Empirical models for determination of hydraulic conductivity of the Ajali formation using sedimentological analysis in the Idah Area, Northern Anambra Basin, Nigeria

Abstract

This study examines the hydraulic conductivity of the Ajali Sandstone Formation in Idah axis of the northern Anambra Basin, Nigeria. The investigation aims to determine the hydraulic conductivity cutoff for the Ajali Sandstone, which is important for the development and management of groundwater resources in Idah area. The study utilizes thin section and grain size analysis on five samples to determine hydraulic conductivity. The Sedimentological analysis indicates medium to coarse-grained, subangular quartz, monocrystalline structures. The modal composition from the thin section ranges from 65-85% of quartz, 10-20% of feldspar, 5-25% of others. Iron-rich samples in the study area display that quartz is between 25-30%, with opaque matrix containing Fe-oxides between 70-75%, respectively. The coefficient of uniformity (U) estimated based on Hazen's model ranges from 0.21 to 4.95, with an average of 2.92. The hydraulic conductivity estimated from other model ranges between 3.61×10^-4 to 4.41×10^-4 m/s, with an average of 4.24×10^-4 m/s. This finding provides evidence that the beds of Ajali Sandstone in Idah area have the capability to serve as aquifer zones, exhibiting a hydraulic conductivity of medium magnitude. The hydraulic conductivity values, determined using the USBR method, range from 189.17 m/day to 1054.0 m/day, aligning with the results obtained from the Hazen model. This study is in line with previous research on established relationships, despite the lack of comparison on hydraulic conductivity in the study area. Differences in estimation model are observed, with Hazen's technique yielding more consistent but smaller values, while the USBR method provides a wider range. Further investigation is advised to address these inequalities and improve understanding.