MJSTEM

Abstract

Groundwater in basement terrain is predominantly controlled by weathered regolith thickness and fracture systems, yet detailed quantitative characterization remains limited in parts of Minna Sheet 164 SW, North Central Nigeria. This study evaluates groundwater flow dynamics, structural control, and vulnerability within an 81 km² area underlain mainly by granite and schist. Geological mapping at a scale of 1:12,500 was integrated with a systematic grid-based inventory of 117 hand-dug wells. To improve methodological transparency, the study area was subdivided into approximately 500m x 500m grid cells to ensure spatial representativeness of hydrogeological measurements. Static water levels ranged from 0.9-10.3m (mean = 4.23m), well depths from 1.6-10.6 m (mean = 5.05m), and water column thickness from 0-4.8m. Water table elevations were interpolated using Ordinary Kriging, and the hydraulic gradient was quantified using I = Δh/Δl, yielding an average gradient of 0.02-0.03 along the dominant NE-SW flow path. Recharge interpretation was supported by a first-order rainfall-runoff water balance estimate based on NiMet data (2013-2023), indicating potential annual infiltration of approximately 3.9 × 10⁷ m³. Structural analysis reveals alignment between NNE-SSW joint orientation and groundwater flow direction, suggesting fracture-controlled anisotropy. Although vulnerability assessment remains conceptual, the thin overburden (0.5-1.0m) indicates moderate to high susceptibility to contamination. Limitations, including seasonal variability, absence of pumping test data, and interpolation uncertainty, are explicitly acknowledged. The study provides a hydrogeological framework to guide sustainable groundwater development in basement complex terrains

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