Seawater intrusion refers to the landward movement of saline seawater into coastal freshwater aquifers. It is a growing concern along India’s 7,500 km coastline.
Concerns Associated with Seawater Intrusion
Loss of Potable Water – Eg – Chennai, Digha and Saurashtra face declining freshwater availability.
Saline irrigation water damages soils and reduces crop yields.
Alters wetland hydrology and harms mangroves and estuaries. Eg – in Sundarbans.
Raises economic burden on households and municipalities. Eg – Chennai’s tanker dependence during summer months.
Causes of Seawater Intrusion
Excessive Groundwater Extraction – Over-pumping near coasts lowers freshwater pressure, drawing seawater inland.
Urbanisation – Concretisation and wetland loss reduce aquifer replenishment. Eg- Chennai has lost 85% of its wetlands. (WWF)
Sea-Level Rise due to Climate Change – Eg- global mean sea level rose by 0.20 m between 1901 and 2018. (IPCC)
Sand Mining & Shoreline Alteration – weakens natural coastal barriers.
Cyclones, and storm surges lead to seawater infiltration in shallow aquifers.
Coastal areas with sandy soils, porous rocks, or low-lying physiographic depressions allow rapid seawater percolation.
Absence of systematic groundwater management and poor infrastructure regarding artificial recharge
Dams and upstream diversions reduce the freshwater outflow that naturally counters seawater intrusion. Eg – Narmada estuary showing increased salinity.
Remedial measures
Artificial Recharge – Use percolation ponds, recharge shafts, injection wells, and subsurface dykes
Regulation of Groundwater Extraction – Introduce withdrawal caps, borewell licensing, coastal aquifer zoning
Adopt low-water crops and saline-resistant varieties to reduce irrigation stress on aquifers. Eg – ICAR-CSSRI (2022) developed salt-tolerant rice
Rainwater harvesting to reduce dependency on shallow wells (NCCR, 2023). Eg- Chennai
Mangrove afforestation for reducing wave energy and preventing soil erosion.
Ecosystem-based coastal protection– Eg- Oyster beds along the coast can serve as natural breakwaters.
Mitigating seawater intrusion is essential to safeguard coastal aquifers and advance SDG 6 and SDG 13