Enhancing Groundwater Potential Mapping Through Integrated Validation and Aquifer Characterization in Diverse Geologic Settings: A Case Study of Central Ethiopian Highlands and Adjacent RIFT

The study area is located in central Ethiopia within Abay (Blue Nile) and Awash basins covering parts of Ethiopian highlands, escarpment, and rift floor. The area is characterized by complex volcanic terrain (fresh to deeply weathered Tertiary to Quaternary rocks/sediments), large topographic and climatic variations, and drained by perennial rivers. The distinct sets of faults and geological variations govern the movement and occurrence of groundwater. In this study emphasis was to make groundwater potential delineation, to understand dynamics, water quality variations, and possible reasons. AHP rating, weighting, and GIS overlying techniques integrated with conventional methods/data were used to map, and validate results. The integrated GIS based analysis and geophysical data clearly demonstrated groundwater potential variation in short distance mainly within fractured zones and thick sediments, with variability attributed to changes in the permeability of the different volcanic/sediment layers, and to the density and orientation of fault systems. Aquifers are layered, discontinuous with variable potential (well yield ranging from 2.5 to 117 L/S yield for cased wells). Major groundwater potential areas are localized dominantly along NW, NS, NE–SW and minor EW trending faults and their intersections in the highland. Aquifers are often discontinuous, stratified and both fractured and porous media aquifers with variable water quality in the rift. In some areas of the rift groundwater with high salinity is evident along major regional NS faults, and those trending E–W, N–W, and NE–SW which are aligned sub-parallel to the rift axis strongly controls the groundwater dynamics  with contribution of topography variations. In summary, the integrated multi-criteria analysis under GIS environment indicated the vital role of the groundwater localization and movement along the highland and rift transect in a complex volcanic province covered with variable volcanic rocks and sediments.