Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

State of the art concerning basic concepts related to debris flow

Firstly, a standard form devoted to “debris flow risk analysis” was a reference document. It was designed by ARMINES.M.GI/ENSMP.CGI in a previous research project.

The predisposition factors, related to a whole catchment, concern topographical factors, geological and hydrogeological conditions, slope erodibility and slope stability conditions (with the role of vegetation), geotechnical factors (grain size distribution curves of materials in the potential material source areas, looseness of materials, etc), available volume of material liable to be mobilized near a torrent channel or in the torrent bed.

During this research project, this methodology was improved for the mapping of the predisposition factors and resulted in a synthetic “debris flow initiation hazard map”. Field investigations were performed in the Arbonne catchment (Savoie, France). This map allows the identification of material sources areas and then various potential scenarios of debris flow initiation can be analysed, with the associated volumes.

These scenarios have to be characterized with reference to a typology of debris flow initiation and mobilization processes. This typology, previously established, refers to 12 main processes. The classification proposed is based on geomorphologic surveys performed in many Alpine debris flow source areas and underlines the importance of local conditions related to geology, geomorphology, hydrology and hydrogeology.

These analyses have to be performed at the scale of a whole catchment and may demonstrate that, in some cases, large parts of the catchment contribute to the initiation and mobilization of a given debris flow event during a heavy rainfall, for example, and that, in other cases, only a specific initiation area is concerned.

As a consequence of these general results, scenarios of debris flow events can be analysed in a qualitative manner, with the objective of determining orders of magnitude of the following volumes, considering field conditions:
- Volumes available in the source areas,

- Volumes which are liable to be mobilized into debris flow materials,

- Volumes which are liable to reach the lower parts of the catchment.

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UMLV-CGI, Bât IFI, 5 Bd Descartes
77454 Champs-sur-Marne, Marne-la-Vallé
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