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Zwahlen, François
Résultat de la recherche
Percolation and Particle Transport in the Unsaturated Zone of a Karst Aquifer
2008, Pronk, Michiel, Goldscheider, Nicola, Zopfi, Jakob, Zwahlen, François
Recharge and contamination of karst aquifers often occur via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles, and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide, and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer), and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 μm) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.
Karst groundwater protection: First application of a Pan-European Approach to vulnerability, hazard and risk mapping in the Sierra de Líbar (Southern Spain)
2006, Andreo, Bartolomé, Goldscheider, Nicola, Vadillo, Iñaki, Vías, Jesús María, Neukum, Christoph, Sinreich, Michael, Jiménez, Pablo, Brechenmacher, Julia, Carrasco, Francisco, Hötzl, Heinz, Perles, María Jesús, Zwahlen, François
The European COST action 620 proposed a comprehensive approach to karst groundwater protection, comprising methods of intrinsic and specific vulnerability mapping, validation of vulnerability maps, hazard and risk mapping. This paper presents the first application of all components of this Pan-European Approach to the Sierra de Líbar, a karst hydrogeology system in Andalusia, Spain. The intrinsic vulnerability maps take into account the hydrogeological characteristics of the area but are independent from specific contaminant properties. Two specific vulnerability maps were prepared for faecal coliforms and BTEX. These maps take into account the specific properties of these two groups of contaminants and their interaction with the karst hydrogeological system. The vulnerability assessment was validated by means of tracing tests, hydrological, hydrochemical and isotope methods. The hazard map shows the localization of potential contamination sources resulting from human activities, and evaluates those according to their dangerousness. The risk of groundwater contamination depends on the hazards and the vulnerability of the aquifer system. The risk map for the Sierra de Líbar was thus created by overlaying the hazard and vulnerability maps.
Main concepts of the "European approach" to karst-groundwater-vulnerability assessment and mapping
2002, Daly, D., Dassargues A., Drew, D., Dunne, S., Goldscheider, Nicola, Neale, S., Popescu, I., Zwahlen, François
Pour atteindre, au niveau européen, une certaine cohérence dans l'établissement de cartes de vulnérabilité des eaux souterraines, une approche originale est proposée par le Groupe de Travail 1 de l'Action européenne COST 620 "Cartographie de la vulnérabilité pour la protection des aquifères carbonatés (karstiques)". La procédure générale présentée ici est très flexible afin de permettre des applications dans tout un continent, pour différentes conditions géologiques, à des échelles variables, et à l'aide de données et de ressources diverses.
La méthodologie proposée est conçue pour être plus compatible avec la physique des processus que ne le sont les méthodes existantes de cartographie de la vulnérabilité. Elle tient compte des spécificités des milieux karstiques sans pour autant exclure son applicabilité dans d'autres contextes géologiques. Des facteurs principaux tenant compte des couches supérieures et de la concentration des flux d'infiltration permettent de tenir compte du degré relatif de protection des eaux souterraines en tenant compte de toutes les infiltrations préférentielles possibles qui évitent les couches supérieures protectrices.
Un facteur dit précipitation est distingué pour décrire les caractéristiques de l'entrée d'eau dans le système. Une différence est faite entre les cartes de vulnérabilité intrinsèque des ressources en eaux souterraines et les cartes de vulnérabilité intrinsèque relatives à une source ou émergence. Pour ce dernier type de cartes, un paramètre décrivant le développement du réseau karstique est pris en compte. Cette note technique succincte décrit le premier pas de la démarche du Groupe de Travail 1 de l'Action COST 620. Des étapes suivantes concernant une quantification plus précise des paramètres et l'application pratique sur différentes zones pilotes européennes sont maintenant en cours de réalisation., In order to achieve some consistency in the establishment of groundwater intrinsic vulnerability maps in Europe, a new approach is proposed by Working Group 1 of the European COST Action 620 on "Vulnerability mapping for the protection of carbonate (karst) aquifers". A general procedure is offered which provides consistency while allowing the required flexibility for application to a continent and under conditions of varying geology, scale, information availability, time, and resources.
The proposed methodology is designed to be clearly more physically based than the existing vulnerability-mapping techniques. It takes the specificity of the karstic environments into account without necessarily excluding the applicability to other geological conditions. Combined "core factors" for overlying layers and for concentration of flow account for the relative protection of groundwater from contamination while taking into account any bypass of the overlying layers.
A precipitation factor is distinguished for describing characteristics of the input of water to the system. Differentiation is made between groundwater resource intrinsic vulnerability mapping and source intrinsic vulnerability mapping. For the latter, a factor describing the karst network development is relevant. This short technical note describes a first step in the work program of Working Group 1 of the COST Action 620. Future steps are now in progress to quantify the approach and to apply it in various European pilot areas., El Grupo de Trabajo 1 de la Acción Europea COST 620, dedicado a la confección de una "Cartografía de la vulnerabilidad para la protección de acuíferos carbonatados (kársticos)", ha propuesto un nuevo enfoque orientado a lograr más coherencia en el establecimiento de mapas de vulnerabilidad intrínseca de las aguas subterráneas en Europa. Se ofrece un procedimiento genérico que proporciona coherencia a la par que permite la flexibilidad suficiente para su aplicación en un continente y en condiciones variables de geología, escala, disponibilidad de información, tiempo y recursos.
La metodología propuesta se basa más en los fundamentos físicos del problema que las técnicas existentes de cartografía de la vulnerabilidad. Se considera la especificidad de los medios kársticos, sin excluir necesariamente su aplicabilidad a condiciones geológicas distintas. Se combina "factores fundamentales" de las capas superiores y de la concentración del flujo para tener en cuenta la protección relativa de las aguas subterráneas frente a la contaminación, incluyendo potenciales vías de flujo preferencial.
El método utiliza un factor de precipitación para describir las características del agua de entrada al sistema. Se diferencia entre cartografía de vulnerabilidad intrínseca de los recursos subterráneos y cartografía de la vulnerabilidad intrínseca de la fuente. En relación con ésta, hay un factor esencial que describe el desarrollo de la red kárstica. Esta breve nota técnica describe la primera fase de la labor del Grupo de Trabajo 1 de la Acción COST 620. Actualmente, se está desarrollando las fases siguientes con el fin de evaluar el enfoque y aplicarlo en distintas áreas piloto de Europa.