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?

Introduction

Seawater intrusion, the process where saline seawater infiltrates freshwater coastal aquifers, poses a significant threat to India's coastal regions. With over 7,500 km of coastline, this phenomenon jeopardizes drinking water supplies, agriculture, and ecosystems. The problem is exacerbated by over-extraction of groundwater, rising sea levels due to climate change, and unplanned urbanization in coastal areas.

Key Dimensions of Seawater Intrusion

Causes of Seawater Intrusion

1. Over-extraction of Groundwater

• Excessive pumping of groundwater for agriculture, industry, and domestic use reduces the freshwater pressure, allowing seawater to infiltrate.
• Example: Chennai and Gujarat have reported significant seawater intrusion due to over-extraction.

2. Sea Level Rise

• Rising sea levels, driven by global warming, increase the hydraulic pressure of seawater, pushing it into coastal aquifers.
• According to the IPCC, global sea levels are rising at an average rate of 3.7 mm per year.

3. Unplanned Coastal Urbanization

• Construction activities and land-use changes disrupt the natural recharge of aquifers, reducing their ability to resist seawater intrusion.
• Example: Mumbai and Kochi face challenges due to rapid urban expansion.

4. Aquifer Characteristics

• Coastal aquifers with high permeability (e.g., sandy aquifers) are more prone to seawater intrusion.
• Shallow aquifers are particularly vulnerable.

5. Climate Change Impacts

• Increased frequency of cyclones and storm surges lead to temporary or permanent salinization of coastal aquifers.
• Example: The Sundarbans region frequently experiences salinity ingress after cyclones.

6. Reduction in River Flows

• Reduced freshwater inflows from rivers due to dams and upstream water usage decrease the natural flushing of saline water from coastal aquifers.

Remedial Measures to Combat Seawater Intrusion

1. Sustainable Groundwater Management

• Regulate groundwater extraction through policies and community participation.
• Promote micro-irrigation techniques like drip irrigation to reduce water demand.

2. Artificial Recharge of Aquifers

• Construct recharge wells, percolation tanks, and check dams to enhance groundwater recharge.
• Example: Managed Aquifer Recharge (MAR) projects in Gujarat have shown success.

3. Coastal Zone Management

• Implement Integrated Coastal Zone Management (ICZM) to regulate land use and protect aquifers.
• Example: The ICZM project in Odisha focuses on sustainable coastal development.

4. Use of Salinity Barriers

• Construct physical barriers or inject freshwater into aquifers to create a hydraulic barrier against seawater intrusion.
• Example: Subsurface dams in Japan have been effective in controlling salinity ingress.

5. Afforestation and Mangrove Restoration

• Mangroves act as natural barriers against seawater intrusion by stabilizing coastlines and reducing storm surges.
• Example: Mangrove restoration in the Sundarbans has mitigated salinity ingress.

6. Desalination and Alternate Water Sources

• Promote desalination plants to reduce dependence on groundwater in coastal areas.
• Example: Chennai's desalination plants provide an alternative to groundwater use.

7. Monitoring and Early Warning Systems

• Establish real-time monitoring systems to track salinity levels in coastal aquifers.
• Use remote sensing and GIS for mapping vulnerable areas.

Conclusion

Seawater intrusion is a critical challenge for India's coastal regions, threatening water security and livelihoods. A combination of sustainable groundwater management, coastal zone regulation, and climate-resilient strategies is essential to mitigate this hazard. Aligning these efforts with SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action) will ensure long-term water security and environmental sustainability.