Seawater intrusion in the coastal aquifers is a major concern in India. What are the causes of seawater intrusion and the remedial measures to combat this hazard?

Causes

Fresh water in a coastal aquifer floats in a balance with denser seawater (the Ghyben-Herzberg idea). Heavy pumping for cities, industry and monsoon-failure irrigation lowers the freshwater head, and the salt water creeps inland. Sea-level rise and storm surge push the same interface. Reduced recharge — paved cities, dying tanks — weakens the freshwater side. Aquaculture ponds, poorly lined canals, and tsunami or cyclone floods can salt a shallow lens in a week. Sand mining and lost mangroves remove buffers.

Remedies

• The first remedy is less greed at the pump: licensing, electricity reform so that free power does not mean a dry, salty well, and shifting water-hungry crops. The second is recharge: check dams, spreading basins, and injection wells of treated water where geology allows. The third is engineering: subsurface barriers, and in extreme cases desalination for drinking (costly, energy-heavy). The fourth is land: protect recharge areas, restore mangroves, stop building on every dune. Monitoring — a salinity map that a panchayat can see — is the unglamorous core.

Without cutting extraction, a barrier is a delay. With only lectures, the next summer still tastes of the tide.