L’infiltration correspond à l’ensemble des écoulements contribuant à la recharge des réserves des systèmes karstiques ou aux variations des débits à leurs exutoires. L’objectif de cette thèse est la caractérisation de l’infiltration et son utilisation dans l’étude des transferts pour la compréhension du fonctionnement des systèmes karstiques.Deux sites sont utilisés pour analyser cette infiltration : celui de la colline de Lascaux en Dordogne et celui du Nord du Vaucluse en Provence composé de plusieurs sources karstiques. Ces sites, en milieu carbonaté, se différencient tant par leur structuration – système épikarstique et aquifère karstique perché, pour le premier, et systèmes épikarstique, fissuré ou karstiques à zone noyée, pour le second – que par les conditions climatiques rencontrées au niveau de leurs impluviums respectifs.L’étude hydrodynamique des systèmes épikarstiques par les modèles réservoirs ne convient actuellement pas : la fonction de production ne permet pas la génération d’une infiltration satisfaisante. L’utilisation d’un modèle réservoir, initialement basé sur les équations de Coutagne, a permis de souligner la nécessité d’ajouter deux modules de calcul. Le premier concerne l’estimation d’une évapotranspiration effective, issue d’une loi exponentielle, considérant la hauteur d’eau dans le réservoir sol. Le deuxième module insiste sur l’utilité d’une fonction de stockage de l’épikarst pour caractériser au mieux les transferts vers l’aval du système.L’étude hydrochimique s’appuie majoritairement sur les équilibres calco-carboniques de l’eau et donc sur les transferts de masses de carbone inorganique. Ils permettent d’accéder à différentes grandeurs telles que la pression partielle de dioxyde de carbone – équilibrante (Pco2_eq) ou à saturation (Pco2_sat) – et à l’indice de saturation vis-à-vis de la calcite (ISc). La mise en relation de ces deux paramètres au sein d’un graphique {–log(Pco2) : ISc} a permis de distinguer différents types d’eaux issus des différents compartiments du karst. Il en a résulté un schéma de transfert des différents types d’eaux passant à l’exutoire tenant compte de l’état d’ennoiement du système. L’évolution pluriannuelle de l’infiltration a aussi été mise en avant par la variation de sa composition chimique pouvant être en relation avec des facteurs climatiques.A l’issue de ce travail, il apparaît que la connaissance des processus liés à l’infiltration est fondamentale pour la compréhension des écoulements en milieux karstiques dans un objectif de quantification de la recharge et de protection de la ressource. / Infiltration corresponds to flows contributing to the system recharge and its discharge variations. This thesis aims at characterize infiltration and its utilization in transfer analyses to understand karst system behavior.Two sites are used to study this infiltration: this of the Lascaux hill in Dordogne and one in the North of the Vaucluse county composed of several karst springs. These locations are different in their structure as well as climatic conditions on their respective intake areas. The first site consists on an epikarst and a perched karst aquifer systems, since the second is composed of an epikarst, a fissured and a developed saturated zone systems.Nowadays, hydrodynamic study of an epikarst system using reservoir models is not satisfying: the production function is not able to generate a sufficient infiltration. In this study, a reservoir model initially based on Coutagne’s equations had been used. Results highlighted the necessity to add two new calculation functions. The first is related to an evapotranspiration estimation using an exponential law considering the amount of water in the soil reservoir. The second underlines the necessity of taking into account the storage function of the epikarst to characterize in a better way flows in karst systems.Hydrochemical study was carried on from calcium-bicarbonate equilibriums and then by mass transfers. They permit to describe several parameters as the carbon dioxide partial pressure at atmospheric equilibrium (Pco2_eq) or at saturation (Pco2_sat) and the saturation index with respect to calcite (SIc). These parameters can be expressed through the {–log(Pco2); SIc} graph to identify different water types. A transfer schema had been proposed, considering the saturation state of the system. Multi-year evolution of the infiltration had been underlined by variations of the chemical composition of infiltration water. This evolution can be linked to climatic conditions.Finally it appears that the knowledge of infiltration processes is essential to understand karst flows to quantify karst recharge and protect the resource.

