Q. 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?

Model Answer:

India’s ~7,500 km coastline faces severe groundwater salinization as excessive freshwater extraction disrupts the natural Ghyben-Herzberg balance, contaminating critical coastal aquifers.

1. Causes of Seawater Intrusion

• Groundwater Over-extraction: Unregulated pumping for agriculture and industries reverses seaward hydraulic gradients, pulling saltwater inland (e.g., Minjur aquifer, Chennai).
• Climate Change & Sea-Level Rise: Rising sea levels and frequent cyclonic storm surges push the marine saline wedge further inland (e.g., Sundarbans).
• Unregulated Aquaculture: Extensive brackish-water shrimp farming leaks high-salinity water into shallow coastal aquifers (e.g., Andhra Pradesh coast).
• Reduced Natural Recharge: Urban concretization and destruction of coastal wetlands restrict freshwater percolation, preventing natural aquifer flushing.

2. Remedial Measures to Combat the Hazard

• Artificial Recharge: Pumping rainwater or treated wastewater into injection wells to build a freshwater ridge and restore hydrostatic pressure (e.g., Saurashtra recharge initiatives).
• Structural Barriers: Constructing subsurface dams, tidal regulators, and coastal embankments to physically block salinity ingress.
• Regulatory Enforcement: Strict enforcement of Central Ground Water Authority (CGWA) guidelines for coastal pumping and CRZ 2019 restrictions on borewells.
• Agro-Ecological Shifts: Promoting saline-tolerant crop varieties (e.g., Pokkali rice) and restoring mangrove bio-shields to reduce groundwater dependency and regulate coastal hydrology.

Combating coastal salinity requires an Integrated Coastal Zone Management (ICZM) approach, combining scientific groundwater budgeting with ecological restoration to ensure long-term water security.