Barcelonnette Basin: debris

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Research Training Network
Mountain Risks
Barcelonnette Basin: debris-flow activity
Æ Presence of 26 torrents prone to debris flow activity and 3 large mudslides (La
Valette, Poche, S.-Sauze) in the upper part of torrential catchments Î landslideinduced debris flows
Barcelonnette Basin: debris-flow activity
Research Training Network
Mountain Risks
Æ Example of the 2003 debris flow in the Faucon stream: damages on the fan
- Volume: ca. 100’000 m3
- Huge damages on the housing
located on the debris fan
- Estimated cost: 2.5 millions €
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Barcelonnette Basin: debris-flow activity
Research Training Network
Mountain Risks
Æ Since 1850: >100 debris flows and ca. 500 torrential floods have been observed
Æ History of debris-flow
activity & mitigation activity
in the Barcelonentte Basin
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Debris-flow risk management
4th RTM law
Catastrophic events (Val d’Isère, Passy)
3rd RTM law (1882)
RTM laws (1860 and 1864)
Intensity of RTM investments
Flooding crisis (1856)
Research Training Network
Mountain Risks
Æ Locally, there is one public administration managing the natural risks: ONF - RTM
ONF – RTM has been created in 1860 after some huge torrential events
in the French Alps
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Research Training Network
Mountain Risks
Debris-flow risk management
1. Non structural mitigation:
Æ Bio-engineering in the source areas
Plantation of black pine at Uvernet (04), 1905
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Debris-flow risk management
Research Training Network
Mountain Risks
1. Non structural mitigation: Æ Bio-engineering in the source areas
1881: 5-10% of forests
Change in vegetation cover in the Riou-Bourdoux catchment
2000: 55-60% of forests
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Debris-flow risk management
Research Training Network
Mountain Risks
1. Non structural mitigation: Æ Bio-engineering in the source areas
1894
Riou Bourdoux (30 juillet 1909): grazing of the slopes
2000
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Debris-flow risk management
Research Training Network
Mountain Risks
1. Non structural mitigation: Æ Bio-engineering in the source areas
1904
Fieldwork of tree plantation, once the tree is > 3 years old, Riou-Bourdoux
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Debris-flow risk management
Research Training Network
Mountain Risks
1. Non structural mitigation: Æ Bio-engineering in the source areas
1909
Tree plantation along the elevation lines
2000
Ravin du Puy
Pra Loup
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Research Training Network
Mountain Risks
Debris-flow risk management
2. Structural mitigation:
Æ Hydraulic engineering in the streams
Debris-flow risk management
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Research Training Network
Mountain Risks
2. Structural mitigation: Æ Hydraulic engineering in the streams
Faucon torrent: ‘dry stone dams’ in the upper part of the stream
Debris-flow risk management
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Research Training Network
Mountain Risks
2. Structural mitigation: Æ Hydraulic engineering in the streams
Riou Bourdoux torrent: ‘large concrete dams’ in the middle part of the stream
Debris-flow risk management
Research Training Network
Mountain Risks
2. Structural mitigation: Æ Hydraulic engineering in the streams
… Dam construction,
from the past to the present …
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Debris-flow risk management
Research Training Network
Mountain Risks
2. Structural mitigation: Æ Hydraulic engineering on the torrential fans
Concrete channel
Erosion control blankets
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Lateral levee
Debris-flow risk management
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Research Training Network
Mountain Risks
Æ Practical daily work of the local risk managers
1. Description of the torrents (field survey, 1-2 field visits per year, notes, photographs)
2 . Description of the structural mitigation works in a database
* date of building
* location, elevation
* height, shape, type of construction material (stone, concrete), etc
* state of degradation
* geomorphological characteristics of the channel (reach, occurrence of landslides, natural
dams, etc)
3. Decision for the construction or replacement of old dams
* for Barcelonnette, the total budget per year for dam construction is ca. 1M € (eg. 5 – 10
dams per year)
* Total number of dams in the Barcelonnette area: ca. 900