Les muons, particules chargées d'origine cosmique, ont la particularité d'être très pénétrants. L'atténuation du flux de muons dans la matière témoigne de la quantité de matière traversée (profondeur x densité). Sur la base de ce principe, la muographie est une technique permettant d'étudier la densité in-situ de cibles volumineuses telles que des édifices géologiques. Le projet Tomographie Temporelle de la Densité par la Mesure des Muons (T2DM2) a pour objectif la caractérisation des variations spatiales et temporelles de la densité des roches avec un premier champ d'application dans la Zone Non Saturée (ZNS) de l'aquifère karstique de Fontaine-de-Vaucluse, située au-dessus du LSBB. Ce travail de thèse se concentre sur la simulation numérique du flux de muons en profondeur et une première campagne de mesures durant 16 mois consécutifs à différentes profondeurs dans les galeries du LSBB. Les simulations menées sont en accord avec les variations de densité attendues en contexte hydrogéologique. L'influence de la composition atomique de la roche et des processus de diffusion sont discutés ainsi que des pistes pour réduire les durées d'acquisitions (et/ou surfaces de détection et/ou angles solides). Les mesures réalisées au LSBB ont permis d'identifier des zones de plus faibles densités telles que le point X1. Les données acquises ont pu être corrigées de l'influence de la pression atmosphérique grâce à la détermination du coefficient barométrique permettant ainsi l'analyse temporelle du flux de muons. / The muons, charged particles of cosmic origin, have the particularity of being very penetrative. The attenuation of muon flux in matter highlights the quantity of matter (depth x density) passed through. Based on this principle, the muography is a technique allowing the study of the in-situ density of large targets as geological structures. The Temporal Tomography of rock Density using Muon Measurements (T2DM2) aims at characterizing the spatial and temporal density variations with a first application in the unsaturated aquifer of Fontaine-de-Vaucluse located above the LSBB. This thesis work is focused on the numerical simulation of muon flux at depth and a first campaign of measurements during 16 consecutive months at various depths in LSBB galleries. The performed simulations are in agreement with the expected density variations in an hydrogeological context. The influences of the rock atomic composition and of the scattering processes are discussed as well as strategy to reduce the acquisition duration (and/or detection surfaces and/or solid angles). The measurements performed at LSBB allowed to identify areas of lower density such as the X1 point. The acquired data have been corrected thanks to the determination of the barometric coefficient allowing the temporal analysis of muon flux. The comparison of the recorded flux at different depths (~ 60 m, ~ 200 m and ~ 500 m) with the numerical simulations leads to an estimation of the average density of the rocks located above the LSBB of 1.9 ± 0.1 g.cm-3 testifying their important porosity.

Ce travail de recherche porte sur l’étude du paléo-environnement du massif des Calanques, sur la mise en place d’une structure karstique de surface (poljé de Cassis, SE France) et sur l’empreinte de l’Homme sur son milieu. L’étude se base sur la réalisation de mesures géophysiques (électrique, gravimétrie, sismique passive) et sur l’analyse de plusieurs sondages, dont le principal est un enregistrement sédimentaire de 50 m de long carotté dans un paléo-lac situé à 2 km du littoral méditerranéen qui retrace le paléo-environnement du massif des Calanques au Pléistocène supérieur et à l’Holocène.Le paléo-lac de Cassis a été formé par la dissolution du calcaire barrémien et/ou par l’effondrement d’une cavité karstique, et a été rempli par une sédimentation laminée fine issue de l’érosion des marnes aptiennes, sédimentation qui caractérise un milieu de dépôt anoxique profond. Les observations spéléologiques et les analyses sédimentaires supposent l’existence d’une connexion entre le poljé et la rivière souterraine du Bestoaun.L’environnement holocène, stable sur toute la période holocène, est dominé par les formations herbacées sèches. L’impact de l’Homme sur l’environnement du massif des Calanques est visible au travers des modifications du réseau hydrographique local, de la métallurgie du plomb et de la mise en place de pratiques agro-pastorales. / This Phd research work focuses on : (1) paleo-environment of the Calanques, (2) karst structure formation (polje of Cassis, SE France) and (3) Holocene environmental changes linked to human activities.The study is based on a multi-geophysical methods approach (electrical resistivity tomography, gravimetric, passive sismic survey) and on several sedimentary records studies. The main sedimentary record is 50 m-long core coming from a pleistocene paleolake located 2 km from the Mediterranean Sea. Limestone dissolution and/or cavity collapse led to the development of a polje, rapidly filled by the erosion of Aptian marls in glacial period. The connection between the polje and the three kilometer long Bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections.The Holocene environment is dominated by dry herbaceous formations. Human activities impact on the environment is visible through (1) local water network changes, (2) lead metallurgy activity and (3) agro-pastoral practices.

