SOURCES SOUS-MARINES ET AQUIFERES KARSTIQUES CÔTIERS MEDITERRANEENS. FONCTIONNEMENT ET CARACTERISATION

Abstract : The main goal of the present work was to shed a new light in both coastal karst aquifer resource exploitation and management. Based on previous research, the first part of this study aimed at studying and describing relationships between sea and these karsts: e.g. phenomenon of seawater encroachment and brackish or freshwater submarine springs. There is, however, a lack of valuable data in those studies. By the way, there is a crucial need for research in this area since actual data are not sufficient to fully understand the functioning of karsts aquifers open on the sea. Three particular coastal karst systems with submarine outlet were thus studied. There are all along the Mediterranean coast. The first system is the system of "la Mortola" in Italy and France, the second is the system of Moraig-Toix in Spain and the last one is the system of Thau in France. Firstly an analysis of the recharge area, of the karst structure and of the characteristics of the aquifer was undertaken. This allowed characterising the kind of sea-aquifer connections, which is fundamental to understand relationships between the freshwater and the seawater. Secondly, a survey of the three systems hydrological functioning was undertaken over a hydrological year. In this context, the flow rate or water head and temperature and conductivity were then measured. Rainfall data on the recharge area were collected as well. Those data allowed in each system a modelling of the flow rate and the salinity relationship at the spring. The present study exhibited that the functioning of the aquifers varied as a function of the development of the karst network. For the Mortola system, the karst little is functional, flow rates are limited and water is always fresh. Concerning Moraig-Toix karst, it is well developed in depth. Moreover, it is open on the sea in several places and a strong inflow of seawater could be evidenced. Flow rate are huge and water is brackish all year long at this place. At last, though well developed, Thau karst system is partially isolated from the sea. The whole year, water is found to be relatively fresh, and flow rate high. This results exhibit that karsts occurring in the Mediterranean area, mainly developed during the messinian salinity crisis. The latter was, indeed, responsible of a great karstification potential in this region. This work showed, for the first time that coastal karst system functioning is linked to the structure of the aquifer and to the various types of connections to the sea. A three-category classification of coastal karst aquifers has been proposed. Depending on the karst system, different technical solutions are then proposed by either (i) sampling of the freshwater with no risk of aquifer contamination by seawater or (ii) preventing seawater inflow which could transform brackish water into freshwater.
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  • HAL Id : tel-00789234, version 1

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Perrine Fleury. SOURCES SOUS-MARINES ET AQUIFERES KARSTIQUES CÔTIERS MEDITERRANEENS. FONCTIONNEMENT ET CARACTERISATION. Sciences de l'environnement. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00789234⟩

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