Ladouche Bernard
@brgm.fr
BRGM: National geological survey
Scopus Publications
Scopus Publications
V. Bailly-Comte, B. Ladouche, J. B. Charlier, V. Hakoun, and J. C. Maréchal
Springer Science and Business Media LLC
AbstractKarst aquifers are complex hydrogeological systems that require numerous in-situ measurements of hydrological and physico-chemical parameters to characterize transfer processes from the recharge area to the karst spring. Numerous graphical, statistical or signal processing methods have been developed for decades to interpret these measurements, but there is no simple and standardized tool that can be used for this purpose, which is necessary for a rigorous comparison of results between case studies. This Technical Note presents XLKarst, which has been developed to provide a simple and easy-to-use tool to process a selection of proven methods that characterize the functioning of karst systems. This tool allows (i) time series analysis based on correlation and spectral analysis and, for flow measurements, the use of other statistics and base flow separation, (ii) calculation of the cumulative distribution function to build a spring flow probability plot, and (iii) analysis of spring flow recession and expression of the results in a karst system classification scheme. These methods are first described by providing the key elements of their use and interpretation in the scientific literature. Then, an application to the Fontaine de Nîmes karst system (southern France) is used to highlight the complementarity of the methods proposed by XLKarst to describe the hydrodynamic behavior of a karst system based on daily data of rainfall and discharge over 22 years.
L. Marien, A. Crabit, B. Dewandel, B. Ladouche, P. Fleury, S. Follain, J. Cavero, V. Berteloot, and F. Colin
Elsevier BV
B. Ladouche, J.C. Maréchal, C. Lamotte, V. Durand, V. Bailly-Comte, and V. Hakoun
Elsevier BV
Pierre-Yann David, Didier Pennequin, Jean-Baptiste Charlier, Bernard Ladouche, Baptiste Meire, Véronique Feeny-Fereol, Stephane Helouin, Matthieu Fournier, Camille Riviere, and Germain Sanson
Geological Society of London
Abstract Rivers in karstic environments are known to be greatly influenced by surface water–groundwater interactions, with significant localized inflows during floods from springs, or with losses that can dry up rivers. The Middle Risle River is frequently affected by the development of sinkholes in a chalk karst area (Normandy, France). In the 2010s, two new major sinkholes in the riverbed caused a complete loss of water into the underlying phreatic aquifer, causing the river to dry up over several kilometres. The resulting changes in hydrogeological processes and surface water–groundwater interaction greatly affected water quality, water use and water-dependent ecosystems, causing a political crisis in this river-dependent touristic valley. To understand these phenomena and improve crisis management, the Middle Risle Critical Zone Observatory was set up to enhance monitoring, surveying and/or modelling of groundwater and river levels, river and spring flow, water temperature and conductivity, and ecosystem characteristics (fish, macro-invertebrates and vegetation). The results showed notable impacts on fish, macro-invertebrates and vegetation, some plants proving to be reliable indicators of surface-water–groundwater interaction. The dynamics of local hydrogeological processes were assessed and linked to the measured effects on ecosystems and water supply. Inverse modelling based on an analytical solution of the diffusive wave equation assessed lateral flow during floods, quantifying the spatial–temporal variability of surface-water and groundwater exchanges. It also highlighted the important role of karst zones in both storage and flood-peak attenuation processes, thereby protecting downstream villages against floods.
