Variability of groundwater flow and transport processes in karst under different hydrologic conditions (original) (raw)
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Karst groundwater: a challenge for new resources
Hydrogeology Journal, 2005
Karst aquifers have complex and original characteristics which make them very different from other aquifers: high heterogeneity created and organised by groundwater flow; large voids, high flow velocities up to several hundreds of m/h, high flow rate springs up to some tens of m 3 /s. Different conceptual models, known from the literature, attempt to take into account all these particularities. The study methods used in classical hydrogeology-bore hole, pumping test and distributed models-are generally invalid and unsuccessful in karst aquifers, because the results cannot be extended to the whole aquifer nor to some parts, as is done in non-karst aquifers. Presently, karst hydrogeologists use a specific investigation methodology (described here), which is comparable to that used in surface hydrology. Important points remain unsolved. Some of them are related to fundamental aspects such as the void structureonly a conduit network, or a conduit network plus a porous matrix-, the functioning-threshold effects and nonlinearities-, the modeling of the functioning-double or triple porosity, or viscous flow in conduits-and of karst genesis. Some other points deal with practical aspects, such as the assessment of aquifer storage capacity or vulnerability, or the prediction of the location of highly productive zones.
Chapter 4 Overview of Methods Applied in Karst Hydrogeology
2015
Karst aquifers have a different hydraulic structure and behavior than porous media and therefore require specific investigation methods (Goldscheider and Drew 2007). As discussed in Chap. 3, they are characterized by a high degree of heterogeneity and discontinuity, resulting in a duality of recharge, infiltration, porosity, flow, and storage (Bakalowicz 2005; Ford and Williams 2007). Recharge either originates from the karst area itself (autogenic) or from adjacent non-karst areas that drain toward the karst aquifer (allogenic). Infiltration occurs diffusely through soil and epikarst or concentrated via dolines or swallow holes. Karst aquifers show double or triple porosity, consisting of intergranular pores and fractures (often summarized as matrix porosity), and solutional conduits. Flow in the network of conduits and caves is often rapid and turbulent, while flow in the matrix is generally slower and laminar (Fig. 4.1). Storage occurs in the matrix and conduits, but residence ti...
Hydraulic Behavior of Karst Aquifers
Water
The objective of this Special Issue, “Hydraulic Behavior of Karst Aquifers”, is to focus on recent advances in karst hydrogeology in different areas of the world, focusing on topics dealing with the peculiar characteristics of karst aquifers. In particular, thirteen peer-reviewed articles were collected, focusing on hydraulic aspects and their relationship with geological features, geochemical and bacteriological aspects, tunneling and engineering mining inrush, and forecasting water resources and drought occurrences. Overall, these contributions describe several aspects of karst aquifers and are of great value for water resource management and protection.
Environmental Earth Sciences, 2010
As it is expected that global warming will induce changes in hydrological regimes, the presented study has been conducted to understand how karst groundwater resources may be affected during long-term dry periods. A multi-tracer test with three injection points aimed at identifying the dynamics of underground drainage through a well-developed system of karst channels and through vadose zone. Results show low apparent dominant flow velocities (through well developed karst conduits between 5.9 and 22.8 m/h, through vadose zone 3.6 m/h), multiple peaked and extended breakthrough curves. These findings are relevant for groundwater quality monitoring, protection and management, as they infer that contaminant transport in karst, at least in the studied area, may be retarded and long-lasting.
Preface: Five decades of advances in karst hydrogeology
Hydrogeology Journal, 2021
Carbonate rocks have a worldwide distribution. Karst groundwater has been an essential resource for humanity since the establishment of civilization in the karstified areas of the Middle East and Mediterranean. Goldscheider et al. (2020) estimated that 15.2% of Earth’s continental surface is covered by karst aquifers, with 1.18 billion people (16.5% of the global population) living on karst areas. Karst aquifers supply drinking water to approximately 10% of the world’s population (Stevanović 2019). Interest in the intriguing nature of groundwater flow in karst has led to early scientific debates since the beginning of the twentieth century (Grund 1903; Katzer 1909; Martel 1910; Cvijić 1918). Exploring and explaining karst and its groundwater have always been challenging tasks, because of its inherent specificities: karst aquifer anisotropy and heterogeneity, mechanisms of recharge and their intensity, role of epikarst and soil cover, prevalence of turbulent regime rather than lamina...
