DELINEATING GROUNDWATER STORAGE POTENTIAL ZONES

ABSTRACT

The availability of water is the driving force of any sprawling population like the city of Ilorin. The need for water is critical to the development of such cities hence exploration of groundwater in Ilorin which is sitting on a basement complex is a challenging task and needs baseline information to help in decision-making. A GIS-based Analytical Hierarchical Process (AHP) was adopted to assess the groundwater storage potential of Ilorin and its environment using eight (8) groundwater potential parameters. Slope and drainage patterns were determined from Digital Elevation Model (DEM) sourced from Shuttle Radar Topography Mission (SRTM) and used to generate slope and drainage maps. The spatial analyst package in ArcGIS Pro was used to generate slope and drainage density maps. Aeromagnetic data obtained from Nigerian Geological Survey Agency (NGSA) and Landsat 8 data obtained from the United States Geological Survey (USGS) were used to gather lineament data of the study area. Oasis Montaj Software and PCI Geomatica software were used to process aeromagnetic data and Landsat 8 data respectively into distinct lineament maps which were then combined to form the lineament map of the study area. ArcGIS Pro was further used to generate the lineament density map. Soil, land-use and geological maps were sourced from Harmonized Soil World Database (HSWD), ESRI’s Land Use 2020 map and NGSA respectively. The rainfall map was sourced from Climate Hazards Group InfraRed Precipitation (CHIRPS) at 0.05° resolution. Eighty-two vertical electrical sounding (VES) data were collected across the study area to determine lithologic properties within the study area. The VES data were processed with the Interpret-VES software, and the result was used to characterize the curve-types present. The VES analysis revealed sixty-eight 4-layered curves, twelve 5-layered curves and two 6-layered curves models. The total aquifer thickness (TAT) which is a combination of the weathered rock layer and fractured  rock layer was determined from the curve models ranged between 0.4m to 108m with an average thickness of 25.4m. The TAT data of the VES locations were kriged using the spatial analyst module in ArcGIS Pro to produce the total aquifer thickness map.