Landslide dam

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A landslide dam, debris dam, or barrier lake is a natural damming of a river by some kind of mass wasting: landslide, debris flow, rock avalanche or volcano.[1] If it is caused by earthquake, it may also be called a quake lake. Some landslide dams are as high as the largest existing artificial dam. [2]

Causes[edit]

The major causes for landslide dams investigated by 1986 are landslides from excessive precipitation and earthquakes, which account for 84%. Volcanic eruptions account for a further 7% of dams. [3] Other causes of landslides account for the remaining 9%.

Consequences[edit]

The water impounded by a landslide dam may create a dam reservoir (lake) that may last from short times to several thousand years. [2]

Because of their rather loose nature and absence of controlled spillway, landslide dams frequently fail catastropically and lead to downstream flooding, often with high casualties. A common failure scenario is overflowing with subsequent dam breach and erosion by the overflow stream. [2]

Landslide dams are responsible for two types of flooding: backflooding (upstream flooding) upon creation and downstream flooding upon failure. Compared with catastrophic downflooding, relative slow backflooding typically presents little life hazard, but property damage can be substantial.

Profiles of the dam reservoir and groundwater upstream (the landslide dam is not shown in the figure)
Groundwater after dam failure downstream

While the dam is being filled, the surrounding groundwater level rises. The dam failure may trigger further catastrophic processes. As the water level rapidly drops, the uncompensated groundwater hydraulic pressure may initiate additional landslides. Those that fall into the dam reservoir may lead to further catastrophic spillages. Moreover, the resulting flood may undercut the sides of the river valley to further produce landslides downstream. [2]

After forming, the dam leads to aggradation of the valley upstream, and dam failure leads to aggradation downstream.[2]

Construction engineers responsible for design of artificial dams and other structures in river valleys must take into account the potential of such events leading to abrupt changes in river's regimen.

Examples[edit]

  • Among the most destructive landslide lake outburst floods in recorded history occurred in the Sichuan province of China on 10 June 1786 when the dam on the Dadu River burst, causing a flood that extended 1400km downstream and killed 100,000 people.[7]

References[edit]

  1. ^ "Natural Debris Dams and Debris-Dam Lakes" (web). USGS/Cascades Volcano Observatory, Vancouver, Washington. 2003. Retrieved 2008-03-16. 
  2. ^ a b c d e f Robert B. Jansen (1988) "Advanced Dam Engineering for Design, Construction, and Rehabilitation", ISBN 0-442-24397-9
  3. ^ R.B. Jansen refers to Schuster R.L. and Costa J.E., "A Perspective on Landlside Dams", in Landslide Dams by the American Society of Civil Engineers, 1986, pp. 1-20.
  4. ^ Offer, R.E. (Robert) (1997). Walls for Water: Pioneer Dam Building in New Zealand. Palmerston North: The Dunmore Press Ltd. ISBN 0-86469-313-3. 
  5. ^ Amid race to drain Chinese quake lake, emergency plans proceed_English_Xinhua
  6. ^ Flooding spreads more destruction in town below 'quake lake' - International Herald Tribune
  7. ^ Schuster, R.L. and G. F. Wieczorek, "Landslide triggers and types" in Landslides: Proceedings of the First European Conference on Landslides 2002 A.A. Balkema Publishers. p.66