Groundwater Potential Zone Mapping of Ondo State Using Multi-criteria Technique and Hydrogeophysics

The delineation of groundwater potential zones in Ondo State was carried out using Remote Sensing, Geographic Information Systems (GIS) and Hydrogeophysics. In this study, various thematic maps such as: soil map, slope, drainage map, land use/Land cover map, geological map, rainfall map, lineaments map were obtained from enhanced satellite imagery. These maps were overlaid in terms of weighed overlay method using Spatial Analysis tool in Arc GIS 10.5. During weighed overlay analysis, different ranks were given to each individual parameter of each thematic map and weights were assigned according to their influence. Results showed that spatial distribution of the most promising sites for groundwater exploration was dependent on the interrelated factors of lithology, topography and geologic structure. The groundwater potential map obtained from the study area showed that 17.5% of the total study area lie within the “very high” potential zone, 12.0% of the area falls within the “high”, 39.5% lies within the “moderate” zone, 25.7% lies within the “low “potential zone while 5.3% lies within the very low potential zone. The very high potential areas lie within the sedimentary zone in the southern part of the study area with high alluvial deposits, while the “very low” prospect zone lies majorly within the basement complex zone in the northern part of the study area. The query results on Ijapo Vertical electric sounding (VES) data analysis shows the presence of four lithology: top soil, sand (which contains the fresh water), sand clay (which contains the brackish water) and the clay (which contains the saline water). The boreholes susceptible to salt water intrusion were identified and the best drilling point with respect to depth were also determined.