Vajont Dam: Its story, told again

A Brief History of the 7th tallest dam in world

Almost everyone has, in some way or another, heard about the Vajont Dam. Still, not everyone remembers what happened, exactly, or the main villages involved in the tragedy. If one mentions "Vajont Dam", memories of the event that hit the nearby villages and towns in the first years of the '60s, during the last century, immediately come to mind.

For the way the accident occurred, or the fact that the dam was already famous, due to its technical characteristics, even before the tragedy occurred. For all these reasons, the Vajont disaster always raises many new points.

Building the Vajont Dam

In the 50's, Italy was a quickly developing country in need of electricity. This is when the Vajont Dam project designed by the engineer Carlo Semenza was approved. It would create an artificial reservoir, in the gorge created by the Vajont torrent, in the Province of Pordenone, in the little village of Erto.

Works began in 1957 and were completed in 1960: At the time, it was the world's tallest dam. The barrier had an overall height of 261.5 metres. To this day, it still is the world’s 7th tallest dam. Its height was not the only thing that made it very popular during the first years of the 60s, but also its structure. This curved double-arched dam was built to resist the force created by the water.

The reservoir created behind the dam's barrier reached 168.715 million cubic metres of water. Through very long pipings, part of the waters of the Piave, Maè and Boite rivers were channeled into that large artificial lake. A system of small hydropower stations was created, which reached the Vajont River. Semenza had already conceived this capillary and integrated system, known as the "Grande Vajont" Project (Great Vajont), in 1929, almost thirty years before the dam was built.

The project was perfect on paper, and despite the many protests of its inhabitants, and the study of the Austrian specialist Leopold Müller, who foresaw the possibility of landslides occurring - the dam's construction was finished. The "Great Vajont" was made to operate, while, in the meantime, Mount Toc was moving, almost unnoticed, behind. Interesting to note that in the dialect of the Italian region of Friuli, the name Toc means "damaged", as it refers to the crumbly quality characterizing it.

The mount's movements increased, when the dam was filled. The companies managing the dam were put on the alert. In October 1960, Mount Toc was moving at a speed of 3 centimetres per day. With this evident threat, the dam’s water level was reduced, and during the two following months, all movements stopped.  

A "Bypass tunnel" was built. The dam was filled, once again, in April 1963, and waters had been authorized to be raised to 715 metres a.s.l., although this level was never reached. In fact, in September, the water level reached 710 metres, and Mount Toc started to move again, at 2 centimetres per day. The water level was gradually reduced to 700 metres. Things did not improve, though, and, on October 9, 1963, at 10.39 p.m., a landslide that extended for more than 2 kilometres, with approximately 270 cubic metres of earth and rocks, came off Mount Toc.

The Vajont Disaster

As the landslide hit the dam, it created three gigantic waves. The first hit the village of Casso; the second destroyed parts of Erto. The third wave, with an estimated volume of 50 million cubic metres of water, headed beyond the Vajont Dam, towards Longarone. When it reached the lake, the wave measured 250 metres in height. As it reached the bottom of the valley, it measured 30 metres.

It was calculated that the force of the wave of water, rocks and debris that hit the southern part of Longarone caused a pressure wave similar to the one of the Hiroshima atomic bomb. The small town of Longarone was swept away, and only the small town-hall and a few houses, in the northern part of the town, managed to survive. That night, 1,917 people died (although it is extremely difficult to perfectly estimate how many actually lost their lives). The victims came from Longarone, Erto and Casso, Castellavazzo Codissago and other inhabitated centres reached by the wave and debris.

In 1971, after 7 years of trial, Italy's Court of Cassation, named the two main people liable for the Vajont tragedy: Francesco Sensidoni, Head of the Dam Service of the Ministry of Public Works and member of the commission that did the testing, and Alberico Biadene, Director of the hydraulic construction service of Adriatica Di Elettricità. It is now certain that this disaster could have been avoided then. It was clearly evident, then, as it is now, that Mount Toc was very unstable.

The Vajont Dam, today

More than a century has passed since the Vajont tragedy. Longarone was rebuilt and is now completely different from the village destroyed in 1963. The Vajont Dam is still there: huge, just like it was then. The project’s excellent engineering quality allowed the dam to resist a force ten times greater than the one for which it was made. Today, in remembrance of what that night, it is possible to visit the Vajont Dam and to book guided tours to see the old remains of the houses hit by the landslide.