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Saturday, December 07, 2019

What led to mass fish death in Narmada dam? Maybe a tremor

With Narmada dam, also called as Sardar Sarovar Dam, being the lifeline of Gujarat as water from it is supplied to almost the entire state, the Gujarat Pollution Control Board has begun a comprehensive process of “qualitative and quantitative evaluation” of the water from the dam.

Written by Aditi Raja | Vadodara | Published: February 7, 2019 7:47:46 am
What led to mass fish death in Narmada dam? Maybe a tremor Experts believe a seismic activity at the bottom of the reservoir released toxic gases.

Baffled by the sudden mass death of fishes in Narmada dam in Gujarat that had raised an alarm about the quality of water and possible contamination, the authorities are now inclined to believe that a seismic activity at the bottom of the reservoir could have caused a temporary release of toxic gases.

With Narmada dam, also called as Sardar Sarovar Dam, being the lifeline of Gujarat as water from it is supplied to almost the entire state, the Gujarat Pollution Control Board (GPCB) has begun a comprehensive process of “qualitative and quantitative evaluation” of the water from the dam.

Quashing rumours that miscreants may have released toxic chemicals into the dam or the release of effluents into the dam could have caused widescale fish death, experts from the GPCB are veering towards the likelihood of a turbulence at the base of the dam that possibly caused the water to temporarily turn toxic. “We can confirm that the toxicity reported in the dam waters on January 30 was not a result of any external pollutant or waste or chemical being dumped into the dam as many rumours are making rounds. In fact, this incident has necessitated that a thorough qualitative and quantitative analysis of the water has to be undertaken. What we can say as of now is that the level of dissolved oxygen (DO) was very low from its ideal point of 4.2 mg/litre,” R B Trivedi of Ankleshwar GPCB department said.

Dissolved oxygen in water is vital for the survival and growth of aquatic organisms and is used as an indicator of the health of surface-waterbodies. If oxygen level drops below 1-2 mg/litre for few hours, it could result in massive fish kills. The GPCB has suggested to the Sardar Sarovar Narmada Nigam Ltd (SSNNL), that operates the dam, that water samples from the bottom of the dam must be collected and analysed for reaching to a conclusion.

According to hydrological experts, the silt at the base of dams that have stagnant reservoirs could emit toxic gases following a seismic activity at the base. The GPCB, which concurs with the view, confirmed that it had sought the seismology report of the Narmada basin from January 25 onwards to ascertain if any such tremor could have triggered the toxicity.

The GPCB has also sought a water sample of the bottom of the dam, of which the foundation was laid in 1971. However, sources in the SSNNL said that the expertise to collect samples from the lowest levels of the basin is not available with the department. “We might have to jointly seek the help of the Oceanography Department which is most likely to have the equipment to collect samples from the base of reservoirs,” a SSNNL official said.

According to SSNNL officials, the monsoon deficit for the last two years and the simultaneous increase in the height of the dam meant that there was no overflow from the reservoir, thus causing the water to remain stagnant for over two years. “The presence of the original acquatic flora and fauna, as well as the silt in the stagnant water, can result in acidic reactions with the oxygen in the water. Even the sample collected from the surface for three consecutive days were heavily diluted as we suspect that the seismic activity took place around January 25 and triggered the emission from the bottom. Given the vast expanse of the water body, it would take several days for the effects to show, which is why we were informed about it five days later,” an official said.

“If there would be a continuous discharge of effluent or chemical into the waters, it would be seen continuously. The fact that this was a phenomenon that lasted about 2-3 days is an indication that the water is reacting,” the official added.

While a preliminary report of the sample of the Gujarat Water Supply and Sewage Board (GWSSB) has indicated the presence of sulphide in the water, the Gujarat Pollution Control Board (GPCB) has also sent a sample of the water for micro-testing to a Gandhinagar lab.

Meanwhile, the water supply to 138 villages in Narmada and Chhota Udepur district has been stopped as the authorities await the detailed analysis of the water. Chief Secretary J N Singh, who is also a member of the SSNNL, said that the government was taking serious note of the issue and ensuring that the water being supplied to all civic bodies is filtered. “We are ensuring that the output from the Narmada dam is well filtered, chlorinated and fit for consumption. There is no reason to panic or worry as the departments are making sure that the water is safe. The reports are awaited and all measures are being taken to arrive to a conclusion about what went wrong. However, the fishes may have died due to the cold temperatures during that week,” Singh told The Indian Express.

Officials of the GPCB, who are working in tandem with the Fisheries Department as well as the Gujarat Water Supply and Sewage Board (GWSSB) and SSNNL, have also connected with their counterparts in Madhya Pradesh in the jurisdiction of the Omkareshwar and Indirasagar reservoirs to test the water quality at source.

Deputy Chief Minister Nitin Patel on Wednesday told mediapersons that the dam was releasing about 17,000cusec water in the Narmada main canal for drinking and irrigation, which, he said, was “potable and safe”.
The water level of the reservoir as on Wednesday stood at 118.82 metres.

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