Research frontiers and practical challenges in karst hydrogeology
Acta Carsologica, 2010
Besides t�e possible future impacts of climate c�ange, t�ere are many ot�er urgent groundwater-related environmental problems. Accessibility to safe drinking water in sufficient quantities for �uman needs is t�reatened by different types of contamination, overexploitation, saltwater intrusions, and inappropriate irrigation practices. Soil erosion, natural disasters, and t�e protection of ecosystems and biodiversity are ot�er important water-related issues. These problems exist today, but will get worse in many regions according to t�e current climate c�ange scenarios. All of t�ese issues are interrelated and are especially relevant in karst areas. For example, deforestation leads to ecosystem degradation and a loss of biodiversity, but also promotes soil erosion (Fig. 1), w�ic� increases t�e vulnerability of groundwater resources to contamination, alters rec�arge processes and reduces t�e water storage and buffering capacity of t�e �ydrogeologic system, t�us posing a t�reat to quality and quantity of drinking water and ultimately to public �ealt�. Furt�ermore, t�e degradation of soil and vegetation also releases CO 2 and reduces t�e efficiency of karst processes as a natural sink of t�is green�ouse gas (Liu & Z�ao 2000). Finding solutions to all of t�ese problems requires a multidisciplinary approac�, to w�ic� karst and groundwater researc�ers could and s�ould contribute more t�an t�ey currently do.
Role of karstification and rainfall in the behavior of a heterogeneous karst system
Environmental Geology, 1997
The complex functioning of karst systems depends on several factors (e.g., geology, karstification status, climate) which influence flow conditions. Understanding a system requires monitoring that includes a sampling interval well adapted to the system's size, and the use of hydrodynamic and geochemical approaches. From our own observations, the general physical and geochemical characteristics of the aquifers are perennial and representative of karst evolution at a given moment. The Notre-Dame-des-Anges karst system, which is situated in France on the rim of the Vaucluse karst region, was studied during 2 water years. This study demonstrates that several parameters are not definitive, and that they do not provide information about the actual status of the karst evolution of the system. We were able to observe that hydrological parameters in particular are dependent on the configuration of the outlets, which can dramatically change. For example, a heavy storm (300 mm of rain in 4 h), which occurred in the intake area on 22 September 1992, produced a piston effect in the aquifer, which was expressed by extensive unclogging of the whole aquifer. The appearance of a new gryphon at the outlet induced a change in the flow rate and added to the unclogging. The other major result of this study is the demonstration of intensive, even preponderant, participation of water originating in the infiltration zone in the behavior of the system. This contribution, often minimized in previous studies, is closely dependent upon flow conditions and especially upon the recharge status of the infiltration zone. Physical and chemical parameters allowed us to trace this water, and to demonstrate the existence of an actual hanging reserve which plays not a negligible part in flow, during both high and low water levels. This paper demonstrates the necessity of coupling a hydrodynamic study with a hydrochemical approach, and of questioning the representativeness of parameters during a given period, for a better understanding of the functioning of the karst system. This is especially true if the infiltration zone of the karst system is heavily developed, and if external factors (e.g., river, landslip, clogging) influence the outlet
Hydrogeological Investigation of a Karst Aquifer System
Environmental Processes, 2017
This study aims to present the hydrogeological and hydrochemical characteristics of Paradisos Karst aquifer system (PAS), Northeast Greece. The average area of the PAS is estimated according to Thornthwaite and Mather (1957) (T-M) procedure at 74.2 km 2. The karst system, which is largely fault-controlled, discharges through three permanent karst springs: KS15, KS20 and KS21. The average discharge rate was calculated for two of them at 0.726 m 3 /s. The time series analysis shows that: (a) the memory effect for the PAS is extremely high; and (b) the karst system is a poorly developed with high storage capacity and absence of a quick flow component. The chemical type for the majority of the groundwater samples is of Ca-HCO 3 type. The chemical properties of the groundwaters are strongly influenced by alkaline earth metals and weak acids. The presence (sporadically) of high NH 4 + content and slightly increased nitrate, ammonium and phosphate values in springs KS20 and KS21 is attributed to the presence of anthropogenic sources, especially septic tanks and agriculture. All studied groundwaters are oversaturated in calcite and aragonite, which suggests a mechanism of diffuse flow. The morphology and geology of the PAS catchment area, and data from hydrographs and chemographs, show that the hydrologic system is dominantly of diffuse flow. The use of time series analysis combined with classic hydrogeological techniques (i.e., degree of karstification, T-M procedure, chemographs and
GROUNDWATER PROTECTION IN KARST ENVIRONMENT
Protection of karstic groundwater quality can be successful only if it is based on reliable reconstructions of conceptual models of the karstic aquifers, which are normally of high complexity: this requires the integration of classical hydrogeological information with that obtainable by using natural tracers, according to multi-tracing methods. The definition of the conceptual model includes elements as the identification of recharge areas, their connection with discharge areas, the sequence of physical -chemical processes acting into the aquifer and the transport mechanisms. With reference to the identification of recharge areas, two casestudies are illustrated. The first deals with a continental karstic aquifer (Monti Simbruini, Central Italy) discharging through springs used for drinking purposes: it has been studied by using the stable deuterium and oxygen-18 isotopes according to the "mass-center" method coupled with the "inverse hydrogeological budget" method. The second regards a platform karstic aquifer (Murgia, Southern Italy), discharging through coastal brackish springs, which is exploited by wells for both drinking and agricultural purposes: for recognizing some elements of the conceptual model a multi-tracing approach has been adopted, which uses the crossverification of information coming from the interpretation of isotopic, chemical and physical tracers. Moreover, with the aim of outlining the factors that control the pollutant transport in karstic aquifers, two case-studies related to Murgia aquifer illustrate a first method for defining the hazard due to direct injection of effluents from treatment plants and a second approach for defining, through monitoring data, the transport mechanisms of pollutant released at land surface.
