20 May 2010
New images of the Attabad dam and Spillway
Posted by Dave Petley
The Pamir Times is now back in action after the owners were trapped on the road by the landslides caused by the recent heavy rain. Tonight they have posted a selection of images of the site taken yesterday or today – go and take a look, they are good. I will reproduce two here as they help to understand the current situation.
First, this picture shows the spillway from the lake side:
Two things to note here. First, the freeboard appears to be in the order of 3 m, suggesting that the NDMA figures are about right. Second, it looks to me like the far side of the spillway failed in the heavy rainfall earlier this week, which appears to have dumped a lot of loose material in the spillway, and it has narrowed it considerably. I may be wrong about this, but that is how it looks to me. Needless to say this is not a good sign.
The second image shows the area downstream of the main landslide mass:
The water that is flowing here is the seepage – there is clearly a considerable amount. Note just how deeply the channels have incised, which shows just how erosive the materials in this mudflow deposit actually are. Again, this is not a good sign.
The lake is now 18 km long.
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.
Any estimates on lake water volume? I worked on an event where there was an instantaneous release of 30,000 cu. m of water. The resultant debris flow was confined to a steep valley. 20 km downstream the wave front was 7m high. 50 km downstream the wave was 1m high. The overall gradient of the stream was less than 5%.
Yeah I was just going to ask something similar. Found some stats on the 1841 Indus with Google earlier today, the lake was 19km long, 800m wide and 120m deep. Another source estimated water volume of this flood at 10^9 cu.m and ~400km dowstream (two days later) the front was 9m high. Surely this one has to be similar scale??
I find particularly disturbing the image entitled "Large sinkholes have developed on the lake barrier, close to the spillway": http://pamirtimes.files.wordpress.com/2010/05/112.jpgDoesn't that look like a conduit has already formed through the barrier? When the lake rises, I hope this doesn't become the failure point…
I agree. From the look of that sinkhole pic, and the rate of seepage graph surely the chances of the whole dam liquifying and generating a massive mud/debris flow are (unfortunately) increasing?