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Réf. Vallet et al. 2013 - P

Référence bibliographique
VALLET A., CHARLIER JB., CHANUT MA., BERTRAND C., DUBOIS L., et al.. Seasonal and long term analysis of precipitation-displacement relationships on a deep seated unstable slope (Séchilienne, French Alps). JAG - 3èmes journées Aléas Gravitaires, Sep 2013, Grenoble, France. pp.1-6. <hal-01062428>

Abstract: Time series analysis and cross-wavelet analysis are used to characterize the relationship between water input and displacement in the most active zone of the Séchilienne unstable slope. Time series analysis shows a displacement long term trend and seasonal intra-annual variations, respectively independent and synchronous to precipitations. Wavelet analysis has allowed identifying and characterizing the precipitationdetrended displacement relationship which shows that the Séchilienne destabilisation is rather linked to effective rainfall than to raw precipitation (rainfall + snowfall), involving then groundwater process. Seasonal analysis of this relationship was performed, showing that displacement rate follows the behaviour of the hydrological cycle. Finally, trend was analysed and a weakening model approach was developed with an attempt to forecast the next modifications in unstable slope destabilisation behaviour.

Mots-clés
 

Organismes / Contact

Authors/Auteurs :

VALLET A., UMR6249 Chrono-Environnement, Besançon, France

CHARLIER JB., BRGM, Montpellier, France

CHANUT MA., CETE, Bron, France

BERTRAND C., UMR6249 Chrono-Environnement, Besançon, France

DUBOIS L., CETE, Bron, France

MUDRY J., UMR6249 Chrono-Environnement, Besançon, France


(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
       

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
France Isère Séchilienne      

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 Seasonal analysis was performed in order to quantify infra-annual relationships between recharge rate and detrended displacement. Three periods called “Autumn Recharge”, “Winter Recharge”, and “Low Recharge”, were identified from multiannual monthly statistics on temperature, recharge, precipitation, and snow melt time series.

Autumn Recharge period follows the summer dry season, and is characterized by high recharge amount and intensity. Hydrosystem saturation state is at its lowest level of the year, so that the major part of infiltration recharges the micro-fracture stock component. The recharge signal is largely buffered by water supply of matrix, which confers a low transfer velocity through the hydrosystem. The Séchilienne destabilisation rate increases over time, and becomes more and more reactive as saturation increase.
Winter Recharge period is characterized by an aquifer drainage functioning. Aquifer saturation state is at its highest level of the year, and most of infiltration is drained by the macro-fracture drainage component which is predominant (micro-fractures are already saturated). The aquifer is more transmissive and less inertial, in relation to infiltration signal. The Séchilienne destabilisation rate is high and reactive to rainwater input, although the recharge signal is diffuse when snow melt occur.
The Low Recharge period is characterized by an aquifer stock functioning. Water stored in micro fractures during previous winter, drain out to supply spring aquifer base flow. Recharge is low, due to high evapotranspiration component, and destabilisation rate decreases with time.

Detrended displacement is considered as the landslide response to groundwater hydraulic stress during the hydrological cycle. It corresponds to the hydraulic stress amount cumulated by the Séchilienne unstable slope until an irreversible strength/cohesion damage threshold is reached in the rock, sufficient to yield to a significant change in the destabilization behaviour. This require stress amount which will be referred as “destabilisation stress threshold” (DST).

Evolution of DST follows an exponential law, showing that it requires less and less stress amount to increase the destabilization rate. This demonstrates that the Séchilienne unstable slope is more and more sensitive to hydraulic stress. DST time evolution follows a softening/weakening model, which involves that stress is accumulated over a period until a rock weakening threshold inducing a worsening of the destabilisation rate behaviour.

Modélisations
 
Hypothèses
 

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 
 

(4) - Remarques générales

(5) - Syntèses et préconisations
 

Références citées :

Aleotti, P. and Chowdhury, R.: Landslide hazard assessment: summary review and new perspectives, Bull. Eng. Geol. Environ., 58(1), 21–44, doi:10.1007/s100640050066, 1999.

Antoine, P., Camporota, P., Giraud, A. and Rochet, L.: La menace décroulement aux Ruines de Séchilienne, Bull. Liaison Lab. Ponts Chaussées, (150-151), 55–64, 1987.

Berti, M., Martina, M. L. V., Franceschini, S., Pignone, S., Simoni, A. and Pizziolo, M.: Probabilistic rainfall thresholds for landslide occurrence using a Bayesian approach, J. Geophys. Res. Earth Surf., 117(F4), n/a–n/a, doi:10.1029/2012JF002367, 2012.

Bogaard, T., Guglielmi, Y., Marc, V., Emblanch, C., Bertrand, C. and Mudry, J.: Hydrogeochemistry in landslide research: a review, Bull. Soc. Geol. Fr., 178(2), 113–126, doi:10.2113/gssgfbull.178.2.113, 2007.

Cowpertwait, P. S. P.: Introductory time series with R, Springer, Dordrecht ; New York., 2009. Grinsted, A., Moore, J. C. and Jevrejeva, S.: Application of the cross wavelet transform and wavelet coherence to geophysical time series, Nonlin Process. Geophys, 11(5/6), 561–566, doi:10.5194/npg-11-561-2004, 2004.

Labat, D., Ababou, R. and Mangin, A.: Rainfall–runoff relations for karstic springs. Part II: continuous wavelet and discrete orthogonal multiresolution analyses, J. Hydrol., 238(3–4), 149–178, doi:10.1016/S0022- 1694(00)00322-X, 2000.

Vallet, A., Bertrand, C. and Mudry, J.: Effective rainfall: a significant parameter to improve understanding of deep-seated rainfall triggering landslide - a simple computation temperature based method applied to Séchilienne unstable slope (French Alps), Hydrol. Earth Syst. Sci. Discuss., 10(7), 8945–8991, doi:10.5194/hessd-10-8945-2013, 2013.


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