Cauvery river flowing through Mettur Dam in Tamil Nadu. (File Photo)

CHENNAI: For long, Tamil Nadu has been waging a war with Karnataka to secure its due share of Cauvery water . Now the fight, if the state goes by the report of the Central Pollution Control Board, may not just be about the quantity of water. It would also be about quality. Karnataka is polluting the river before it enters Tamil Nadu, says a report filed by the board in the Supreme Court on Friday.

The board said the Thenpennaiyar and Arkavathi, both tributaries of the Cauvery, were being polluted before they flow into Tamil Nadu. The report was submitted in the apex court in connection with a case filed by Tamil Nadu in 2015 to restrain Karnataka from letting untreated sewage and industrial effluents into the river.

The river is the lifeline for people in western, central, northern and southern parts of the state.

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About 1,200 million litres of sub-surface Cauvery water from wells along the banks of the river are tapped by the state government every day to provide drinking water to about 20% of the state’s population in 19 districts. In all, 127 combined drinking water supply schemes in the state are fed by the river.

The water samples from the three rivers were tested jointly by the CPCB and the Karnataka and Tamil Nadu pollution control boards between September and December last year. The samples were lifted from Ajjibore (river Cauvery), Chokkarasanapalli (river Thenpennaiar) and from the Arkavathi river near Sangama, before it joins the Cauvery river, for four months.

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"River Thenpennaiyar is polluted and comprehensive plan of action is required for restoration of its water quality. The Arkavathi and Cauvery rivers were found to be polluted due to higher count of faecal coliform, attributed to open defecation and requires vigilance from the concerned organisations in the state to prevent further pollution," the CPCB report said.

The joint monitoring and analysis of samples revealed that river Arkavathi, before Sangama and river Cauvery at Ajjibore met the desired water quality criteria for the first three rounds in September, October and November with respect to presence of organic pollution measured as Biochemical Oxygen Demand (BOD). However, it exceeded limits in December. Total coliform and faecal coliform, an indicator of bacteriological pollution, exceeded the limits during September and October in the Arkavathi river. Same was the case in the Cauvery in October. In the case of Thenpennaiyar, the samples did not meet the criteria with respect to all parameters in all four rounds of monitoring. The sampling locations were identified after CPCB held elaborate discussions with the two states.

CPCB also pointed out that Karnataka raised objections to monitoring the Arkavathi river, even as Tamil Nadu maintained that the river was the source of pollution. The meeting decided that CPCB would collect the samples only from the river near Sangama for assessing the pollution load contributed by the river. "No state should let polluted water into another state. Tamil Nadu will submit its remarks to the apex court for stringent action during the next hearing, scheduled after two weeks," said a senior TN official. Arkavathi river joins Cauvery at Sangama, about 55kms from Bengaluru, and passes through Mekedatu, four kms away from Sangama, before entering Tamil Nadu near Hogenakkal. Tamil Nadu’s contention is that untreated sewage and industrial effluents are let into the river in and around Bengaluru.

Thenpennaiyar river originates at Nandidurg Hills in Karnataka and enters Chokkarasanapalli village in Tamil Nadu, 25 kms from Hosur, and passes through five northern districts — Krishnagiri, Dharmapuri, Tiruvannamalai, Villupuram and Cuddalore. Tamil Nadu argued that the river received untreated sewage and industrial effluents from Belandur Lake and Vardhur Lake in Karnataka. About one-third of Bengaluru city falls in the Cauvery basin, and twothirds of the area falls in the Thenpennaiyar basin. The rainfall runoff from Bengaluru in the Cauvery basin drains through Arkavathi river and joins Cauvery, while rainfall from the other two-thirds drains into a tributary of Thenpennaiyar and reaches Kelavarapalli reservoir in Hosur. "It is unfortunate that Karnataka has not taken efforts to ensure proper sewage treatment in and around Bengaluru," the official said.

