Mapping saltwater intrusion via Electromagnetic Induction for planning a Managed Aquifer Recharge facility in Maltese island

Submitted: 15 December 2023
Accepted: 4 March 2024
Published: 28 March 2024
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PDF: 112
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In coastal areas, saltwater intrusion causes a depletion of the resource by reducing potable and irrigation freshwater supplies and causing severe deterioration of groundwater quality. This trend is observed in Pwales Valley, in the northern part of Malta, where the management of water resources plays a crucial role for the environmental sustainability of the area, given the importance of intensive agricultural activity along this valley. In order to tackle such a phenomenon, actions or adaptation measures against climate change are strongly required. For example, managed aquifer recharge (MAR) is an increasingly important water management strategy to maintain, enhance, and secure stressed groundwater systems and to protect and improve water quality. To accurately plan a MAR scheme, it is crucial to define a hydrogeological model of the studied area with the use of traditional hydrogeological measurements and innovative unconventional techniques. In recent years, electromagnetic induction measurements based on the induction of EM fields have been increasingly used for investigating saltwater intrusion dynamics due to their high sensitivity to salinity. In the study area of Pwales Valley, a managed aquifer recharge scheme is being planned, and, for this aim, a hydrogeological model has been developed through an electromagnetic induction survey. More than 20,000 apparent electrical conductivity (ECa) data points were collected to generate a quasi-3D high-resolution model of the electrical conductivity of the Pwales Valley. The results highlighted the spatial extension of the tongue-shape salt water intrusion from east to west along the valley, as well as some geological-hydrogeological peculiarities such as the thickness of the salt wedge and the irregular top surface of the bottom impermeable layer, otherwise undetectable with other direct techniques at the field scale resolution. The approach was confirmed to be a useful tool for effective hydrogeological characterization, essential for planning adaptation measures to a changing climate, such as the implementation of a managed aquifer recharge scheme.

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