13 July 2010
Attabad – lake level is high but steady
Posted by Dave Petley
The latest NDMA reports show that the lake level at Attabad is at its highest level to date, but is holding steady. As before, I have used the reports and the NDMA data to reconstruct the lake level data, to produce a graph that is consistent with NDMA for the last two weeks:
Meanwhile, it appears that the discharge through the spillway has increased again, once more using the NDMA data:
This allows us to look at the discharge – lake level graph again:
The most recent three values are indicated by open diamonds. There are some suggestions that operations are underway again to widen the spillway, which may explain the increased discharge, but I have no way of verifying this suggestion.
Finally, the press are also reporting that the IDPs will be allowed to return to their villages in early August, when the river discharge has peaked. Fortunately the enhanced level of landslide activity from the Attabad scar that was observed last week has now reduced.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
An interesting video recently uploaded to YouTube (apparently taken July 12th) gives you a pretty good sense of what the recent landslide activity has done. Specifically, see the bank of the lake just before the spillway channel at about 21 secs into the video: http://www.youtube.com/watch?v=OBTsDSdFNl0Compare the scene to this video (at about 32 sec) to see the difference: http://www.youtube.com/watch?v=QCagYRecgiULooks like a lot of material dumped into the lake on that side.
Divalent- Dr. Dave has already stated that it's not possible for a landslide to fortify the dam–Trust him.That said, there must be some reason that the lake is rising, but the outflow is decreasing. As Dr. Dave put it, "This increase in lake level is interesting though because at the same time the reported outflows have declined from those of a week or so ago."What more can I say?
Landsliding on 12th july 2010http://gulbtur.wordpress.com/
According to my sources in Attabad,the outflow at Sarat bridge yesterday was about 18,000 cusecs and the lake level same ( no increase).It seems that the water now coming over the spillway is quite muddy and there is erosion in mouth of spillway.Some landsliding continues.FOCUS had invited ex-Director of GSP on Saturday with FOCUS geologist to look at recent landslide in Attabad in past 6 days. No idea about the report.
From my point of view the muddy water comes not unexpected. Most propably there is now much loose material from the recent landslides in the lake. The bigger elements will sink down, the smaller will be pulled out with through the spillway. If landslides stop the water could be clear within a few days.So from my point of view the mud in the water is not nessecarily a sign for enhanced erosion in the spillway.Just my 2 Cts….
J.David Rogers has an interesting collection of pdf's that document, among others, the Grand Teton Dam failure. Some, like the Background piece, show the theory behind large dams. The Grand Teton had a height of 305 feet, comparable to the Attabad dam.Rogers' index page is here: http://web.mst.edu/~rogersda/Another interesting dam failure is the St Francis. Rogers shows that failure was initiated by a landslide and, I think, tipping.
Make that just the Teton Dam, strike Grand, which is an altogether different flavor.
Today, from Pamir Times.http://pamirtimes.net/2010/07/15/pictory-images-from-the-attabad-lake-barrier/
Today, from Pamir Times.http://pamirtimes.net/2010/07/15/pictory-images-from-the-attabad-lake-barrier/
The upper midstream boulder is still there, but not much of it shows above water any more. The flow is definitely up and material on the right bank below that boulder now seems to drop vertically. The parallel cracks above the right bank indicate slumping towards the water. While there's been very little movement over the last few weeks, there's always the possibility of a sudden widening. It does not look possible to land equipment on the right bank any more and landing people there would be risky.GeorgeGeorgeLandslide debris has now filled in the bay that was at the mouth of the right bank and may be at the point of constraining flow. Possibly there was some additional constriction that was washed away.
One of the latest Pamir Times photos shows the upper tongue terminating at a ledge running straight across about half the stream width from the right bank. Perhaps the underlying slab is rotating upstream because of undermining at the upstream end. At this flow level I would expect to see backcurling waves below the ledge, but perhaps there's not much drop at that point.The rotation of that slab could explain the increase of lake level. The top of the flow now shows a drop by the left bank boulder that was blasted. Water in the tongue below seems to be shifting left above the new ledge.Detailed photos and videos of the water are much appreciated.George