Michel Bakalowicz

Analysis of the karst aquifer structure of the Lamalou area (Herault, France) with ground penetrating radar

The study site at Lamalou karst spring (Hortus karst plateau) is situated 40 km north of Montpellier in France. It consists of a limestone plateau, drained by a karst conduit discharging as a spring. This conduit extends for a few dozen meters in fractured and karstified limestone rocks, 15 to 70 m below the surface. The conduit is accessible from the surface. The main goal of this study is to analyze the surface part of the karst and to highlight the karstic features and among them the conduit, and to test the performances of ground penetrating radar (GPR) in a karstic environment. This method thus appears particularly well adapted to the analysis of the near-surface (<30 m in depth) structure of a karst, especially when clayey coating or soil that absorbs and attenuates the radar is rare and discontinuous. A GPR pulseEKKO 100 (Sensors and Software) was used on the site with a 50-MHz antenna frequency. The results highlight structures characterizing the karstic environment: the epikarst, bedding planes, fractured and karstified zones, compact and massive rock and karrens, a typical karst landform. One of the sections revealed in detail the main conduit located at a depth of 20 m, and made it possible to determine its geometry. This site offers possibilities of validation of the GPR data by giving direct access to the karstic conduits and through two cored boreholes. These direct observations confirm the interpretation of all the GPR sections.

Apports du traçage isotopique naturel a la connaissance du fonctionnement d'un systeme karstique - teneurs en oxygene-18 de trois systemes des Pyrenees, France

Abstract Three karstic systems in the Pyrenees (France) have been subjected to a monthly systematic sampling in view of isotopic analysis of oxygen-18. In addition, a higher frequency sampling in overflow conditions has been made in one of the systems which is also continuously studied as regards hydrodynamics, geochemistry and biology. After analysing the sample representativity, an attempt has been made to find out the meaning of the variations of the contents in oxygen-18 in function of time. In the case of these systems of the Pyrenees, a relation between the altitude of the catchment area and the contents in oxygen-18 of their risings has been established which does not agree with Dansgaards relation. The variations of the isotopic contents in function of the hydrogeologic events confirm the heterogeneity of the submerged zone and the importance of the part played by the percolation, chiefly by considering the connection with the surface saturated zone, named “epikarstic aquifer”. These results, obtained with those of hydrodynamic, geochemical and biological studies of the karst, are not likely to be interpreted without the help of these disciplines.

The World Karst Aquifer Mapping project: concept, mapping procedure and map of Europe

Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.ZusammenfassungKarstgrundwasserleiter leisten in vielen Regionen der Welt einen wichtigen Beitrag zur Wasserversorgung, sind aber aufgrund ihrer hydrogeologischen Eigenschaften besonders verletzlich gegenüber Schadstoffeinträgen und schwierig zu bewirtschaften. Viele Karstsysteme sind über weite Gebiete hydraulisch verbunden und erfordern daher grenzüberschreitende Ansätze zur Erkundung, zum Schutz und zur Bewirtschaftung. Um einen besseren globalen Überblick der Karstaquifere zu erhalten, eine Grundlage für nachhaltiges und internationales Wasserressourcenmanagement zu etablieren und das Bewusstsein in der Öffentlichkeit und bei Entscheidungsträgern zu erhöhen, wurde das Welt-Karstaquifer-Kartierprojekt (WOKAM) ins Leben gerufen. Ziel dieses Projektes ist es, eine Weltkarte und Datenbank der Karstaquifere zu erstellen, als Weiterentwicklung existierender Kartenwerke. Dieser Fachbeitrag präsentiert die grundlegenden Konzepte und die detaillierte Vorgehensweise bei der Kartierung. Am Beispiel von Frankreich wird der Arbeitsablauf Schritt für Schritt illustriert, von der Generalisierung über die Differenzierung von Gebieten mit kontinuierlichen und diskontinuierlichen Carbonatgesteinen bzw. Evaporiten, bis hin zur Identifizierung von tiefen und bedeckten Karstaquiferen. Die Karte zeigt auch ausgewählte Höhlen und Karstquellen, welche in einer assoziierten globalen Datenbank gesammelt werden. Die Karstaquifer-Karte von Europa zeigt, dass 21.6% der Landfläche durch (kontinuierliche oder diskontinuierliche) Carbonatgesteinen charakterisiert sind; anstehende Carbonatgesteine sind auf etwa 13.8% der Fläche anzutreffen.RésuméLes aquifères karstiques contribuent pour une part significative à l’alimentation en eau potable de nombreuses régions du monde, mais ils sont vulnérables à la pollution et sont difficiles à gérer du fait de leurs caractéristiques hydrogéologiques particulières. De nombreux systèmes karstiques présentent des connections hydrauliques sur de vastes étendues et requièrent de ce fait des études, une protection et une gestion transfrontalières. Afin de disposer d’une meilleure vue d’ensemble des aquifères karstiques, de créer une base pour une gestion internationale durable de leurs ressources en eau et de mieux sensibiliser le public et surtout les décideurs, le programme de la Carte Mondiale des Aquifères Karstiques (World Karst Aquifer Mapping, WOKAM) a été réalisé. Son but est de créer une carte et une base de données mondiales des aquifères karstiques, pour améliorer les cartes antérieures. Cet article présente les concepts de base et le détail de la procédure de cartographie, en prenant la France comme exemple pour illustrer la démarche pas à pas, comprenant la généralisation, la différenciation des zones continues et discontinues de carbonates et d’évaporites et l’identification des aquifères karstiques sous couverture. La carte montre également une sélection de cavités et de sources dont les informations ont été rassemblées dans une base de données globale. L’ébauche de la carte des aquifères karstiques d’Europe montre que 21.6% du territoire européen sont caractérisés par la présence de roches carbonatées, continues ou discontinues, et qu’environ 13.8% de la surface sont des affleurements de roches carbonatées.ResumenLos acuíferos kársticos contribuyen sustancialmente al suministro de agua dulce en muchas regiones del mundo, pero son vulnerables a la contaminación y difíciles de manejar debido a sus singulares características hidrogeológicas. Muchos sistemas kársticos están conectados hidráulicamente en grandes áreas y requieren exploración, protección y manejo transfronterizo. Se estableció el proyecto World Karst Aquifer Mapping (WOKAM) con el fin de obtener una mejor visión global de los acuíferos kársticos, crear una base para una gestión internacional sostenible de los recursos hídricos y aumentar la concientización en el público y entre los responsables de la toma de decisiones. El objetivo es crear un mapa mundial y una base de datos de acuíferos kársticos, como un desarrollo adicional de mapas previos. Este trabajo presenta los conceptos básicos y el procedimiento detallado del mapeo, utilizando a Francia como ejemplo para ilustrar el flujo de trabajo paso a paso, que incluye la generalización, la diferenciación de las áreas continuas y discontinuas con rocas carbonatadas y evaporíticas, y la identificación de acuíferos kársticos no expuestos. El mapa también muestra cavernas y manantiales kársticos seleccionados, que se recopilan en una base global de datos asociados. El mapa del acuífero kárstico de Europa muestra que el 21.6% de la superficie europea se caracteriza por la presencia de rocas carbonatadas (continuas o discontinuas); aproximadamente el 13.8% de la superficie es roca carbonatada aflorante.摘要在全世界范围内岩溶含水层提供了重要的淡水资源,但由于独特的水文地质特征,使其极易受到污染且难以开发和管理。许多大型的岩溶含水系统不仅分布范围广,而且其内部水力联系通畅,因此需要跨国界的调查、保护和管理。为了更好地获得对全球范围内岩溶含水层空间分布的认识,为国际水资源可持续性利用创造基础,并且提高公众和决策者对岩溶水资源的认识,国际水文地质学家协会建立了世界岩溶含水层制图项目(WOKAM)。该计划的目标是参考现有文献资料,绘制世界范围内岩溶含水层分布图,并且建立相关的地理信息数据库。本文记述了制图过程所使用的概念和编制步骤,并且以法国及周边地区为例逐步说明了制图流程,重点讨论了怎样界定连续及非连续型碳酸盐岩的空间分布特征,如何显示蒸发岩,如何识别非出露型即覆盖型和埋藏型岩溶含水层等关键问题。除此以外地图上还简要地显示了具有重要区域水文地质意义的洞穴及岩溶泉,更加详细的数据可以参考数据库。世界岩溶含水层分布图欧洲部分样图显示,在欧洲有21.6%的陆地面积具有岩溶水文地质特征,其中碳酸盐岩出露面积大约占13.8%。ResumoAquíferos cársticos contribuem significativamente para a suprimento de água doce em muitas regiões do globo, mas são vulneráveis à contaminação e apresentam dificuldades de gerenciamento devido a características hidrogeológicas peculiares. Muitos sistemas cársticos são hidraulicamente conectados em vastas áreas e requerem exploração, proteção e manejo que ultrapassam limites políticos. O Projeto Mapeamento Global de Aquíferos Cársticos (WOKAM – World Karst Aquifer Mapping Project) foi estabelecido de modo a se obter uma síntese mais abrangente sobre aquíferos cársticos no planeta, assim como para se criar uma base para manejo sustentável de recursos hídricos em âmbito internacional e para aumentar a conscientização tanto do público em geral quanto entre responsáveis por tomadas de decisões. O objetivo é elaborar um mapa mundial e banco de dados sobre aquíferos cársticos tomando como base mapas anteriores. Baseando-se na França como exemplo, este artigo apresenta os conceitos básicos e procedimentos adotados de modo a ilustrar as etapas executadas para a confecção do mapa, que inclui generalização, diferenciação de áreas contínuas e descontínuas de carbonatos e evaporitos e identificação de aquíferos cársticos não expostos superficialmente. O mapa também mostra algumas cavernas e nascentes cársticas, selecionadas a partir de um banco de dados global. Esta versão do mapa de aquíferos cársticos da Europa mostra que 21.6% da superfície europeia caracteriza-se pela presença (sob forma contínua ou descontínua) de rochas carbonáticas e cerca de 13.8% da superfície apresenta afloramentos de carbonatos.

