The recent unprecedented rain that pounded Tirunelveli and Thoothukudi districts has left a trail of destruction in the form of over 720 breaches of bunds in 515 irrigation tanks in the two districts.
Over 200 engineers of Water Resources Department, drawn from across Tamil Nadu , are working over-time to plug the breaches at the earliest to replenish the tanks from where major quantity of water had drained into the sea.
Engineer-in-Chief (WRD), A. Muthiah, said the average rainfall of Tirunelveli and Thoothukudi districts is over 650 mm. “The districts had received 75% of their annual rainfall by December 15. However, on December 17, the two districts had recorded close to the annual rainfall,” he said.
Kayalpattinam in Thoothukudi district alone had recorded 93 cm of rainfall, followed by Tiruchendur 67 cm, Srivaikuntam 61 cm and Thoothukudi 36 cm. Tirunelveli district too had recorded extremely heavy rainfall and reported an average of 36 cm of rainfall.
“With such a heavy downpour (in both the districts), which could happen once in 100 years, we assume Tamirabharani river had water flowing upto 2 lakh cusecs in Srivaikuntam (in Thoothukudi district) as against the maximum flood discharge capacity of 1.50 lakh cusecs of Srivaikuntam Anaicut (on December 18),” he said.
Water had flowed a few feet above the anicut.
Flash flood in Tamirabharani instead of flowing towards downstream flowed laterally and outflanked on both sides. This flow of flood water enlarging beyond the banks prevented the usual process of draining of rain water into the river and led to the deluge downstream Srivaikuntam, another engineer said.
“It was water everywhere. While at least 22-feet deep water was flowing in the river, around 11-feet depth of water was flowing on both sides of the river submerging everything in the plains,” he said.
The surplus water that flows from one tank to another in the chain of tanks started to breach the bunds of tanks and canal and thus wreaked havoc.
‘Storage in tanks uncontrollable’
To the criticism that water stored in the irrigation tanks should have been drained in advance anticipating such an extremely heavy rainfall, Mr. Muthiah said that all surplus water automatically flows out of the tanks through the weirs.
“Unlike the shutters that are used to control water storage in dams, there is no control mechanism for weirs of tanks,” he said.
The damages of the tanks were more in Tirunelveli district as the sloppy terrain led to higher current of water.
Korampallam tank in Thoothukudi which has a storage capacity of 230 mcft saw some 4 TMC of flood water flowing through the tank that suffered breach. While only 30,000 cusecs could be discharged from it, the peak discharge from the tank was around 46,000 cusecs, he said.
The tank breaches led to soil erosion that eventually washed out road structures at many stretches in the district. Similarly, earthen formation and ballast under railway tracks were damaged for a depth of upto 25 feet for few hundred metres on Sedunganallur-Tiruchendur section.
All these sudden surplussing of the tanks happened despite the fact that only one-third of the total 3,000 number of tanks in the four southern districts of Tirunelveli, Thoothukudi, Kanniyakumari and Tenkasi districts having registered 100% storage before December 17.
Restoration on war-footing
Three senior officials in the cadre of Chief Engineers are supervising the restoration works of bund breaches in both the districts.
Not just engineers, but also contractors from other parts of the State have been entrusted with the task of plugging the breaches in the bunds with labourers and machineries brought from outside.
“In places where the roads have been cut-off, our contractors are carrying out temporary restorations to transport men and materials. We have planned to complete the work on all 720 breaches by December 29 so that any further rain water could be stored in the tanks,” he added.
Already works on some 250 breaches have been attended and the progress of works are being reviewed on a daily basis. With all the dams in Tirunelveli district having higher storage, water could be released through the canals after their breaches are rectified, Mr. Muthiah added.
