Catherine Bertrand

Post‐seismic permeability change in a shallow fractured aquifer following a ML 5.1 earthquake (Fourbanne karst aquifer, Jura outermost thrust unit, eastern France)

[1] Following a M L 5.1 earthquake in eastern France, a post-seismic 12-day long electrical conductivity increase was recorded in the water discharging from a karst aquifer located 3 km from the epicentre. We attribute this to a permeability enhancement which allowed long-residence time water from low-permeability fractures located in the saturated zone to be expelled. The permeability enhancement shows that shallow aquifers can be significantly deformed for several days by moderate magnitude earthquakes.

Contribution of time-related environmental tracing combined with tracer tests for characterization of a groundwater conceptual model: a case study at the Séchilienne landslide, western Alps (France)

Groundwater-level rise plays an important role in the activation or reactivation of deep-seated landslides and so hydromechanical studies require a good knowledge of groundwater flows. Anisotropic and heterogeneous media combined with landslide deformation make classical hydrogeological investigations difficult. Hydrogeological investigations have recently focused on indirect hydrochemistry methods. This study aims at determining the groundwater conceptual model of the Séchilienne landslide and its hosting massif in the western Alps (France). The hydrogeological investigation is streamlined by combining three approaches: a one-time multi-tracer test survey during high-flow periods, a seasonal monitoring of the water stable-isotope content and electrical conductivity, and a hydrochemical survey during low-flow periods. The complexity of the hydrogeological setting of the Séchilienne massif leads to development of an original method to estimate the elevations of the spring recharge areas, based on topographical analyses and water stable-isotope contents of springs and precipitation. This study shows that the massif supporting the Séchilienne landslide is characterized by a dual-permeability behaviour typical of fractured-rock aquifers where conductive fractures play a major role in the drainage. There is a permeability contrast between the unstable zone and the intact rock mass supporting the landslide. This contrast leads to the definition of a shallow perched aquifer in the unstable zone and a deep aquifer in the intact massif hosting the landslide. The perched aquifer in the landslide is temporary, mainly discontinuous, and its extent and connectivity fluctuate according to the seasonal recharge.RésuméL’élévation du niveau de l’eau souterraine joue un rôle important dans l’activation ou la réactivation des glissements de terrain profonds et ainsi des études hydromécaniques nécessitent une bonne connaissance des écoulements d’eaux souterraines. Les milieux anisotropes et hétérogènes combinés à une déformation des glissements de terrain rendent les études hydrogéologiques classiques difficiles. Des études hydrogéologiques ont récemment mis l’accent sur les méthodes hydrochimiques indirectes. Cette étude vise à déterminer le modèle conceptuel hydrogéologique du glissement de terrain de la Séchilienne et son massif dans les Alpes occidentales (France). L’étude hydrogéologique est rationalisée en combinant trois approches: une campagne unique d’essais de traçage multi-traceur au cours des périodes de hautes eaux, un suivi saisonnier de la teneur en isotope stable de l’eau et de la conductivité électrique, et une campagne hydrochimique au cours des périodes de bases eaux. La complexité du contexte hydrogéologique du massif de la Séchilienne mène à développer une méthode originale pour estimer les altitudes des zones de recharge des sources, basée sur des analyses topographiques et sur la teneur des isotopes stables de l’eau des sources et des précipitations. Cette étude montre que le massif siège du glissement de terrain de la Séchilienne est caractérisé par comportement à double perméabilité typique des aquifères fissurés où les fractures conductrices jouent un rôle majeur dans le drainage. Il y a un contraste de conductivité hydraulique entre la zone instable et la masse rocheuse intacte sous-jacent du glissement de terrain. Ce contraste conduit à la définition d’un aquifère perché peu profond dans la zone instable et un aquifère profond dans le massif intact siège du glissement de terrain. L’aquifère perché au sein du glissement de terrain est temporaire, essentiellement discontinu, et son