Florian Widhen, Michel Séranne, Grégory Ballas, Pierre Labaume, Erwan Le-Ber, Philippe Pezard, Flavia Girard, Claudine Lamotte, and Bernard Ladouche
EDP Sciences
Securing and managing underground water resources requires a good knowledge of the structure, texture and connections of the reservoir, in order to develop realistic and reliable hydrogeological models. On the coastline of the Gulf of Lion Margin (S. France), the Balaruc-les-Bains deep karst reservoir is subjected to interactions between fresh, marine and deep thermal waters, respectively. Water resource usage for drinking, spa resort, and fish-farming raises important economic and social issues. These were addressed by an integrated research program, involving drilling of an exploratory borehole across the Jurassic carbonate reservoir. This contribution analyses the 750 m cores, in order to (i) characterise the architecture and evolution of the karst reservoir and (ii) investigate the paleo-fluids circulations, witnessed by calcite and dolomite mineralization in the fractures, karst cavities, and as cement of tectonic beccia. The structure of the reservoir is characterised by the superposition of several aquifers separated by marly intervals. At shallow level, the initial grainstone is incompletely dolomitized in metre-thick intervals, while limestone in the 210–340 m interval was completely dolomitized at an early stage. Dolomite has been subjected to penetrative extensional cataclastic deformation, while the preserved limestone is affected by normal faulting, resulting from NNE–SSW extension. Distinct types of karsts have been documented, from the top of the reservoir (paleo-lapiaz filled with Burdigalian marine marls), down to 500 m depth (paleo-endokarst filled with continental silts). The upper reservoir (75–150 m) is intensely karstified, and includes 0.1 to 1 m-wide cavities, where present day water fluxes are documented. Analyses of calcite and dolomite crystallisation under natural light and cathodoluminescence indicate precipitation from distinct fluids: formation water in chemical equilibrium with the host rock, water rich in oxides and hydroxides, ascending hydrothermal fluid and corrosive water of meteoric origin. Alternate dolomitization and calcitization observed in the upper reservoir suggests alternate flows of karstic freshwater and marine salt-water. Vertical, metre-long and centimetre wide open cracks are presently used for large water flows; several generations of syntaxial calcite growth provide evidence for varying chemistry of the circulating fluids. Structural cross cutting relationships allowed us to establish a relative chronology of events, which can be correlated with the regional geodynamic evolution. The study reveals that the present-day reservoir architecture results from the superimposition of structures formed during the Early Cretaceous extension, Maastrichtian-Eocene Pyrenean shortening, and Oligocene rifting of the Gulf of Lion. The reservoir was also shaped by successive karstification episodes and marine transgressions. Although the present-day hydrological system is controlled by, and reactivates structures inherited from a long-term evolution, it is characterised by frequent turn-overs of the water flow, tuned by high-frequency external forcings such as sea-level changes driven by Pleistocene glacio-eustasy, or varying precipitation rates.
Vianney Sivelle, Laïna Pérotin, Bernard Ladouche, Véronique de Montety, Vincent Bailly-Comte, Cédric Champollion, and Hervé Jourde
Frontiers Media SA
The objective of this study was to evaluate the relevance of using excess air (EA) for the characterization of drain/matrix exchange in karst systems using a rainfall discharge model coupled with the simulation of EA measured at the outlet of the studied system. The conceptual model assumes a linear relationship between the formation of EA and the increase of hydrostatic pressure in the capacitive part of the aquifer. The simulated EA at the spring consists of the mixing of water circulating in the different compartments of the aquifer, with their own EA signature. The analysis is performed taking as an example the Durzon karst system (Larzac, France). The modeling is applied using daily rainfall discharge time series and 18 EA measurements at the main outlet of the karst system within 3 hydrological cycles. The main modeling results show that EA variations measured at the karst spring can be explained by recharge processes and exchange between conduit and matrix. EA measurements at the spring thus contain valuable information about the flow dynamics within the aquifer. Furthermore, results show that the use of EA measurements, despite their sparse temporal resolution, allows for reducing uncertainties in the estimation of some parameters of the reservoir model used for the simulation of karst spring discharge.
Benoît Dewandel, Vivien Hakoun, Sandra Lanini, Bernard Ladouche, Claudine Lamotte, and Jean-Christophe Maréchal
Elsevier BV
Thibaut Garin, Bruno Arfib, Bernard Ladouche, Julio Goncalves, and Benoit Dewandel
Springer Science and Business Media LLC
The study of groundwater resources using pumping test data is usually carried out with the Theis solution, which enables the hydraulic parameters of porous aquifers such as the transmissivity and storage coefficient, to be estimated from the water-level drawdown. However, the data fitting can fail and provide only an indication that the pumped aquifer has a complex structure. Here, a diagnostic plot on log-derivative drawdown is used to identify flow regimes and thus aquifer heterogeneities, leading to plausible conceptual models. Nevertheless, the diagnostic plot is insufficient and must be accompanied by further modelling because of the nonuniqueness of the drawdown log-derivative signal. The proposed approach is applied to an alluvial plain in France, known to be complex because the deposition processes change over time, resulting in channel belts limited by low-permeability deposits in the floodplain or three-dimensional (3D) interconnected structures. Six analytical models were used to simulate drawdown and its derivatives during a three-day transient pumping test. The diagnostic performed on the pumping well showed that four conceptual models, with highly contrasted hydrodynamic behaviours, may correspond to the diagnostic. The joint use of pumping-well and observation-well data allowed the only appropriate model to be identified—a dual-permeability model characterizing a multilayer aquifer. The conceptual model matched the geological observations in boreholes and corroborates the fluvial sequence stratigraphy of the alluvial plain. The pumping test used here is a tool to explore the 3D architecture of the fluvial reservoir at the scale of the depositional sequence in the floodplain.
