Integrated AMT and VES investigation of the transboundary Continental Intercalaire aquifer in the Sebaa Basin, southern Algeria

Groundwater resources in arid and semi-arid regions of the global south are increasingly under pressure due to agricultural intensification, population growth, climate variability, and limited monitoring. On the other hand, effective management of these resources requires a detailed understanding of subsurface, flow dynamics, and water quality at scales relevant to decision-making. In Algeria, the Sebaa Basin of the Adrar Province represents a critical area where groundwater, supplied by the transboundary Continental Intercalaire (CI) aquifer, supports rapidly expanding agricultural activities. Despite its socio-economic importance, this hydrogeological system remains poorly characterized due to sparse observational data and limited subsurface information.

To address these challenges, we implemented an integrated hydrogeophysical and hydrochemical study combining Audio-Magnetotelluric (AMT) surveys, Vertical Electrical Sounding (VES), piezometric measurements, and hydrochemical analyses. Fourteen AMT stations were deployed along a 3 km east–west profile with a spacing of approximately 200 meters to achieve high-resolution imaging of the subsurface. AMT was selected to capture the overall structure and geometry of the aquifer system, revealing depth, thickness, lateral continuity, and structural heterogeneities of the CI aquifer that are not apparent from surface geological observations alone. In parallel, 50 VES soundings were conducted to track variations in piezometric levels, providing insight into localized drawdown effects. Piezometric measurements from existing wells were used to validate the VES interpretations and to map spatial variations in hydraulic head across the study area.

Hydrochemical sampling and analysis were integrated to characterize water quality, assess spatial variability, and identify potential mixing between fresh, slightly mineralized, and more saline groundwater. Major ions and salinity indicators were analyzed to provide additional constraints on aquifer connectivity and flow dynamics. The combined interpretation of AMT, VES, piezometric, and hydrochemical data allowed the development of a comprehensive conceptual model linking subsurface structure to observed hydraulic behavior and water quality patterns. Low-resistivity zones observed in AMT and VES inversions were interpreted as potential groundwater pathways and preferential recharge areas, while high-resistivity anomalies corresponded to consolidated formations or structural highs that limit flow.

This integrated approach demonstrates how coupled geophysical, hydrological, and geochemical methods can overcome limitations associated with sparse data in arid regions. By providing a detailed understanding of both the geometry of the aquifer and the spatial variability of groundwater levels, this study supports sustainable management of a critical transboundary water resource. The results highlight the importance of aligning hydrogeophysical investigations with field-based monitoring and chemical analyses to generate actionable insights for groundwater management.