Prediction of changes in landslide rates induced by rainfall

National audienceThis work focuses on the use of a combined statistical-mechanical approach to predict changes in landslide displacement rates from observed changes in rainfall amounts. The forecasting tool associates a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the input signal (e.g. rainfall) and the output signal (e.g. displacements) and a simple 1D mechanical (MA) model (e.g. visco-plastic rheology) to take into account changes in pore water pressures. The models have been applied to forecast the displacement rates at the Super-Sauze landslide (South East France), one of the most active and instrumented clayey landslide in the European Alps. Results indicate that the three models are able to reproduce the displacement pattern in the general kinematic regime with very good accuracy (succession of acceleration and deceleration phases); at the contrary, extreme kinematic regimes such as fluidization of part of the landslide mass are not being reproduced: this statement, quantitatively characterised by the Root Mean Square Error between the model and the observations, constitutes however a robust approach to predict changes in displacement rates from rainfall or groundwater time series, several days before it happens. The variability of the results, depending in particular on the fluidization events and on the location of displacement data is discussed

An integrated analysis of surface velocities induced by rainfall in the Séchilienne landslide (Western Alps, France)

International audienceAn integrated analysis on the relationship between rainfall and displacement in the most active area of the Séchilienne unstable slope was performed. This study combines several techniques and models to adequately reproduce the landslide movement induced by the rainfall. The analysis of available time series shows a long term trend and seasonal variations in the displacement, respectively independent and synchronous to precipitations. In particular wavelet analysis highlights that the movement is rather linked to groundwater recharge than to precipitation (rainfall + snowfall), involving then the importance of groundwater process in the area. A first and simple relationship between the water input and the fluctuations of displacements apart from the general trend is shown using a tank model. Moreover, a seasonal analysis of this relationship was performed, showing that displacement rate follows the behavior of the hydrological cycle. Two different models were applied to the long temporal series of extensometric and precipitation data: the FLAME model, from BRGM and the FORESEES model, from Univ. Lausanne. These tools are based on a combined statistical-mechanical approach to predict changes in landslide displacement rates from observed changes in precipitation amounts. The forecasting tool FLAME associates 1) a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the rainfall and the displacements, and 2) a 1D mechanical (ME) model (e.g. visco-plastic rheology), in order to take into account changes in pore water pressures. The performance of different combinations of models was evaluated against observed displacement rates at the selected pilot study area. Our results indicate that both models are able to reproduce, with a high degree of accuracy, the observed displacement pattern in the general kinematic regime. Finally the variability of the results, depending in particular on the input data, is discussed

Estimation of intensity duration frequency curves for current and future climate

Climate variability and change are expected to have important impacts on the hydrologic cycle at different temporal and spatial scales In order to build long-lasting drainage systems, civil engineers and urban planners should take into account these potential impacts in their hydrological simulations. However, even if Global Climate Models (GCM) are able to describe the large-scale features of the climate reasonably well, their coarse spatial and temporal resolutions prevent their outputs from being used directly in impact assessment models at regional or local scales. This study proposes a statistical downscaling approach, based on the scale invariance concept, to incorporate GCM outputs in the derivation of Intensity-Duration-Frequency (IDF) curves and the estimation of urban design storms for current and future climates under different climate change scenarios. The estimated design storms were then used in the estimations of runoff peaks and volumes for urban watersheds of different shapes and different levels of surface imperviousness using the popular Storm Water Management Model (SWMM). Finally, a regional analysis was performed to estimate the scaling parameters of extreme rainfall processes for locations with limited or without data. In summary, results of an illustrative application of the proposed statistical downscaling approach using rainfall data available in Quebec (Canada) have indicated that it is feasible to estimate the IDF relations and the resulting design storms and runoff characteristics for current and future climates in consideration of GCM-based climate change scenarios. Furthermore, based on the proposed regional analysis of the scaling properties of extreme rainfalls in Singapore, it has been demonstrated that it is feasible to estimate the IDF curves for partially-gaged or ungaged sites.La variabilité et les changements climatiques devraient avoir des impacts considérables sur le cycle hydrologique aux différentes échelles spatio-temporelles. Afin de construire des systèmes de drainage durables, les ingénieurs se doivent de prendre en considération ses modifications probables dans leur simulation. Toutefois, si les Modèles de Circulation Globale (MCG) sont capables de reproduire raisonnablement bien les caractéristiques à grande échelle du climat, leurs résolutions sont trop grossières pour permettre une utilisation immédiate de leurs informations dans les modélisations urbaines.Cette étude propose une approche de mise à l’échelle statistique, basée sur les propriétés d’invariance d’échelle, afin d’incorporer les résultats des MCG dans la conception des courbes Intensité-Durée-Fréquence (IDF) futures. Ces courbes sont ensuite utilisées pour l’estimation de l’évolution des quantités de ruissèlement. Enfin, une analyse régionale permet une évaluation des paramètres de réduction d’échelle pour des stations partiellement jaugées, voir non jaugées. C’est ainsi que des courbes IDF peuvent être construites avec un nombre limité de données