Laïna Pérotin, Véronique de Montety, Bernard Ladouche, Vincent Bailly-Comte, Thierry Labasque, Virginie Vergnaud, Rémi Muller, Cédric Champollion, Sarah Tweed, and Jean-Luc Seidel
Elsevier BV
Andreas Hartmann, Scott Jasechko, Tom Gleeson, Yoshihide Wada, Bartolomé Andreo, Juan Antonio Barberá, Heike Brielmann, Lhoussaine Bouchaou, Jean-Baptiste Charlier, W. George Darling,et al.
Proceedings of the National Academy of Sciences
Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world’s population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from <1% to around 20 to 50% of their concentrations during infiltration. Assuming realistic application rates, our simulations show that degradable pollutants like glyphosate can exceed their permissible concentrations by 3 to 19 times when reaching the groundwater. Our results are supported by independent estimates of young water fractions at 78 carbonate rock springs over Europe and a dataset of observed glyphosate concentrations in the groundwater. They imply that in times of continuing and increasing industrial and agricultural productivity, focused recharge may result in an underestimated and widespread risk to usable groundwater volumes.
Tunde Olarinoye, Tom Gleeson, Vera Marx, Stefan Seeger, Rouhollah Adinehvand, Vincenzo Allocca, Bartolome Andreo, James Apaéstegui, Christophe Apolit, Bruno Arfib,et al.
Scientific Data Springer Science and Business Media LLC
Tunde Olarinoye, Tom Gleeson, Vera Marx, Stefan Seeger, Rouhollah Adinehvand, Vincenzo Allocca, Bartolome Andreo, James Apaéstegui, Christophe Apolit, Bruno Arfib,et al.
Scientific Data Springer Science and Business Media LLC
Marie-Amélie Pétré, Bernard Ladouche, Jean-Luc Seidel, Romain Hemelsdaël, Véronique de Montety, Christelle Batiot-Guilhe, and Claudine Lamotte
Copernicus GmbH
Abstract. Submarine springs are a common discharge feature of the karst aquifers along the Mediterranean coast. In some instances, occasional and localized saltwater intrusions can occur through the submarine spring and negatively impact the quality of the groundwater resource. The hydraulic and geochemical behaviour of a submarine spring discharging into the Thau Lagoon just offshore of the Balaruc peninsula near Montpellier, France, has been characterized to determine the impacts of such phenomena to better understand the dynamics of a regional karst aquifer and improve its groundwater management. This work is based on both historical and new hydrogeological and geochemical data, illustrating six occasional saltwater intrusion events (from 1967 to 2014) in the Thau Lagoon area (southern France). Hydraulic perturbation of the aquifer is propagated instantly within the Balaruc-les-Bains peninsula and reaches a distance of about 5 km upgradient within 9 d. Comparison of hydraulic heads during seawater intrusion events in 2010 and 2014 indicates an aggravation of the phenomenon with an increase in hydraulic head variations. In contrast, isotopic tracers (87Sr∕86Sr, D/H, 18O∕16O) and rare earth elements (REEs) demonstrate that the geochemical impact of these inversac events is only observed at the local scale but is still perceptible several years after the event. For example, some of the thermal wells had not recovered their initial geochemical state 20 and 40 months after the last two inversac events (2010 and 2014, respectively), suggesting a geochemical legacy of this phenomenon within the complex karst system. By contrast, an adjacent deep karst compartment located south of the study area is not affected by the saltwater intrusion and is characterized by distinctly different hydrodynamic behaviour. Overall, this work on occasional and localized saltwater intrusions constitutes a key step in understanding the dynamics of this complex karstic and thermal aquifer and will support the management of the groundwater resource.
