Assessing the progression of seawater intrusion in the Dradère-Souière coastal aquifer (Northwest Morocco): A hydrogeological, hydrochemical, and geophysical investigation

• Impact of climate change and intensive groundwater pumping on coastal aquifers. • Salinization of coastal aquifers by seawater intrusion. • Seawater intrusion in the Dradère – Souière coastal aquifer. • Multidisciplinary approach to seawater intrusion characterization. • Protecting coastal aquifers against marine salinization. Seawater intrusion is a critical issue affecting coastal aquifers worldwide, particularly in regions facing overexploitation and climatic. The Dradère-Souière coastal aquifer, one of the most heavily exploited aquifers in Morocco, is increasingly vulnerable to this phenomenon due to climatic challenges and anthropogenic pressures. This study investigates the progression of seawater intrusion in this aquifer through a comprehensive hydrogeological, hydrochemical, and geophysical characterization. Initially, piezometric measurements were taken to draw up a piezometric map, identifying areas vulnerable to seawater intrusion. At the same time, physico-chemical analyses were carried out to determine the chemical composition of the groundwater and identify salinity indicators. In addition, geophysical investigations based on electrical resistivity tomography produced detailed imagery of the aquifer structure, highlighting the interfaces between freshwater and saltwater zones. The methodology included piezometric measurements and hydrochemical analyses of 17 wells, and 72 electrical resistivity tomography (ERT) profiles perpendicular to the coastline. Piezometric data reveal significant aquifer vulnerability, with low piezometric levels (below 10 m) and weak hydraulic gradients (approximately 0.8%) along the coastal strip and near the Merja Zerka lagoon. Hydrochemical analyses confirm groundwater salinization, particularly in wells within the first two kilometers from the ocean, showing high electrical conductivity, elevated chloride (Cl - ) concentrations, and calcium-sulfate to chloride-dominated water facies. ERT profiles highlight the inland advancement of the seawater intrusion front, reaching up to 360 meters, with low-resistivity zones (<10 Ω·m) indicating saline groundwater. Consequently, any groundwater management strategy for the Dradère-Souière aquifer must critically assess seawater intrusion risk and implement appropriate preventive measures. Overall, our findings underscore the need for continuous monitoring, managed aquifer recharge, and the development of a numerical model to predict future intrusion scenarios for sustainable governance of this critical aquifer.