5.1.5 Consequences of the flow process

The damages caused by a flow event depend on the quantity of material (debris, soil, mud) displaced. In the deposit areas, flows develop successive lobes and can spread on considerable surfaces. These are rapid phenomenon, thus they can be very dangerous for the infrastructures and the population. The socio-economic impact and the loss of life, property and agriculture can be catastrophic in the case of large flows through populated areas. In the case of channelized flows (debris flows), material often overflows the banks and interrupts roadway systems. The deposits are also responsible for severe indirect damages and hazards such as damming of rivers or sudden debris supply to river systems.

Figure 1: Different effects of a flow event on a house (modified from Léone and al., 1996)
Figure 2: Debris flows at Schlans, Switzerland, in 2000 caused the destruction of a part of the village and the death of about 10 people (from Remaître, 2006)
Figure 3: Mudflow at Gondo, Switzerland, in 2000. About 10 people were killed (from Remaître, 2006)
Figure 4: The village of Täsch, Switzerland, damaged by a debris flow in June 2001 (from Ancey, 2007)
Figure 5: Houses damaged by a debris flow at San Matéo, California (from Cannon et Ellen, 1985)
Figure 6: House damaged by a debris flow (from USG)
Figure 7: Road cut off by a debris flow at Hashi, Japan, in 2004 (from Remaître, 2006)
Figure 8: Bridge destroyed by a debris flow occurred in the Pisse torrent, in Reallon, Hautes-Alpes, France, on June 18 2005 (photo by Arnaud)
Figure 9: Bridge and road damaged by a debris flow occurred in the Faucon torrent, in the Barcelonnette Basin, France, on August 19 1996. Debris overflowed 50 cm above the bridge. At the confluence with the Ubaye river, 2 to 4 m-thick debris spread up to a width of 250 m (from Sivan, 2000)
Figure 10: House damaged by a debris flow also occurred in the Faucon torrent, in the Barcelonnette Basin, France, on August 5 2003. The road and the bridge were cut off again, and six houses were damaged (photo by Peyron)
Figure 11: Inhabitants of Angra dos Reis, Brazil, during a mudflow in 2002 (from Remaître, 2006)
Figure 12: Effects of a debris flows in Shields Canyon, California, February 1978 (from Slosson and al., 1992)


ANCEY C., 2007. Notes de cours – Risques hydrologiques et aménagement du territoire. Laboratoire hydraulique environnementale, École Polytechnique Fédérale de Lausanne
LEONE F., ASTE JP., LEROI E., 1996. Vulnerability assessment of elements exposed to mass movements: working toward a better risk perception. In: Senesset K (Ed): Landslides, Proceedings of the 7th International Symposium on landslides, Balkema, Rotterdam
REMAITRE A., 2006. Morphologie et dynamique des laves torrentielles : Applications aux torrents des Terres Noires du bassin de Barcelonnette (Alpes du Sud). PhD Thesis: Laboratoire Geophen, Université de Caen/Basse-Normandie, 487 p.
SLOSSON E., KEENE A.G., JOHNSON J.A., 1992. Landslides/Landslide mitigation. In: Reviews of Engineering Geology, Volume IX, Colorado


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