The Vajont Dam in Italy, built in 1956 to supply hydel power to the city of Venice burst in 1961. A 200 m high wall of water surged down the river valley causing havoc and threatening townships 100 kms away. 20,000 acre-feet of water were released by the dam break. The dam was never rebuilt.
Vajont Dam is located on the Vajont River, a tributary of the Piave River, snow fed rivers, just upstream of Longarone in northeast Italy. Longarone is approximately 60 miles north of Venice, Italy. The dam was built in a steep and narrow limestone canyon, high in the Dolomite region of the Italian Alps, sculpted by downcutting and erosion of the river.
Vajont is considered the most disastrous rockslide ever to occur in Europe. The event created strong earth tremors, recorded as far away as Vienna and Brussels. The rockslide displaced the Vajont reservoir, causing wind and water to travel in all directions. An updraft of air, rocks, and water climbed the canyon walls to around 850 feet above the reservoir. Waves of water reached greater than 330 feet above the dam crest. Approximately 20,000 acre-feet of water went over the dam, creating a flood depth at the mouth of Vajont River of about 230 feet, one mile downstream.
Five downstream towns were destroyed including Longarone, Pirago, Rivalta, Villanova, and Fae. The water first arrived in Longarone at 10:43 pm, around 4 minutes after the rockslide. The town was completely leveled due to the depth and speed of the flood wave (high severity flooding). Of an estimated 1,328 people in Longarone who were at risk at the time of the floodwave, 1,269 fatalities occurred, resulting in a fatality rate of 94 percent. Longarone, like many towns in northern Sikkim, was a tourist destination, a mountain village made up of mostly residential and commercial structures. The flood wave completely destroyed the town, resulting in one of the highest known fatality rates ever recorded due to flooding from a dam failure or incident. The dam break changed the landscape permanently. It was never rebuilt.
History should not be allowed to repeat, because of shortsightedness and stupidity.
https://damfailures.org/case-study/vajont-dam-italy-1963/