Thenpannai river flood: Followed SOP, averted disaster, say WRD officials

CHENNAI: The torrential downpour triggered by Cyclone Fengal led to uncontrollable inflow from Thenpennai river’s tributaries in the upstream and downstream of Sathanur reservoir, which in turn resulted in the devastating flood, said the Water Resources Department. Denying the allegation of it being a ‘man-made disaster’, officials said their priority was to avoid loss of lives and ensure the safety of reservoirs.

Flash floods from the tributaries – Koraiyar, Kallar, Thrinjal river, Pambar, Varattar, Aliyar, Thurinjalar, and several other streams – in the upstream and downstream of the reservoir intensified the flow of water in the Thenpennai river, which was already in spate, from Sunday noon.

“We adhere to the Compendium Rules to avert any major flood-induced destruction that could jeopardise the lives of the people downstream,” said an official who closely monitored the discharge of water from Sathanur reservoir.

Explaining the sequence of events, he said Thenpennai river’s catchment area received an unprecedented 170 cm rainfall, including 50 cm in Uthangarai in Krishnagiri, from 2 pm on December 1. This rapidly increased the water level in the reservoir, forcing them to act swiftly to maintain the stability of the 66-year-old dam that irrigates around 50,000 acres in Tiruvannamalai and Villupuram.

Though they can assess the discharge quantum from Kelavarapalli and Krishnagiri reservoirs to Sathanur reservoir, the fifth-largest dam in the State in terms of capacity, they have no mechanism to gauge the volume of water from Thenpennai’s tributaries, Koraiyar and Kallar, in the upstream of Sathanur dam. Similarly, there is no facility to measure the flow of water to Thenpennai from Pambar, Varattar, Aliyar, and Thurinjal downstream.

“Apart from the major tributaries, several streams came to life and discharged huge quantities of water into the already overflowing Thenpennai on December 1 and 2,” said an official.

He explained that rules permit them to store up to 114 feet of water in Sathanur reservoir in October, which is five feet below the full capacity. In November, storage can be maintained up to 117 feet.

“In December, we are allowed to store water up to the reservoir’s full capacity. This is as per the Compendium of Rules for Water Regulation (Sathanur), which we have been following for decades. We do this to ensure supply for irrigation on 45,000 acres in Villupuram and Tiruvannamalai,” he said, maintaining that what happened in the aftermath of Cyclone Fengal’s landfall was a natural disaster.

After the storage touched 117.55 ft on Sunday noon, the officials discharged the entire inflow which ensured that there was no loss of life or major damage downstream, he said.

“The heavy inflow from the tributaries compounded the situation and resulted in flooding in the river. Without a regulating and controlling mechanism in place for the tributaries and assured inflow, it is not feasible to preemptively manage the storage or release a significant quantum of water well in advance. Our actions are always aimed at controlling the flow of the floodwater and limiting the damage during such situations,” he added.

Defending the management of the heavy rainfall and floodwater, another official said if they had not stuck to the standard operating procedure, the situation would have been beyond imagination.