Hydrogeological characterization of fractured basement aquifers using an integrated analysis in the Agnéby-Tiassa region of southern Côte d’Ivoire

Access to safe drinking water in the Agnéby-Tiassa region (southern Côte d’Ivoire) faces major challenges due to the inadequacy of surface water resources and a poor understanding of the potential of basement aquifers, which are often obscured by a thick regolith mantle and dense vegetation. This study proposes an integrated methodological approach aimed at a detailed characterization of the hydrogeological potential of these fractured formations to optimise the siting of high-yield boreholes. This synergistic approach combines: (i) the processing of Sentinel-1 radar images in VV and VH polarisations for structural lineament mapping, (ii) the acquisition of electrical resistivity data by profiling (Schlumberger array) over identified anomalies, and (iii) the statistical analysis of the technical parameters from 307 boreholes (yield, regolith thickness, depth and lithology). Interpretation of the radar imagery enabled the production of a dense structural lineament map comprising 458 major lineaments, with dominant east–west (N82°-N97°), Liberian (N120°-N160°), and Eburnean (N30°-N60°) trends, confirming the intensity of tectonic deformation in the region. Ground geophysical investigations, targeted at these structures, revealed conductive anomalies in “U”, “V”, or “W” shapes, interpreted as zones of open fractures and/or thickened regolith, favourable for water storage. An analysis of the borehole data indicates that the most productive yields (Q > 2.5 m³/h) are associated with granitic and volcano-sedimentary schist lithological contexts, characterized by a regolith thickness (RT) ranging from 15 to 80 m. This study demonstrates the relevance and effectiveness of a multisource approach for overcoming geological challenges in basement terrain groundwater exploration. It contributes to reducing borehole failure rates and improving the siting and design of rural water supply boreholes through a methodological framework.