Q8. Seawater intrusion in the coastal aquifers is a major concern in India. What are the causes and the remedial measures to combat this hazard? (10 Marks, 150 Words)
| Approach |
| Begin with a concise definition of seawater intrusion and India’s vulnerability (cite IPCC/UNEP/CGWB). Next, outline causes in two categories—anthropogenic (over-extraction, recharge loss, agriculture/tourism, coastal works, ecosystem degradation, dams, subsidence) and natural (sea-level rise, cyclones, geology, deltaic processes, tidal/ENSO variability). Then, present remedial measures using a multidimensional frame—nature-based, policy, technology, structural solutions with best practices. Conclude by stressing climate adaptation and sustainable coastal water governance. |
Seawater intrusion refers to the inland encroachment of saline water into freshwater aquifers when the balance between freshwater hydraulic head and seawater pressure is disturbed.
In coastal aquifers, freshwater head inland normally prevents seawater from advancing. Freshwater is lighter than saline water (density ≈ 1.0 vs 1.025 g/cm³), so it floats above, forming a freshwater lens.
However, due to reasons such as sea-level rise, extreme events, and groundwater overuse are expected to intensify it (IPCC AR6). UNEP (2022) ranks it among the top five global groundwater risks. With ~7,500 km of coastline, India is highly exposed for Tamil Nadu, Gujarat, Andhra Pradesh, and island territories (CGWB).
A. Anthropogenic Causes
- Groundwater Overuse
- Excessive pumping for irrigation, cities, and industry lowers inland freshwater head.
- Deep pumping causes saline upconing from lower aquifers.
- Ex. Chennai – seawater ingress detected up to 15 km inland (CGWB).
- Land-Use and Recharge Suppression
- Urbanization, concretization, and wetland reclamation reduce natural recharge of freshwater.
- Ex. Kochi wetlands lost to reclamation aggravated salinity.
- Sectoral Water Demands
- Agriculture (tube wells, water-intensive crops), industrial clusters, and tourism resorts create localized stress by drawing freshwater from groundwater.
- Saline irrigation return flows worsen secondary salinization.
- Cases: Saurashtra (cotton irrigation); Goa (tourism aquifers).
- Coastal Engineering & Extractive Works
- Sand mining, dredging, and port expansion increase permeability and disturb the sea–aquifer balance.
- Ex: Ennore & Paradip ports, Kerala coasts.
- Ecosystem Degradation & Maladaptation
- Loss of mangroves and wetlands removes natural salinity buffers (IPCC AR6).
- Shrimp aquaculture and fish ponds leak saline water into aquifers (Odisha, Andhra).
- Desalination plants discharge brine nearshore, steepening gradients.
- Ex. Sundarbans mangrove depletion.
- Upstream River Regulation
- Dams/diversions reduce freshwater discharge and sediment supply, allowing saline wedges to penetrate deltas.
- Ex. Cauvery delta (Tamil Nadu).
- Land Subsidence (Human-induced)
- Over-extraction compacts aquifers → land sinks relative to sea → higher seawater pressure.
- Ex. Peri-urban Chennai/Kolkata.
B. Natural Causes
- Climate-Driven Pressures
- Sea-level rise increases saline pressure.
- Cyclones, storm surges, and tsunamis push seawater inland.
- Ex. 2004 Tsunami (Andaman & Nicobar); Cyclone Aila (2009, Sundarbans).
- Geological & Hydrogeological Settings
- Sandy soils, fractured rocks, and coral limestone aquifers allow rapid ingress.
- Shallow aquifers form thin freshwater lenses with weak resistance.
- Ex. Lakshadweep coral aquifers.
- Deltaic & Coastal Dynamics
- Natural delta subsidence, erosion, and barrier island breaches open pathways.
- Connate saline pockets (trapped paleo-marine water) get mobilized under reduced pressure.
- Ex. Krishna–Godavari delta.
- Hydrodynamic & Climatic Variability
- Tidal pumping and estuarine saline wedge migration during low flows infiltrate aquifers.
- Weak monsoons reduce recharge; ENSO extremes (El Niño droughts) prolong low-head conditions.
Impact of Seawater Intrusion
Seawater intrusion causes water scarcity, soil salinization, crop loss, livelihood shifts, ecosystem damage, infrastructure corrosion, economic decline, and migration, with IPCC warning climate change will intensify impacts through sea-level rise and cyclones.
Remedial Measures for combating sea-water intrusion
| Phase | Nature-Based Solutions | Policy / Governance | Science & Technology | Structural / Engineering |
| Prevention | Mangrove & wetland restoration (Muthupet, TN)
Coastal dune protection |
– Enforce CRZ norms
– Zoning to limit borewells |
– Aquifer vulnerability mapping (NAQUIM) | – Coastal setback zones
– Land-use planning |
| Mitigation | – Rainwater harvesting, percolation ponds (Saurashtra model)
– Salt-tolerant crops |
– Conjunctive water use
– Community groundwater budgeting (AP Water User Associations) |
– Salinity monitoring sensors
– Crop diversification |
– Subsurface barriers (Japan, Israel)
– Freshwater ridge via injection wells |
| Preparedness | – Eco-buffers: mangroves, seagrass
– Agroforestry for soil resilience |
– Integrate SLR projections in SAPCCs/NAPCC
– Community training & awareness |
– GIS-based early warning
– Community desalination kits (Lakshadweep pilot) |
– Storm surge barriers, levees
– Emergency recharge wells |
| Response | – Use alternative freshwater (ponds, tanks) | – Emergency extraction controls
– Tanker supply schemes (Chennai, 2019 drought) |
– Mobile desalination plants (A&N Islands, post-tsunami)
– Blending saline with freshwater |
– Temporary pumping barriers
– Aquifer flushing |
| Recovery | – Soil reclamation with gypsum/organic matter
– Afforestation on degraded lands |
– Access climate finance (GCF projects in coastal Odisha)
– Build coastal community cooperatives |
– Long-term monitoring networks
– Managed Aquifer Recharge (MAR) |
– Treated wastewater recharge (Israel MAR systems)
– Underground dams (Japan, Gujarat pilot) |
| Modes of Sea-water intrusion |
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