Audrey Taillefer, Laurent Guillou-Frottier, Roger Soliva, Fabien Magri, Simon Lopez, Gabriel Courrioux, Romain Millot, Bernard Ladouche, and Elisabeth Le Goff
American Geophysical Union (AGU)
Hydrothermal systems involving dormant faults within orogenic belts are rarely targeted for geothermal exploration, partly because of the complexity of the 3-D topography, the unknown permeability of the fault zones and the basement lithology, and the lack of deep-level data. This study brings together various types of surface information (spring features, geological data, topography, hydrochemistry) to explain the alignment of 29 hot springs (29-73°C) along the dormant Tet fault (Eastern Pyrenees, France). Water ion concentrations, stable water isotopes and lithium isotopic ratios indicate that (i) fluids originating from meteoric water infiltrate above an altitude of 2000 m, (ii) the rocks interacting with the fluids are similar for all the springs, and (iii) the maximum fluid temperatures at depth show similar variations along the fault and at the surface. A 3-D numerical model of the system, assembled from field structural data and from a Digital Elevation Model, explores the permeability combinations for the basement and for a three-fault network. The models indicate that for a relatively permeable basement (10-16 m2), fluids are topography-driven down to thousands of meters (until -3700 m) before being captured by the more permeable Tet fault. Hot spring temperatures can be numerically reproduced when fault permeability is around 10-14 m², a value slightly lower than the critical permeability for which free-convection would occur within the Tet fault. Our study shows that thermal anomalies are possible along dormant faults close to elevated topography in the core of an orogenic belt, thereby opening new perspectives for geothermal exploration.
Pierre Belle, Bertrand Aunay, Patrick Lachassagne, Bernard Ladouche, and Jean-Lambert Join
MDPI AG
Among the processes controlling landslide dynamics, piezometry plays a major role. The characterization of a landslide’s aquifer recharge (=inflows) is thus indispensable for predicting displacements. In this research, the recharge of the large Grand Ilet landslide in the humid tropical, Reunion Island was characterized through a multi-disciplinary and robust hydrological approach, notably comprising a precise water budget of the landslide (outflows = inflows). Surface processes play a major role in the landslide recharge regime. Runoff is less than 1% of rainfall (2400 mm/year) due to the soil’s high permeability. A large quantity of water (250 mm) is adsorbed in this shallow layer. This reservoir is submitted to high real evapotranspiration (1500 mm/year) due to the dense tropical broad-leaved vegetation. This explains the low aquifer recharge (860 mm/year), the fact that only major rainfall episodes during the rainy season induce recharge, with a consequent increase in landslide velocity, and finally low outflow from the landslide. Therefore, among other operational recommendations, it is necessary to maintain natural vegetation cover over such landslide surface in order to limit aquifer recharge and thus displacements. This study provides a methodological framework for landslide studies, particularly for modeling their recharge/piezometry, and key parameters of their dynamics.
H. Jourde, N. Massei, N. Mazzilli, S. Binet, C. Batiot-Guilhe, D. Labat, M. Steinmann, V. Bailly-Comte, J.L. Seidel, B. Arfib,et al.
Wiley
Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface–groundwater interactions. Improving the understanding of karst functioning is thus a major issue for the efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems across a wide range of spatiotemporal scales under different geological, geomorphological, climatic, and soil cover settings. The objective of the French Karst National Observatory Service (SNO KARST) is to supply the international scientific community with appropriate data and tools, with the ambition of (i) facilitating the collection of long-term observations of hydrogeochemical variables in karst, and (ii) promoting knowledge sharing and developing cross-disciplinary research on karst. This paper provides an overview of the monitoring sites and collective achievements, such as the KarstMod modular modeling platform and the PaPRIKa toolbox, of SNO KARST. It also presents the research questions addressed within the framework of this network, along with major research results regarding (i) the hydrological response of karst to climate and anthropogenic changes, (ii) the influence of karst on geochemical balance of watersheds in the critical zone, and (iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds.
