Fresh Water Depth Determination and Mapping of Saline/Fresh Water Interphase Using Geographical Logs in Coastal Aquifers of Niger Delta, Nigeria

Abstract

The introduction of salt/saline water into boreholes has been a major issue in groundwater utilisation in the Niger Delta.  Aim: The study was aimed at determining the depth of saline/saline water and freshwater aquifers in the region. Study Design:  The study was designed to use combined geophysical borehole logs to delineate saline water and fresh water aquifers by determining the depth of such aquifers. Place and Duration of Study: Research took place in 7 locations within the Southern Niger Delta between March 2021 and November 2021. Methodology: This involved the interpretation of downhole electrical resistivity, natural gamma ray and spontaneous potential logs using the difference in their values in different lithologic formations.  Results: Two levels of fresh water zones (a shallow unconfined aquifer between 0 and <150m and beyond) were revealed. Both are separated by a zone of saline water. The freshwater aquifers are mainly sand and gravel, while the saline zone has clay, sandy clay, and silt mixed in various proportions. However, some areas have multiple freshwater aquifers while some do not have a shallow freshwater zone. The variation in depth at various locations could be due to differences in lithology and the rate of abstraction.