Hydrogeology Journal, 2007
In a karst system, the characterization of transport properties is based on the comparison of natural tracers observed at the inlet (a swallow hole on the karst plateau) and the outlets of the system (a spring and a well). At Norville, northwest France, electrical conductivity (EC) and turbidity (T) were used as natural tracers for characterizing dissolved elements (surface water geochemistry) and particulate matter transport, respectively. Two methods were used for this study: (1) a comparison of the relations between EC, T and spring discharge (Q) by means of normalized EC–T–Q curves, and (2) a principal component analysis (PCA) including water geochemistry data in addition to EC, T and Q. Three different characteristic flood events have been chosen for the analyses. EC–T–Q curves highlighted the direct transfer, resuspension and deposition of particles during their transport in the karst network. Transport from the swallow hole to both the spring and the well appeared to be dominated by karst-conduit flow. On the other hand, PCA results showed a diffuse source of contamination of groundwaters by nitrate and a point-source contamination of groundwaters by streaming/runoff surface waters with high turbidity and phosphate concentration infiltrated at the swallow hole. Dans un système karstique, la caractérisation des propriétés de transport est basée sur la comparaison des traceurs naturels observés à l’entrée (une dépression sur le plateau karstique) et à la sortie du système (une source et un puits). A Norville, Nord-Ouest de la France, la conductivité électrique (EC) et la turbidité (T) ont été utilisées comme traceurs naturels pour caractériser les éléments dissous (géochimie des eaux de surface) et le transport des particules en suspension, respectivement. Deux méthodes ont été utilisées dans cette étude: (1) une comparaison des relations entre EC, T et le débit de la source (Q) au moyen de courbes EC–T–Q normalisées, et (2) une analyse en composante principale (ACP) incluant les données géochimiques de l’eau en complément de EC, T et Q. Trois différents évènements de crues caractéristiques ont été choisis pour les analyses. Les courbes EC–T–Q ont mis en évidence le transfert direct, la remise en suspension et le dépôt des particules durant leur transport dans le réseau karstique. Le transport de la dépression vers la source et le puits apparaît comme dominé par l’écoulement en conduit karstique. D’un autre côté, les résultats de l’ACP ont montré une source diffuse de la contamination des eaux souterraines par les nitrates et une contamination ponctuelle des eaux souterraines par des eaux de surface de ruissellement et de cours d’eau présentant une turbidité et une concentration en phosphate élevées, infiltrées dans la dépression. En un sistema kárstico, la caracterización de las propiedades de transporte se basa en la comparación de trazadores naturales observados en la entrada (una sima somera en una superficie kástica) y la salida del sistema (un manantial y un pozo). En Norville, al Noroeste de Francia, la conductividad eléctrica (EC) y la turbidez (T) se usaron como trazadores naturales para caracterizar los elementos disueltos (geoquímica de aguas superficiales) y transporte de material particulado, respectivamente. Para este estudio, fueron utilizados dos métodos: (1) una comparación entre las relaciones de EC, T y descarga del manantial (Q) mediante curvas normalizadas EC–T–Q, y (2) un análisis de componentes principales (PCA) que incluye datos geoquímicos además de EC, T y Q. Para el análisis, se seleccionaron tres eventos de flujo característicos. Las curvas EC–T–Q pusieron de manifiesto la transferencia directa, resuspensión y sedimentación de las partículas durante su transporte en el sistema kárstico. El transporte desde la sima somera al manantial y al pozo parece estar dominado por el flujo por los conductos kársticos. Por otro lado, los resultados de PCA muestran una fuente difusa de contaminación de aguas subterráneas por nitratos y una contaminación puntual de aguas subterráneas por aguas superficiales con alta turbidez y concentraciones de fosfatos infiltradas en la sima somera.