Groundwater Flow Model Part Of Sokoto-Rima Hydrological Basin, Northwestern Nigeria

Abstract

The aim of this work is to model the groundwater system of Zamfara part of Sokoto-Rima hydrological basin, under three objectives which are to evaluate the water budget, assess the interaction between surface water and groundwater, and to predict the temporal and spatial distribution of groundwater head and groundwater flow. MODFLOW-NWT, which is a Newtonian formulation for MODFLOW-2005, was used in the study. The result of sensitivity analysis revealed groundwater (RCH), evapotranspiration (EVT) and hydraulic conductivity (HKZ) had the highest composite scales. The water budget of the calibrated model showed that groundwater recharge was 5,571,293 m³ d^-1, contributing 65.7% of total inflow (8,478,903 m³ d^-1) to the aquifer. Inflow from river seepage represented 30.7% of the total inflow to the aquifer by 2,597,995 m³ d^-1 while seepage from the general head boundary contributed 3.7% of the inflow to the aquifer by 309,615 m³ d^-1.  The outflow quantification of the aquifer showed that 75.8% (6,428,824 m³ d^-1) of the total outflow was accounted to by evapotranspiration, the remaining 15 % (1,273,747 m³ d^-1) outflow represented the river recharge, 8.6% (730,656 m³ d^-1) to general head boundary (GBH), and 0.5% (45,678 m³ d^-1) by pumping wells from the aquifer. Simulated groundwater level ranges between 202.9 m. asl and 688.5 m. asl, with an average level of 414.14 m. asl. Groundwater Flow model results indicated that the topography and geologic structures control groundwater flow in the study area and that base flow to river is an important factor moderating groundwater movement. This implies that the study area currently has sufficient groundwater resources to meet the demand, despite its fragile climate condition.