Shutters of Chennai’s three major reservoirs reopened in view of heavy rainfall from Cyclone Ditwah

With Cyclone Ditwah predicted to bring heavy rainfall over north Tamil Nadu, including Tiruvallur, this weekend, the shutters of Chennai’s three drinking water reservoirs were reopened on Thursday to release a minimal quantity of water and create flood buffer space.

Floodgates of the Red Hills reservoir were opened for the fifth time this northeast monsoon to let out a minimum of 100 cubic feet per second (cusecs) of water as a precaution against flooding in the downstream areas.

The Water Resources Department (WRD) has been maintaining a flood cushion this monsoon by controlling water discharge according to rain and inflow.

Recalling that the shutters of the Red Hills reservoir were closed on November 19, WRD officials said the waterbody now has a storage of 2,823 million cubic feet (mcft), which is 85% of its total capacity. “We plan to gradually step up the water discharge into the surplus course and maintain the reservoir storage at 80%. This will help store heavy inflow during the wet spell expected during the weekend and avert flash floods,” an official said.

About 600 mcft, which translates to a fortnight’s drinking water supply, was discharged from the Red Hills reservoir since the shutters were first opened on October 15. With another month to go before the monsoon ends, the storage levels have been regulated to maintain a comfortable level and reduce flood risk, officials said.

Similarly, 200 cusecs of water was released from the Chembarambakkam and Poondi reservoirs on Thursday. Poondi reservoir, built across Kosasthalaiyar river in Tiruvallur district, receives a flood run-off of about 800 cusecs from catchment areas and another 470 cusecs from Araniyar anicut.

On Thursday, the city’s five waterbodies, including Thervoy Kandigai-Kannankottai reservoir, had a combined storage of 9,665 mcft, which is nearly 82% of their total capacity. This is a significant increase compared to the same day last year, when the five reservoirs together had a storage of 5,435 mcft. The available resources would help maintain daily water supply for a year, officials said.