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

Abstract

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.