Geoelectric Mapping of Aquifer Vulnerability Using Dar-Zarrouk Parameters in Parts of Bayelsa State, Southern Niger Delta, Nigeria

Aquifer vulnerability assessment is essential for identifying areas where groundwater may be susceptible to contamination and for supporting sustainable groundwater protection. This study evaluated aquifer vulnerability in selected parts of Bayelsa State and the adjoining Mbiama area of Rivers State, southern Niger Delta, Nigeria, using Vertical Electrical Sounding (VES) data and Dar-Zarrouk parameters. Fifteen VES stations were investigated using the Schlumberger electrode configuration. The apparent resistivity data were interpreted through one-dimensional inversion using IPI2Win software to estimate subsurface layer resistivities, thicknesses and depths. Longitudinal conductance and transverse resistance were calculated using the interpreted overburden layers, while Surfer 18 and the Natural Neighbor interpolation method were employed to map the spatial distribution of vulnerability classes. The interpreted aquifer resistivities ranged from 130 Ωm at Etegwe to 9694 Ωm at Oyiakiri, with inversion root mean square errors ranging from 0.957% to 3.63%. Longitudinal conductance varied from 0.00653 S at Oyiakiri to 2.58715 S at Oloibiri, indicating substantial spatial differences in overburden protective capacity. Oyiakiri, Okorodia and Ojuokpoti were classified as having very high vulnerability, whereas Opu Nembe, Ogobiri, Tombia, Etegwe, Igbedi, Oloibiri, Agbalamabugokiri and Sampou were assigned low vulnerability. The overburden transverse resistance ranged from 434.66 Ωm² at Opu Nembe to 79,891.67 Ωm² at Oyiakiri, providing complementary information on subsurface electrical properties. The resulting vulnerability map identifies locations that warrant priority attention in groundwater-protection planning. However, the mapped patterns are preliminary estimates based on 15 VES stations, and the geoelectric interpretations do not independently establish groundwater contamination or water quality. Borehole lithological logs and groundwater-quality analyses are therefore recommended to validate the results and improve the reliability of vulnerability assessment in the study area.

Aquifer vulnerability; Dar-Zarrouk parameters; longitudinal conductance; transverse resistance; vertical electrical sounding; Bayelsa State

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• Geophysical Evaluation of Groundwater Potentials Using Electrical Resistivity Method at Umunede.