GROUNDWATER POTENTIAL MAPPING USING SWAT MODEL AND GIS BASED MULTI-CRITERIA DECISION ANALYSIS: A CASE STUDY IN GIDABO WATERSHED, RIFT VALLEY LAKES BASIN, ETHIOPIA

Abstract

Groundwater is the water that is located in the subsurface and saturates the rocks and soil beneath the ground surface. Groundwater is the most valuable natural resources for mankind for drinking, industrialization and irrigation in present day, but the availability is reduced gradually due to over exploitation and lack of management. However, identifying the groundwater potential zones in certain areas of Ethiopia is still challenging in terms of time and cost for resolving water scarcity problems and the management system of groundwater. A systematic assessment and identification of groundwater is essential for proper utilization and management of this precious natural resource. In recent years, Geographic information system based studies have gained much prominence in groundwater exploration, because it is rapid and will provide first-hand information on the resource for further developments. Therefore, the present study was conducted with an objective to identify the groundwater potential of Gidabo catchment, Rift Valley Lakes Basin of Ethiopia using SWAT and GIS-based MCDA techniques. Thematic maps were developed, for ten major parameters (recharge, soil, lineament density, lithology, land-us/ land-cover, geomorphology, slope, drainage density, Roughness and Topographic wetness index (TWI)) that affect the occurrence and movements of groundwater. Recharge was simulated by using SWAT model, the rest thematic layers were developed using ArcGIS 10.4 and Weights assigned to each thematic maps were based on their characteristics and water potential capacity through analytic hierarchy approach (AHP). The thematic layers were subjected to weight sum overlay in ArcGIS spatial analysis tool box, to delineate groundwater potential zone map. The resulted groundwater potential zone was categories in to four classes, namely high, moderate, low and very low. Generally Low and very low groundwater potential zones were found around highland area which coincide with structural hills, peak of the mountain and hard geological formation. The accuracy of the output was cross-validated with information on groundwater prospects of the catchment. Finally, it can be concluded that SWAT and GIS-based MCDA-AHP techniques is very effective and useful for the delineation and identification of groundwater potential zones in the study area.