Grain size distribution analysis of lokoja formation: implication for aquifer characteristics

Abstract This study investigates the aquifer properties of the Lokoja Formation in the southern Bida Basin using grain-size analysis and empirical estimation methods. Although groundwater is the primary water source in the region, previous studies have focused mainly on lithostratigraphy and depositional settings, leaving a gap in quantitative hydrogeological characterization. This work provides a detailed grain-size-based estimation of porosity and hydraulic conductivity for the Lokoja Formation, offering a cost-effective alternative where pumping test data is limited. Twelve sandstone samples were analyzed to determine grain-size distribution, sorting, and gradation, and the Vukovic and Soro model was applied to estimate hydraulic properties. Porosity ranges from 28% to 43%, while hydraulic conductivity spans 0.59–11.60 m day −1 (mean = 4.45 m day −1 ), indicating moderate to high permeability. Effective grain size (d 10 ) shows a very strong positive correlation with K (R 2 = 0.944), confirming it as the primary control on aquifer performance. These results demonstrate that the Lokoja Formation contains productive groundwater zones, particularly in coarser, better-graded intervals, but spatial heterogeneity necessitates site-specific evaluation. The findings fill a critical data gap in regional hydrogeology and provide practical guidance for borehole siting and sustainable groundwater management.