Les karsts sont l'une des formations aquifères les plus présentes au monde. Exploités, ils fournissent de l'eau potable pour près de 25% de la population mondiale. Cependant la forte hétérogénéité de leur structure implique un comportement non-linéaire et les rendent particulièrement difficiles à étudier, à simuler et à prévoir. Les réseaux de neurones formels sont des modèles d'apprentissage statistiques qui ont été largement utilisés en hydrologie de surface depuis les années 1990, grâce à leurs propriétés de parcimonie et d'approximation universelle.Dans cette thèse, il est proposé d'utiliser les réseaux de neurones pour étudier le comportement des aquifères karstiques. L'aquifère du Lez est choisi pour appliquer le modèle par réseaux de neurones. Cet aquifère, situé près de l'agglomération de Montpellier (400 000 habitant), est exploité pour fournir de l'eau potable à une grande partie de l'agglomération.Dans un premier temps, un réseau de neurones « classique », de type boîte noire, est appliqué à la simulation et à la prévision des débits de la source du Lez. Une méthode de sélection des entrées de pluie est proposée, couplant analyse par corrélations croisées et méthode de validation croisée. Les résultats montrent l'adéquation du modèle neuronal pour la simulation et la prévision du débit de la source d'un aquifère karstique complexe. Le test du modèle est effectué sur les deux cycles hydrologiques comportant les crues les plus intenses de la base de données. Les hydrogrammes montrent que le modèle neuronal a été capable d'extrapoler puisque les débits prévus pour les crues majeures en test sont corrects et supérieurs aux débits présents dans la base d'apprentissage du modèle. La prévision est acceptable jusqu'à un horizon de prévision de un jour. Dans un second temps, une méthode d'extraction des données contenues dans la boîte noire est proposée. Afin de contraindre le modèle neuronal à donner des valeurs physiquement interprétables, des connaissances a priori sur la géologie de l'aquifère sont incluses dans l'architecture du réseau de neurones. La méthode KnoX (Knowledge eXtraction) proposée dans cette étude permet d'extraire du modèle les contributions des différentes zones géologiques à la source du lez ainsi que les temps de réponse correspondants. L'application de la méthode KnoX a un hydrosystème fictif dont on contrôle en particulier les temps de réponse et les contributions des différents sous-hydrosystèmes fictifs a permis de valider cette méthode. Les résultats obtenus sur le bassin du Lez sont très satisfaisants et en adéquation avec les connaissances actuelles que l'on a sur ce système. De plus la méthode a permis d'affiner ces connaissances, notamment l'infiltration retardée par des aquifères perchés et concernant la limite du bassin d'alimentation de la source du Lez. Enfin, la méthode KnoX est générique et applicable à tout hydrosystème pour lequel on dispose de mesures de pluie et de débit. / Karst is one of the most widespread aquifer formations in the worlds. Their exploitation provides fresh water to practically 25% of the global population. The high level of structure heterogeneity in these aquifers however makes them complex and their behavior is difficult to study, simulate and forecast.Artificial neural networks are machine learning models widely used in surface hydrology since the 90's thanks to their properties of parsimony and universal approximation.In this thesis, artificial neural networks are used to study karst aquifer behavior. Application is done in the Lez. This aquifer situated near Montpellier conurbation (400 000 inhabitants) provides fresh water for a large part of this population.First, a “classical” black box neural network is applied to simulate and forecast Lez spring discharge. A rainfall input selection method is proposed, using cross correlation analysis and cross validation method at the same time. Results show neural model efficiency in order to simulate and forecast the spring discharge of a complex karstic aquifer. The model was tested using two hydrologic cycles including the two most intense floods of the database. Hydrographs shows that neural model was able to extrapolate the maximum flood discharge of the learning database. Forecasting is satisfactory until a one-day horizon.In a second time, extraction of the knowledge data included in the black box is proposed. In order to constrain the model to give physically plausible solution, a priori knowledge about aquifer geology is included into the network architecture. KnoX (Knowledge eXtraction) method proposed in this study aims at extract geological zone contributions to the Lez spring and corresponding response times. The KnoX methodology was applied to a fictitious hydrosystem built using a model with controlled parameters, in particular contributions of subbasin to the outlet and lag time of each subbasin. This application permitted to validate the KnoX methodology. Results obtained on the Lez basin are satisfactory and agree with current knowledge about this hydrosystem. In addition, the KnoX methodology allows to refine this knowledge, in particular concerning delayed infiltration because of infiltration in perched aquifer and concerning Lez spring alimentation basin boundaries. Lastly the KnoX methodology is a generic methodology that can be applied on any basin with available discharge and rainfall data.

