Construction at Pakistan's 1,530MW Tarbela Dam Fifth Extension Hydropower Project has been suspended after the collapse of a protective bund at the under-construction Tunnel-5 triggered a sudden influx of water from the reservoir, India Today reported.

Authorities declared an emergency and ordered workers to move to safer locations while project activities were halted.

The affected civil works contract had been awarded to China's Power Construction Corporation of China Limited (PCCCL). The latest incident marks the second major setback at the Tarbela-5 project since 2025 and has renewed scrutiny of project management, engineering decisions and oversight arrangements.

The collapse follows an earlier cofferdam failure that prompted an independent investigation commissioned by Pakistan's Water and Power Development Authority (WAPDA). A three-member inquiry committee later concluded that unauthorised modifications to the cofferdam design after the contract award played a central role in the earlier disaster.

According to the inquiry, responsibility was shared among the contractor, consultant and WAPDA. The contractor proposed design changes that were not permitted under contractual provisions, while the engineer conditionally accepted a design deficiency without ensuring full technical compliance. WAPDA subsequently approved the alteration when construction was nearing completion, despite concerns regarding its contractual validity and engineering adequacy.

The committee stated that all parties had effectively ignored their respective contractual obligations and responsibilities. As a result, a structurally vulnerable cofferdam was built, ultimately leading to failure, flooding, project disruption and substantial financial losses.

Stakeholders attempted to attribute the collapse to flooding conditions. However, investigators found that water flows remained within historically recorded annual levels and should have been incorporated into the original design assumptions.

The report found that PCCCL had proposed replacing the original cofferdam concept with a rock-filled structure across multiple sections of the project, including the channel area. Investigators described the alternative as a weaker solution and concluded that the revised structure subsequently failed.

The committee further determined that WAPDA approved the change without properly assessing whether it complied with contractual requirements. It also rejected arguments that unusually high water levels were responsible, noting that the recorded flows were significantly below the cofferdam's intended design capacity.

Instead, investigators attributed the failure primarily to inadequate protective layers and insufficient filter arrangements within the structure.

Additional shortcomings emerged during the review. In July 2023, WAPDA instructed the consultant to undertake an assessment of the cofferdam's performance. Rather than conducting an independent evaluation, the consultant passed the request directly to the contractor. The contractor eventually submitted a monitoring report in October 2024, more than a year after the original request.

The inquiry also identified concerns over project payments. It found that payments had been made for temporary works in place of permanent works, weakening the government's ability to pursue compensation claims against the contractor after the collapse.

The consequences for the project have been severe. The earlier cofferdam failure alone contributed to delays of at least two years and drove project costs dramatically higher. Estimated expenditure has risen by more than 285 per cent, increasing from PKR 82.36 billion to approximately PKR 317 billion.

Pakistan's Planning Commission has warned that the project's levelised electricity generation cost over a 30-year period could reach PKR 27-28 per unit. That would make it the country's most expensive renewable energy project and raise serious concerns regarding its long-term economic viability and sustainability.

Reflecting these setbacks, the project's completion target has been pushed back from 2026 to the end of June 2028.

The development carries wider significance because the project is partly financed through loans totalling USD 700 million provided by the World Bank and the Asian Infrastructure Investment Bank. Tarbela is one of Pakistan's most important hydropower facilities and forms a key component of efforts to expand electricity generation capacity and reduce energy shortages.

Companies involved include China's Power Construction Corporation of China Limited, Harbin Electric International Company Limited and Harbin Electric Machinery Company Limited. Project consultancy services were provided through a joint venture involving Pakistan's MM Pakistan and China's BIDR, while WAPDA served as the employer.

WAPDA later terminated its consultancy agreement with MML-UK, alleging that the firm failed to provide a suitably qualified project manager and suffered persistent staffing deficiencies throughout the contract. The authority also stated that MML had issued a termination notice in May 2025 and withdrew personnel from the site unilaterally without observing the contractually required 30-day notice period.

The inquiry ultimately concluded that a combination of contractual breaches, inadequate oversight and technical failures across all principal stakeholders led to the cofferdam collapse. The resulting disruption has increased costs, delayed completion and further complicated the future of the strategically important Tarbela-5 hydropower expansion project.

Agencies