Séchilienne LAnd movement: Multidisciplinary Studies from hazard assessment to associated risk and consequences – SLAMS

Huge landslides induce dramatic socio-economical consequences within the world. The various and complex mechanisms at the origin of mass movements and the external factors modifying their internal dynamics are various and complex, leading to large uncertainty in prediction in both space and time domains. This last triggers a lot of misunderstanding between the scientific community and people in charge of civil society, because the management of uncertainties is approached according to various protocols, which are actor dependent. This is the main reason why quantitative risk assessment of this hazard and its time evolution requests the participation of these different actors. This project proposes to federate these different actors on a emblematic site, the Séchilienne landslide. Indeed, in metropolitan French territory, the Séchilienne landslide is by far the natural phenomenon that does yield the strongest potential combined risk in term of socio-economical consequences. Indeed, the failure of this huge landslide can dam the Romanche valley. It induces the impoundment of the ongoing lake, which rupture could generate large flood flowing along the Romanche valley and threatening the town of Grenoble and the downstream chemical factories of Jarrie. This site is an emblematic example of the prickly questions raised for 25 years after administrative, scientific and political managements, notably owing to its multidisciplinary dimension. The considerable investment performed these last 25 years favoured the management of risk, notably via a competitive and dense system of surveillance (based on the temporal monitoring of displacements). In the opposite, this site suffered from the lack of projects of fundamental and interdisciplinary research. We offer so an ambitious projects, which aims at studying at the same time hazard and organizational vulnerability, but also to offer a better structuring of the risk governance. Major problems, which are still highly debated, are: (1) the physical cause and the history of the slope mechanical deformation, (2) the present-day structure of the landslide and hence the implied volume, (3) the identification of the main parameters controlling the destabilization and the prediction of the slope evolution before, during and after the rupture, and (4) the uncertainty on vulnerability and (5) the political governance in the context of the societal risk acceptance. An analysis of the past, present and potential future risk management at different levels will be performed from human and social point of views. For hazard assessment, we propose a multidisciplinary based on the surveillance system, coupled to new measurements, which will contribute to a better knowledge of deep mechanisms (present and passed), of new potential surveillance techniques and of fluid flows and hydro-mechanical coupling mechanisms, which seems to control the present-day dynamics. These data will constitute the input parameters of different types of numerical modelling which will aim at reconstructing the past kinematics of movement, at reproducing actual dynamics and at assessing the effects of external factors. Different rock falls scenarios will be modelled considering a benchmark of numerical methods. All this work will be considered as inputs for creating decision-tree models, which take into account uncertainties at each step. These obtained results of this project will be able to be applied to other similar cases, and to other types of risks, especially considering risk governance and management studies.