Srisailam dam safety under lens

Deepening plunge pool cause for concern, not alarming: Official

By Author  |  Published: 17th Aug 2019  12:37 amUpdated: 17th Aug 2019  1:26 am
The scouring of the river bed where water from spillway falls is learnt to have left a gaping hole that is more than 200 feet in depth

Hyderabad: An ever-deepening plunge pool that formed about 100 m away from the Srisailam dam spillway, following years of battering of the river bed by the sheer force of water released from the dam, has emerged as a cause of concern for the dam’s long-term safety.

The scouring of the river bed where water from the spillway falls is learnt to have left a gaping hole that is more than 200 feet in depth. The breadth at which water from the spillway falls when 10 of the dam’s 12 gates are open, as is the case this year so far, is some 700 feet.
‘Telangana Today’ has learnt that studies of the plunge pool by National Institute of Oceanography in May indicated a possible creep of the pit towards the dam. The NIO had conducted bathymetric survey and also had teams of divers with underwater cameras film the insides of the plunge pool.

Also of some concern is the predominantly basalt and shale rocks that form the river bed, which by their very nature, are more prone to erosion.

“The situation is not very threatening. But it is not to be neglected,” B Narayana Reddy, Chief Engineer, Kurnool, of the Andhra Pradesh Irrigation Department told ‘Telangana Today’ on Friday.

A senior official involved with the recent investigations echoed this saying: “There shouldn’t be an unnecessary alarm. But the plunge pool does require immediate attention.”

Narayana Reddy said his department sought some clarifications from NIO on its report and “once we get them, we will take remedial steps.” “If required, we will have a panel of experts examine the report and take their suggestions,” he added.

Incidentally, this issue was discussed by Andhra Pradesh Irrigation Minister P Anil Kumar with senior department officials on Friday, officials said.

It was initially believed that the plunge pool pit was more marked towards the river’s left bank, towards the Telangana side, but it has now been established that most of the scouring of the river bed occurred towards the right bank, on the Andhra Pradesh side of the river.
“When you look down from the dam, you can see a deeper blue area on the river bed to the right side. It is a huge ditch,” an official said.

The issue of Srisailam dam’s safety and the impact on the structure because of the growing plunge pool, is something that the National Committee on Dam Safety of Central Water Commission has been talking about for some years now. Safety of the dam has been a staple at NCDS’s annual meetings, particularly with reference to flood control measures. The plunge pool too has figured prominently in its discussions over the past few years.
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