Seawater intrusion into coastal aquifers is a growing global concern, driven by climate change, sea-level rise, and intensive groundwater exploitation. Effective assessment and monitoring strategies are crucial for sustainable water resource management. Traditional hydrogeological investigations, such as borehole measurements, provide point-source data but lack the spatial resolution necessary for comprehensive regional assessments. Geophysical techniques, in particular Electrical Resistivity Tomography (ERT) and Frequency Domain Electromagnetics (FDEM), offer non-invasive alternatives with distinct advantages and limitations.
This study presents a comparative evaluation of ERT and FDEM techniques for mapping shallow seawater intrusion at four test sites along the northern coastal margin of Friuli Venezia Giulia, Italy, each with different salinity levels, lithological conditions, and seasonal variations. ERT surveys provided high-resolution subsurface conductivity data, used as the reference dataset. The FDEM measurements were carried out using two different instruments: a multi-depth, constant-frequency system and a single-offset, multi-frequency system, both of which allow rapid and extensive data acquisition.
To ensure robust comparability, FDEM-derived apparent electrical conductivity (ECa) values were normalized against ERT-derived conductivity data. The results indicate that, despite its rapid acquisition capabilities, FDEM can provide reliable estimates of subsurface conductivity without site-specific calibration, using appropriate data normalization techniques.
This research underscores the potential of FDEM as a cost-effective and scalable solution for monitoring seawater intrusion, providing valuable insights into groundwater salinization dynamics and advancing methodologies for large-scale environmental and water resource management.