Benoît Dewandel, Julie Jeanpert, Bernard Ladouche, Jean-Lambert Join, and Jean-Christophe Maréchal
Elsevier BV
Abstract Estimating the transmissivity or hydraulic conductivity field to characterize the heterogeneity of a crystalline aquifer is particularly difficult because of the wide variations of the parameters. We developed a new approach based on the analysis of a dense network of water-table data. It is based on the concept that large-scale variations in hydraulic head may give information on large-scale aquifer parameters. The method assumes that flux into the aquifer is mainly sub-horizontal and that the water table is mostly controlled by topography, rather than recharge. It is based on an empirical statistical relationship between field data on transmissivity and the inverse slope values of a topography-reduced water-table map. This relationship is used to compute a transmissivity map that must be validated with field measurements. The proposed approach can provide a general pattern of transmissivity, or hydraulic conductivity, but cannot correctly reproduce strong variations at very local scale (less than10 m), and will face of some uncertainties where vertical flows cannot be neglected. The method was tested on a peridotite (ultramafic rock) aquifer of 3.5 km 2 in area located in New Caledonia. The resulting map shows transmissivity variations over about 5 orders of magnitude (average LogT: −5.2 ± 0.7). Comparison with a map based on measured water-level data (n = 475) shows that the comparison between LogT-computed values and LogT data deduced from 28 hydraulic tests is estimated with an error less than 20% in 71% of cases (LogT ± 0.4), and with an error less than 10% (LogT ± 0.2 on average) in 39% of cases. From this map a hydraulic-conductivity map has been computed showing values ranging over 8 orders of magnitude. The repeatability of the approach was tested on a second data set of hydraulic-head measurements (n = 543); the mean deviation between both LogT maps is about 11%. These encouraging results show that the method can give valuable parameter estimates, and can characterize aquifer heterogeneity. The computed LogT and LogK maps highlight the spatial distribution of parameters that show a pattern clearly controlled by the fault network of this ultramafic massif. However, the faults are mainly characterized by low-permeability zones; this differs from results on other crystalline aquifers and may be due to the fact that weathering products of peridotite are clay-like materials. The resulting transmissivity map can be used as a starting point for modelling or to direct additional fieldwork.
B. Dewandel, M. Alazard, P. Lachassagne, V. Bailly-Comte, R. Couëffé, S. Grataloup, B. Ladouche, S. Lanini, J.-C. Maréchal, and R. Wyns
Elsevier BV
Crystalline thermo-mineral and carbo-gaseous (CTMCG) hydrosystems are well known for their economic importance in fields such as thermal, spa activities and natural mineral water (NMW) bottling. Such systems are usually associated with strong structural complexity, which is rarely characterised in detail or robustly. This research focuses on a CTMCG hydrosystem associated with a peri-alpine graben. A multidisciplinary approach with a very large set of data and methods – geological modelling with geophysics and geological data from outcrops and several boreholes, hydrodynamic data, hydrochemistry, hydrogeological and geochemical modelling – reveals very novel results and allows a robust conceptual model to be constructed. The aquifer at the origin of the carbo-gaseous natural mineral water is the 100–125 m-thick fractured stratiform layer of the weathering profile of the crystalline rock (granite). It forms a rather large and thick inertial aquifer that can be numerically modelled, in a similar fashion to a porous medium. The majority of tectonic faults length act as impervious boundaries that divide this aquifer into around ten elongated compartments that were precisely delineated. These tectonic faults are permeable only along two small areas that were also precisely located. These permeable zones feed some aquifer compartments with deep, highly mineralised carbo-gaseous water, which mixes with “fresher” water and forms the exploited NMW. These results can be generalised and in particular show a strong opposition between low-inertia CTMCG hydrosystems without a subsurface reservoir, as the weathering profile was eroded, and high-inertia hydrosystems such as the one studied.
Emmanuelle Petelet-Giraud, Philippe Négrel, Bertrand Aunay, Bernard Ladouche, Vincent Bailly-Comte, Catherine Guerrot, Christine Flehoc, Philippe Pezard, Johanna Lofi, and Nathalie Dörfliger
Elsevier BV
The Roussillon sedimentary Basin (South France) is a complex multi-layered aquifer, close to the Mediterranean Sea facing seasonally increases of water abstraction and salinization issues. We report geochemical and isotopic vertical variability in this aquifer using groundwater sampled with a Westbay System® at two coastal monitoring sites: Barcarès and Canet. The Westbay sampling allows pointing out and explaining the variation of water quality along vertical profiles, both in productive layers and in the less permeable ones where most of the chemical processes are susceptible to take place. The aquifer layers are not equally impacted by salinization, with electrical conductivity ranging from 460 to 43,000μS·cm(-1). The δ(2)H-δ(18)O signatures show mixing between seawater and freshwater components with long water residence time as evidenced by the lack of contribution from modern water using (3)H, (14)C and CFCs/SF6. S(SO4) isotopes also evidence seawater contribution but some signatures can be related to oxidation of pyrite and/or organically bounded S. In the upper layers (87)Sr/(86)Sr ratios are close to that of seawater and then increase with depth, reflecting water-rock interaction with argillaceous formations while punctual low values reflect interaction with carbonate. Boron isotopes highlight secondary processes such as adsorption/desorption onto clays in addition to mixings. At the Barcarès site (120m deep), the high salinity in some layers appear to be related neither to present day seawater intrusion, nor to Salses-Leucate lagoonwater intrusion. Groundwater chemical composition thus highlights binary mixing between fresh groundwater and inherited salty water together with cation exchange processes, water-rock interactions and, locally, sedimentary organic matter mineralisation probably enhanced by pyrite oxidation. Finally, combining the results of this study and those of Caballero and Ladouche (2015), we discuss the possible future evolution of this aquifer system under global change, as well as the potential management strategies needed to preserve quantitatively and qualitatively this water resource.