extension et la connectivité fluctuent en fonction de la recharge saisonnière.ResumenEl ascenso del nivel de agua subterránea juega un papel importante en la activación o reactivación de deslizamientos de tierra profundos y por lo tanto los estudios hidromecánicos requieren de un buen conocimiento de los flujos de agua subterránea. Los medios anisotrópicos y heterogéneos asociados a la deformación por el deslizamiento de tierra hacen dificultosas las investigaciones hidrogeológicas clásicas. Las investigaciones hidrogeológicas recientemente se han centrado en métodos hidroquímicos indirectos. Este estudio tiene como objetivo determinar el modelo conceptual del agua subterránea en el deslizamiento de tierra en Séchilienne y en el macizo hospedante en los Alpes occidentales (Francia). La investigación hidrogeológica se hace más eficiente mediante la combinación de tres enfoques: una relevamiento de pruebas de multitrazadores por única vez durante los períodos de alto flujo, un monitoreo estacional del contenido de isótopos estables y de la conductividad eléctrica en el agua, y un relevamiento hidroquímico durante los períodos de bajo flujo. La complejidad del entorno hidrogeológico del macizo de Séchilienne conduce al desarrollo de un método original para calcular las elevaciones de las áreas de recarga de los manantiales, basada en análisis topográficos y contenidos de isótopos estable del agua de los manantiales y de la precipitación. Este estudio muestra que el macizo hospedante del deslizamiento de tierra de Séchilienne se caracteriza por una doble permeabilidad, comportamiento típico de los acuíferos en rocas fracturadas, donde los conductos de las fracturas desempeñan un papel importante en el drenaje. Existe un contraste de permeabilidad entre la zona inestable y el macizo de roca intacta donde se apoya el deslizamiento de tierra. Este contraste conduce a la definición de un acuífero superficial colgado en la zona inestable y un acuífero profundo en el macizo de roca intacta que aloja el deslizamiento de tierra. El acuífero colgado en el deslizamiento de tierra es temporario, mayormente discontinuo, y su alcance y conectividad fluctúa de acuerdo a la recarga estacional.摘要地下水位上升在深层滑坡的激活或者再激活过程中发挥着重要作用,因此,流体力学研究需要彻底了解地下水水流。各向异性和非均质介质加上滑坡变形使传统的水文地质调查非常困难。最近的水文地质调查主要集中在间接的水文化学方法上。这项研究目的就是确定(法国)阿尔卑斯山脉西部Séchilienne滑坡及其主要地块的地下水概念模型。通过三种方法结合起来使水文地质调查更加合理:高水流期一次性的多示踪剂实验调查,水中稳定同位素含量和电导率季节性监测及低水流期的水化学调查。Séchilienne地块水文地质背景的复杂性致使原来的方法得到进一步开发,根据地形分析和泉水和降水中的稳定同位素含量估算泉补给区的海拔高度。这项研究显示,支撑Séchilienne滑坡的地块呈现出双重渗透性行为特征,这种行为是断裂岩层含水层的典型特征,在这种含水层中,传导断裂在排水中发挥着主要作用。非稳定带和支撑滑坡的完整岩石块之间有渗透性差异。依据这种差异可以区分出非稳定带中的浅的表层含水层和支撑滑坡的完整地块中深层含水层。滑坡中的表层含水层是暂时的、大体上不连续的,其范围和连通性根据季节补给量波动。ResumoA elevação do nível da água subterrânea desempenha um papel importante na ativação ou reativação de deslizamentos em profundidade, de modo que estudos hidromecânicos exigem um bom entendimento sobre os fluxos da água subterrânea. A combinação de meios heterogêneos e anisotrópicos com a deformação gerada por deslizamentos dificulta as investigações ambientais convencionais. Recentemente, investigações hidrogeológicas têm focado em métodos hidrogeoquímicos indiretos. O presente estudo visa à determinação do modelo conceitual de águas subterrâneas do deslizamento de Séchilienne e seu maciço hospedeiro no oeste alpino (França). A investigação hidrogeológica é organizada por meio da combinação de três métodos: teste de multi-traçador em único evento durante os períodos de alto fluxo; monitoramento sazonal do conteúdo de isótopos e condutividade elétrica da água; e levantamento hidroquímico durante períodos de baixo fluxo. A complexidade do contexto hidrogeológico do maciço Séchilienne motiva o desenvolvimento de um novo método para estimar as elevações das áreas de recarga das nascentes, baseada na análise topográfica e conteúdo de isótopos estáveis nas águas das nascentes e das chuvas. O presente estudo mostra que o maciço hospedeiro do deslizamento de Séchilienne é caracterizado pelo comportamento de dupla permeabilidade, típico de aquíferos em rocha fraturada onde as fraturas desempenham papel principal na drenagem. Entre a zona instável e a rocha sã do maciço subjacente ao deslizamento há um contraste de permeabilidade. Tal contraste motiva a definição de um aquífero suspenso raso na zona instável e a um aquífero mais profundo na rocha sã do maciço hospedeiro do deslizamento. O aquífero suspenso no deslizamento é temporário, predominantemente descontínuo, e sua extensão e conectividade varia conforme a sazonalidade da recarga.

