The Wrong Monsoon

The diaphragm wall under the earth-cum-rockfill dam at Polavaram, on the Godavari in Andhra Pradesh, is the first of its kind in India. A continuous plastic concrete cut-off wall, 1.5 metres thick, designed to depths between 40 and 120 metres below the riverbed, anchored two metres into the underlying rock. Its purpose is to seal the foundation of the embankment dam against seepage. Nothing of comparable scale or depth had been attempted in the country before.

The original wall was executed by Bauer, the German specialist foundation contractor, in joint venture with L&T GeoStructure, and reported complete on 11 June 2018. Trial laboratory programmes, mix design qualification, and QC testing during construction confirmed the concrete quality of the placed wall. In engineering terms, the wall itself was not the question.

The question was the staging.

By the 2019 monsoon, the diaphragm wall was complete. The upper cofferdam, the temporary structure that was supposed to protect the wall and the rest of the embankment foundation works during construction, had not been built up to its design height. When the Godavari rose in August 2019, water moved through gaps in the partly built cofferdam. The resulting scour reached the diaphragm wall and damaged it in places. The 2020 monsoon, with another major flood event on the Godavari, repeated the exposure. By the time the second flood season ended, the wall that had been the technical centrepiece of the project required external assessment.

Expert teams from the Central Water Commission, the Dam Design Review Panel of the Ministry of Jal Shakti, and the Central Soil and Materials Research Station, joined by consulting specialists from the United States and Canada, inspected the damage. After multiple rounds of review, the consensus was that the existing wall could not be reliably repaired in place. The recommendation was a new parallel diaphragm wall, with the damaged sections of the original wall left in the ground.

Multiple news reports of expert committee findings, 2022 to 2025

Construction of the new wall commenced in early 2025. The cost figures cited across various reports differ widely; the cost is not the lesson.

The lesson is the sequence.

The diaphragm wall did not fail because of a defect in the concrete mix, the depth of the panels, or the workmanship of the construction. It failed because a permanent works element was exposed to monsoon discharge it was never designed to resist directly. The cofferdam was supposed to take that load. The cofferdam was not finished in time. Two monsoons in succession found the gap.

The lesson: Staging is part of the design. Every QC engineer entering monsoon at a partly built dam site this May has the same problem in compressed form: which permanent works are unprotected, which temporary works must be in position, which placements happen now versus after the season. Polavaram is one of the most prominent documented cases in Indian practice of a permanent works element completed to specification and exposed prematurely. It will not be the last unless the staging review is treated as part of the engineering review, not a logistics afterthought.

Read more: Monsoon Concreting in Dam Construction: Lessons from Indian Projects →