Jean-Baptiste Charlier, Roger Moussa, Vincent Bailly-Comte, Laurent Danneville, Jean-François Desprats, Bernard Ladouche, and Arthur Marchandise
Springer Science and Business Media LLC
The aim of this study is to assess the spatio-temporal variability of lateral flows in the streams of a large karstic basin to construct a conceptual model of karst contributions to flood generation. The lateral flows of the Tarn River, which crosses the Grands Causses karst zone in Southern France, were investigated between several gauging stations along the river. First, through analysing the lateral flows on an event time scale of 30 floods, it was possible to identify the losing and gaining reaches, highlighting a highly variable attenuation/amplification role of karsts on flood generation. Second, the diffusive wave model was used to quantify the lateral flows on an hourly time step within a flood event. The simulations show a high variability of lateral outflows and inflows within a same reach according to the hydrometeorological conditions, with in some cases an inversion of the lateral flow direction during the flood. The results highlight complex surface/groundwater exchanges during a single flood event, with high river losses despite the concurrent flow of large springs feeding the stream. This spatio-temporal variability of the karst influence on flood generation was linked to the aquifer’s structure, which has improved the understanding of the hydro(geo)logical functioning of the Grands Causses massif. Finally, the new methodology proposed here opens challenging perspectives towards a framework for the analysis of surface–groundwater exchanges in karstic rivers.
Jean-Baptiste Charlier, Bernard Ladouche, and Jean-Christophe Maréchal
Elsevier BV
This paper assesses the implications of climate and anthropic pressures on short to long-term changes in water resources in a Mediterranean karst using wavelet analysis. This approach was tested on 38-year (1974–2011) hydrogeological time series recorded at the Lez spring (South France), which is exploited for water supply. Firstly, we investigated inter-relationships in the frequency domain by cross-correlation across multiresolution levels. Our results showed that rainfall and spring discharge are highly correlated in the high frequency domain which reflects the hydrogeological response during flood events of typical highly karstified systems. Pumping and groundwater level are correlated in a lower frequency domain, illustrating seasonal to multi-year relationships. Secondly, continuous wavelet transform was applied to characterize the temporal variability of the inter-relationships involved. On the contrary to examples of “non-managed” karst aquifers in the literature, our results showed that the 10-year rainfall component was attenuate in the discharge signal. We assume that the reason is that the storage variations are strongly affected by pumping. This interesting result shows that possible long-term impacts of rainfall variability due to climate change may be masked by a high pumping rate. We showed also that despite an increase of the pumping rate from the 1980s, the stress on the groundwater resource does not increase from year to year. The present pumping strategy does not affect the drawdown in the long term, avoiding an over-exploitation of the aquifer. Finally, this study highlights the effectiveness of wavelet analysis in characterizing the response variability of karst systems where the hydrogeological regime is modified by pumping.
