3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics.

Pondthai, Potpreecha, Everett, Mark E., Micallef, Aaron , Weymer, Bradley A. , Faghih, Zahra, Haroon, Amir and Jegen, Marion (2020) 3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics. Open Access Water, 12 (6). Art.Nr. 1566. DOI 10.3390/w12061566.

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Abstract

Electromagnetic (EM) geophysical methods are well equipped to distinguish electrical resistivity contrasts between freshwater-saturated and seawater-saturated formations. Beneath the semi-arid, rapidly urbanizing island of Malta, offshore groundwater is an important potential resource but it is not known whether the regional mean sea-level aquifer (MSLA) extends offshore. To address this uncertainty, land-based alongshore and across-shore time-domain electromagnetic (TDEM) responses were acquired with the G-TEM instrument (Geonics Ltd., Mississauga, ON, Canada) and used to map the onshore structure of the aquifer. 1-D inversion results suggest that the onshore freshwater aquifer resides at 4–24 m depth, underlain by seawater-saturated formations. The freshwater aquifer thickens with distance from the coastline. We present 2D and 3D electromagnetic forward modeling based on finite-element (FE) analysis to further constrain the subsurface geometry of the onshore freshwater body. We interpret the high resistivity zones that as brackish water-saturated bodies are associated with the mean sea-level aquifer. Generally, time-domain electromagnetic (TDEM) results provide valuable onshore hydrogeological information, which can be augmented with marine and coastal transition-zone measurements to assess potential hydraulic continuity of terrestrial aquifers extending offshore.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/H2020/677898
Keywords: coastal hydro-geophysics; groundwater; mean sea-level aquifer; transient electromagnetics
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: Yes
Publisher: MDPI
Projects: MARCAN, SMART
Date Deposited: 03 Jul 2020 07:52
Last Modified: 08 Feb 2023 09:28
URI: https://oceanrep.geomar.de/id/eprint/50049

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