Exploring hydrogeological parameters by integration of geophysical and hydrogeological methods in northern Khartoum state, Sudan

Abstract

The recent study aims to detect the spatial distribution of the hydraulic parameters and evaluate the protective capacity of the groundwater aquifers in northern Khartoum state using geophysical and hydrogeological methods. The study area is located in the transition zone between the sedimentary basin and the area dominated by crystalline basement rocks. Vertical electrical sounding (VES) measurements, using Schlumberger configuration, were taken along three profiles to delineate the thicknesses of the sediments and groundwater aquifers. The VES measurements were combined with the lithology logs to reduce the uncertainty of the resulting models. VES findings denoted that the study area comprises two hydraulically connected aquifers. The upper aquifer is composed of fine sandstone with an average thickness of 50 m, and the lower aquifer has a thickness of up to 150 m. These two aquifers are confined to semi-confined, separated by relatively thick aquitards. To evaluate the aquifer quantitively, pumping test analysis using Cooper-Jacob method was applied to estimate the aquifer's hydraulic parameters, including transmissivity and hydraulic conductivity. The pumping test approach is costly and time-consuming, and extrapolation of the results is restricted to homogeneous boundary conditions. Since groundwater aquifers are mostly heterogeneous, a geophysical-based method called Dar Zarrouk parameters was applied to give a continuous estimate for the hydraulic parameters. Dar Zarrouk parameters include longitudinal conductance and transverse resistance, combining the true resistivity and thickness obtained from the inverted VES data to determine the hydraulic parameters. The calculated hydraulic parameters from the pumping test and Dar Zarrouk parameters showed high compatibility. Furthermore, longitudinal conductance was used to predict the protective capacity of the aquifers. Generally, it ranged from good to very good protective capacity suggesting potable water quality. The findings of this research indicated that the groundwater aquifer in the study area is ideal for groundwater exploitation. However, this study recommends applying a detailed geophysical survey to reduce the uncertainty of the resulting geological and hydrogeological models.