No description available.

Banana holes are a common karst feature of The Bahamas and several theories have been presented to explain their origin. The current model for banana hole formation places their dissolution at the mixing zone at the top of the fresh water lens. This theory is based on the observation that banana holes are often found in the interior of islands, far from the dissolutionally aggressive fresh water lens margin. This study proposes that banana holes form at the lens margin as it follows a prograding strandplain. Spatial observations show that banana holes appear to be associated with low inland ridges and their orientation appears to correlate with features found on modern shorelines. Bedding features such as herringbone cross beds and back-beach rubble found in banana hole wall rock point to a progradational environment of deposition for banana hole host rock.

Groundwater is a very important resource since water volumes stored underground are much larger compared with those located at the surface, such as rivers and lakes. Aquifers supply a high percentage of freshwater for human consumption as well as supplying economic activities like industry, agriculture, and livestock production. Among them, karst aquifers stand out due to their special hydrologic characteristics and behaviour. In karst aquifers, infiltration occurs faster in comparison with unconsolidated aquifers, due to high permeability features at the surface like dolines, karren, epikarst, and swallow holes that allow precipitating water to recharge the aquifer at higher rates. Nevertheless, these characteristics also increase the aquifer’s susceptibility to being affected by pollution generated by anthropogenic practices. With a low natural pollutant degradation capacity, karst systems mostly experience problems related with water quality rather than water quantity. At present, this represents a significant challenge because a high percentage of the world population is settled on karst areas and is solely dependent upon karst aquifers to fulfil their necessary water supply. A good example to represent this case is the Yucatan Peninsula. The Peninsula is a transboundary limestone platform, covering parts of Mexico, Belize, and Guatemala, whose characteristics do not allow surface streams to generate. Therefore, the karstic aquifer provides water for nearly 4.5 million inhabitants within Mexican territory; this estimation excludes water volumes used for economic activities. The anthropogenic impacts over this karst aquifer have generated problems for water intended for human consumption, furthered by weak environmental regulations that allow the disposal of wastewater without adequate treatment. In the Mexican state of Yucatan, roughly 10% of the population has access to public sewer services where wastewater is treated. Additionally, the use of fertilizers and pesticides is not regulated in agricultural areas, while pig farming is an increasing activity, which fails to keep the necessary standards for the proper disposal of pig slurry. Similar situations can be found around the world, thus the development of plans and strategies to preserve karst groundwater quality that aim to find a balance between resource protection and regional development is increasingly necessary. One important tool emerged to support decisions regarding groundwater protection: the groundwater vulnerability concept. However, due to the hydrologic differences among detritus and karst aquifers, the vulnerability concept, which was first promoted for the former aquifer type, necessitated the development of a specialized vulnerability method to consider the natural characteristics of karst landscapes. Nevertheless, due to the high heterogeneity and anisotropy present in karst systems several methodologies to estimate karst groundwater vulnerability have arisen. Current methodologies are theoretical approximations to differentiate areas where an assumed pollutant particle, released at the surface, is more likely to reach the aquifer due to the natural characteristics of the area. These methods have shown themselves to be useful in defining protection areas and in highlighting regions in which further studies can be performed. However, the high subjectivity and exclusion of anthropogenic influences as part of the analysis is a drawback for these methods. In order to estimate karst groundwater vulnerability for current and future scenarios, an integrated approach is highly necessary. Since most of the methods focus solely on the travel time of a theoretical pollutant from the surface towards groundwater or to a spring, inclusion of pollutants residence time and concentration as parameters to estimate vulnerability is of the uttermost importance. To reach this goal, it is necessary to investigate current intrinsic-based methods in terms of their applicability and regional congruence in order to highlight advantages and probable misclassifications among them and to propose improvements. Pollutant residence time and concentration can be estimated from modelling, which can highlight areas where pollution can represent a problem due to anthropogenic practices, such as wastewater disposal and water extraction fields influencing groundwater flow. Other problems to be contemplated are the data availability and the variable processes by which areas are classified as vulnerable or not. Evaluation of multiple criteria to define degrees of vulnerability is complicated, since several factors, such as subjectivity, data quality, scale, and regional conditions, will always be present. This work presents the results from the application of eight karst groundwater vulnerability methods to the Yucatan karst and outcomes from solute transport. Important considerations are explained in order to improve the workflow for intrinsic groundwater vulnerability assessment. Possible parameters, to be included as part of vulnerability analysis, are evaluated by modelling, demonstrating the importance of anthropogenic impacts for current vulnerability scenarios. Results obtained in this research are displayed as the basis for an Integrated Karst Aquifer Vulnerability (IKAV) method proposed as an alternative for vulnerability studies.

