GIS-based integrated groundwater potential assessment of Osun drainage basin, southwestern Nigeria
A GIS-based integrated approach was adopted to assess the groundwater potential of Osun Drainage Basin underlain by the Basement Complex terrain of Southwestern Nigeria. Topographic parameters including surface curvatures, slope and elevation were derived from SPOT DEM and used to generate landform and relief maps for the study area. Spatial Analysis Module of ArcGIS 10.3 software was used to generate lineament proximity, hydrolineament density and drainage density maps for the study area. Vegetation Index module was employed to model the pattern of vegetation from Landsat imagery.Lithologic and soil layers were extracted from existing geological and soil maps. Five hundred Vertical Electrical Sounding datasets were quantitatively interpreted using partial curve matching technique and computer assisted 1-D forward modeling. Overburden thickness and aquifer thickness maps were generated from the VES interpretation results. Eleven raster-based thematic maps (lineament density, lineament proximity, drainage density, vegetation index, slope, elevation, landforms, overburden thickness, aquifer thickness, lithology, soil) were prepared from the generated maps and their individual influence on groundwater systematically determined. The thematic layers were subjected to Fuzzy Logic Overlay in ArcGIS environment in order to delineate the basin into various groundwater potential zones. The basin was delineated into five groundwater potential zones comprising very high, high, moderate, low and very low. Sixty one percent of the study area was rated very low to low, 16 percent was rated moderate and the remaining 23 percent was adjudged to have good groundwater potential. Seventy-six percent of the borehole yields correlated with the groundwater potential model with correlation coefficient of 0.872 at α = 0.01. The study concluded that groundwater potential was generally low across Osun Drainage Basin. However, isolated zones with high groundwater potential were identified particularly in the upland area of the basin.
Keywords: Groundwater Potential, Remote Sensing, Lineaments, Hydrogeology, Topographic Parameters, Geo-electric Parameters