Evidence of karst from behaviour of the Asmari limestone aquifer at the Khersan 3 Dam site, southern Iran

Abstract The Asmari limestone formation is the major aquifer system at the Khersan 3 Dam site, Zagros, Iran. Characterization of the aquifer system and study of karst development are essential for forecasting leakage potential and to plan remediation works. The aquifer functioning and karst structure were evaluated by geology, well hydrodynamics and natural tracing studies, showing one unconfined and three artesian sub-aquifers, the last being characterized by rapid flow, with contributing old recharge water, and a recharge at higher elevation than the unconfined sub-aquifer. The anticline structure outcrops the artesian sub-aquifers downstream of the site. The confining layers disappear and the aquifer system discharges as a mix of all groundwater. Artesian groundwater is estimated to contribute about 80% (dry season) and 50% (wet season) of flow in the mixing zone. Very few karst features are observed in cores and galleries at the site, despite some karst landforms in the reservoir area. However the aquifer exhibits fast flow of karst type in the artesian sub-aquifers.

Management of Karst Groundwater Resources

Karst aquifers are especially difficult to exploit, manage, and protect because of the extreme variability of their hydraulic properties which are almost impossible to determine at a local scale. Moreover, their functioning may be influenced by non-linearities and threshold effects. Considering long-term aquifer exploitation, karst system complexity does not allow for easy behavioral modeling, such as using the classical isochrone method for determining a protection zone. However, because karst aquifers may offer great storage capacity and high local hydraulic conductivity, high flow rates can be pumped from single sites, allowing for effective management of an aquifer. After outlining the main characteristics of karst aquifers, the management of their groundwater is examined from both quantity and quality viewpoints in order to highlight benefits and problems with this resource. Finally, some new avenues of research are proposed.