Vaiont Flood Disaster - No “Damn” Break

Steve's picture

I’ve blogged previously about the hazards associated with dam-break floods. A curious case is the 1963 Vaiont Flood Disaster. In just minutes on one autumn evening, 20% of the water (30 million m3) held in Vaiont reservoir spilled out.  What’s the curious aspect about the affair?  -- This was no dam break! In fact, the dam still stands intact today.   Puzzled?  Then read on.

The early 1960’s saw Vaiont Dam rise at the mouth of a narrow and deep valley bordering the southern Alps, 60 miles north of Venice Italy. A marvelous concrete arch structure, it towered 260 meters, fully 40 meters more than Hoover Dam. On its flanks rising 1000 m higher still, two mountains wedged the reservoir behind into a cigar shape 400 meters wide and 5 km long. Unbenounced to the builders however, under the entire southern arm of that wedge,  a paleo landslide lurked.

Virtually on dam’s first filling, that old landslide reactivated and restarted its march downward. On the night of October 9, 1963 it all let go --  260 million m3 of material accelerated northward into the reservoir at speeds of 15 m/s (33 mph). In less than 60 seconds, the avalanche squeezed the half-km-wide Vaiont Valley shut and lifted up its fluid contents. With no other escape, the water simply poured over the dam. We calculate that for two or three minutes the flow amounted to 80 times that of Niagara Falls. This Niagara however, was not for tourists. Downstream in Piave Valley, the torrent devastated several towns and villages with a loss of 2000 souls. Litigations dragged through the Italian court system for decades.

If you ever find yourself in northwest Italy, stop by Longarone. You’ll see a memorial to the dead, exhibits detailing events and that marvelous dam -- now forlornly holding a reservoir of dirt. 

I’ve made these physics based simulations of the landslide and flood to provide you with a visual appreciation of the story.

Most engineering failures arise in the least expected ways. I suppose that the message of Vaiont is that both scientists and the man in the street get No “Damn“ Break when it comes to natural hazards.


Steven N. Ward   Santa Cruz



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