Swell in Yamuna kills the stink

NEW DELHI: If you thought the Delhi stretch of Yamuna had long become a sewage pool, visit the river now. Flooded to the brim, it is reminiscent of what Yamuna may have originally looked like. The flood may have played havoc by displacing communities but it has also managed to dilute the polluted water and enliven a dead river.

Towards Okhla (downstream) the river water usually has a biochemical oxygen demand of 40 to 50 mg/l but since June 15, the BOD measured less than10 mg/l according to Central Pollution Control Board.

BOD is an important determinant to show how polluted the river water is. It is a measure of the quantity of oxygen used by microorganisms in the oxidation of organic matter. The acceptable limit of BOD is 3 mg/l.

"The pollutants have been washed away but the water is very turbid because of the debris that has come with the floodwater and runoff from agricultural fields. Even after the water level recedes, there will still be surplus water and we expect that pollution levels will be low for about two months," said a senior officer from CPCB.

The flooding will also have an impact on the groundwater say scientists. Saumitra Mukherjee, professor of geology and remote sensing, School of Environmental Sciences, JNU, says that there are lots of negative effects of flooding but one of the positive impact is the improvement in soil quality. "The flood brings with it fine silt, clay and sand. These and the sediment formed from them are usually fertile and can be beneficial for agricultural purposes. The floodwater also helps recharge underground aquifers," he says.

However, he warns that the floodwater loaded with fecal matter can contaminate both the surface water and groundwater. "There has to be intensive monitoring of the water quality to check if it can cause contamination. When the floodwater starts receding there is a high chance of an epidemic and spread of bacterial infection among communities living by the river," he adds.

The flooding also impacts aquatic life. The dead river may now have enough water to create the environmental conditions for spawning of certain species of fish.

"Floods are very important for Yamuna in Delhi. Earlier we had a lot of wetlands but development has eaten in to those. Usually during floods when the floodwater recedes, these pools or wetlands are recharged. Even our floodplains have been encroached upon. We need forests and grasslands by the river to retain and use the floodwater. We need a river front forest ecosystem," adds Faiyaz A Khudsar, scientist at Yamuna Biodiversity Park.

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