Delhi: Deluge gives Yamuna clean sweep, its best on record

NEW DELHI: If the Yamuna looked more like a river recently than it has in a long while, it is because of the strong flow caused by excess water released upstream. The river reclaimed its territory and the water cleaned it of the stubborn effluents.

The report on the water quality for Sept shows remarkable change in the major parameters. Delhi Pollution Control Committee said that on some stretches downstream of the Najafgarh drain, the water even met the standards for faecal coliform, which marks the presence of sewage in the water, dissolved oxygen (DO) which signifies life in the river, and biochemical oxygen demand (BOD), which depicts its self-healing capacity.

While the urban floods kept the administration on its toes, the river saw its health improving remarkably. Samples collected on Sept 4, a day before the river swelled past 207 metres, showed faecal coliform levels at 3,500 MPN/100ml, a dramatic drop from an astounding range of 21,000-2,000 lakh units logged since 2019. In Aug, the faecal count was 54,000 MPN/100ml.


While DPCC was monitoring the river quality since 2013, the faecal levels were consistently monitored only after Sept 2019, prior to which records on coliform are mostly missing. However, those available exceeded the standards by an exponential value. Even if compared with 2013, parameters like BOD showed remarkable improvement this Sept, which at its worst was 13 mg/l only. The records also show that the river is cleaner than in previous flood months or on occasions when the water level hit the 207m mark.

The Sept analyses show BOD levels ranging from 2.5 to 13.5 mg/l, which always used to degrade south of the Najafgarh lake and hovered well above 50 mg/l. DO measurements ranged between 9.5 to 3.7, which otherwise plummeted to nil after the confluence with the Najafgarh drain.

Rainwater always infuses life into the river, but this year's improvement was unprecedented. In 2013 and 2023 too, when the river level breached the 207m mark, the river didn't end up as clean as this year. In 2023, the faecal coliform levels were 220,000 units in Sept, 1,70,000 in Aug and 320,000 in July. In 2021, when Sept saw a record precipitation of 413.3mm, the max faecal levels was 3,50,000 MPN/100ml.

While Delhi govt deployed garbage and solid waste collecting machines in the river, the effluents still contaminated the river due to a poor sewage treatment system, as also noted by Delhi High Court in Aug.

According to the experts, the DPCC report for Sept is on expected lines. "The Yamuna shows significant improvement in the key parameters primarily due to the flood spell in the river. The samples were taken on the day when a huge volume of floodwater from the Hathnikund barrage had already reached and was passing through the Delhi segment, flushing out the legacy pollutants. This is also a time when the major city drains are kept closed to avoid back flooding, thus greatly reducing the entry of large volumes of effluents in the river system," noted Bhim Singh Rawat of the South Asia Network on Dams, Rivers and People.

Rawat, however, pointed out some problems with the analyses, including not figuring out permissible limits for three parameters - chemical oxygen demand (COD) and the presence of phosphates and ammoniacal nitrogen.