The coming flood

In January, a large landslide occurred in the Hunza Valley of Pakistan’s Karakoram Range, near the village of Attabad. Like the Madison River landslide in Montana (1959), or the Gros Ventre landslide in Wyoming (1925), a river was dammed by the slide debris, and the impounded waters began to rise.

At Gros Ventre, the landslide-dammed lake overtopped the debris and caused a catastrophic flood which killed 6 people in Kelly, Wyoming. At the Madison River, the U.S. Army Corps of Engineers feared another Kelly-style flood, with Ennis, Montana being the (larger) vulnerable town downstream. They carved a spillway through the debris which accommodated the flow the Madison River, though a “Quake Lake” still remains upstream of the dam.

Dave Petley has been covering this growing threat at Attabad since the initial landslide on his blog, Dave’s Landslide Blog. I think Dave’s coverage has been absolutely superb — it represents the best of what geoblogging can be. He has been soberly reporting the facts and offering his considered interpretations for more than four months. He has tracked the continuing mass wasting in the area, the Pakistani government’s attempts to dig a spillway, and the growing seepage through the dam (with attendant erosion). On an almost daily basis, he has been posting graphs showing the rising lake levels and decreasing “freeboard” (distance between the lake’s surface and the lowermost point on the dam — the spillway mouth).

Now, the day has arrived when the rising lake is projected to finally overtop the dam. Dave’s prognosis is not a positive one: the spillway appears to be inadequate in size to handle the flow of the river even at normal rates of discharge (and certainly not during floods). The material composing the dam appears to be easily erodible, which raises the likelihood that the overtopping waters will rapidly incise downward, widening the spillway gorge rapidly into a lake-draining chasm. A flood is not guaranteed, nor is it guaranteed that if there is a flood, that it will happen today — but the situation offers little hope for optimism. We might get lucky and avoid a catastrophe — but there seems to be ample reason for grave concern.

Dave Petley seems to have been a lone western voice raising awareness of this growing hazard, and I feel he should be strongly commended for it. Dave  is accompanied by coverage from the Pamir Times, and a daily lake level dataset being gathered by an on-the-ground volunteer team called “Focus.” One can only hope that their collective efforts have not been in vain. The people downriver of the slide will need to move to higher ground until the threat has abated. It seems unrealistic to expect Dave, the Focus team, and the Pamir Times don’t convince them via blogging. I would venture to say that the Pakistani government should have called a mandatory evacuation of the area several days ago. It is their responsibility to be sufficiently on top of things and protect their citizens.

Good luck and best wishes to the people of the Hunza Valley.

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