Environmental Engineering Reference
In-Depth Information
Fig. 1.3 Losses from major
flood disasters in Europe
between 1970 and 2008
(IPCC [
3
-
5
]
second decades (between 1973 and 2002), and remained stable during the third. In
France, 64 % of the floods we have information on, report less than 1,000 people
affected, and 21 % have between 1,000 and 10,000 affected. Bigger flood events
have been reported in 1977 (25,000 affected), 1988 (more than 50,000 affected), and
especially in 1995 (120,000 affected) and 1999 (200,000 affected) [
7
].
At the end of the nineteenth century, the Ubaye Valley was considered as the
most dangerous torrential flooding area in France. The high frequency of debris
flow interfered with the development of human activities. The correction of the
active torrents was an emblematic challenge for the RTM services (Service de
Restauration des Terrains de Montage—Mountain and Restoration Service) who
were in charge of the torrential mitigation. At that time, torrentiality in the South
French Alps resulted from intensive deforestation and land degradation [
8
].
According to the French Forest Office, more than 550 events have occurred
since 1850. A total of 450 events were recorded as torrential events and 100 events
were recorded as debris flows (Fig.
1.4
).
Flageollet [
9
] indicated that there were six major inundations and 15 other
hydrologic hazards such as debris flows, and overflows since 1950, though the
numbers of references were around 428. Of this record, 13 % included debris
flows, 12 % inundations, 2 % gullying, and 73 % were only torrential flows.
Among these statistical reports, 15 events can actually be accredited as floods [
9
].
This area constitutes an elongated form. Elongated or linear villages are usually
found along channels, rivers, or road sites that promote attenuated settlement
forms. The elongated structure makes it highly dependent on structural measures
such as dykes and levees to protect it against flooding.
The Ubaye Valley is representative of climatic, lithologic, geomorphologic, and
land use conditions observed in the South French Alps, and is highly affected by
flood hazards [
10
]. The city is mainly a tourist center hosting many ski lodges. The
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