Prediction of dam's collapse undermined by faulty figures

Two different public agencies have been giving the Pakistani government significantly divergent figures on how fast the Hunza valley lake is filling up.

GILGIT // The Pakistani government's prediction that the landslide dam would overflow yesterday was inaccurate because of contradictions in the measurement of water levels by two agencies. The prediction of an overflow o May 25, the critical test of the dam's structural integrity, was made on Friday by Yousaf Raza Gilani, the prime minister, after he was briefed by the National Disaster Management Authority (NDMA).

However, during a tour of the dam site on Monday the NDMA chairman, Nadeem Ahmed, discovered significant differences in measurements recorded by the Frontier Works Organisation (FWO) and the Gilgit-Baltistan region's public works department. "He was furious when he noticed the discrepancies and realised the NDMA had been reporting inaccurate data," a participating official said. Mr Ahmed immediately ordered a dam-site demonstration of the methods used by the two government agencies, before declaring that the public works department's "freeboard auto-level gauge" system, based on instrumentation manufactured by Nikon of Japan, should in future be the sole official data source.

The surface of the lake was 3.33 metres below the spillway on Monday afternoon, about a metre higher than the level recorded 24 hours earlier. Meanwhile, engineers working at the dam have expressed fresh concerns about the utility of a spillway excavated by the FWO to act as a pressure valve for the dam and prevent its collapse. The engineers said the 25-metre-deep spillway was too narrow to accommodate outflows of more than 2,400 cusecs from the lake, which held an estimated 1.2 million cusecs on May 17. A cusec is a unit of water flow equal to one cubit foot per second.

"There is a serious possibility that the entry of water into the spillway could trigger a collapse of debris that would block it altogether," an engineer said.