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Zwahlen, François

Nom
Zwahlen, François
Affiliation principale
Fonction
Professeur.e émérite
Email
francois.zwahlen@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/147

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  • Publication
    Métadonnées seulement
    Percolation and Particle Transport in the Unsaturated Zone of a Karst Aquifer
    (2009)
    Pronk, Michiel 
    ;
    Goldscheider, Nico
    ;
    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 mu m) 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.
  • Publication
    Métadonnées seulement
    Karst groundwater protection: First application of a Pan-European Approach to vulnerability, hazard and risk mapping in the Sierra de Libar (Southern Spain)
    (2006)
    Andreo, Bartolomé
    ;
    Goldscheider, Nico
    ;
    Vadillo, Iñaki
    ;
    Vias, Jesús María
    ;
    Neukum, Christoph
    ;
    Sinreich, Michael
    ;
    Jimenez, Pablo
    ;
    Brechenmacher, Julia
    ;
    Carrasco, Francisco
    ;
    Hotzl, 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 Libar, 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 coliforrns 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 Libar was thus created by overlaying the hazard and vulnerability maps. (C) 2005 Elsevier B.V. All rights reserved.