With storage in the city’s two major reservoirs falling to nearly 50% of their capacity, citizen groups and activists seek timely desilting to recover lost storage capacity.

The Water Resources Department (WRD) is examining a revenue-based model for the exercise. The combined storage of the five major reservoirs, including Chembarambakkam, stands at 6,148 million cubic feet, which is nearly 52% of their total capacity.

The storage in Red Hills and Poondi reservoirs has dropped to nearly 51% and 34% of their capacity.

Dry patches are visible in the rear portions of the waterbody in Red Hills due to the receding water level.

Residents and representatives of citizen groups said similar dry stretches had emerged in the Poondi reservoir — one of the city’s primary sources of drinking water — from where water is diverted to other reservoirs.

They underlined the need for timely desilting of the waterbodies to recover the lost storage capacity.

S. Sameer, founder, SWOTT (Social Work Team Trust), a non-governmental organisation engaged in waterbodies conservation, said the rear portions of the Red Hills reservoir had dried up and were clearly visible near places such as Surapet and Kannappasamy Nagar, Puzhal.

The department must attempt targeted desilting measures to enable additional storage of water during the rainy season, he said.

He also sought action against the discharge of sewage into the Red Hills reservoir at various locations, including Surapet, Pammadhukulam, Padianallur, and Venkatachalam Nagar in Thirumullaivoyal.

The Poondi reservoir receives about 210 cubic feet per second (cusecs) of Krishna water from Andhra Pradesh, which is diverted to the Chembarambakkam reservoir to raise the water level and facilitate distribution in city.

In 2018, the department proposed desilting of the major reservoirs, which it decided to carry out as a revenue generation model.

While the work made some progress in Cholavaram reservoir, the project, aimed at creating an additional capacity of about 1,900 million cubic feet across the reservoirs, was not executed. This was partly because the waterbodies had ample storage in the subsequent years.

The WRD officials said Krishna water had increased the storage of Poondi reservoir by nearly 450 mcft since May 27. Talks are in progress with Andhra Pradesh authorities to increase the release of Krishna water to Chennai, they said.

The city’s reservoirs have sufficient storage to sustain water supply this year, they added.

While the study to augment the capacity of Poondi reservoir is under scrutiny, the department is exploring ways to make the revenue generation model more effective for desilting works, officials said.