Rock collapse floods tunnel at Pakistan's Tarbela dam extension, halting work indefinitely

The rock failed while crews were cutting the second bench of a connecting tunnel, Pakistan's Water and Power Development Authority, known as WAPDA, said in a statement. Water from the intake pit then ran into the tunnel and the area around the powerhouse. Haripur Deputy Commissioner Waseem Ahmed told The Express Tribune that a protective bund gave way and that one Pakistani worker was carried off by the water before rescue teams pulled him out. Nobody was killed. Pakistani and foreign workers were all taken to safe ground.

WAPDA said the intake pit had been drained, no more water was reaching downstream work areas and pumps were running in the powerhouse. The authority denied reports that Tunnel 5 itself had collapsed and said the main tunnel, powerhouse, switchyard and tailrace culvert were undamaged. Ahmed said work is suspended indefinitely and a high-level committee will examine whether a structural weakness or a technical fault caused the breach.

The extension adds 1,530 MW through three 510 MW units and would lift Tarbela's installed capacity from 4,888 MW to 6,418 MW. Business Recorder puts the approved cost at $807 million, with $390 million from the World Bank and $300 million from the Asian Infrastructure Investment Bank. Power Construction Corporation of China won WAPDA's $354.6 million contract for civil works in May 2021.

This is the project's second big failure. In July a government inquiry blamed the contractor, the consultant and WAPDA for an earlier cofferdam collapse and cited unauthorized design changes made after contract award, Minute Mirror reported. That collapse pushed the estimated cost from Rs82 billion to Rs317 billion and the finish date to June 2028, before this week's breach.