Srisailam Dam Safety - Conditions More Fragile Than Ever Before

Hyderabad: The condition of the Srisailam dam on the Krishna may be more fragile than previously believed, with the latest scientific study commissioned by the Andhra Pradesh government of the huge void immediately downstream of the dam’s plunge pool area revealing damage on a much larger, and worse, scale than what was known before.

The study conducted in June has revealed that the huge void formed by the lakhs of cusecs of water crashing down from the dam’s gates has deepened significantly.

Even worse, the 36-metre-wide apron that was built between 1977 and 1981 to prevent damage to the ‘toe’ of the dam from scouring due to falling water, was found to have developed a huge hole – some four metres deep under its visible surface and extending between 14 and 15 metres towards the dam.

“This means nearly half of the width of the apron, meant to protect the dam, is like a wide overhanging ledge with nothing to support it from below,” sources with knowledge of the contents of the June underwater study told Deccan Chronicle.

The void in the plunge pool too has become worse. Previous studies found that the deepest portion, as calculated from the river bed level, was 35 metres. “Now, the depth has increased to 45 metres. This begins from 15 metres after the apron, and continues to about 150 metres in the downstream direction,” the sources said.

As per a February 2024 report by the National Dam Safety Authority (NDSA), the Central Water Commission (CWC), and the Central Water and Power Research Station (CWPRS), Pune, the depth of the void closer to the dam was 17 metres, indicating severe erosion creeping towards the dam and its foundations since then.

The study in June was commissioned by the AP irrigation department, which picked the Visakhapatnam-based Sea Lion Offshore Diving Pvt. Ltd to take up the underwater videography and data analysis. The study yielded a nearly-200 page report, along with around two hours of footage of underwater videography of the plunge pool area. The report and the footage were learnt to have been received by the AP irrigation department in October.

To protect the apron — which also formed a visible hole from the top in its centre — the project authorities had installed 62 huge concrete-filled steel cylinders. Several of them were found damaged in the June survey. The NDSA, in one of its reports on safety aspects of the dam, had previously noted that five such cylinders opposite the dam’s blocks 9 and 10 were washed away.

With the revelation that the depth and breadth of the plunge pool void has increased significantly from 32 metres to 45 metres up to a distance of 150 metres of the nearly 400-metre-long void, the situation requires urgent attention, the sources said. The NDSA, based on the previous 2018 study of the plunge pool by the National Institute of Oceanography, had pointed out that even at the deepest point of 32 metres found then, the void had already overtaken the depth of the deepest foundations of the dam.

Coupled with the severe damage and erosion to the surviving steel cylinders, as well as serious damage to the protective apron itself, the Srisailam dam needs urgent attention, the sources said.