Attabad: a different set of discharge data

Thanks to Aftab Sadiq of the School if Civil and Environmental Engineering at NUST for passing on a revised set of spillway discharge data.  This set was collected by the FWO.  It is almost identical to that published here previously, with one important exception.  The graph of discharge against time is as follows (correct to 17:00 yesterday, local time):

The difference between this and the data that I have published previously is shown in this graph:

The key difference is for the data of 2nd June, when the FWO recorded a rather higher discharge than did the earlier dataset.  I noted yesterday that the linear trend in the earlier dataset was somewhat odd - the FWO data does not show this.  The difference is minor on the one hand, but important on another.  If we take the original dataset, the apparent sudden stepped increased in discharge yesterday appeared to suggest a major change in process - i.e. that erosion had initiated.  The FWO data suggests that the process is unchanged - i.e. we are continuing to see an increase in flow associated just with the increasing lake level.  Given that as far as I am aware no breach has developed, my inclination is that the FWO data may have captured the processes on 2nd June better, but this is uncertain at the moment.


It will be very interesting to see what today's data might bring.  As it appears that discharge and inflow are now coming close to each other we might expect to see the discharge plateauing.  However, some channel erosion will continue, so the situation is far from resolved.

Discussions with the team that dealt with Tangjiashan showed  that one of their key concerns was that overtopping would be followed by equilibrium conditions, leaving the hazard in place and creating a very difficult management task downstream.  At Hunza we have a repeat of this situation.  In the end at Tangjiashan they resolved this by blasting the boulders that controlled the flow in order to initiate a breach event. Given that they do not communicate with me at all, I have no idea what the plans of NDMA might be.


Finally, there is a new NASA ASTER image, collected on 1st June, of the site available:

However, thanks to G.M. Shah of AKU for pointing out that there are some errors in the labeling on this series of images.  The key issue is that the location of Shishkot is incorrect:

I will post again when I have further information.  And finally, from a personal perspective, thanks to all who wished me luck in my move - it is complete.  I am now getting used to living on my own for the first time in 16 years!

Attabad appears to have shifted to the next stage

In brief, the discharge at Attabad appears to have dramatically increased in the last few hours, as the graph below shows:

I am trying to find out more information, but it appears to have shifted to a new phase of activity. Inflows and outflow may be approaching a balance. Downstream communities need to be very alert now.

More as soon as I get it.

Attabad - so why hasn't it breached yet?

Several people have emailed to ask why the lake has yet to breach.  Well, I would like to emphasise two things - first, that every landslide is different, so predicting the behaviour of any particular slide is effectively impossible.  Second, there is a peculiarity about the spillway that appears to be delaying the breach event.

Regular readers (of which there are now several thousand each day I think - thanks to you all) may remember that a few days ago I noted the presence of a large boulder in the channel, right at the crown of the spillway:

 Well it is this boulder that is preventing the scour from propagating upstream and that is, in effect, protecting the upper part of the channel against further erosion, as this image shows.  The boulder is circled:

The lower part of the channel is continuing to erode with some power, and the channel is widening.  The red lines show substantial cracks suggesting further potential widening.  The steepest part of the channel is continuing to erode backwards, such that sooner or later the boulder will start to be undercut.

Meanwhile, there appears to be an increasing level of frustration about the very confused spillway discharge statistics emerging from NDMA.   This is understandable.  If we take the last four daily reports we get:
29th May 18:00: 150 cusecs (cubic feet per second) from the spillway, 350 total discharge

30th May 18:00: 900 cusecs total discharge

31st May 18:00: 900 cusecs total discharge

1st June: 18:00: 1050 cusecs discharge at Ganesh Bridge.



This is a quite bizarre mixture of measurements, but we should all understand that the NDMA team dealing with this are under huge pressure too. 

Meanwhile, the more reliable measurements of inflow suggest that the rate is continuing to increase linearly with time, probably because of the choke provided by that boulder.  However, I am very surprised by just how linear this increase is proving to be, so please treat this with some caution:

The lake level upstream continues to rise, increasing both the damage and the amount of water in the lake.  In the last 24 hours the lake level rose by 75 cm, perhaps suggesting that the rate of inflow is further increasing. 


