In previous studies, the mean geothermal gradient of the Tlemcen region has been estimated as low (3.7°C/100m). The existing boreholes in the Remchi plain (North of the Tlemcen Mountains) reveal thermal waters (26-48°C) and a remarkable artesianism. To understand the hydrodynamics and origin of thermalism of this groundwater, we merged geophysical and physical-chemical data. Geophysical data allowed us to improve the resolution of the fault network, to estimate the thickness of various sandstone beds connected with the thermal reservoir and to delimit the productive aquifer. Chemical characteristics of waters have been used for a statistical analysis, which displayed two independent water clusters resulting from two hydrodynamic patterns throughout the aquifer. The hydrothermal analysis identifies the depth reached by water and the relationship between water circulation and the fault network. Comparison with previous studies allowed us to build a schematic geological model, which explains hydrodynamics, origin and role of this structure in the groundwater flow.

For any hydrological or hydrogeological system, the arrival of new rains is the input signal to the system. This isotopic signature of precipitation is of major interest in understanding the recharge processes of the aquifer system. On the scale of a given basin, staged stations at different altitudes and spread out in space allow this input signal to be well characterized and to draw the local meteoric water line. In south-eastern Morocco, specifically, in the Errachidia region, several chemical and isotopic studies of the waters of the various aquifers have been carried out. In the absence of a local meteoric water line, these studies were based on the use of the global meteoric water line (GMWL). Thus, the objective of this work is the isotopic characterization and the elaboration of the local meteoric water line of the rainwater of the Ziz watershed. This characterization of the input signal in the study area is based on 41 measurements of stable isotopes (δ18O and δ2H) relating to the precipitations collected during the period from December 2019 to November 2020 in four staged stations at different altitudes and spread over the space from upstream to downstream of the watershed. The linear relationship of δ2H as a function of δ18O describes the local meteoric water line (LMWL) by equation δ2H = 7.5 ± 0.3 δ18O + 4.6 ± 1.7; R2 = 0.93. This equation displays evaporation confirmed by the arrival of continental currents in an arid environment. The variation in precipitation δ18O as a function of the sampling altitudes for the rains highlighted the relationship δ18O = −0.0026 ∗ Z − 1.67, with R2 = 0.93, which means an altitudinal gradient of −0.26‰ per 100 m of altitude. In this regard, the development of the local meteoric water line and the determination of the altitudinal gradient for the first time in this arid to semi-arid region of the watershed will be of great use to researchers and water resource managers; for example, to help determine the groundwater recharge areas, determine the exchanges between surface water and groundwater, and analyze many other hydrological problems.

The objective of this research was to determine the recharge of the Cretaceous aquifers by the High Atlas, as well as the interaction and possible mixing phenomena between the waters of the different aquifers, by investigating the hydrochemical and isotopic evolution of groundwater flow paths from the limestone karst systems of the High Atlas to the Cretaceous basin of Errachidia. Geological techniques were used to investigate and confirm the chemical and isotopic characteristics of the waters. Although the Gibbs diagram shows that water–rock interaction is the dominant hydrochemical process, some water samples in the Cretaceous basin are influenced by both evaporation and water–rock interaction, indicating a mixture of rainfall and deep waters. A saturation index study indicated that limestone minerals were supersaturated in parts of the groundwater samples (calcite and dolomite). This result was confirmed by isotope data. Indeed, some Cretaceous basin samples show isotopic similarities to those from the Jurassic High Atlas. The geological cross-sections illustrate that the High Atlas Jurassic limestones are in direct contact with the Cretaceous basin’s permeable rocks, allowing groundwater to circulate from the High Atlas to Errachidia’s Cretaceous basin.

L’hydrogeologie est la science de l’eau souterraine. Elle a pour objectif de planifier au mieux l’exploitation des ressources en eau. Elle doit non seulement caracteriser des aquiferes ou nappes d’eau souterraines, mais surtout, aujourd’hui, proteger et gerer les ressources en eau. L’hydrogeologie permet aussid’identifier et de prevenir les sinistres lors de grands travaux d’amenagement.Cet ouvrage presente les notions fondamentales (cycle de l’eau, differents types d’aquiferes, qualite des eaux…) et les outils et methodes indispensables a toute etude hydrogeologique. Cette cinquieme edition actualisee offre une approche pluridisciplinaire des applications et enjeux de l’hydrogeologie.Un lexique anglais-francais et francais-anglais de 900 entrees qui rassemble les principaux termes employes en hydrogeologie complete l'ouvrage.

