Landslides Falling into Water Reservoirs

Landslides Falling into Water ReservoirsIntroductionSeveral disasters have been caused by landslides and rock avalanches falling onto natural or artificial water basins. The most studied case occurred in northern Italy on October 9th, 1963, when a volume of 270 Mcum. of limestone collapsed into the artificially dammed Vaiont lake. The dam survived the impact, but water overtopped the dam by about 200 m and the ensuing water wave took 2,000 lives.Probably the disaster could have been avoided if the danger of landslides falling at high speed in water reservoirs and their capability of displacing the water had been recognized.Introduction (Contd.)The fall of a landslide into a water reservoir may displace a large amount of water.If the water reservoir is large (a vast lake, a fjord, or the open sea) waves created can travel fast as a tsunami and discharge their power in distant locations. However, also landslides falling in small water reservoirs may cause local damage. Several physical-dynamical problems arise during the process of landslide impact with water.General ClassificationFirst kind. If the mass of displaced water is much less than the landslide mass, the latter will be only weakly affected by the water. Water is totally displaced. Example: Val Pola and Vaiont.

General Classification (Contd.)Second kind. If the amount of water is comparable to the landslide mass, the movement of the slide and the water displacement are interconnected. The landslide will be more delayed by water than in the previous case.

General Classification (Contd.)Third kind. If the mass of the landslide is much less than that of water, the movement of the landslide is strongly affected by water; water is displaced locally but not permanently, and will promptly return to the equilibrium level.

Depending on the speed of the landslide and on the local geometry of the basin, it may generate a tsunamiCritical ParameterThe ratio between the water mass in the reservoir and the landslide mass is considered as a critical parameter for assessing the behaviour of a landslide falling onto a water reservoir. (Erismann and Abele (2001))

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