This study provides a detailed assessment of groundwater salinization in the Quaternary aquifer of the Samba Dia region, Senegal, using an integrated approach that combines hydrochemical, stable isotopic (δ²H, δ¹⁸O), and electrical resistivity tomography (ERT) techniques. Fourteen high-resolution ERT profiles, along with comprehensive chemical and isotopic analyses, were performed to identify the main causes of salinity and their spatial distribution. Results show that groundwater salinization in the area is primarily driven by three mechanisms: seawater intrusion, surface salt leaching, and ion exchange. Hydrochemical facies evolution diagrams, ionic ratios, and isotopic signatures helped differentiate marine-influenced zones from inland salinization areas. ERT imaging also mapped the three-dimensional extent and geometry of saline interfaces, confirming zone-specific mixing of seawater and freshwater. The findings indicate that salinization of the coastal aquifer has worsened over the past twenty years, mainly due to human activities and climate variability. This study recommends a sustainable monitoring strategy to support aquifer management, focusing on accurately identifying vulnerable zones and enabling adaptive resource planning in semi-arid Senegal.

Groundwater resources in the Global South are increasingly at risk due to overextraction, contamination, and the impacts of climate variability. These threats are most critical in rapidly growing urban areas, where limited data and inadequate monitoring infrastructure hinder effective resource management. In Dakar, Senegal, the Sebikotane aquifer, a vital freshwater source for the city’s population, has faced severe saltwater intrusion (SWI) caused by decades of overexploitation. Currently, water withdrawals from the aquifer are three times greater than its natural recharge capacity, leading to freshwater wells being increasingly contaminated by saline water.To address this urgent issue, we present an integrated approach that combines innovative geophysical methods, numerical groundwater modeling, and targeted infrastructure rehabilitation. Advanced techniques such as Electrical Resistivity Tomography (ERT) and Time-Domain Electromagnetic (TEM) surveys are used to delineate the freshwater-saltwater interface and identify key subsurface features influencing aquifer behavior. These geophysical datasets are paired with process-based numerical models (e.g., MODFLOW coupled with MT3DMS) to simulate aquifer flow dynamics, track the movement of freshwater and saline fronts, and assess optimal recharge scenarios. Such simulations are critical to predicting how interventions can combat SWI over time and restore aquifer functionality.A key structural intervention is the reconstruction of the Panthior Dam, originally built to enhance aquifer recharge but rendered ineffective due to repeated structural failures. The dam is proposed to function as a Managed Aquifer Recharge (MAR) system, channeling surface water into the aquifer through natural infiltration. Additionally, a real-time network of piezometers and water quality sensors will be established to monitor chloride concentrations, aquifer levels, and the progress of recharge efforts. This monitoring infrastructure plays a central role in enabling adaptive management by providing actionable insights into both localized and aquifer-wide conditions.Our approach showcases the necessity of combining geophysical surveys, hydrological modeling, and engineering solutions to develop robust, data-driven strategies for managing saltwater intrusion and securing freshwater supplies. While the focus of this study is on Dakar, the methodology and findings have broader relevance for other vulnerable coastal aquifers in the Global South experiencing similar groundwater challenges. By integrating scientific tools and infrastructure improvements, this work provides a pathway toward more sustainable, climate-resilient groundwater management for regions where limited resources and data scarcity have historically hindered effective action.