J.-B. Charlier, R. Moussa, V. Bailly-Comte, J.-F. Desprats, and B. Ladouche
Springer Berlin Heidelberg
This paper investigates the role of karst aquifers on flood generation and propagation using the Hayami Diffusive Wave (DW) model accounting for uniformly distributed lateral flows. The inverse model was applied on the main channel reaches of the Tarn basin at Millau (2,400 km2) in southern France to assess lateral inflows from karstic springs as well as lateral outflows from river losses. Results show that the DW model, which is simple, parsimonious, and easy-to-use, is able to quantify lateral flows avoiding difficult parameterisation. Surface/groundwater exchanges were characterised on several reaches along the stream, showing a highly variable attenuation/amplification influence of flood peak by karst units during a single flood event. We showed that the upstream part of the karst area have a dominant attenuation role by re-infiltrating part of runoff from the head-water basin in hard-rock areas, while the downstream part have a dominant amplification role due to high contributions of karst groundwater. These results improved the conceptual hydrogeological model of the Grands Causses region.
Bernard Ladouche, Jean-Christophe Marechal, and Nathalie Dorfliger
Elsevier BV
Summary In this paper inverse modeling is used to characterize the regime of a karst aquifer subjected to extensive pumping in a conduit located upstream of its main outlet. The systemic approach uses a transfer model that is based on computing the convolution integral of up to several signals, e.g., efficient rainfall, pumping, to simulate flow rates and groundwater levels in both the karst conduit and the carbonate matrix at the aquifer outlet and in several parts of the catchment area. The model is a semi-distributed lumped model which simulates the hydrological response of a heterogeneous karst aquifer made up of different hydrologic compartments, and is applied to the Lez karst system, France. Groundwater is abstracted near the system’s major outlet at a higher rate than the low-water spring discharge, thereby mobilizing stored groundwater during low-water periods (‘active management’). The model’s results are very satisfactory, especially for the karst system outlet, where the water levels are particularly well reproduced. The model can also simulate the natural, i.e., non-pumping, state of the karst system and thereby estimate the impact of active management on the water resource.
J. C. Maréchal, P. Lachassagne, B. Ladouche, B. Dewandel, S. Lanini, P. Le Strat, and E. Petelet-Giraud
Springer Science and Business Media LLC
Natural mineral waters (NMW), often used to produce bottled water, are of high socio-economic interest and need appropriate management to ensure the sustainability of the resource. A complex sparkling NMW system at La Salvetat, southern France, was investigated using a multidisciplinary approach. Geological and geophysical investigations, pumping test analyses, time-series signal processing, hydrogeochemical and isotopic data (both stable and radiogenic), and numerical modelling provided complementary information on the geometry, hydrodynamic characteristics and functioning of this mineral system. The conceptual model consists of a compartmentalized reservoir characterized by two subvertical, parallel deeply rooted hydraulically independent permeable structures that are fed by deep CO2-rich crustal fluids. The non-mineralized shallow aquifer system corresponds to a fissured layer within the weathered zone that is recharged by leakage from the overlying saprolite. This surficial aquifer responds rapidly to recharge (40–80 days), whereas the deep system’s response to recharge is much longer (up to 120 days). This research demonstrates the need for multidisciplinary approaches and modelling (quantity, hydrochemistry) for understanding complex NMW systems. This knowledge is already being applied by the bottling company that manages the resource at La Salvetat, and would be useful for conceptualising other NMW sites.RésuméLes Eaux Minérales Naturelles (EMN), souvent utilisées pour produire de l’eau embouteillée, présentent un fort intérêt socio-économique et requièrent une gestion adaptée pour garantir la durabilité de la ressource. Un système complexe d’EMN gazeuse à La Salvetat, sud de la France, a été étudié au moyen d’une approche multidisciplinaire. Des investigations géologiques et géophysiques, l’analyse de pompages d’essai, le traitement du signal de séries chronologiques, des données hydrogéochimiques et isotopiques (isotopes stables et radiogéniques) et une modélisation