The Srisailam dam on River Krishna not only faces a serious problem with a large plunge pool that has formed immediately after the dam’s spillway but also has several other issues that require urgent attention to ensure its safety, according to a team of experts from the NDSA, CWC, and CPWRS, whose report was submitted to Andhra Pradesh this February.It may be recalled that Telangana had urged the National Dam Safety Authority (NDSA) several times to ensure that AP took up the required repairs, and during the NDSA chairman Anil Jain’s visit to Hyderabad on April 30, following his inspection visit to the dam the day before, had again stressed on the need for the repairs.The report has said that there were several issues that require ‘immediate attention’ with the plunge pool condition topping the list. It said the bottom levels of the plunge pool are much below the deepest foundation grade of the dam. It further said a deep scour in the plunge pool was progressing towards the dam, “causing potential danger of stability of dam if left unattended.” The plunge pool first formed after the heavy 2009 floods and ever since has been growing with each passing year and the deepest portion of it is more than 120 metres.Telangana has been repeatedly urging the NDSA to impress upon AP to at least begin filling the plunge pool with cement concrete tetrapods to cut down the scouring effect of water before full and final repairs can be taken up. “There is just one month left before the monsoon sets in and work cannot be done then. AP must take up the repairs as any danger to the dam will result in severe cascading effects all the way downstream to Nagarjunasagar dam, and as well as will impact Vijayawada if there is a catastrophic dam failure,” Telangana engineer-in-chief (general) G Anil Kumar said.The report also raised serious concern over choked drainage holes in the foundation gallery of the dam saying this was impacting the ability of the dam to withstand uplift pressures. “The pressure in the foundation drain holes have implications on uplift being experienced by the dam section and consequently the stability of the dam,” the report said, calling on AP to clean the drainage holes, and adding that this was also resulting in a lot of discharge of water into the foundation gallery.The experts’ report also said there were two horizontal cracks in blocks 17 and 18 of the dam and called for an investigation into the reasons for this, and their monitoring, and if found to be stable, then repair them.Among several other worries that currently plague the structure is the exposed aggregates in the downstream portion of the dam just abutting the spillway under gates 4, 5, 9 and 10. The report said the actual extent of the “distress” could not be determined as that portion was inaccessible, but said this must be investigated to figure out how to address it. “If these gates are operated in the next monsoon season, it is likely to deteriorate at a faster rate,” the report said.
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