Rota Island, the southernmost island in the Commonwealth of the Northern Mariana Islands in the western Pacific, has the types of caves previously documented on the other limestone mantled islands in the Mariana Arc that have been investigated for caves: Aguijan, Guam, Tinian and Saipan. Caves developed at the edge of the fresh-water lens by zones of enhanced carbonate dissolution produced by fresh-water/salt-water mixing are most common. Among these mixing zone caves, flank margin caves dominate. Flank margin caves were found singly and in extensive horizons representing significant sea-level still stands. However, another type of mixing zone cave was found on Rota in numbers not documented on neighboring islands. Mixing zone fracture caves, apparently formed as zones of enhanced dissolution, produced fresh-water discharging from the lens along fractures, migrated vertically as sea-level changed. Some mixing zone fracture caves on Rota are developed in clusters from two to four caves. The mixing zone caves of Rota reflect the interaction of eogenetic limestone, glacioeustasy, local tectonics and enhanced carbonate dissolution via mixing of disparate waters. The development of mixing zone caves on Rota is in agreement with the Carbonate Island Karst Model (CIKM). Rota has a few caves developed along the contact between limestone and the insoluble volcanic rock that makes up the core of the island. The most important of these is Water Cave, a large spring that is the source for most of the municipal water on Rota. Rota also two extensive zones of vertical fissures developed along bedrock fractures; Fissure City and As Mundo Fissure Zone. In addition, Rota has one cave apparently developed along a fault; Gagani Cave. Some of the caves documented on Rota are difficult to classify and warrant further investigation.

Abaco Island is located on Little Bahama Bank at the northwestern extent of the Bahamian Archipelago. Karst features on Abaco include: flank margin caves, karren, blue holes, pit caves, banana holes, and cone karst. As part of this study all known flank margin caves on Abaco were GPS located and surveyed. The presence and locations of the other karst features were recorded as part of the karst inventory of Abaco. The cone karst is of particular interest because cone karst has not been documented on other Bahamian islands. These cones form from the dissection of an eolianite ridge due to karst, fire, and vegetative processes. Tafoni-like recesses, originally believed to be high flank margin caves, were formed during cliffing of an eolianite ridge during the OIS 5e highstand. The geologic evolution of representative depositional sequences on Abaco fits within the accepted Bahamian stratigraphy.

Eight dissolution caves from the Helderberg Plateau in Schoharie County, New York were studied to investigate unusual sediment packages previously interpreted to be deposits laid down during stagnant ice-cover conditions of the Wisconsin glaciation. The sediment package, consisting of white finely laminated silts and clays are overlain by coarse gravels, in turn overlain by dark silts and clays. Analysis of 63 sediment samples was inconclusive in terms of organic content, but indicated a higher degree of fine-grained calcite material in the white clays than in the overlying units. The caves with the white clays exist only within the footprint of Glacial Lake Schoharie, with lower elevation caves containing a thicker white clay sequence, a measure of the duration of lake cover. The sediment sequence represents glacial rock flour formed under stagnant lake conditions, overlain by outwash deposits emplaced during lake termination, and more recent sediment from soil-loss deposition.