Appraising groundwater potential zones using geospatial and multi-criteria decision analysis (MCDA) techniques in Andasa-Tul watershed, Upper Blue Nile basin, Ethiopia

An integrated approach of remote sensing, geographic information system and multicriteria decision analysis of analytical hierarchical process (AHP) were applied to delineate groundwater potential (GWP) zones in Andasa-Tul watershed, Upper Blue Nile Basin, Ethiopia with an area of 1872 km(2). Nine GWP influencing thematic layers comprising lithology, lineament density, geomorphology, slope, soil, drainage density, land use/land cover, rainfall and depth to groundwater level prepared from conventional and satellite data were used. The thematic layers and classes within them were given scale values based on literature and experts' decision by using Satty's AHP. The thematic layers have been integrated via their weights/rates using weighted overlay spatial function tool of ArcGIS to provide GWP map. The result shows that GWP map comprises 250.8 km(2) (13.4%) very good, 132.9 km(2) (7.1%) good, 441.8 km(2) (23.6%) moderate, 662.7 km(2) (35.4%) poor and 383.8 km(2) (20.5%) very poor zones. Validation of the GWP map with existing boreholes and springs yield shows 83.8% agreement indicating good accuracy of the method. The map removal sensitivity analysis result reveals that GWP is more sensitive to lithology (mean variation index, 1.92%) and less sensitive to geomorphology (mean variation index, 0.59%). Similarly, from the single layer sensitivity analysis, lithology and slope are found to be more effective parameters, whereas rainfall and depth to groundwater level are less effective variables. The generated GWP map in the study region can be used as important guideline for locating GWP areas for further exploration, planning and management of the groundwater resources.