Gis Based Groundwater Potential Assessment in Lower Omo Valley Sub-basin፡ in the Case of Selamago Woreda, Ethiopia

Water is the pillar of socio-economic activity and environmental functions. Groundwater is the most important natural resource found beneath the earth‘s surface. A systematic evaluation of groundwater is essential for the proper utilization and management. This study is mainly aimed at identifying and mapping the groundwater potential zones of the lower Omo sub-basin in the case of Selamago Woreda. ArcGIS overlay analysis was conducted to obtain the groundwater potential zone map. A total of nine thematic layers were used in Arc GIS, including geology, slope, rainfall, lineament density, geomorphology, soil, land use land cover, drainage density, and elevation used for overlay analysis. Weights were assigned for each thematic layer, and then each thematic layer was compared using the AHP (Analytic Hierarchy Process) tool. The identified factors affecting groundwater potential were geology (27%), slope (21%), rainfall (14%), geomorphology (10%), lineament density (9%), soil (5%), land use land cover (5%), drainage density (5%), and digital elevation model (4%). The first four thematic layers were the most influencing parameters of groundwater in the study area. There were five groundwater potential zones identified and mapped in the study area: very low, low, moderate, high, and very high. The high potential zones correspond to alluvial plains, lacustrine sediments, fracture valleys, and valley fills, which coincide with the low slope and high lineaments density areas. The low zones mainly comprise structural hills and an escarpment. Compared with an independent set of groundwater point data (existing drilled wells), the qualitative results partially validate the result. The validation analysis showed a good agreement between the observed well data and groundwater potential zone map. Therefore, this research demonstrates that GIS and remote sensing techniques are an efficient and robust method for delineating and mapping groundwater potential zones. This groundwater potential information will be useful for water resources management in the study area