Use of time-domain electromagnetic (TDEM) method to investigate seawater intrusion in the Lebna coastal aquifer of easte
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ORIGINAL PAPER
Use of time-domain electromagnetic (TDEM) method to investigate seawater intrusion in the Lebna coastal aquifer of eastern Cap Bon, Tunisia Amira Ziadi 1 & Najla Tlatli Hariga 1,2 & Jamila Tarhouni 1
Received: 31 March 2017 / Accepted: 26 October 2017 # Saudi Society for Geosciences 2017
Abstract A multi-method geophysical survey, using timedomain electromagnetic (TDEM) fields, is conducted on the north-eastern coastal aquifer of Cap Bon, Tunisia. The aim of the study is to investigate the inland extent saltwater intrusion, to estimate the fresh-saltwater transition zone, and to characterize the lithologic spatial variability of the underground layers. Moreover, the TDEM is used to determine both fluid resistivity and bulk resistivity which are required to calculate the porosity by applying the Archie’s equation. The survey of TDEM profiles is carried out along the left and right overbanks of the Lebna river from the coast until the Lebna dam. The interpretation and the analysis of these profiles allow us to better identify the flux exchanges between the river and the underlying aquifer. On the basis of the 1D and 2D longitudinal and transversal resistivity profiles as well as the existing boreholes data and groundwater quality, it seems that the freshwater-saltwater interface is moving forward inland. Furthermore, electromagnetic results combined to the Archie’s law show that the porosity values are at the ranges of 12–36 and 5–31% for the Quaternary outcropping and Pliocene formation, respectively.
* Amira Ziadi [email protected] Najla Tlatli Hariga [email protected] Jamila Tarhouni [email protected] 1
Laboratory of Research, Sciences and Technologies of Water (LRSTE), National Agronomy Institute-Tunis (INAT), University of Carthage, Tunis, Tunisia
2
Laboratory of mathematical and numerical modeling in the Engineer Sciences (LAMSIN), National Engineering School of Tunis (ENIT), University of Tunis El Manar,, Tunis, Tunisia
Keywords Coastal aquifer . TDEM . Pseudo-section . Resistivity maps . Porosity . Seawater intrusion
Introduction Many coastal aquifers in the world, especially shallow ones, showed an intensive seawater intrusion caused by both natural processes and anthropogenic activities. In the last years, we note a growing interest in the phenomenon of marine invasion, which may extend over several kilometers inland, constituting a significant risk for coastal areas around the world especially those that rely on groundwater for their water supply. To study this problem, it is important to understand how the geological conditions control the flows’ dynamics in the coastal aquifers and how water and chemicals fluxes change the freshwatersaltwater interface (Han et al. 2011). Many researchers using different methods have studied the coastal aquifer behaviors, the environmental effect, the salinization and remediation. In north China (Han et al. 2011), in the southeastern of Tunisia (Trabelsi et al. 2011), in the southeastern of Australia (Currell et al. 2015), they used hydrochemical
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