Why did Chennai Flood in 2015?

CAG report says PWD indiscriminately discharged 29,000 cusecs of water from Chembarambakkam.

Published: 10th July 2018 04:56 AM  |   Last Updated: 10th July 2018 04:03 PM   |  A+A-

Express News Service

CHENNAI : A to a report by the Comptroller and Auditor General of India (CAG), the Chennai floods of 2015 could have been avoided if the Public Works Department (PWD) had followed Central Water Commission’s (CWC) guidelines on dam safety, as the northeast monsoon was vigorous. The report hit out at PWD’s Water Resources Department (WRD) for failing to revise Compendium of Rules of Regulation of Chembarambakkam Tank for 23 years from the date of installation of regulated arrangement to the tank. No lessons were learned from damage caused in the 2005 floods, it said.

The report says the CWC guidelines on Release Procedure states that the aim of reservoir operation was to reduce the risk of man-made floods through careful preparation of reservation regulation schedule, release procedure and gate opening schedules with accurate and reliable flood forecasting and warning system.“In the absence of any gate opening schedule as prescribed under Central Water Commission norms, the decision to release water results with Section officer incharge of the tank.

Since no record was made available, CAG observed from data that on December 1, 2015, there was a huge discharge of 29,000 cusecs of water by the section officer. Though the department claimed a telephonic conversation was made by in-charge of tank and chief engineer of PWD, who was personally monitoring the entire activity, the documentation of telephonic conservation was not found on record to ascertain the veracity of the claim,” the report stated.

“The indiscriminate discharge of water in excess of inflow took place... as a result, the burden on Adyar river was more leading to a massive flood in Chennai and suburban areas. Though a watchful supervision was in place as claimed by WRD, it could not be even ensured that total outflow from Chembarambakkam Tank did not exceed the inflow for 13 hours as no schedule for gate opening was available,” the report explained.

“This implies that due to nonensuring of discharge of water in sustained manner, the catastrophe that had happened during North- East Monsoon 2015 may be categorised as a man-made disaster as per CWC Guidelines.” The report recommended updation of Compendium of Rules of regulation of Chembarambakkam Tank and fixing responsibility on officials for failure to follow CWC guidelines


Chennai downed in 2015 due to the release of 29,000 cusecs of water as the Central Water Commission norms were not abided by Water Resources Department. The department wanted to protect a private patta land in the water spread area from getting submerged, according to a Comptroller and Auditor General (CAG) of India report. According to Compendium of Rules for Regulated Tanks, WRD should store water at the Full Reservoir level in December, and it does not allow presence of private patta land inside water spread area.

  1. The patta land was required to be acquired  for ensuring storage of water till the full capacity of the reservoir. It  as observed that the full tank capacity of Chembarambakkam was 3.645 TMC at a storage depth of 24 ft.
  2. However, the same was not achieved on December 1 and December 2 as water was stored only up to a maximum of 3.481 TMC leaving 0.164 TMC of remaining capacity unutilised to protect possible submergence of patta land on foreshore area which was in absolute violation to Compendium of Rule and regulations.
  3. The indiscriminate release of water was done to protect private patta land.
  4. This was a serious failure in operation of reservoir and it contributed to Chennai floods.
  5. The discharge of 29,000 cusecs of water for 21 hours coupled with surplus water in upstream tanks and catchments caused a huge disaster for Chennai.
  6. The state lacked a law on Flood Plain Zone and an updated Water Policy to protect natural waterways.
  7. Though Tamil Nadu District Municipalities Building Rules, 1972 had envisaged for maintaining 15 m buffer zones from margin of waterways, CMDA’s second master plan failed to demarcate flood plain zones to regulate construction along waterways.
  8. Failure of WRD to create two new reservoirs in upstream of Chembarambakkam tank as recommended by nucleus cell for flood mitigation.
  9.  Encroachment of tank, lakes and river beds played a major role in causing floods.
  10.  The scrutiny of a periodical inspection report on safety of Chembarambakkam dam submitted to Dam Safety Directorate revealed that wireless communication facility was not functioning for more than six months prior to the floods, highlighting that WRD did not possess adequate emergency preparedness plan as envisaged in the Dam Safety Procedure.

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