Estimating waste induced by earthquakes within damage scenarios

International audienceThe objective of this work was to find and test tools to estimate waste tonnage caused by earthquakes. These estimations can be useful for prevention actions like exercises or waste plans but also during the seismic crisis management. Three different methods have been tested using building damage scenarios done in Nice city (Southern France): Hirayama method which is based on Japan experience and Japanese building stock, MECADEPI-HAZUS method which is a hybrid method based on works done in France about floods wastes and HAZUS methodology used in the USA and finally a method based on L’Aquila experience in Italy. Even if needed input data is quite different for the three methods, results using these methods tends to the same order of magnitude on inert rush. Finally the work compares potential waste tonnage caused by seismic scenarios with local/regional annual waste storage and treatment capacities, as a measure of the waste overflow

Estimation of landslides activities evolution due to land–use changes in a Pyrenean valley

International audienceGlobal changes would have impacts worldwide, but their effects should be even more exacerbated in areas particularly vulnerable. Mountainous areas are among these vulnerable territories. Ecological systems are often at a fragile equilibrium, socio-economical activities are often climate-dependent and climate-driven natural hazards can be a major threat for human activities. In order to estimate the capacity of such mountainous valleys to face global changes (climate, but also climate- and human- induced land-use changes), it is necessary to be able to evaluate the evolution of the different threats. The present work presents a method to evaluate the influences of the evolution of both climate and vegetation cover on landslides activities over a whole valley, to propose adequate solutions for current and future forestry management. It is therefore necessary to properly estimate the vegetation influences on slope stabilities. In the present study, we develop a complementary module to our large-scale slope stability assessment tool to take into account the effects of vegetation on the mechanical soil properties (cohesion and over-load), but also on the slope hydrology (change in interceptions, run-off, and infiltration). Hence the proposed method combines a mechanical stability model (using finite slope analysis), a hydrological model, and a vegetation module which interfere with both aspects. All these elements are interfaced within a GIS-based solution. The whole chain is applied to a 100-km² Pyrenean Valley, for the ANR Project SAMCO (Society Adaptation for coping with Mountain risks in a global change COntext), as a first step in the chain for risk assessment for different climate and economical development scenarios, to evaluate the resilience of mountainous areas

Findings on the Earthquake Risk Preparedness of the City of La Paz, Bolivia

International audienceLocated on the Bolivian altiplano and built on the slopes of the canyon network eroded by the Choqueyapu river and its main tributaries, the city of La Paz is no stranger to natural disasters, having suffered catastrophic floods, hailstorms and landslides in recent memory, such as the hailstorm in 2002 that caused at least 69 deaths and 100 disappearances or the 2011 Pampahasi-Cayapa mega-landslide, which destroyed more than 800 homes. However, despite its location in the South American subduction context and evidence of paleoseismicity in local fault networks, historical and instrumental seismic activity has been relatively low and therefore not a priority in local settlement and construction practices. As part of an ongoing effort by local authorities to increase risk preparedness, a preliminary diagnosis of the earthquake risk preparedness of the city was commissioned by the Municipality of La Paz, with funding from the European Commission DIPECHO programme. This study, whose main findings are presented in this paper, is based on a review and analysis of seismic hazard literature as well as a series of interviews with local actors in the fields of catastrophe management, geological research, seismographic surveillance, land-use planning and structural design. An assessment of the seismogenic potential of local faults and a simple deterministic seismic hazard analysis are first carried out to give an idea of possible hazard. This information is then completed with an analysis of existing vulnerabilities from a legislative and urban planning point of view, as well as commentary on current risk management efforts. Finally, the earthquake hazard is analyzed in the context of a high landslide hazard, analyzing the interactions between risk management strategies for both types of hazards particularly with respect to earthquake-induced landslides

