Evaluating the Effects of Sea Level Rise on Saltwater Intrusion in Coastal Aquifers of Bayelsa State

Coastal aquifers in Bayelsa State, South South Nigeria, provide freshwater to communities where piped water supply is absent or unreliable, yet they are acutely vulnerable to saltwater intrusion driven by tidal fluctuations, overpumping, and the progressive influence of sea level rise. This study develops an integrated numerical model to evaluate present and future saltwater intrusion dynamics in coastal aquifers of Bayelsa State under projected sea level rise scenarios. Hydrogeological field investigations encompassing 25 boreholes include slug tests for hydraulic conductivity determination, geophysical surveys (vertical electrical sounding, transient electromagnetic) to delineate the freshwater-saltwater interface, and monthly water quality monitoring for electrical conductivity, chloride, sodium, and stable isotopes. A density-dependent groundwater flow and transport model is constructed in SEAWAT-2000 using the characterised aquifer geometry and hydraulic properties. The model is calibrated against observed water table elevations and chloride profiles and validated against independent historical salinity records. Scenario simulations project saltwater intrusion extent under 0.5-metre and one-metre sea level rise combined with 20 and 40 percent groundwater abstraction increase by 2050. Results are expected to demonstrate that even the conservative 0.5-metre scenario causes loss of potable freshwater supply for communities within 500 metres of the coast under current abstraction rates. Groundwater protection zones and managed aquifer recharge interventions are recommended for the Bayelsa State Rural Water Supply Agency. Keywords: sea level rise, saltwater intrusion, coastal aquifer, Bayelsa State, SEAWAT modelling