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Seawater intrusion threatens drinking water source along India's coast

Read time: 4 mins
8 Jan 2020
Seawater intrusion threatens drinking water source along India's coast

The impacts of climate change on coastal areas are severe than inland as they are vulnerable to flooding and extreme weather phenomena like cyclones, tornadoes etc. As the climate crisis deepens, a quarter of India's population, who live along the coasts, have another issue to worry about – availability of freshwater. Due to unchecked pumping of groundwater for daily use and rainfall variation, freshwater sources are being depleted. Besides, saltwater from the sea is unwittingly finding its way into local aquifers through a process called seawater intrusion.

Although many independent studies, conducted at different locations, have observed depletion in freshwater sources along India's coasts, there is no comprehensive study yet. Now, researchers at Anna University, Chennai, have tried to address the extent of seawater intrusion in the Indian coastal regions in a study published in journal Environmental Science and Pollution Research. The study was funded by the National Centre for Earth Sciences Studies, Earth System Science Organisation, and the Ministry of Earth Sciences.

The researchers scanned through many peer-reviewed articles on the effects of seawater intrusion in India. The selected studies employed various methods to identify seawater intrusion, namely - Groundwater Level Method, Geophysical Method, Geochemical method, Isotopic Signatures, Chemical Indices and Groundwater modelling. They also used data on groundwater levels of 991 wells for the years 2007 and 2017 obtained through WRIS-WebGIS, an ingeniously developed water resources information system. This combination of data provides a thorough understanding of the problem of seawater intrusion.

The study found that few coastal regions of Gujarat, Tamil Nadu and Andhra Pradesh are greatly affected by seawater intrusion because the groundwater level was below the mean seawater level. However, the extent of seawater intrusion along the west coast was lower compared to the east coast as the west coast is at a higher altitude. The total area affected by seawater intrusion is nearly 2600 sq km—an increase of approximately 500sqkm between 2007 and 2017. Chennai was found to be the most affected city with observed seawater intrusion of about 14 km.

If the current trend continues, "climate change and sea-level rise will make the groundwater unusable due to an increase in seawater intrusion," warns Prof Elango L from Anna University, who led the study. "Overuse of groundwater from the coastal region will increase the extent of seawater intrusion and the groundwater will no longer be usable due to an increase in salinity," he adds.

The researchers suggest controlling the unchecked pumping of groundwater near the coastline and moving of pumping wells, which are adjacent to the seaside, inland. Another mitigation process involves the pumping of contaminated groundwater from coastal aquifers, which will replace saline groundwater with freshwater. Among all the tested mitigation efforts by various researchers, the most efficient method, as per the researchers of the current study, is to allow for increasing groundwater recharge, via permeable pavements and percolation ponds. These structures store rainwater and recharge the subsurface water.

Though the study identifies possible critical locations, the researchers call for more focused studies to get better and accurate data on seawater intrusion. Since rainfall in India is seasonal, the researchers say that the temporal dynamics of seawater intrusion also needs to be assessed.

As water demand increase exponentially due to population growth and unchecked 'development' along the coasts, such an imminent threat needs to be tackled immediately by the authorities in sync with the experts and the citizens. Policymakers should employ all the mitigation solutions and mainly, put a stop to this unchecked pumping of groundwater along the coasts.

To quote American humorist Will Rogers, "First thing to do when you find yourself in a hole, is to stop digging." 

This article has been run past the researchers, whose work is covered, to ensure accuracy.