17. Methods to Countermeasure the Intrusion of Seawater into Coastal Aquifer Systems

Seawater intrusion is a widely occurring environmental problem, which concerns the majority of the coastal aquifers in the world, having large negative impacts – from an economic, developmental, environmental as well as social point of view – on the coastal local communities. The fact that almost 40% of the world’s population lives within a distance of 80 km from the coastline gives rise to the significance of the aforementioned problem and emphasises the necessity for its prevention. This chapter analyses the engineering, managerial as well as techno-economical aspects with respect to the prevention of seawater encroachment into freshwater coastal aquifers and presents some state-of-the-art methods that are currently applied worldwide. It provides a critical review of the application of different type of coastal barriers (either by hydraulic, biological or construction means), management of aquifer recharge (through the application of underground or surface artificial recharge techniques), control of groundwater abstraction and exploitation scheme (by means of suggesting the optimal allocation of abstraction areas for minimising the risk of further intrusion) and other methods of prevention. Finally, this chapter investigates the current enacted legislation as well as adopted policy – mainly developed at a European level – with respect to the prevention of seawater intrusion, together with all the observed gaps and problems which create difficulties for its enforcement.