The floods in Chennai on December 1st, 2015 were a rarest of rare natural calamity and were not caused by any failure in the management of water releases from reservoirs, said Chief Secretary

Floods not man-made disaster Five things TN Chief Secretary said defending govt
news Monday, December 14, 2015 - 12:02

 After being heavily criticized by various media organizations over Chennai floods, the Tamil Nadu government has for the first time come out to defend itself and clear its stand on the issue.

Read: Chennai floods: What happened at Chembarambakkam, negligence or natureā€™s fury?

Here are the five things Tamil Nadu Chief Secretary K. Gnanadesikan said defending the Government:

1. The allegation that the State Government had not given sufficient alert to the people is not true.

Revenue and corporation officials went from street to street alerting the people about the water release through megaphone. 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 the low lying areas including Saidapet, Jaffarkanpet, Kotturpuram and Ramapuram. Over 30,000 persons were evacuated from these low lying areas. The Collector of Kanchipuram evacuated 17,300 persons. Therefore Earlier, Chief Minister had a review with senior Ministers and officials on the forenoon of December 1, 2015 and had clearly instructed that since there were heavy rains from the night of 30.11.2015 and since the IMD had predicted heavy rainfall on December 1, 2015, all the precautionary measures have to be taken.  The Chief Minister had also instructed the senior Ministers to oversee relief and rescue measures. 

2. No uncontrolled discharge of water

From the inflow, outflow and storage level data of Chembarambakkam Tank, the following becomes self evident:-

i. The discharge levels were steadily stepped up based on inflows and not all of a sudden.

ii. At night time, the tank was skill-fully and judicially managed in order to moderate the flow in the Adyar river at night.  The reservoir level was steadily brought down from the morning of December 2, 2015.

iii. The maximum water level in the tank at 9PM on December 1, 2015 was only 23.40 ft. and had not reached the FTL of 24 ft. Hence, reports in sections of the media of overflow from Chembarambakkam Tank after the Tank reached its full capacity of 24 ft. is factually incorrect and contrary to facts. The entire discharge was through the regulators and there was no uncontrolled discharge through the surplus weirs.  

Some media reports have suggested that the water level could have been brought down even further below 22 feet to18 feet or so and the realization of inflows from December 1, 2015 could have been stored in the tank thereby preventing floods. The reservoir levels are managed based on the Rules for Flood Regulation of the Compendium of Rules of Regulation which requires the water level to be maintained at 2 feet below the Full Tank Level. That rule was followed in the Chembarambakkam Tank on this occasion as well.

3. We followed rules.

The Rule balances the interests of flood control, storage of water for the period of scarcity and the safety of the tank. Given the cross sectional shape of the reservoir, the top two feet of the reservoir have the greatest water spread and hence the highest storage capacity. The reservoir received about 2.13 TMC ft. of water in a span of 24 hrs from 12.00 noon on 1.12.2015 to 12.00 noon on 2.12.2015 which is about 60% of the capacity of the reservoir. Hence, no significant difference from the flood control perspective would have been made by lowering the level below 22 feet.  Even if the water level had been kept at 75% of the capacity of the tank it would have delayed the release of the heavy inflows merely by two hours. It must be noted that Chembarambakkam accounts for only 44 percent of the catchment of the Adyar. 

4. Heavy rains worsened situation

Further, due to heavy rains, 4 tanks namely, Nandhivaram, Urappakkam, Mannivakkam and Adanur Tanks breached on reaching  their maximum water level. This, in turn, resulted in heavy inflow into the Adyar River. Chennai City also received a rainfall of more than 30 cm on 1.12.2015. The flow in Adyar River reached its full capacity due to the surplus from Chembarambakkam Tank, the inflow from the catchment areas of Adyar within Chennai City and the surplus received from the other tanks. In view of the heavy flow in the Adyar River, the high intensity runoff of local rain fall in Chennai City and adjoining urban areas could not fully drain into the Adyar and hence contributed to the inundation of the City.

5. Rarest of rare occurence

It is clear that the flooding on 1st December, 2015 was caused primarily due to the very high rainfall in November, 2015, the second highest recorded in more than 100 years followed by high intensity of rainfall in Chennai, Kanchipuram and Tiruvallur Districts  on 1st December, 2015. The floods in Chennai on December 1st, 2015 were a rarest of rare natural calamity and were not caused by any failure in the management of water releases from reservoirs. In fact, the work of keeping the Adyar River mouth open for free flow of flood water into Bay of Bengal which is being continuously executed throughout the year using machinery helped in the faster discharge of the flood waters, preventing even greater inundation of the City.

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