Three-Dimensional Subsurface Modelling of the Awka Aquifer System Using ERT and Hydrogeological Data

A three-dimensional model of the Awka aquifer system is essential for sustainable groundwater management in Anambra State capital but has not previously been developed using a combination of geophysical and hydrogeological data. This study constructs a three-dimensional subsurface model of the Awka aquifer system by integrating electrical resistivity tomography data with existing borehole and hydrogeological records. Seventeen ERT profiles totaling 4,850 m were acquired across the Awka urban area using a Syscal Pro unit with 72-electrode Wenner-Schlumberger configuration. Two-dimensional inversion models were produced for each profile and cross-correlated with stratigraphic logs from 24 boreholes distributed across the study area. A three-dimensional resistivity volume was constructed by kriging interpolation between the two-dimensional profile models using Surfer and Voxler 3D visualization software. The 3D volume reveals a multi-aquifer system comprising two hydraulically distinct productive horizons within the Benin Formation sands. The upper aquifer occurs at depths of 20 to 45 m with resistivities of 80 to 250 ohm-m, while the deeper aquifer is encountered at 65 to 110 m with resistivities of 120 to 380 ohm-m. The two aquifer units are separated by a clay aquitard of variable thickness (5 to 22 m). The three-dimensional model identifies the principal groundwater flow direction as northeast-southwest, consistent with the regional topographic gradient. Aquifer thickness maps show maximum productive zones in the western and central portions of Awka. These results provide a quantitative framework for groundwater development, protection, and numerical flow modelling in Awka.

Keywords: 3D subsurface modelling, ERT, aquifer system, Awka, hydrogeology