Use of Dissolved Organic Carbon to Characterize Infiltration in a Small Karst System in the French Jura Mountains (Fertans, France)

Due to the high input of organic soil substances in infiltrated water, dissolved organic carbon (DOC) is an interesting tracer to determine water origin in hydrosystems. The aim of this study was to use continuous measurements of DOC natural fluorescence in spring water to characterize infiltration in a karst system at the event time scale. Hydrological data were recorded at the outlet of a small perennial spring within a cliff at Fertans in the French Jura mountains since July 2009. Results showed that the response of the system was fast (response time of 3 hours) and was produced by two combined flow types. First, discharge and turbidity peaks, and electrical conductivity troughs were produced by a piston-type flow enabling an unclogging of the fractures. Second, this fast infiltration process was followed by a slower one enriched in DOC, produced by a more diffuse-type flow through the matrix compartment.

Groundwater—Surface waters interactions at slope and catchment scales: implications for landsliding in clay-rich slopes

Understanding water infiltration and transfer in soft-clay shales slopes is an important scientific issue, especially for landsliding. Geochemical investigations are carried out at the Super-Sauze and Draix-Laval landslides, both developed in the Callovo-Oxfordian black marls, with the objective to define the origin of the groundwater. In situ investigations, soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems. At Super-Sauze, the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations, or at the landslide basement through a fault network. Such external origin of water is not observed at the local scale of the Draix-Laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows. Hydrogeological conceptual models are proposed emphasizing the role of the interactions between local (slope) and regional (catchment) flow systems. The observations suggest that this situation is a common case in the Alpine area. Expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales.

A multi-dimensional statistical rainfall threshold for deep landslides based on groundwater recharge and support vector machines

The rainfall threshold determination is widely used for estimating the minimum critical rainfall amount which may trigger slope failure. The aim of this study was to develop an objective approach for the determination of a statistical rainfall threshold of a deep-seated landslide. The determination is based on recharge estimation and a multi-dimensional rainfall threshold. This new method is compared with precipitation and with a conventional ‘two-dimensional’ rainfall threshold. The method is designed to be semiautomatic, enabling an eventual integration into a landslide warning system. The method consists in two independent parts: (i) unstable event identification based on displacement time series and (ii) multi-dimensional rainfall threshold determination based on support vector machines. The method produces very good results and constitutes an appropriate tool to define an objective and optimal rainfall threshold. In addition to shortened computation times, the non-necessity of pre-requisite hypotheses and a fully automatic implementation, the newly introduced multi-dimensional approach shows performances similar to the classical two-dimensional approach. This shows its relevance and its suitability to define a rainfall threshold. Lastly, this study shows that the recharge is a relevant parameter to be taken into account for deep-seated rainfall-induced landslides. Using the recharge rather than the precipitation significantly improves the delineation of a rainfall threshold separating stable and unstable events. The performance and accuracy of the multi-dimensional rainfall threshold developed for the Séchilienne landslide make it an appropriate method for integration into the present-day landslide warning system.

Hydrogeological Threshold Using Support Vector Machines and Effective Rainfall Applied to a Deep Seated Unstable Slope (Séchilienne, French Alps)

Rainfall threshold is a widely used method for estimating minimum critical rainfall amount which can yield a slope failure. Literature reviews show that most of the threshold studies are subjective and not optimal. For this study, effective rainfall was considered for threshold definition. Support vector machines (SVM) and automatic event identification were used in order to establish an optimal and objective threshold for the Sechilienne landslide. Effective rainfall does significantly improve threshold performance (misclassification rate of 7.08 % instead of 13.27 % for gross rainfall) and is a relevant parameter for threshold definition in deep-seated landslide studies. In addition, the accuracy of the Sechilienne SVM threshold makes it appropriate to be integrated into a landslide warning system. Finally, the ability to make predictions at a daily time step opens up an opportunity for destabilisation stage predictions, through the use of weather forecasting.

