1 September 2010

The latest NASA image of Attabad

Posted by Dave Petley

NASA have released another spectacular satellite image of the Attabad dam and lake.  In the article they focus on the upstream end of the lake:

The article states that the water level can be seen to have dropped as the area upstream  of Hussaini is no longer inundated.  Now there is some evidence that the water level has dropped a little – the Pamir Times reports 12 feet (4 metres), although this may well be a downslope distance rather than a vertical fall.  As inflow decreases the water level should decline until the outflow balances this amount.  The Pamir Times article above also alludes to operations on the spillway, though it is unclear as to whether these have actually started.  I think that it is more likely that the apparent drop in the imagery is actually due to sedimentation in the river channel.  This is supported by a close look at Hassaini itself, which shows no signs of a drop in water level.

To me the most interesting aspect of this new image lies in the main part of the lake:

This is a comparison of the two most recent images of the landslide scar, dam and spillway area.  The first was collected on 7th July.  Note that it is partially obscured by dust:

Whilst the second is the most recent image, collected on 23rd August:

The key thing to note is that the spillway has evolved considerably – it has widened and become more sinuous.  There is also some apparent change in the water flow upstream end of the channel, which appears to be more turbulent now.  This could be due to a change in the volume of flow.  Finally, note that there also appears to be a couple of dust clouds in the upper part of the scarp area, suggesting that this is still evolving.

All of this means that system has not yet reached an equilibrium state, and thus remains a threat.  Fortunately though as winter approaches the risk of a rapid collapse is reducing, although unfortunately not to residual levels.