Litho-structural control on interbasin groundwater transfer in central Ethiopia

Abstract

In central Ethiopia, litho-structural setup of the three sub-basins of the southern flank of the Middle Blue Nile basin (Guder, Muger and Jema) and the adjacent Upper Awash River basin have been investigated to develop conceptual groundwater flow model and to characterize the groundwater hydrodynamic relationship between the aquifer systems of the two basins. The development of conceptual groundwater flow model is based on interpretation of Digital Elevation Model (DEM) from SRTM and Landsat images together with field geological observation, integrated with existing boreholes lithologic logs and pumping test data. The litho-structural framework, reconstructed from regional stratigraphy and analysis of major regional fault systems, controls the size of recharge area for aquifer systems and aquifer distributions in the groundwater sub-basins. The study has indicated the distinctive geometric setting of the litho-strata of aquifers and aquicludes. The NW–SE trending horsts beneath the volcanic successions and the overlying volcanic ridges control aquifer distribution in the Guder, Muger and Jema groundwater sub-basins, while the E–W trending horsts control aquifer distribution between the Middle Blue Nile and the Upper Awash Rivers basins. Impermeable mudstone constitutes the upper part of the E–W oriented horst at the center of the Muger River sub-basin. This mudstone capped horst underlying the volcanic aquifers is a groundwater divide channeling recharged water in the Blue Nile basin partly towards the Upper Awash basin. Significant proportion of groundwater recharged in the Middle Blue Nile basin (Muger and Jema River sub-basins) contributes to the storage of the aquifer systems of the Upper Awash basin.