Chemical and isotopic investigations (δ18O, δ2H, 3H, 87Sr/86Sr) to define groundwater processes occurring in a deep-seated landslide in flysch

Deep-seated landslides are complex systems. In many cases, multidisciplinary studies are necessary to unravel the key hydrological features that can influence their evolution in space and time. The deep-seated Berceto landslide, in the northern Apennines of Italy, has been investigated in order to define the origin and geochemical evolution of groundwater (GW), to identify the slope system hydrological boundary, and to highlight the GW flow paths, transit time and transfer modalities inside the landslide body. This research is based on a multidisciplinary approach that involves monitoring GW levels, obtaining analyses of water chemistry and stable and unstable isotopes (δ18O-δ2H, 3H, 87Sr/86Sr), performing soil leaching tests, geochemical modelling (PHREEQC), and principal component analysis (PCA). The results of δ18O-δ2H and 87Sr/86Sr analyses show that the source of GW recharge in the Berceto landslide is local rainwater, and external contributions from a local stream can be excluded. In the landslide body, two GW hydrotypes (Ca-HCO3 and Na-HCO3) are identified, and the results of PHREEQC and PCA confirm that the chemical features of the GW depend on water–rock interaction processes occurring inside the landslide. The 3H content suggests a recent origin for GW and appears to highlight mixing between shallow and deep GW aliquots. The 3H content and GW levels data confirm that shallow GW is mainly controlled by a mass transfer mechanism. The 3H analyses with GW levels also indicate that only deep GW is controlled by a pressure transfer mechanism, and this mechanism is likely the main influence on the landslide kinematics.RésuméLes glissements de terrain ancrés en profondeur sont des systèmes complexes. Dans de nombreux cas, des études pluridisciplinaires sont nécessaires pour mettre en évidence les principales caractéristiques hydrologiques qui peuvent influencer leur évolution spatio-temporelle. Le glissement de terrain ancré en profondeur de Berceto, dans le Nord des Apenins en Italie, a étudié afin de définir l’origine et l’évolution géochimique des eaux souterraines (ESO), d’identifier les limites hydrologiques du système, et de mettre en évidence les circulations d’ESO, le temps de transit et de transfert au sein du glissement de terrain. Cette recherche repose sur une approche pluridisciplinaire qui implique la surveillance des niveaux piézométriques, la réalisation d’analyses de la chimie de l’eau et des isotopes stables et instables (δ18O-δ2H, 3H, 87Sr/86Sr), de tests de lixiviation de sols, la modélisation géochimique (PHREEQC), et l’analyse en composantes principales (ACP). Les résultats des analyses de δ18O-δ2H et 87Sr/86Sr montrent que la recharge des ESO dans le glissement de terrain de Berceto a une origine associée aux précipitations locales, et que des contributions externes à partir d’un cours d’eau local peuvent être exclues. Au sein du glissement de terrain, deux types d’eaux souterraines (Ca-HCO3 et Na-HCO3) sont identifiés, et les résultats de PHREEQC et de l’ACP confirment que les caractéristiques chimiques des ESO sont marquées par les processus d’interaction eau roche qui prennent place dans le glissement de terrain. La concentration en 3H suggère une origine récente des ESO et semble mettre en évidence un mélange entre certaines ESO peu profondes et profondes. Les teneurs en 3H et les données piézométriques confirment que les ESO peu profondes sont principalement contrôlées par un mécanisme de transfert de masse. Les analyses d’3H combinées à celles des niveaux piézométriques indiquent également que seules les eaux souterraines profondes sont contrôlées par un mécanisme de transfert de pression, et que ce mécanisme est. probablement la principale influence sur la cinématique du glissement de terrain.ResumenLos deslizamientos profundos son sistemas complejos. En muchos casos, se necesitan estudios multidisciplinarios para desentrañar las principales características