Introduction

Seawater intrusion is the process by which saltwater infiltrates a coastal aquifer, leading to contamination of fresh groundwater. With nearly 7,500 km of coastline, India faces this as a growing concern, particularly due to over-extraction of groundwater and rising sea levels linked to climate change.

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Causes of Seawater Intrusion

Natural Causes

• Sea Level Rise due to Climate Change: Rising sea levels increase hydrostatic pressure along coastlines, pushing saline water into freshwater aquifers.
  • Eg: The Sundarbans and Odisha coasts have reported increasing salinity linked to sea-level rise (Source: PIB).
• Tidal Fluctuations and Storm Surges: High tides, cyclones, and storm surges force seawater to flow inland and infiltrate shallow aquifers.
  • Eg: The 2004 Indian Ocean tsunami caused severe seawater ingress in parts of Tamil Nadu.
• Geological and Hydrogeological Conditions: Coastal areas with sandy soils, porous rocks, or low-lying physiographic depressions allow rapid seawater percolation.
  • Eg: Mongrol–Chorwad coast in Saurashtra, Gujarat, faces salinity due to natural hydrogeology and tidal inundation (Source: CGWB).

Anthropogenic Causes

• Over-Extraction of Groundwater: Pumping groundwater beyond natural recharge levels lowers water tables below sea level, reversing flow gradients.
• Eg: Saurashtra and Kutch (Gujarat) experience saline ingress due to excessive groundwater withdrawal.
• Industrial and Agricultural Overuse: Coastal industries and irrigated farming withdraw large volumes of groundwater. This disturbs the freshwater–seawater balance and accelerates intrusion.
• Human-Induced Land Subsidence: Excessive extraction of groundwater, oil, or gas can cause land to sink, reducing the elevation of coastal aquifers. This lowers hydraulic head relative to the sea, increasing the risk of saline water advancing inland.
• Lack of Comprehensive Aquaculture Impact Assessment: Despite documented salinity issues, the Ministry acknowledges there are no specific studies examining how rising groundwater salinity affects coastal aquaculture, highlighting a critical research gap (Source: PIB).

Remedial Measures to Combat the Hazard

• Artificial Recharge Structures: Check-dams, percolation ponds, and recharge wells to restore water balance.
• Controlled Pumping: Enforcing groundwater regulations, shifting to surface water for irrigation and urban supply.
• Subsurface Barriers: Underground dams and cut-off walls to physically block seawater intrusion.
  Eg: Japan uses subsurface barriers effectively in coastal aquifers.
• Conjunctive Use of Water: Integrating groundwater with canal or desalinated water to reduce stress on aquifers.
• Desalination & Treated Wastewater: Using desalination plants and recycled water for urban/industrial use, reducing groundwater dependence.
  Eg: Chennai’s desalination plants supply city needs, cutting coastal aquifer exploitation.

Conclusion

Seawater intrusion threatens livelihoods, agriculture, and drinking water in coastal India. Addressing it requires sustainable groundwater use, ecosystem restoration, and smart recharge methods. Protecting aquifers today secures freshwater and coastal resilience for the future.

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