Amidst the appalling tragedies playing out in southern Pakistan and in China, Northwest Pakistan continues to grapple with its own problems. Unfortunately the problems at Attabad have not gone away as yet, even though the NDMA reports on the situation have now dried up completely. However, the Pamir Times are still on the case, with a somewhat concerning report yesterday that "Three more houses were dismantled in Gulmit Gojal due to sudden increase in water level of the dammed Hunza River...Rains and floods in different parts of Gojal valley have taken the water level up by around three feet during the last 36 hours, according to local people."
That new houses are being dismantled suggests that the lake is at its highest level so far. I do hope that the spillway is being watched carefully.
Meanwhile, the Frontier Post reports two substantial landslides in Gilgit-Baltistan on Friday and Saturday. The first occurred at Qamrah village in Skardu district late on Friday night, reportedly killing 35 people. The second occurred in Shout village in Ghanche district, killing four people. Flash floods are also causing substantial problems.
The only near real time proxy that I have found is the Partab Bridge hydrograph. It's at peak values right now, mitigated by the thought that perhaps the other tributaries from Skardu et al are also high.
ReplyDeleteThus it looks like our low resolution view of an Attabad dam failure will be a profoundly scarey spike on the Partab chart -- if you see a huge vertical jump, suspect the worst. Or if Partab drops off the charts altogether, worry. (Dave, do you have a comparative view of a dam failure vs the recent gilgit flood? What would the difference be?)
The Gilgit max temperature graph has been in line with the seasonal averages. Without rainy (and therefore cloudy) weather, it looks like the glacier runoff is also high. Today's temperature graph suggests rain and cooling after 3 days of warmth. So perhaps the lake level will fall again. (But if rain comes in the form of downpours -- or really, significant amounts; water does not stay on those mountains unless it's frozen -- all bets are off.)
As I understand the physics, at the current lake level the pressure is around 170 lbs per square inch at the bottom of the water column. And if a significant fraction of that pressure gets to place where it can be applied sideways, boulders move. (Limestone is only 163 pounds per square foot.) Fortunately, the very long profile of the landslide dam -- remember that long upriver slope leading up to the spillway when it was being made? -- have prevented so far a catastrophic failure. Currently, mu guess is that the spillway is just like an overflowing bathtub; the water we see going over the top is in a minimum pressure regime. But as the downstream side erodes and the long leading toe shortens, the potential pressure differential increases. Eventually the sideways force of the water may exceed the weight of the dam. And even a single point of flow may be enough to start the process.
One hopes that there's at least one aware set of eyes watching that dam and that they have a hot line to the powers that be.
oops, 163 pounds per cubic foot.
ReplyDeleteThere are also reports that landslides have "narrowed" the spillway, sugesting that the lake level is also being affected by outflow constriction. http://www.southasianow.com/47-dead-in-skardu-ghanchhe-flooding/
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