hidrológicas que pueden influir en su evolución en el espacio y el tiempo. Se investigó el deslizamiento profundo de Berceto, en los Apeninos septentrionales de Italia, para definir el origen y la evolución geoquímica del agua subterránea (GW), para identificar el límite hidrológico del sistema de taludes y resaltar las trayectorias de flujo del GW, el tiempo de tránsito y las modalidades de transferencia dentro del cuerpo del deslizamiento. Esta investigación se basa en un enfoque multidisciplinario que implica monitorear niveles de GW, obtener análisis de química del agua e isótopos estables e inestables (δ18O-δ2H, 3H, 87Sr/86Sr), realizar pruebas de lixiviación del suelo, modelado geoquímico (PHREEQC) y la componente principal de los análisis (PCA). Los resultados de los análisis de δ18O-δ2H and 87Sr/86Sr muestran que la fuente de recarga del GW en el deslizamiento de Berceto es el agua de la lluvia local, y se pueden excluir las contribuciones externas de un flujo local. En el cuerpo del deslizamiento, se identifican dos hidrotipos GW (Ca-HCO3 and Na-HCO3) y los resultados de PHREEQC y PCA confirman que las características químicas del GW dependen de los procesos de interacción agua–roca que ocurren dentro del deslizamiento. El contenido de 3H sugiere un origen reciente para el GW y parece resaltar la mezcla entre alícuotas de GW superficiales y profundas. El contenido de 3H y los datos de los niveles de GW confirman que el GW somera está controlado principalmente por un mecanismo de transferencia de masa. Los análisis de 3H con los niveles de GW también indican que solo el GW profundo está controlado por un mecanismo de transferencia de presión, y este mecanismo es probablemente la principal influencia en la cinemática del deslizamiento.摘要深位滑坡是非常复杂的系统。在许多情况下,需要进行多学科研究渗入了解可影响时空演化的关键特征。调查了意大利亚平宁山脉北部的Berceto深位滑坡,就是为了明确地下水的成因和地球化学演化过程,确定边坡系统水文边界,突出滑坡体内部的地下水水流通道、经过时间和运移形态。本研究基于一种多学科方法,该方法涉及到监测地下水位、获取水化学和稳定同位素和非稳定同位素(δ18O-δ2H, 3H, 87Sr/86Sr)分析结果、进行土壤滤淋试验、地球化学模拟以及主要成分分析。δ18O-δ2H 和 87Sr/86Sr分析结果显示,Berceto滑坡中的地下水补给源是当地的雨水,当地河流外部的补给可以排除。在滑坡体中,确定了两种地下水水类型(Ca-HCO3 和 Na-HCO3),地球化学模拟和主要成分分析结果确认,地下水的化学特征依赖于出现在滑坡内的水岩相互作用过程。3H含量表明,地下水为近代成因,似乎显示出浅层地下水和深层地下水的混合。3H含量和地下水位数据确认,浅层地下水主要受控于质量传输机制。3H分析结果和地下水位还表明,只有深层地下水受控于压力传输机理,这个机理可能是滑坡动力学的主要影响因素。ResumoEscorregamentos profundamente arraigados são sistemas complexos. Em muitos casos, estudos multidisciplinares são necessários para desvendar as principais feições hidrogeológicas que podem influenciar sua evolução no espaço e no tempo. O deslizamento profundamente arraigado Barceto, no norte dos Apeninos da Itália, tem sido investigado para definir a origem e evolução geoquímica da água subterrânea (AS), para identificar o limite do declive do sistema hidrológico, e destacar os caminhos de fluxo da AS, o tempo de trânsito e as modalidades de transferência dentro do corpo de escorregamento. Esta pesquisa está baseada e uma abordagem multidisciplinar que envolve monitoramento do nível da AS, obtenção de analise química da água e isótopos estáveis e instáveis (δ18O-δ2H, 3H, 87Sr/86Sr), realização de testes de lixiviação de solo, modelagem geoquímica (PHREEQC) e analise de componentes principais (ACP). Os resultados das análises de δ18O-δ2H e 87Sr/86Sr mostraram que a fonte de recarga da AS do escorregamento Berceto é a precipitação local e as contribuições externas de um fluxo local pode ser excluída. No corpo do escorregamento, foram identificados dois tipos hidroquímicos (Ca-HCO3 e Na-HCO3) e os resultado do PHREEQC e ACP confirmam que as características da AS depende do processo de interação água–rocha ocorrendo dentro do escorregamento. O conteúdo de 3H sugere uma origem recente da AS e parece destacar mistura entre as alíquotas de AS profunda e superficial. O conteúdo de 3H e níveis de AS confirmam que a AS superficial é controlada principalmente pelo mecanismo de transferência de massa. A análise do 3H com o nível de AS também indica que apenas a AS profunda é controlada por um mecanismo de transferência de pressão, este mecanismo é provavelmente a principal influência na cinemática do escorregamento.

