come back to bite the project in the behind. When looking at the dam face on upstream you can see the likely start point of the failure, that right hand abutment, the one with the 10m high concrete abutment, that was leaking. It was discovered after a thorough geological survey that there in fact was a fault line downstream from the dam, this stopped infiltration water from flowing away and instead collected below the foundation of the dam. As the weight and pressure built up from the filling of the reservoir, it unseated the dams foundations, this formed cracks which were then filled by the impounded water in the reservoir thus weakening the structure which led to the base being stripped from the valley. And when the right hand side failed the rest would follow. Pretty disastrous but the issues with the dam were not just geological but human as well, although the dam was a good design, but placed incorrectly, people were the cause ultimately of the failure. You see the regulators saw the malpasset dam differently to others because it was mainly due to be used for agriculture, this attracted less scrutiny than that of a hydroelectric dam, and thus fewer inspections. Little was done to check out the design due to the designer being so successful in his career, with over 70 structures under his belt, pretty much all of which were problem free. The long time it took to fill the reservoir was also an issue, as in 1959 the dam was still on its first filling, which really when testing out such a structure it should be filled and emptied a number of times building up to its final capacity. Instead they just decided to reach full capacity in the middle of a downpour, they should have opened the gate way earlier. The building up of water behind the dam gradually by emptying and filling successive times gives time to find any issues and fix them as they arrive. Interestingly over a number of court cases, the design of the dam was cleared, more putting the blame on the choice of location. André Coyne the dams designer died a few months after the disaster admitting full responsibility, but as we've seen the real cause was not just down to one man but a whole selection of issues. The dam was never replaced but left as a reminder of the all too common issues of corner and cost cutting. So I'm going to rate the disaster as oh balls people will hear about this and a 6 on my legacy scale do you agree? All videos on the channel are creative commons Attribution-ShareAlike. Plainly difficult videos are produced by me John, in a wet and windy suburban Southeast corner of London, uk. Help the channel grow by liking commenting and subscribing! Check out my twitter for all sorts of photos and odd and sods, as well as hints on future videos! I've got patreon and youtube membership as well so if you fancy check them out! All that's left to say is thank you for watching! https://damfailures.org/case-study/malpasset-dam-france-1959/ https://www.aria.developpement-durable.gouv.fr/wp-content/files_mf/FD_29490_malpasset_1959_ang.pdf