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.
Highlights
Groundwater resources in many coastal regions worldwide are currently under stress because of increasing population, agricultural demands, tourism and economic growth
These are interpreted as the signature of a brackish water-saturated geological medium, in this case corresponding to the Lower Coralline Limestone (LCL) formation hosting the mean sea-level groundwater body
Based on the preferred 3D time-domain electromagnetic (TDEM) model in Figure 13, the top layer up to 5 m deep is interpreted as the overlaying Globigerina Limestone and there is no geophysical indication of freshwater in this low-resistivity formation
Summary
Groundwater resources in many coastal regions worldwide are currently under stress because of increasing population, agricultural demands, tourism and economic growth. Fresh groundwater in coastal regions may be a resource that can help to mitigate the water scarcity experienced by coastal communities [1]. Several first-order questions need to be addressed before the fresh groundwater can be used sustainably. There is a lack of understanding regarding the location, nature, and geometry of coastal aquifer systems and their offshore connectivity. Large-scale desalination of seawater is a technologically viable solution, but there are important energy and environmental impacts that must be considered [2]. Terrestrial time-domain electromagnetic (TDEM) methods of geophysical exploration employing a loop or grounded dipole source can be used to explore the
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
