Water flooded a tunnel and the under-construction powerhouse of the Tarbela Fifth Extension Hydropower Project on Monday after a weak section of rock gave way during excavation, the Water and Power Development Authority (WAPDA) said. Emergency procedures were launched to pull workers out of the area.
A WAPDA spokesperson said everyone was brought to safety and no one died. The breach happened while crews were digging the second bench of the connecting tunnel, when the rock failed and let water from the reservoir’s intake structure pour into the tunnel and powerhouse.
Drainage efforts and assessment at the project site
According to the spokesperson, the intake structure has been fully emptied, and water is now being pumped out of the under-construction powerhouse. No additional water is reaching the downstream work sites. Senior WAPDA officials, consultants and contractors are assessing conditions to work out how to tackle the problems the project now faces.
WAPDA also rejected circulating reports that Tarbela’s Tunnel No 5 had collapsed. The authority said the main tunnel, the powerhouse under construction, the tailrace culvert and the switchyard had not been damaged.
Earlier cofferdam failure and government inquiry findings
The latest incident follows an earlier setback. In August 2025, the project’s protective cofferdam gave way, allowing floodwater into the construction area and forcing a halt to work.
A later government inquiry held WAPDA, the contractor and the consultant responsible for that failure. It cited unauthorised design changes, weak supervision and breaches of contract. The inquiry found that the cofferdam had been switched from roller-compacted concrete to a rock-fill design, which weakened it and contributed to its collapse.
That failure caused significant delays and drove up the estimated cost from Rs82 billion to around Rs317 billion, an increase of more than 285 per cent. The project, which was originally expected to be finished far sooner, is now targeted for completion by the end of June 2028.
Plans to add capacity by converting Tunnel No 5
The Tarbela Fifth Extension Hydropower Project, also known as T5, is meant to add 1,530 megawatts by turning the dam’s fifth irrigation tunnel into a power-generation facility. Tarbela Dam, located on the Indus River in Khyber Pakhtunkhwa, was completed in 1976 and stores water for irrigation, regulates river flows and produces electricity.
The dam started with an installed capacity of 700MW, which later rose through extensions involving Tunnels 1, 2, 3 and 4. The fourth extension added 1,410MW and became operational in 2018, bringing the total to 4,888MW.
The fifth extension will install three generating units of 510MW each at Tunnel No 5, a tunnel originally built to release irrigation water when reservoir levels were low. The project is expected to deliver about 1.347 billion units of relatively low-cost, clean hydropower to the national grid each year, raising capacity to 6,418MW. It is being financed through loans of $390 million from the World Bank and $300 million from the Asian Infrastructure Investment Bank (AIIB).
WAPDA says converting the tunnel will allow water releases to generate power while keeping its irrigation role. The authority presents the project as part of its push for green, cost-effective energy and better use of Tarbela’s water resources as Pakistan’s electricity demand grows.
