Imaging of Seawater Intrusion in a Coastal Alluvial Aquifer Using Transient Electromagnetic Data and Laterally Constrained Inversion in Northern Oman

Seawater intrusion poses a major threat to groundwater quality in the Al-Batinah Coastal Plain of northern Oman, where intensive groundwater abstraction has disrupted the natural freshwater–seawater equilibrium in the coastal alluvial aquifer. This study investigates the extent and geometry of seawater intrusion in the eastern sector of the aquifer, between Al-Jifnain Dam and the Oman Sea, using the transient electromagnetic (TEM) method. A total of 45 TEM soundings were acquired along four profiles and inverted using a laterally constrained inversion (LCI) scheme to recover spatially coherent subsurface resistivity models. The results resolve the principal hydrostratigraphic units of the coastal aquifer system, including a highly resistive unsaturated near-surface gravel cover, a moderately resistive freshwater-bearing gravel aquifer, and localized conductive horizons interpreted as clay-rich gravel interbeds. The most prominent feature is a laterally extensive wedge-shaped conductive body, with resistivities close to 1 Ω·m, extending inland beneath the freshwater aquifer and interpreted as seawater intrusion. This saline wedge extends approximately 8 km inland from the coast, between elevations of about −70 and −220 m, with maximum thickness near the shoreline and progressive thinning landward. The study demonstrates that TEM, combined with LCI, is an effective approach for delineating deep seawater intrusion in arid coastal aquifers and provides a baseline for future monitoring of aquifer salinization and for assessing the impact of managed aquifer recharge in the Al-Jifnain area. These findings support sustainable groundwater management and contribute to achieving the United Nations Sustainable Development Goal 6 (Clean Water and Sanitation).