Simulation of Saltwater Intrusion into Coastal Aquifer of the Western Niger Delta

Coastal aquifers by nature are vulnerable to the ingress of saltwater from the adjoining sea consequent upon the intensive abstraction of groundwater. The degradation of coastal aquifers becomes more aggravated by increasing demand for groundwater and climate change. How coastal aquifers respond to the effect and degree of aquifer stressing and recharging conditions is unknown. The extent of movement and the process driving its direction is poorly understood. A 3D numerical model was developed to simulate lateral intrusion of saltwater into groundwater aquifer using SEAWAT. Different pumping and recharge conditions were simulated to determine the effects of these variables on the movement of the position of the freshwater-saltwater interface relative to inland aquifers. The results revealed that the freshwater/saltwater interface is near the sea and has not transgressed into inland aquifers. Realistic pumping rates that ranged from 9558 to 17,058 m³/day have no significant effect on the freshwater/saltwater interface. However, the position of the freshwater/saltwater interface was affected by an unrealistic pumping rate that ranged from 3.9 to 6 million m³/day. This underscores the present rate of groundwater demands and usage in the western Niger Delta is insufficient to trigger saltwater intrusion into groundwater aquifers. In addition, simultaneous simulation of recharge reduction with unrealistic pumping conditions enhanced freshwater/saltwater interface movement toward the inland. The sensitivity analysis showed that the freshwater-saltwater interface responded more to groundwater pumping and recharge than the hydraulic conductivity of the aquifer. Understanding how aquifers react to stress and recharge is critical for maximizing the exploitation of coastal aquifers for long-term groundwater resource management and development.