Groundwater budgeting of the fractured sedimentary aquifer of the Abakaliki Region (southern Benue Trough, Nigeria) using Modflow-Owhm and Gis

Abstract

Groundwater in the fractured sedimentary rocks of the Abakaliki region, southeastern Nigeria, is the principal source of potable water but is increasingly threatened by population growth, climate variability, and rising groundwater abstraction. This study develops what is, to our knowledge, the first three-dimensional groundwaterflow model for the region by integrating MODFLOW-OWHM2 with GIS and ModelMuse. A three-layer hydrostratigraphic model was constructed using digital elevation data, hydraulic properties and pumping rates from 25 boreholes, river networks, and meteorological data (2000–2023). Model calibration using PEST under steadystate and transient conditions produced satisfactory agreement between simulated and observed hydraulic heads (R² = 0.668; RMSE = 12.12 m). Simulated hydraulic conductivity ranged from 8.64 × 10⁻² to 1.21 m day⁻¹. Groundwater flow is primarily controlled by regional topography and is directed toward the Asu and Ebonyi Rivers. Water-budget analysis indicates that precipitation provides ≈99% of groundwater recharge, while groundwater evapotranspiration accounts for about 91% of total outflow. Climatic records reveal ≈18% decline in precipitation,a 12% increase in evapotranspiration, and a 39% reduction in infiltration over the past decade, indicating declining recharge. Together with increasing groundwater abstraction, these trends threaten long-term aquifer sustainability. The model provides a valuable decision-support tool for groundwater management and climate-resilient waterresource planning in fractured sedimentary aquifers.