Interpretation of Geometric Elements of the Fahs Aquifer System, Northeast Tunisia: Joint Use of Vertical Electrical Sou
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Original Paper
Interpretation of Geometric Elements of the Fahs Aquifer System, Northeast Tunisia: Joint Use of Vertical Electrical Sounding Data, Well Logs and Satellite Imagery M. F. Hezzi,1,2,3,6 R. Guellala,1,2 A. Hamed Ferjani,1,2 Y. Ferchichi,4 A. Merzoughi,5 and M. H. Inoubli1 Received 19 March 2020; accepted 29 August 2020
In this study, the characterization of the Fahs aquifer system (northeastern Tunisia) was achieved using data from 13 water boreholes, 70 vertical electrical soundings (VES) and a Landsat TM image. Available lithological columns and their corresponding well logs were compared to define precisely the Quaternary water reservoirs. Qualitative and quantitative interpretations of VES data were carried out to reconstitute the geometry of these reservoirs. They were supported by satellite imagery processing, which allowed identification of superficial lineaments affecting the Fahs plain. The restitution of lithological columns using well logs revealed that the Quaternary series contains three lithological units: two clayey units separated by a gravel and sand unit encompassing some clayey intercalations that increase northward (toward the oued El Kebir downstream). Moreover, it was recognized that, in the southern part of the plain at 22–128 m depth, the substratum of the Quaternary series consists of Cretaceous marls and limestones. This zone, which exhibits high apparent resistivities (45–100 X m) for different AB spacings, appears to be rich in reservoirs. The correlation between the restored lithological columns and the interpreted VES, in the form of geo-electrical cross sections, revealed variations in depth (8–50 m), thickness (14 to > 80 m) and resistivity (12–35 X m) of the coarse unit corresponding to the Fahs aquifer. Seven discontinuities were discerned from these sections, whereas 16 superficial lineaments were determined from the Landsat image. Their joint superposition showed that five of them coincided perfectly; they may correspond to normal faults generating an aquifer system compartmentalized in raised and sunken blocks. KEY WORDS: Tunisia, Fahs, Aquifer, Well logs, Vertical electrical soundings, Satellite imagery.
INTRODUCTION 1
Unite´ des Recherches de Ge´ophysique Applique´e aux Mate´riaux et Minerais, Faculte´ des Sciences de Tunis, Tunis, Tunisia. 2 Laboratoire de Ge´oressources, CERTE, Technopole de BorjCedria, Tunis, Tunisia. 3 De´partement de Ge´ologie, Faculte´ des Sciences de Bizerte, Bizerte, Tunisia. 4 Ge´ne´rale Ge´osciences Services, Ariana, Tunisia. 5 Commissariat Re´gional de De´veloppement Agricole de Zaghouan, Zaghouan, Tunisia. 6 To whom correspondence should be addressed; e-mail: [email protected]
Hydrogeological investigations are often thwarted by limited knowledge of an aquiferÕs geometry. This problem can be resolved successfully by implanting numerous well-spaced boreholes covering the entire aquifer system, but it is impractical given the expensive cost of drilling. The use of methods for remote data capture, such as electrical geophysics and
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