Fluxes of groundwater within the cretaceous sandstones of Lokoja formation, Nigeria

Abstract

Simulation of fluxes of water across the cretaceous sandstone of Lokoja formation has been carried out using GSFLOW 1.0 software. The objective is to use the results of the simulations to predict effects of seasonal variability and geology on groundwater resources of the area. Daily streamflow gauge, temperature, precipitation and evapo-transpiration porosity, permeability and groundwater head data assembled from drilling operations were used as input for the model development. Fluxes of gravity drainage out of the soil to unsaturated zone in the area is greater than flux of groundwater discharge from the saturated zone to the soil zone. Gravity drainage out of the unsaturated zone is greater than groundwater discharge to the unsaturated zone. Net gravity drainage increases proportionately with increase in thickness of the zone, except when the soil-zone storage is depleted. Gravity drainage accounts for much of water in the saturated zone during the wet season, while groundwater discharge depletes the saturated zone during the dry season. Surface runoff, interflow and groundwater discharge directly to streams are the three fluxes of water that contribute streamflow to the watershed. Groundwater discharge is greater than recharge and is the reason for failure of wells in the area.