Prediction of the rainfall-induced landslides: applications of FLAME in the French Alps

This work presents an innovative approach to predict changes in landslide displacement rates for early warning purposes. The forecasting tool associates a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the input signal (e.g. rainfall) and the output signal (e.g. displacements) and a simple 1D mechanical (MA) model (e.g. visco- plastic rheology) to take into account changes in pore water pressures. The models have been applied to forecast the displacement rates at three landslide sites (South East France), among the most active and instrumented landslides in the European Alps. Results indicate that the three models are able to reproduce the displacement pattern in the general kinematic regime with very good accuracy (succession of acceleration and deceleration phases); at the contrary, extreme kinematic regimes such as fluidization of part of the landslide mass are not being reproduced. This statement, quantitatively characterised by the Root Mean Square Error between the model and the observations, constitutes however a robust approach to predict changes in displacement rates from rainfall or groundwater time series, several days before it happens. The variability of the results, depending in particular on the fluidization events and on the location of displacement data, is discussed

Etude de la dynamique d'un glissement de très grande ampleur par modélisation hydrogéologique inverse (Grand Ilet, La Réunion)

International audienceL'étude de l'influence des précipitations sur les mouvements de terrain induit la connaissance de processus hydrogéologiques complexes. Dans le but d'identifier le rôle de ces processus pour le glissement de Grand Ilet (île de la Réunion), un outil de modélisation inverse est utilisé. Les relations obtenues entre précipitations et vitesses de déplacement sont interprétées à l'aide des résultats des analyses corrélatoires croisées, associant piézométrie et débit des sources aux vitesses de déplacements. Les résultats des modèles inverses générés reproduisent de manière très satisfaisante la réponse du glissement aux précipitations sur la période de 2005 à 2011. L'utilisation d'une réponse impulsionnelle bimodale, associant réponse lente (43 jours) et réponse rapide (<20 jours) est nécessaire pour reproduire la dynamique du glissement. Cette caractéristique est mise en relation avec son fonctionnement hydrogéologique. Il apparait par conséquent que les résultats de ce type de modèle sont porteurs d'informations pertinentes sur le contrôle des vitesses de déplacement par la circulation des eaux souterraines. Sa mise en œuvre s'avère particulièrement adaptée pour l'étude de la dynamique des glissements de très grande ampleur

Contribution of physical modelling to climate-driven landslide hazard mapping: an alpine test site

EGU2012-2445The aim of this work is to develop a methodology for integrating climate change scenarios into quantitative hazard assessment and especially their precipitation component. The effects of climate change will be different depending on both the location of the site and the type of landslide considered. Indeed, mass movements can be triggered by different factors. This paper describes a methodology to address this issue and shows an application on an alpine test site. Mechanical approaches represent a solution for quantitative landslide susceptibility and hazard modeling. However, as the quantity and the quality of data are generally very heterogeneous at a regional scale, it is necessary to take into account the uncertainty in the analysis. In this perspective, a new hazard modeling method is developed and integrated in a program named ALICE. This program integrates mechanical stability analysis through a GIS software taking into account data uncertainty. This method proposes a quantitative classification of landslide hazard and offers a useful tool to gain time and efficiency in hazard mapping. However, an expertise approach is still necessary to finalize the maps. Indeed it is the only way to take into account some influent factors in slope stability such as heterogeneity of the geological formations or effects of anthropic interventions. To go further, the alpine test site (Barcelonnette area, France) is being used to integrate climate change scenarios into ALICE program, and especially their precipitation component with the help of a hydrological model (GARDENIA) and the regional climate model REMO (Jacob, 2001). From a DEM, land-cover map, geology, geotechnical data and so forth the program classifies hazard zones depending on geotechnics and different hydrological contexts varying in time