Groundwater Potential Mapping of Asa - Oyun Catchment Areas Over Crystalline Basement of Southwest Nigeria Using Integrated Approach of Remote Sensing and Analytical Hierarchical Analysis

Abstract

Abstract Groundwater exploration in crystalline terrains depends on structural information among other factors like geology, rainfall, drainage, soil type, elevation and/or landuse classification. The spatial distribution of groundwater potential zones (GWPZs) in Asa and Oyun catchment areas, Kwara state, northcentral Nigeria was assessed using six thematic layers derived from satellite data and ancillary data. Landsat 8 OLI (2015), Digital Elevation Model (DEM), and aeromagnetic data were used to extract lineaments. Tropical Rainfall Measuring Mission (TRMM) data was used to generate spatially distributed rainfall using inverse distance weighted interpolation method. Slope and drainage were extracted from DEM. The natural colour composite of Landsat 8 was classified into 4 classes: Bareland, Vegetation, Waterbody, and settlement. The groundwater potential map of the study area was produced using a geographic information system (GIS) based Analytical Hierarchical Process (AHP) model of Lineament density, drainage density, rainfall data, slope, and landuse information. The resulting groundwater potential map was validated using ROC analysis of available groundwater yield data (l/s) from boreholes in the study area. AHP with consistency ratio (CR) of 0.077, making weightage viable for groundwater potential mapping, identified five (5) groundwater potential zones (GWPZs). The majority of very low and low GWPZs fell in the Asa catchment area, while majority of the moderate, high, and very high GWPZs fell in the Oyun catchment area. Validation revealed that low, moderate, high and very high GWPZs had yields of 0.3-1.5l/s, 0.35-1.8l/s, 3.00-3.60l/s, and > 3.60l/s, respectively. The AUC coefficient of 0.777 (77.7%) confirmed the efficacy of the adopted methodology.