Evaluation of seasonal variation of geoelectrical parameters in a part of the basement complex setting, southwestern Nigeria: implication for groundwater

This study investigated the effects of seasonal variation of resistivity on the regoliths in the basement complex setting in Ibadan, southwestern Nigeria, to quantify the variation in the geoelectrical parameters and geohydraulic properties, as well as the aquifer prospects and protective capacity of the bedrocks. Sixty-four vertical electrical soundings (VES) were conducted in the dry and wet seasons (32 VES for each season). The VES revealed resistivity variations in the thin topmost layer, with the variations occurring at 2.4–3.2 m in quartzite–quartz Schist, 1.3–1.8 m in undifferentiated schist, and 1.3–4.2 m in migmatite gneiss. The top layer resistivity varied from 19 to 1385 Ωm (dry season) and 29 to 444 Ωm (wet season), with thicknesses ranging from 03 to 3.4 and 0.2 to 2.5 m, respectively. The longitudinal conductance ( S ) ranged between 0.01 and 0.5 m (wet), and 0.03 and 0.6 m (dry); while, the transverse resistance ( T ) averaged 1943.5 and 2409.5 Ωm 2 in the wet and dry seasons, respectively. The anisotropy coefficient ( λ ) ranged between 0.58 and 2.30 (wet), and 1.00 and 2.03 (dry). The paired t test analysis revealed that the p values for most of the geoelectrical parameters are greater than the significance level ( p value > 0.05), implying that the model does not explain the seasonal variations in the parameters. However, the exponential regression models ( R 2 ) and p values for the topsoil resistivity and λ with corresponding values of R 2 = 0.62, p value < 0.05, and R 2 = 0.8, p < 0.05, suggest a model that explains a good part of the seasonal variations. The aquifer prospects and protective capacity of the bedrocks indicated moderate to good for both seasons, while the quartzite bedrock revealed poor groundwater prospects in the dry season and moderate prospects for the wet season. The study concluded that only the topsoil resistivity and the λ show seasonal variability.