Delineation of groundwater potential zones of the transboundary aquifers within the semiarid Bulal catchment, Southern Ethiopia

Abstract Groundwater is the only reliable drought-resilient water source in the semiarid Bulal transboundary catchment located close to the Kenyan border. The central and southern parts of the catchment are dominantly overlain by Bulal basalts, while the Borena basement complex outcrops in the eastern part. This work aims to identify and delineate the groundwater potential zones of the semiarid Bulal catchment within the boundary of Ethiopia using integrated GIS and RS techniques in combination with the analytical hierarchal process (AHP). Ten input parameters were selected based on their relative significance to groundwater occurrence and movement. The normalized weights were assigned to the input themes and their individual features as per Saaty’s AHP approach. A composite groundwater potential zone index (GWPZI) map was finally generated by integrating all the input layers employing the GIS-overlay analysis technique. The map was validated using the yield of wells from the catchment. The GWPZI map depicts four groundwater potential zones in the catchment: high (representing 27% of the total area), moderate (20%), low (28%) and very low (25%). The geological feature has the greatest influence on the distribution of groundwater potential in the catchment. Areas with high potential are mainly overlain by Bulal basaltic flow and alluvial sediments, while areas covered with regolith developed over the metamorphic basement are attributed to the low and very low groundwater potential zones. The GWPZI map will serve as a quick guide for effectively planning, managing, and developing the groundwater resources of the catchment.