Coastal Dams: Coastal dams are constructed along the coast to prevent the intrusion of saltwater into estuaries or rivers. Coastal dams are effective in controlling saltwater intrusion in low-lying areas and can also be used to regulate water flow | Injection Wells: Injection wells are used to inject freshwater into the aquifer to create a hydraulic barrier that prevents the intrusion of saltwater. Injection wells are most effective in areas where the freshwater aquifer is shallow | Underground Dams: Underground dams are constructed to prevent saltwater from entering freshwater aquifers. Underground dams are most effective in areas with a deep freshwater aquifer and a thin layer of permeable soil |