Hydrogeophysical Investigation of Saline Water Intrusion in Coastal Communities of Bayelsa State, South South Nigeria

Saline water intrusion into freshwater aquifers poses a significant threat to potable water availability in the low-lying coastal communities of Bayelsa State, South South Nigeria, where freshwater lenses overlie saline formations in deltaic settings. This study integrates electrical resistivity measurements and hydrochemical data to assess the extent and geometry of saline intrusion in three communities in Yenagoa Local Government Area. Horizontal profiling and vertical electrical sounding were conducted using the Wenner configuration at 22 measurement sites distributed across transects perpendicular to the coastline. Water samples from boreholes and hand-dug wells were analysed for total dissolved solids, chloride concentration, and sodium adsorption ratio to validate resistivity-based salinity indicators. Inverted resistivity sections reveal a progressive decrease in resistivity values from inland to coastal directions, with values below 5 ohm-metres at near-surface depths in two of the three communities, indicative of saline water saturation. The freshwater-saltwater interface is mapped at shallow depths of 3 to 12 metres in coastal-facing transects. Hydrochemical results confirm elevated chloride concentrations consistent with seawater mixing in affected zones. The study provides a geophysical baseline for monitoring saline intrusion trends and informs the siting of freshwater abstraction points away from contamination zones. Keywords: saline intrusion, resistivity, coastal aquifer, Bayelsa, freshwater lens