numérique procurent des informations complémentaires sur la géométrie, les caractéristiques hydrodynamiques et le fonctionnement de ce système minéral. Le modèle conceptuel consiste en un réservoir compartimenté caractérisé par deux structures perméables subverticales profondément enracinées, parallèles, indépendantes hydrauliquement, qui sont alimentées par des fluides crustaux profonds riches en CO2. Le système aquifère de subsurface non minéral correspond à un horizon fissure-altéré qui est rechargé par drainance par la saprolite sus-jacente. Cet aquifère superficiel réagit rapidement à la recharge (40–80 jours), tandis que la réponse du système profond est beaucoup plus longue (jusqu’à 120 jours). Cette recherche démontre la nécessité d’approches multidisciplinaires et par modélisation (quantité, hydrogéochimie) pour comprendre les systèmes d’EMN complexes. Ces connaissances sont déjà appliquées par la société d’embouteillage qui gère la ressource à La Salvetat et pourraient être utiles pour conceptualiser d’autres sites d’EMN.ResumenLas aguas minerales naturales (NMW), a menudo usadas para producir agua embotellada, son de un alto interés socioeconómico y necesitan un manejo apropiado para asegurar la sustentabilidad del recurso. Se investigó un complejo sistema NMW gaseoso en La Salvetat, sur de Francia, usando un enfoque multidisciplinario. Investigaciones geológicas y geofísicas, análisis de ensayos de bombeo, procesamiento de series temporales de señales, datos hidrogeoquímicos e isotópicos (tanto estables como radiogénicos), y los modelos numéricos proporcionaron información complementaria sobre la geometría, características hidrodinámicas y funcionamiento de este sistema mineral. El modelo conceptual consiste de un reservorio compartimentado caracterizado por dos estructuras paralelas subverticales permeables profundamente arraigados e hidráulicamente independientes que son alimentados por fluidos corticales profundos ricos en CO2. El sistema acuífero somero no mineralizado corresponde a una capa fisurada dentro de la zona de meteorización que está recargada por filtración desde el saprolito suprayacente. Este acuífero superficial responde rápidamente a la recarga (40–80 días), mientras que la respuesta del sistema profundo a la recarga es mucha mayor (hasta 120 días). Esta investigación demuestra la necesidad de enfoques multidisciplinarios y modelado (cantidad, hidroquímica) para entender el complejo sistema NMW. Este conocimiento está ya siendo aplicado por la compañía embotelladora que maneja el recurso en La Salvetat, y sería útil para la conceptualizar de otros sitios NMW.摘要天然矿泉水常常用于生产瓶装水, 具有很高的社会-经济效益, 需要恰当的管理, 以保证资源的可持续性。采用多学科方法对法国南部La Salvetat一个复杂的气泡天然矿泉水系统进行了的调查。地质和地球物理调查、抽水实验分析、时间序列信号处理、水文地球化学和同位素资料 (稳定同位素和放射同位素) 及数值模拟对这个矿泉系统的几何特征、水动力特征和功能提供了补充信息。概念模型由区划的储水池构成, 特点是具有两个接近垂直的、平行的深根的水力上独立的透水构造, 由深部的富含CO2地壳液补给。非矿化的浅层含水层系统与风化带内断裂层相对应, 风化带由上覆的风化土中的越流补给。这个表层含水层对补给反应迅速 (40–80天) , 而深部系统对补给的反应慢很多 (120天以上) 。这项研究说明需要多学科方法和模拟 (量上和水文化学上) 来了解复杂的天然矿泉水系统。这个认知已经被管理La Salvetat资源的拼装公司所采用, 并在概念化其它天然矿泉水场地中非常有用。ResumoAs águas minerais naturais (AMN), frequentemente usadas para produzir água engarrafada, têm um elevado interesse socio-económico e necessitam uma gestão apropriada para assegurar a sustentabilidade do recurso. Um sistema complexo de AMN em La Salvetat, sul de França, foi investigado utilizando uma abordagem multidisciplinar. Investigações geológicas e geofísicas, análises de ensaios de bombeamento, processamento de sinal de séries temporais, dados hidrogeoquímicos e isotópicos (estáveis e radiogénicos) e modelação numérica proporcionaram informações complementares sobre a geometria, as características hidrodinâmicas e o funcionamento deste sistema mineral. O modelo conceptual consiste num reservatório compartimentado caracterizado por duas estruturas permeáveis subverticais independentes, paralelas, profundamente enraizadas, que são alimentadas por fluidos crustais profundos enriquecidos em CO2 . O sistema aquífero não mineralizado superficial corresponde a uma camada fissurada no seio da zona de alteração cuja recarga provém de escoamento a partir do saprólito sobrejacente. Este sistema superficial responde rapidamente à recarga (40-80 dias), enquanto que a resposta do sistema profundo à recarga é muito mais demorada (até 120 dias). Esta investigação demonstra a necessidade de abordagens multidisciplinares e de modelação (quantidade e hidroquímica) para a compreensão de sistemas de AMN complexos. Este conhecimento já está a ser aplicado pela empresa de engarrafamento que gere o recurso em La Salvetat e seria útil para conceptualizar outros locais de AMN.