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.

We propose an approach to study the hydro-mechanical behaviour and evolution of rainfall-induced deep-seated landslides subjected to creep deformation by combining signal processing and modelling. The method is applied to the Séchilienne landslide in the French Alps, where precipitation and displacement have been monitored for 20 years. Wavelet analysis is first applied on precipitation and recharge as inputs and then on displacement time-series decomposed into trend and detrended signals as outputs. Results show that the detrended displacement is better linked to the recharge signal than to the total precipitation signal. The infra-annual detrended displacement is generated by high precipitation events, whereas annual and multi-annual variations are rather linked to recharge variations and thus to groundwater processes. This leads to conceptualise the system into a two-layer aquifer constituted of a perched aquifer (reactive aquifer responsible of high-frequency displacements) and a deep aquifer (inertial aquifer responsible of low-frequency displacements). In a second step, a new lumped model (GLIDE) coupling groundwater and a creep deformation model is applied to simulate displacement on three extensometer stations. The application of the GLIDE model gives good performance, validating most of the preliminary functioning hypotheses. Our results show that groundwater fluctuations can explain the displacement periodic variations as well as the long-term creep exponential trend. In the case of deep-seated landslides, this displacement trend is interpreted as the consequence of the weakening of the rock mechanical properties due to repeated actions of the groundwater pressure.

Aquifer protection from pollution is an important action for a development and wise exploitation of the groundwater resources. In arid and semi-arid zones, rare surface water resources make groundwater the principal source of drinking, industrial and agricultural exploitation water. The idea of this work is to present the different factors participating in natural protection and assessing the groundwater vulnerability in a particular climatic context “arid and semi-arid”, so four factors are chosen for vulnerability mapping: lithology, water surface depth, infiltration conditions and effective rainfall. Each parameter is classified to identify a large variability. The vulnerability index is calculated by multiplication of four factor’s rating. A pilot site, the ElBayadh syncline is used to test this methodology in terms of typical physical and hydrogeological characteristics. The vulnerability map shows about 75% of the surface pilot site is classified as very high vulnerability. These areas could consequently be protected for future development.

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 Séchilienne (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 Séchilienne 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.

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.

Leakage detection and the prediction of the behavior of fractured rocks subjected to variations in hydrostatic pressure are important issues in hydropower engineering. Some large water reservoirs are constructed in karstic carbonate areas. In order to understand underground circulation in the limestone/dolomite foundation of the Vouglans dam (Jura, France), groundwater chemistry analysis, according to geological conditions, is used. Statistical analyses (PCA and DFA) are carried out: (1) to accurately characterize the contrast in chemical composition resulting from the interaction between surface and groundwater in a poorly contrasted environment, due to the shared carbonated context, and (2) to reassign individuals into homogeneous groups with respect to the variables studied. PHREEQC is used to determine the potential for the precipitation of secondary minerals from the water chemistry mainly in order to determine the geochemical control of clogging. Three types of hydrodynamic behavior were identified in the sector. The origin and transfer time of inflows vary with respect to seasons. The area of influence of the rapid transit of the lake water varies predominantly in response to changes in the lake water level. The hydrostatic pressure of the water column influences the opening and closing of cracks at the bottom of the dam. Drains intercepting an upstream fissure are highlighted by hydrochemical measurements. Inflows are oversaturated with respect to calcite and are thus likely to precipitate this mineral. Zones with a strong clogging capacity correspond to the zones with slow transit groundwater.

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.