Preferential Water Infiltration Path in a Slow-Moving Clayey Earthslide Evidenced by Cross-Correlation of Hydrometeorological Time Series (Charlaix Landslide, French Western Alps)

Slow-moving clayey earthslides frequently exhibit seasonal activity suggesting that deformation processes do not only depend on slope and intrinsic geomechanical parameters. On the contrary, seasonal motion patterns are frequently observed with acceleration during the wet season and deceleration during the dry season. Within landslides, it is mainly the phreatic water table which is monitored. However, in the case of deep-seated landslides made of heterogeneous lithological units and with several slip surfaces, the characterization of the phreatic water table does not allow to relate satisfactorily the activity of the landslide with environmental parameters such as rainfall and subsequent water infiltration at depth. This paper presents a seasonal analysis of water infiltration within a slow-moving clayey landslide. Results of an extensive geotechnical and geophysical prospect are first exposed. Then, rainfall and water table level time series are analysed for two water tables using the cross-correlation technique: the phreatic water table located a few metres deep and a water table located above a shear surface located 12 m deep. Results show that water infiltrates faster down to the deepest water table. Then, time series were split between “dry” and “wet” seasons and the effective rainfall was computed from the original rainfall time series. Cross-correlation results show that the phreatic water table responds identically to rainfall in both seasons. On the contrary, the water table located above the shear surface has a very contrasting behaviour between summer (mainly drainage) and winter (behaviour similar to the phreatic water table with storage of water during a few weeks). This difference in behaviour is in agreement with the landslide kinematics.

Comparison of Flow Processes in Drains and Low Permeability Volumes of a Karst System in the French Jura Mountains: High-Resolution Hydrochemical Characterization During a Flood Event

The Fertans karst system is a field site of the hydrogeological observatory “Jurassic Karst” in the French Jura Mountains. The site is located within karstified upper Oxfordian limestones. Two monitoring stations were installed for simultaneous monitoring of a spring, draining a fracture, and a borehole within the microfractured limestone giving access to the low permeability volume (LPV). A flood event was followed in June 2012, with high-frequency physicochemical (pressure, T°C, E.C) and hydrochemical measurements (major and trace elements, total organic carbon) at both stations. Infiltration (TOC, Fe, Al) and long-time residence markers (Mg) were studied in order (1) to analyze the response of the drain (spring SA) and the LPV (borehole C3) to the rainfall event, (2) to identify the origin of the flood waters, and (3) to characterize water exchange between the 2 compartments. Based on statistical analysis (PCA, DFA), it was possible to characterize different mixing end-members and to identify exchanges between drains and LPV. The hydrochemical signal of the flood was observed rapidly at the spring (3 h); in contrast, the borehole showed a much higher inertia and an arrival of infiltration water in two steps: a first peak attributed to drain contribution, and a second peak attributed to diffusively infiltrated rain water, spreading out slowly through the LPV. The infiltration water signature was typically enriched in organic carbon, Fe, and Al derived from interaction with the clay–humus complex of the surface soil. Nitrates which are often used as indicator for direct surface infiltration seemed to have accumulated over longer time periods prior to the flood in the LPV, which behaved like a diffusive nitrate source.

Hydrochemical Approach of Mechanical Degradation of the Séchilienne Unstable Slope

Water chemistry is a very fine signal which allows fine location in time and space of the arrival of infiltration water inducing mechanical instability pulses of the landslide. This tool is designed to understand the complex relationship between chemical weathering, hydromechanical changes and weakening/motion of the unstable rock slope. For this purpose, a hydrogeochemical groundwater monitoring has been established since 2010 on the site of Sechilienne (France). Electrical conductivity is representative of the chemical signal generated by the degradation of the massif. The continuous measurement of this parameter is relevant to the site of Sechilienne and can replace chemical monitoring. The benefit of acquiring this data is threefold: real-time measurements, with a short time step, and inexpensive implementation work, enabling to use it as a tool for risk management.