‘Chennai floods, a rare natural calamity’

The flood in Chennai on December 1 was a rare natural calamity and was not caused by any failure in the management of water releases from reservoirs.

Water discharge from the Chembarambakkam tank was steadily stepped up based on inflows and not all of a sudden. At night, the tank was ‘skillfully and judicially’ managed to moderate the flow in the Adyar River, said a statement issued by Tami Nadu Chief Secretary K Gnanadesikan refuting media reports that flooding of the Adyar River was due to improper management of water releases from Chembarambakkam tank, situated to the south-west of Chennai City in Sriperumpudur Taluk.

Adyar catchment full The water level in the tank on December 1 was 5.08 ft with storage of 228 mcft. The rainfall in November 2015 in Chennai was 1,018 mm, which was the highest rainfall in November since 1918. All the tanks in the Adyar catchment reached full capacity and the surplus water flowed into the Adyar River.

Due to heavy rains, Chembarambakkam tank had copious inflows of water in the middle of November, and 18,000 cusecs was discharged into the Adyar River on November 17. On November 30, the water level was 22.05 ft with an inflow of 750 cusecs and outflow of 800 cusecs.

On December 1 morning, the water inflow started increasing and the water level in the Chembarambakkam tank was at 22.08 ft. As the inflow started increasing, the levels in the reservoir were carefully frequently monitored. Due to continuous heavy rains in the catchment, the tank started to receive heavy inflow in the afternoon, and continued till next day.

Water outflow Based on the field situation, the engineers on the spot increased the outflow to 10,000 cusecs at 10 a.m., 12,000 cusecs at 12 noon and to 20,960 cusecs from 2 p.m. in the afternoon. This outflow was further increased to 25,000 cusecs at 5 p.m. and to 29,000 cusecs at 6 p.m. and maintained at that level till 3 p.m. next day and reduced gradually.

The maximum water level in the tank at 9 p.m. on December 1 was only 23.40 ft and had not reached the full capacity of 24 ft. The entire discharge was through the regulators and there was no uncontrolled discharge through the surplus weirs.

Engineers present at the Chembarambakkam tank site had taken the required decision based on the inflow into the reservoir. Similarly, water was being released from many other tanks and reservoirs, including Red Hills, Cholavaram and Poondi as a result of heavy inflow for which the local controlling officers took the decisions, he said.

Rebuts waiting for CM nod “The allegation that they were waiting for instructions from the Principal Secretary, Public Works Department, and the Chief Secretary, and the imputation that the officers were awaiting the clearance from the Chief Minister are malicious and are canards not supported by the water release data of the reservoir,” he said.

The India Meteorological Department had only given an advisory of isolated extremely heavy rain but did not mention anything about 50 c.m. of rainfall as is being alleged in certain sections of the media, he said.

Flood warning Flood warnings were given by the Collector, Chennai, and other officials in the media, and precautionary measures were taken up by the officials of the District Administration and Corporation of Chennai. The Collector of Chennai issued a first flood warning when the discharge reached 7,500 cusecs at 11.20 a.m. on December 1 and a second flood warning when the discharge reached 20,000 cusecs at 1.32 p.m. on the same day.

The warnings were telecast in television channels and FM Radio channels. There were at least 20 repetitions of the warning in the major regional channels, he said.

Immediately after the second warning, the Collector of Chennai and Corporation of Chennai, in close coordination with Chennai City Police, started the safe evacuation of people from low-lying areas. “Therefore, the allegation that the State Government had not given sufficient alert to the people is not true,” he said.

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