Water surges into Tarbela powerhouse after rockfall at T-5 project

All workers evacuated safely as water enters under-construction tunnel and powerhouse; Wapda rules out damage to main tunnel and key structures amid assessment

Staff Report

SWABI: A rock mass collapse during excavation at the Tarbela Dam 5th Extension Hydropower Project (T-5) on Monday triggered a sudden surge of water into the under-construction powerhouse and a connecting tunnel, prompting an emergency evacuation of workers and suspension of construction activities.

The Water and Power Development Authority (Wapda) confirmed that all workers were evacuated safely and no casualties were reported. However, the incident raised fresh concerns about construction safety and possible delays to the strategically important hydropower project, which has already faced substantial cost escalation and delays following an earlier cofferdam collapse.

According to a Wapda statement, the incident occurred during excavation of the second bench of the Connecting Tunnel, when a weak section of rock collapsed, allowing water from the Intake Pit to enter the tunnel and the under-construction powerhouse.

Following the incident, an emergency was declared and workers were immediately directed to move to safer locations. Wapda said the water accumulated in the Intake Pit had been completely drained and no further inflow was entering the downstream working areas. Dewatering operations at the under-construction powerhouse had also commenced.

The authority said senior Wapda officials, the project engineer, consultants and the contractor were examining the situation to assess the extent of any damage and determine the measures required to resume construction safely.

Wapda also rejected reports circulating about the collapse of the main T-5 tunnel, clarifying that the main tunnel, under-construction powerhouse, tailrace culvert and switchyard had not sustained damage. It maintained that no worker had been injured or killed in the incident.

However, Deputy Commissioner Haripur Waseem Ahmed said authorities were assessing whether the tunnel, powerhouse and other structures in the affected working area had suffered any damage.

In a separate account, the Haripur deputy commissioner said part of the protective embankment at the T-5 intake had broken after a girder fell. He also confirmed the safe evacuation of Pakistani and foreign workers. According to his account, a local worker who had been submerged in the tunnel was rescued by local people.

Meanwhile, sources said construction work at the T-5 project had been suspended for an indefinite period following the incident. The duration of the suspension and its implications for the project's construction schedule were not immediately clear.

The incident also prompted precautionary measures concerning water flows in the Indus River downstream of Tarbela Dam. Swabi Deputy Commissioner Nasarullah Khan said additional water had been released from the dam due to unavoidable circumstances, warning that the discharge could increase the river's flow and water level.

He urged residents to avoid bathing, swimming and boating in the Indus River and asked people to follow official safety instructions to protect themselves and their families. He also advised the public against spreading or believing unverified reports and urged them to obtain information through the district administration's official channels.

Separately, Wapda issued a notification regarding downstream water releases, stating that the discharge into the Indus River would remain above 150,000 cusecs round the clock. The notification directed the relevant authorities to make necessary precautionary arrangements in view of public safety.

The latest incident comes at a difficult stage for the T-5 project, which has already suffered a major setback following the collapse of its cofferdam in an earlier incident.

In July, a government-constituted inquiry committee held all three major stakeholders, including the contractor, consultant and Wapda as the employer, responsible for the cofferdam collapse. The committee identified unauthorised design changes made after the award of the contract among the principal reasons behind the failure.

The cofferdam collapse contributed to a delay of at least two years and a sharp increase in the project's estimated cost. The original cost of Rs82 billion has reportedly escalated to Rs317 billion, representing an increase of more than 285 per cent.

The project, which was initially scheduled for completion in 2026, is now expected to be completed by June 2028. The latest rockfall and water-inflow incident could create further challenges, although its impact on the revised completion schedule will become clearer after the technical assessment.

 The T-5 extension project has an installed generation capacity of 1,530 megawatts. The World Bank and the Asian Infrastructure Investment Bank are financing the project with loans of $390 million and $300 million, respectively.

Upon completion, the fifth extension will increase Tarbela Dam's total installed power-generation capacity from 4,888MW to 6,418MW, strengthening the country's hydropower supply and adding significant generation capacity to the national grid.