Sinking and drift of piers of barrages built on the river beds with deep sand deposits is not uncommon and it has got nothing to do with the design or quality of construction and the recent such incident in Medigadda (Laxmi) Barrage of Kaleshwaram Lift Irrigation Project has disturbed six piers in Block-7.
Special Chief Secretary (Irrigation) Rajat Kumar said here on Friday after holding a meeting on the damage caused to the barrage on October 21 evening. “The exact cause for the damage will be known only after a detailed investigation taken up after constructing a coffer dam to prevent water flowing to the damaged block of the barrage,” he disclosed.
Stating that the restoration work would be possible only after identifying the cause of damage, the official said the contract agency L&T would handle the work with guidance from the Central Designs Organisation. He mentioned that disturbance of piers had taken place in Farakka, Dowlaiswaram and Prakasam Barrages in their early years and they were rectified in due course.
Meanwhile, a highly-placed official source told The Hindu that the Irrigation department was planning to take up detailed sub-surface investigation a the foundation of not only the disturbed piers but all others not just in the Block-7 but the other seven Blocks too (the barrage has a total of 8 Blocks) to arrive at the cause for the damage and also as a safety measure.
The Central team from the National Dam Safety Authority (NDSA) has examined the sinking and cracks in the piers of Block-7 with only the exterior view possible now. They too have opined that the cause could be a change in the river morphology, sand deposit sift/consolidation beneath the foundation of piers or piping developed in the river bed after the July 2022 heavy flood.
After the construction of a coffer dam, dewatering in the Block-7 and its adjacent blocks would be taken up first for taking up sub-surface investigation to find the cause and only after that would the restoration work be taken up. “The design of barrages would be such that all Blocks would act independently and any damage to a block would not have impact on others,” the source explained.
The source stated that no further sinking or cracks in piers was noticed for the last three days giving an indicating that it has stabilised. Once taken up, the restoration work could be completed in 3-4 months time or before the next flood season, he disclosed. The State Dam Safety Authority officials will visit the barrage site on Saturday to examine the damage.
What Irrigation officials say about dams and barrages
Foundation of dams is constructed after going to the depth of rock-bed, while for barrages its on the river bed with sand deposits. It’s difficult to go till rock-bed for laying foundation of barrages.
Storage of water in dams is 70% against concrete wall/structure and 30% against gates. In barrages, small volume of water is stored on the river bed against gates for the purpose of diversion. Irrespective of damage to Block-7 of Medigadda Barrage, water diversion/lifting for Rabi needs is on cards, if need be.
