This landslip at Super-Sauze occurred in the 1960s,on a slope from 2105 m to 1740 m asl. The total volume is estimated at 750 000 m3 (Enchastrayes, 2010). © BRGM - Audrey Baills

Quantitative modelling of the landslide hazard with the Alice tool

07.01.2012
Alice, a BRGM software aid for mapping landslide hazard, enables a quantified approach to the hazard. It is based on a mechanical approach (geotechnical model), in which the main physical properties of the environment are quantified by a mathematical model that calculates a probability of landslide occurrence, and uses a Geographic Information System (GIS) in which the information, notably topographic (digital elevation models), is spatialized as a grid (raster). It requires knowledge of the spatial (if not temporal) distribution of the parameters that will condition the ground stability: mechanical and geometrical characteristics of the layers, hydric state, etc.

Drapeau de l'EuropeImprovement and development of Alice through various projects

Three successive projects led to the development of Alice and its adaptation to different configurations, involving adjustments, additions and development perspectives. In the framework of the European FP7 Safeland project, coordinated by the International Center for Geohazards (Norway), BRGM was in charge of the “integration of global changes in approaches to risk quantification” section. 

For this, the model was used in a high hazard area in the mountainous area of Barcelonnette (PACA region). The first step was, based on observed meteorological data (using a global hydrological software programme, Gardenia), to quantify the landslide hazard, the exposure (material and human issues at stake) and the vulnerability (infrastructure response) as they stand today.

Super-Sauze landslide, near Barcelonnette, studied under the FP7-Safeland and ANR Sisca projects, and by the doctoral research of J. Gance. © BRGM - Audrey Baills

Probabilistic estimate of the unstable surfaces variation between now and the period 2021-2050

Then climate change scenarios provided by the climatologist partners were incorporated into the model (rainfall, evapotranspiration and temperature data). By comparing the results obtained from the observed data and those from the scenarios, the model was able to indicate the likely changes in the unstable surfaces between now and the period 2021-2050. The feasibility of integrating climate change into Alice was thus demonstrated. The tool has also been used for specific applications to meet public authority expectations.

European project DO-SMS: tools for the surveillance and dynamic mapping of landslides

Such is the case of the European DO-SMS (Development of ground-motion monitoring tools for the sustainable management of southwestern Europe) project (Interreg IV) which aims to provide public authorities with tools for the surveillance and dynamic mapping of landslides. BRGM has focused its work on the landslide problem using Alice at a pilot site (42 km long) on the Basque coast.

All existing data (geological, geophysical, mapping...), both numerous and commonly very accurate (of the order of 1 m), along with the collection of additional data, made it possible to draw up a facies map of the area from which it is possible to identify zones having a same stratigraphic column (superimposition of geological formations and identical thicknesses). Alice was then used to compile a very accurate “site susceptibility to landslide” map, the study area being both small and very well documented.

 

Mapping of landslide susceptibility in the Barcelonnette Valley for the current period.

Development of a methodology to assess the risk of ground movement at Département level

Finally, BRGM set up a landslide hazard and risk assessment methodology at Département level (SDR-MVT: Département risk plan). The Jura Département was selected as the pilot area to develop this mapping (1:50,000 scale) with the eventual prospect of deploying the method – in a harmonized way – to France’s major risk basins. 

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