AHP GIS-supported overlay/index models in Okeigbo, southwestern Nigeria, for groundwater susceptibility zonation

This study assessed the level of groundwater vulnerability and zonation in Okeigbo, southwestern Nigeria, using AVI, GOD, DRASTIC, and DRASTIC-LU models. The GOD categorized the area into three vulnerability zones, with predominant very low/low vulnerability zone constituting 96%; which is in contrast to two vulnerability zones of extremely high (55%) and high (45%) vulnerability zones delineated by the AVI. The DRASTIC map distinctly distinguished the area into four zones: high vulnerability zones (9%); the low vulnerable zone (6%); moderate (71%) of the study area; while moderately low susceptibility (14%). Similarly, DRASTIC-LU/LC model categorized as, moderately low, moderate, moderately high, and high vulnerability zones with aerial extent of 12%, 68%, 13%, and 7% respectively. Therefore, there is good correlation between the DRASTIC, DRASTIC-LU and AVI models as they all showed predominant moderate vulnerability zone. The nitrate concentration validated the high vulnerability zones of AVI, DRASTIC, and DRASTIC-LU models.