Updated: February 15, 2021 7:53:14 am
Debris and silt washed down after the Uttarakhand flash flood increased turbidity in the Ganga river, affecting water treatment at two Delhi Jal Board (DJB) plants on Sunday and impacting supply to parts of the city.
DJB vice-chairman and AAP MLA Raghav Chadha said on Twitter that turbidity had increased to “unprecedented levels” of 8,000 NTU. As per officials, the normal seasonal concentration is less than 100 NTU.
“In the aftermath of the Uttarakhand disaster, turbidity in raw water fetched by Delhi from the Upper Ganga Canal has increased to unprecedented levels. As a result, Delhi Jal Board’s Sonia Vihar and Bhagirathi water treatment plants are currently operating at reduced capacity. Water supply in parts of South, East and Northeast Delhi is likely to be affected,” Chadha said.
Turbidity is a measure of relative clarity of a liquid and is measured in Nephelometric Turbidity Units (NTU). Debris, silt and mud in the water are among the reasons behind high turbidity.
DJB officials said they were expecting deterioration of water quality and that it was caused due to strong flow of water in the river following the flood.
“The turbidity levels have increased a week after the disaster. We were expecting it sooner, as it is a natural process and can’t be stopped. As an interim measure, we are adding coagulants in the water to help treat it, but we are expecting that by tonight the water quality should return to normal,” a senior DJB official said.
Coagulants are substances that cause particles in liquid to clump together and form clots which can then be filtered out.
The two treatment plants were affected around 1 am on Sunday and water production capacity had to be reduced to 20% at Sonia Vihar plant and 90% at Bhagirathi, officials said.
By afternoon, the turbidity levels had come down to around 6,000 NTU and the Board had sent staff to Muradnagar in Uttar Pradesh, where the Upper Ganga Canal begins, to take samples of the river’s water quality there.
Officials explained that the DJB can treat around 1,000 NTU of turbidity in raw water and bring it down to 1 NTU as is the acceptable limit in drinking water.
High turbidity is often noted around monsoon and the Ganga canal is closed every year after the seasonal rains to clear the sediment at the bottom, officials said. Water supply is expected to resume to normal in all areas by Monday if the water quality improves by Sunday night, officials added.
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