Race to save Pakistan's 'Shangri-La' valley from devastating flash flood

Engineers are working hard to stop a dam from bursting in the Hunza Valley after a landslide created a huge artificial lake.

Villages in Pakistan's paradisaical Hunza Valley face threats of flash floods and landslides from a glacial lake that has been growing dramatically since last month.

ISLAMABAD // Army engineers are battling against time and the threat of seismic shakes to save a 500km stretch of northern Pakistan from being devastated by a potential flash flood.

The threat has been building since January 4, when a massive landslide temporarily dammed a river in the mountainous area of Hunza, widely believed to be the inspiration for the fictional kingdom of Shangri-La, creating a lake that continues to rise steadily. The landslide removed 120 metres of mountainside, destroyed the village of Ata-abad, killing 19 residents, isolated 25,000 residents upriver from the landslide-dam, and severed a two-kilometre stretch of the Karakorum Highway, Pakistan's only land link with China.

The temporary lake, fed by glacia meltwaters, has since grown dramatically, and now stretches 15km back from the blockage, and is more than 70 metres deep. Engineers of the army's Frontier Works Organisation have been working since last month on the construction of a spillway that authorities hope will gradually drain the water. Scientists said the lake could grow to 20km in length by the onset of summer as, from April onwards, rising temperatures would significantly increase glacial melt and water flow into the lake.

Although the scientists, who have surveyed the site, have endorsed the engineers' strategy, they warn that the instability of the dam made the eventual outcome unpredictable and potentially disastrous. The 900-metre-long mass of landslide debris that formed the dam is largely made up of powder-like sediments. David Petley, director of the International Landslide Centre at Durham University in the United Kingdom said: "The most likely scenario is that the water will flow over the dam when it reaches the top. The other scenario is that the overflow could wash away the top of the dam, after which there would be rapid erosion and collapse. It's very difficult to forecast.

"It would be a prudent conclusion to assume the worst when the water reaches the top, at which point it would be sensible to evacuate all the people downstream." He stressed that a flash flood was "by no means an inevitability", but historical evidence and a report submitted by Nespak, a state engineering firm, have highlighted the potential for disaster. The National Disaster Management Authority, which is overseeing recovery efforts in Hunza, has told local legislators that the collapse of the dam would send a 20-metre-high tsunami-like flash flood crashing down the Hunza Valley.

In that event, the water would sweep down from an altitude of nearly 2,500 metres, being replenished by first the Gilgit River and then the Indus, before hurtling down the narrow northern stretches of the Indus Valley towards the Tarbela Dam, 40km north-west of Islamabad. British colonial records from the 19th century report that two similar incidents caused flash floods that killed several thousand people and inundated huge areas of modern Pakistan.

The force of the flash flood would wreak catastrophic damage, destroying all communities and infrastructure, including most of the Karakorum Highway, a marvel of modern engineering built between 1966 and 1978 that ended centuries of isolation for the people of the region, now known as Gilgit-Baltistan, the scientists said. The region is also among the most seismically active in the world because it is located at the junction of the Asian and Indian geological plates, where the Himalaya, Karakorum and Hindu Kush mountain ranges meet.

Much of it sits upon an island plate squeezed between the two continental landmasses, when they collided hundreds of millions of years ago. The danger of a massive landslide at Ata-abad had been apparent since February 2003, when a huge crack appeared in the terrain four months after an earthquake hit the region, the officials said. Authorities have since been urging residents to relocate, but they have refused to move unless they were provided with alternative residential and farming land.

Officials, backed by community-based non-government organisations sponsored by the Aga Khan, the spiritual leader of Hunza's predominantly Ismaili population, finally persuaded people living at higher altitudes to move just days before the landslide. The weight of evidence last week prompted Hameed-ullah Jan Afridi, Pakistan's environment minister, to order preparation of an emergency plan, including mass evacuations.

"Preparations must start immediately," he said in an official statement. However, local politicians said the government had wasted vital time dithering, unwisely focusing all initially on relief efforts and issuing unrealistic estimates on how long it would take to remove the debris before finally deciding who would undertake the mammoth task. Nazir Sabir, a local politician and Pakistan's premier mountaineer, said: "There were serious errors in understanding the longer-term threats posed by the artificial lake and formulating a strategy based on the right perspective.

"There was too much bureaucracy, both in terms of decision making and assignment of blame [for the landslide], for due attention to be paid to the complicated process of debris removal." @Email:[e-mail]