Pore water pressure build-up by recharge of underground hydrosystems is one of the main triggering factors of deep-seated landslides. In most deep-seated landslides, pore water pressure data are not available since piezometers, if any, have a very short lifespan because of slope movements. As a consequence, indirect parameters, such as the calculated recharge, are the only data which enable understanding landslide hydrodynamic behaviour. However, in landslide studies, methods and recharge-area parameters used to determine the groundwater recharge are rarely detailed. In this study, the groundwater recharge is estimated with a soil-water balance based on characterisation of evapotranspiration and parameters characterising the recharge area (soil available water capacity, runoff and vegetation coefficient). A workflow to compute daily groundwater recharge is developed. This workflow requires the records of precipitation, air temperature, relative humidity, solar radiation and wind speed within or close to the landslide area. The determination of the parameters of the recharge area is based on a spatial analysis requiring field observations and spatial data sets (digital elevation models, aerial photographs and geological maps). This study demonstrates that the performance of the correlation with landslide displacement velocity data is significantly improved using the recharge estimated with the proposed workflow. The coefficient of determination obtained with the recharge estimated with the proposed workflow is 78% higher on average than that obtained with precipitation, and is 38% higher on average than that obtained with recharge computed with a commonly used simplification in landslide studies (recharge = precipitation minus non-calibrated evapotranspiration method).

The study of the neotectonic activity in the Jura Mountains (northwestern most belt of the European Alps) represents a challenge in the application of quantitative geomorphology to extract landscape metrics and discuss potential coupling between tectonic, climatic and lithospheric mechanisms during the evolution of this mountain belt. The Jura Mountains are characterized by a karst calcareous bedrock, slightly affected by Quaternary glaciations, and by moderated uplift rates (< 1 mm/year). In this study, we performed river profile analyses to decipher comparable geomorphological signals along tectonic structures within the entire Jura arc. Our results suggest higher tectonic activity in the High Range of the belt (internal part) than in the External Range, which is discussed in terms of deformation mechanisms. Integration of our results with previous geomorphological, neotectonic and geodetic studies from the literature leads us to propose new potential lithospheric and tectonic mechanism(s) driving the Plio-Quaternary deformation of the Jura Mountains. Our study finally reveals a regional-scale correlation between neotectonic deformations recorded by the Jura drainage network and the predicted isostatic rebound in response to Alpine Quaternary erosion. However, the correlation between our geomorphic signals and compressive structures suggests that the Jura Mountains could be still in horizontal shortening in both the High Range and the External Range.

Chapters in this book are contributions from the 9th Conference on limestone hydrogeology, organized in Besançon in September 2011 selected by the scientific committee of H2Karst.The book presents lat

Karst is a highly heterogeneous medium (i.e. properties vary from one point to another one), and can be studied by variations of water chemical composition, which reflect in space and time differences in origin (runoff on impervious media, diffuse seepage, inflows from evaporites...) or residence time throughout the various aquifer compartments (soil, epikarst, vadose and saturated zones. This natural background is supplemented by anthropogenic inputs (domestic, urban or industrial wastes, leachates from agricultural soils and livestock by-products...). Any natural (cave, chiasm) or artificial (tunnel, mine) penetrable gallery is a means of observation and sampling, at least of infiltration water, and sometimes of water from the saturated zone. Several cave sites in Europe provide examples for understanding the behavior of karst flows, both through the vadose and the saturated zones.

The studied area is located in the extreme part of Algeria. It is limited to the north by the Mediterranean Sea and the desert in the south. This position confers a variation of the climatic mode, a Mediterranean climate in the north and arid in the south, resulting in a very important fall of precipitation, ranging from 1200 mm/year in the north, to 300 mm/year in the south. The hydrographic network is very dense; very important wadis (Seybouse, Mellague, Medjerda, Kebir-Are, Kebir-West) cross this area, which implies important contributions (solid and liquid). Water of aquifers is often fed by these rivers. During its displacement water acquires a certain mineralization. The studies carried out showed that this mineralization increased during recent years, thus translating the influence of the climatic factors on water quality. To explain the origin of this salinity we were interested in the climatic variations and particularly in dryness which affected the area in recent years, due to a considerable fall in the infiltrations being translated in the north by an imbalance of the interface of fresh water and salted water, generating a salinity of water. In the south the dryness accelerated water salinity. To highlight this impact several approaches were used: Statistical tool using the PCA, gives an outline on the elements at the origin of observed salinity; STUYFZAND method, based primarily on chlorides, can determine various classes of salinity; and the thermodynamic tool shows the influence of certain minerals on water salinity. The compilation of all the results enables us to conclude that the observed salinity in various zones remains influenced by the dryness.