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Seawater intrusion seen north of Chennai

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Groundwater quality between Ennore and Ponneri badly hit, finds Anna University study

The coastline north of Chennai is the worst affected along the country’s east coast, with a stretch of nearly 14 km experiencing seawater intrusion.

Owing to seawater incursion, groundwater quality between Ennore and Ponneri has deteriorated, according to a recent study by Anna University.

The study, ‘Seawater intrusion and submarine groundwater discharge along the Indian coast’, by L. Elango and V. Manivannan, noted that a nearly 300-km stretch of the Indian coastline had been affected by seawater incursion.

Extent of the problem

Seawater has entered several locations along the coastline in Tamil Nadu — Cuddalore (9,620 uS/cm), Chennai (25,000 uS/cm), Kanniyakumari (14,650 uS/cm), Cauvery delta region (7,850 uS/cm) and Nagapattinam (12,430 uS/cm).

It has also affected Puducherry (3,310 uS/cm). uS/cm or microseimens per centimetre is a unit of measurement of electrical conductivity.

Normally, if electrical conductivity in coastal groundwater is more than 3,000 uS/cm, it indicates that groundwater near the coast is affected by seawater incursion.

Prof. Elango, professor, Department of Geology, Anna University, said the study attempted to estimate the extent and depth of penetration of seawater into land.

“As seawater is denser, it is natural for it to intrude into coastal aquifer by a few metres. But overexploitation of groundwater resources has led to intrusion to a greater distance, particularly north of Chennai,” he said.

The study also found that seawater had intruded to a depth of 10 m, up to an extent of 2 km, between Thiruvanmiyur and Injambakkam, south of Chennai.

Mitigation measures

The study, published in the Environmental Science and Pollution Research journal, suggested that seawater intrusion could be mitigated by rearranging pumping wells, like closing of Minjur wellfields, reducing the pumping of groundwater and increasing groundwater recharge by constructing check dams on Araniar and Kosasthalaiyar rivers.

“The rivers have more check dams lined up now. We estimate that seawater intrusion, in a distance of 5 km north of Chennai, can be reversed by 2030, with better recharge measures,” Prof. Elango emphasised.

“We also assessed the status of seawater intrusion based on the groundwater table observed over 991 wells between 2007 and 2017. We observed that nearly 1,900 sq. km of the coast had groundwater levels at 0 m to –2 m below mean sea level in 2007 and and this increased to 2,600 sq. km by 2017. The decrease in recharge had led to a dip in water table in many areas of Tamil Nadu, Gujarat and AP,” he said.

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Printable version | Jan 28, 2020 11:32:05 AM | https://www.thehindu.com/news/cities/chennai/seawater-intrusion-seen-north-of-city/article30437575.ece

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