This paper studies the control of seawater intrusion using numerical modelling. A coupled transient density-dependent finite element model was used for modelling seawater intrusion. Also, a new cost-effective method for effectively controlling seawater intrusion in coastal aquifers was presented. This methodology (ADR -Abstraction, Desalination and Recharge) involves abstracting saline water and subsequently desalinating it. This desalinated water is then used for domestic consumption while any excess desalinated water is recharged to the aquifer.

The numerical model was integrated with a genetic algorithm (GA) to simulate different scenarios to control seawater intrusion. The effects that different combinations of abstraction, desalination and recharge have on seawater intrusion were also simulated.

The main objectives of the model were to minimise:

- the total capital and operational costs of the abstraction and recharge wells and

- the salt concentrations in the aquifer.

The results showed that the proposed ADR system performs significantly better than using abstraction or recharge wells alone, as it is the least costly and results in lower salt concentrations in aquifers. From the study, it was found that the cost of the ADR system is about 50% of the abstraction only scenario and 25% of the recharge scenario. This is because the water needed for recharge is provided primarily from the treatment of abstracted saline water. Moreover, excess treated water can be directly used for other purposes. The other aspect of the system’s efficiency is about minimising the total concentration of salinity in the aquifer as it has reduced the total concentration in the system by 15%. This is due to the system’s capability of moving the aquifer transition zone further to the coast.