Groundwater investigation in the southern part of Gabes using resistivity sounding, southern Tunisia

The groundwater hydrogeology of southern Tunisia emphasizes two main groundwater bodies so-called Zeuss-Koutine and south Gabes. These groundwater bodies yielding economically important storage of useful water present complex internal architecture and heterogeneity allowing exchange flows throughout permeable or/and fractured bodies. A geophysical survey using resistivity soundings was carried out along this area to describe in detail the field structure and the 3D extent of these groundwater bodies by the hydrogeological new data and detailed subsurface mapping based on resistivity sounding and seismic data. This survey discusses also the potentialities of some permeable layer in water storage and purposes potential favorable areas for optimum groundwater mining.     

Joint evaluation of gravity, electrical and magnetotelluric methods for geothermal potential of fractured Aptian reefal carbonates in the Hmaima–El Gara area (Oued Serrat basin, Central–Western Tunisia)

Hmaima–El Gara area is located in Central–Western Tunisia and is known as an important geothermal province. In this study, we attempt to delineate the subsurface structures of the area using integrated interpretation of gravity, electrical and magnetotelluric data. The Hmaima thermal aquifer, associated with fractured Aptian reefal limestones, is characterized by high gravity and high resistivity. Horizontal gradient and Euler deconvolution method has been applied to the gravity data and provided fast information about both the depth and trends of the shallower subsurface structures in the area. As several of the mapped lineaments correlate with published geological fault trends, the other lineaments may be indicators of new insights for hydrothermal exploitation in the Hmaima–El Gara area (economical potential favorite zones).     

Évaluation de la qualité de l'eau par application de la méthode géoélectrique : exemple de la plaine d'El Mida–Gabes nord (Sud tunisien)

The Mida plain, which is part of the North Gabès region (southern Tunisia), is characterized by the deep sandy units of the ‘Continental intercalaire’ (CI) or the limestone of the Lower Senonian. A geophysical survey, by electrical sounding (ES), was undertaken in the studied region to better characterize the deep geological structure of this plain and therefore its aquifer resources potential. The analysis of the results shows that the prospected zone is characterized by the succession of several levels with contrasted resistivities, which are often affected by faults. Among these observed geoelectrical levels, the highly conductor one could host a saline aquifer. Another geoelectrical level corresponding to the resistant bedrock detected at Oudhref horst can contain better-quality water than that of the aquifer detected in the El Mida Graben. In this work, we tried to explain the origin of the salinity of this aquifer. Thus, we hypothesise about a contamination from Jebel Zemlet El Beida through a border fault and another one from the Sebkhet El Hamma. To cite this article: A. Mhamdi et al., C. R. Geoscience 338 (2006).     

Hydrogeological characterization of a carbonate aquifer using geophysical and geochemical approach: case of the Krachoua Formation in Tataouine area,Southern Tunisia

An integrated hydrogeological investigation involving geological surface data, well data (lithostratigraphical and piezometric data) and the vertical electrical sounding (VES) method was carried out in Tataouine area, Southern Tunisia to characterize the hydrogeology and the geochemistry of the Krachoua Formation aquifer. The electrical data were used to differentiate lithostratigraphic units and characterize their hydrogeological potentialities. Major elements contents within groundwater samples were assessed and some plots and diagrams have been established in order to investigate the hydrochemical properties of this aquifer and the origin of its mineralization. The Krachoua aquifer exhibits a general drawdown of the piezometric level from 2004 to 2015 reflecting a dramatic decrease in groundwater resources due to increased groundwater abstraction during the last decades. Flow directions shows that the recharge of this aquifer considered as a free aquifer is directly ensured by rainfalls over the outcropping fractured limestones. The geometry of the Krachoua Formation aquifer is tectonically controlled and structured in horst and graben features that impacted greatly the hydrogeology and the hydrodynamics of the area. Subsequent thickness and facies variations within this aquifer influenced the reservoir quality and the groundwater flows. The increased values of salinity to the northwest of the study area seems to be mainly related to the dissolution of the Upper Liassic gypsum of Mestaoua Formation which outcrops widely and can be dissolute easily by meteoric water and contaminate the Krachoua aquifer. This fact is also supported by the sulfated and calci-magnesian chloride facies of this aquifer related to the dissolution of evaporitic rocks (gypsum, anhydrite, and halite). However low salinity values are recorded within the zone where these evaporitic rocks are relatively deep.     

Prospection géoélectrique pour l'étude de l'aquifère thermal des calcaires récifaux, Hmeïma–Boujabeur (Centre ouest de la Tunisie)

The Hmeïma–Boujabeur zone is considered as an important geothermal province for Tunisia. The reef limestone, characterized by intense fracturation and important karstification, confers them the property to be a regional thermal aquifer. A geophysical study based on two complementary geoelectrical methods, the Electrical Sounding (ES) and Magneto-Telluric Sounding (MTS), turned out to be very efficient to provide a complete electrical image of the underground until about 1-km depth. The synthetic approach integrating all data allowed us to delimit the favourable area for thermal water exploitation. To cite this article: M. Gouasmia et al., C. R. Geoscience 338 (2006).