Heavy Discharges to Erode Srisailam Dam’s Scour Further, Say Experts

Hyderabad: A deep and large scour right next to the Srisailam dam that first began as a relatively small pit after the 2009 historic floods of Krishna river which saw the dam release over 20 lakh cusecs of water — far greater than the designed 13.2 lakh cusecs that the dam was capable of handling — is yet again getting pounded this season with the dam releasing around 4.5 lakh cusecs currently and the outflows expected to cross five lakh cusecs in the next two to three days.

Worried over the condition of the deep scour — referred to mostly as ‘plunge pool’ — the NDSA had earlier this year advised the Andhra Pradesh government to take up immediate studies and repairs to plug the scour. However, the studies, including an underwater videography exercise to determine the exact nature of the damages feared to be extending towards the lip of the dam, began late and before any steps could be taken, this year’s monsoon season began and with it, copious inflows into Krishna river on which the dam is built.

Since no repairs can be taken up during the flood season as the dam gates need to be opened, any work to plug the scour can be taken up only during next summer. The authorities opened 10 gates on Tuesday and were releasing 4,43,742 cusecs of water.

Sources said that the recent underwater photography revealed more damage to a number of giant steel cylinders installed several years ago as a stop-gap measure to protect the dam structures from the impact of falling water from the spillway. The underwater survey this June is learnt to have discovered that some 12 of the cylinders have completely disappeared, and several more of the total 60-odd such structures were found to be in various states of disrepair.

As on Tuesday, the dam was releasing around 40 TMC ft of water a day which is expected to rise to around 50 TMC ft in the next two or three days and then gradually subside in the following week with inflows coming down to around 3 lakh cusecs a day mark. When translated into the sheer weight of the water crashing every day into the existing scour, it currently works out to a mind-boggling 113,26,73,864 tonnes.

“But since water is a fluid the way it churns its way into the scour and how much more damage the current heavy outflows add to the pool will need to be evaluated afresh after the monsoon and flood season ends. One thing that is certain is that the scour will suffer more erosion and may need to be revisited as things would have changed before any repairs can be taken up,” a senior irrigation engineer with experience in dam safety issues said.