Model Answer
0 min readIntroduction
Seawater intrusion refers to the inland encroachment of saline water into freshwater aquifers, leading to the contamination of precious groundwater resources. With a vast coastline of approximately 7,500 km, India faces this as a significant and growing environmental concern. This phenomenon degrades water quality, threatens agricultural productivity, impacts livelihoods, and jeopardizes drinking water security for millions residing in coastal areas. The increasing population density along India's coasts, coupled with developmental pressures and the impacts of climate change, has intensified the problem, making its mitigation a critical challenge for sustainable water management.
Causes of Seawater Intrusion
Seawater intrusion is a complex issue driven by a combination of natural and anthropogenic factors that disturb the delicate hydrological balance in coastal aquifers.1. Anthropogenic Causes:
- Excessive Groundwater Extraction: Over-pumping of groundwater for agriculture, industrial use, and urban water supply lowers the freshwater table below sea level. This reduction in hydraulic head allows denser saline water to move inland and displace freshwater. For instance, the Chennai and Cuddalore regions in Tamil Nadu, and Saurashtra and Kutch in Gujarat, face severe saline ingress due to extensive groundwater withdrawal.
- Reduced Natural Recharge: Urbanization, deforestation, destruction of wetlands, and altered rainfall patterns lead to decreased infiltration of rainwater, thereby reducing the natural replenishment of aquifers. Concrete surfaces in urban areas prevent percolation, while land-use changes disrupt aquifer geometry.
- Coastal Development and Land-Use Changes: Infrastructure projects, unregulated borewell drilling, sand mining, dredging, and port expansions can increase aquifer permeability and disrupt natural hydrological systems, exacerbating intrusion.
- Human-Induced Land Subsidence: Excessive extraction of groundwater, oil, or gas can cause the land to sink, reducing the elevation of coastal aquifers and increasing the relative hydraulic head of the sea.
2. Natural Causes:
- Sea-Level Rise: Global warming-induced thermal expansion of oceans and melting glaciers contribute to rising sea levels, which increase hydrostatic pressure along coastlines, pushing saline water into freshwater aquifers. The IPCC AR6 report highlights this as a major intensifying factor.
- Tidal Fluctuations and Storm Surges: High tides, cyclones, and storm surges temporarily raise sea levels, forcing seawater further inland and into shallow aquifers. The 2004 Indian Ocean Tsunami, for example, caused severe seawater ingress in parts of Tamil Nadu.
- Geological and Hydrogeological Conditions: Coastal areas with highly permeable soils (like sandy soils), fractured rock formations, or low-lying physiographic depressions are naturally more susceptible to rapid seawater percolation.
- Deltaic Processes: In river deltas, such as the Krishna and Godavari deltas, low groundwater levels due to intensive paddy cultivation and inefficient canal irrigation can lead to salinization of fine-sediment aquifers.
Remedial Measures to Combat Seawater Intrusion
Addressing seawater intrusion requires an integrated, multi-pronged approach involving policy, technical, and natural solutions.1. Policy and Regulatory Measures:
- Groundwater Management and Regulation: Implementing strict regulations on groundwater extraction, including licensing of borewells, instating withdrawal abatements, and promoting the conjunctive use of surface and groundwater. States like Kerala and Andhra Pradesh are implementing groundwater zoning and digital monitoring systems.
- Integrated Coastal Zone Management (ICZM): Adopting comprehensive plans that balance urbanization, industrialization, and ecological conservation in coastal areas, as guided by the Coastal Regulation Zone (CRZ) guidelines.
- National Aquifer Mapping (NAQUIM 2.0): Detailed mapping of coastal aquifers helps in understanding their hydrogeology and planning site-specific recharge and management strategies. The Central Ground Water Board (CGWB) conducts long-term monitoring networks.
- Community Participation: Empowering local communities through initiatives like Atal Bhujal Yojana to manage groundwater resources, prepare Water Security Plans, and engage in water budgeting and rainwater harvesting.
2. Technical and Structural Solutions:
- Artificial Recharge Structures: Constructing percolation ponds, check dams, recharge shafts, and injection wells to replenish freshwater aquifers and create a freshwater hydraulic barrier against saline intrusion. Gujarat and Tamil Nadu have successfully used injection wells and subsurface dykes.
- Subsurface Barriers: Building underground dams or cut-off walls to physically block the inland movement of seawater.
- Strategic Well Relocation: Moving pumping stations inland from vulnerable coastal areas to reduce the direct impact on the freshwater-saline interface.
- Desalination and Wastewater Treatment: Utilizing desalination plants (e.g., Chennai's 100 MLD plant) and recycled treated wastewater for urban and industrial uses to reduce dependence on groundwater.
- Advanced Monitoring Technologies: Employing remote sensing (e.g., ISRO's Bhuvan programme), Geographical Information Systems (GIS), Electrical Resistivity Tomography (ERT) surveys, and water quality analysis (chloride, sodium, electrical conductivity) to monitor intrusion fronts and groundwater levels.
3. Nature-Based Solutions:
- Coastal Afforestation and Wetland Restoration: Conserving and restoring natural barriers like mangroves, coastal wetlands, and shelterbelts which act as physical impediments to seawater penetration and enhance natural recharge. The destruction of mangroves, as seen in the Sundarbans (40% loss), exacerbates the problem.
- Rainwater Harvesting: Promoting rainwater harvesting at household and community levels to augment local freshwater availability and reduce reliance on groundwater.
Conclusion
Seawater intrusion poses a severe threat to freshwater security and the ecological balance of India's coastal regions, intensified by both human activities and climate change. Effectively combating this hazard necessitates a holistic and integrated approach. This includes stringent groundwater regulation, strategic artificial recharge, development of alternative water sources like desalination, and the restoration of natural coastal ecosystems. Collaborative efforts involving government agencies, local communities, and scientific institutions are crucial for formulating and implementing sustainable water management policies that ensure long-term coastal resilience and freshwater availability for future generations.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.