Finally, several people have emailed to ask why I have not covered the multiple landslide accidents around the world in the last few days, including the multiple slides in Central America (and that amazing sinkhole), the landslides in China, the non-fatal slide in New Zealand, etc.  I will try to catch up on all of those things as and when this event ends - please accept my apologies.  You will understand that I have to maintain my day job whilst doing this, plus yesterday and today I am moving house!

Attabad - flow continues to increase with time

The Pamir Times reports that as of lunchtime today the flow through the spillway had increased to about 850 cubic feet per second - i.e. 24 cubic metres per second, giving a discharge - time graph that looks like this:

For the last 72 hours or so the increase in discharge with time appears to have been linear, which is interesting.  This suggests that erosion of the saddle has yet to initiate fully.  Fortunately so far the in situ (i.e. not excavated) lacustrine silt and clay has been more resistant to erosion than some had speculated, although the disturbed (excavated and dumped) material has proven to be very erodible.  However, the inflow remains more than three times greater than the outflow (seepage plus spillway flow), and retrogressive erosion will in due course steepen the channel, which will increase the erosive potential.


In the meantime the level of the lake is continuing to rise at 50 cm or so per day, with the upshot that further flooding is occurring upstream.  The Pamir Times has a tragic (but beautifully shot) photo piece (plus here) on these continued impacts.  The level of impact up there is all too clear:

Attabad - continued retrogression. Close to the next stage?

The latest images from Attabad suggest that the retrogressive erosion in the channel continues to accelerate, and that this is now by far the most likely failure mechanism.  A breach now looks to me to be inevitable.  This image, taken this afternoon, shows how the spillway has developed:

Note the people on the road for scale. 

Compare it with yesterday's image:

The waterfall has now smoothed out, probably because the water is now eroding the landslide mass rather than the excavated material from the spillway, to create a set of rapids that are clearly eroding back up the channel.  The head of the rapids are close to the saddle.  The key point is probably the location where the channel become notably steeper - this is where scour accelerates.  One this point is reaches and passes the saddle, the rate of flow will start to increase and we might well see the breach developing.  Unless the top of the rapids is being impeded by a large boulder or similar, this will probably develop quite quickly.


It remains hard to know how quickly this will develop once the saddle is reached, but downstream communities need to be prepared for a rapid breach.

Attabad - further retrogressive erosion

The latest photos from the site, taken late yesterday, show that the retrogressive erosion of the channel is continuing to develop rapidly.  This image was taken at about 5 pm yesterday:

The lower part of the channel has widened and, more importantly, the steep section has moved up channel considerably.  Bear in mind that this image is more than 15 hours old now.  The best illustration of the way that this is developing is with this sequence of three images, which are taken about a day apart, starting on 29th May on the left and ending with 31st May on the right:

It seems to me that release of the water in the lake is now highly likely in the next few days.  The most likely mode of failure looks to be this retrogressive erosion, which could lead to a rapid release event, but the initiation of erosion through downcutting cannot be ruled out.  Downstream communities need to be prepared.


I have received no update on the state of flow in the channel - I will post again when some information becomes available.

Attabad - flow and erosion are continuing to accelerate

Flow through the spillway at Attabad has continued to develop during the day.  However, as I suggested in my post this morning, some of the higher discharge values being quoted are without foundation.  At 6 pm the discharge was about 360 cubic feet per second (10.2 cubic metres per second).  Thus, the discharge graph looks like this:

At the moment there appears to be little evidence from these figures that large-scale scour and erosion has been initiated - the increase in flow appears to be the consequence of the increasing lake level, plus perhaps some lateral erosion.

However, erosion at the toe of the slope remains the major concern, with reports suggesting that the gully is continuing to erode back through the channel.  This remains the most likely failure mode of the dam, but this may take a few more days to initiate.  In addition, the increasing channel discharge may cause the flow velocity to increase to the point at which basal erosion starts.  This has not yet happened, but could begin at any stage.

There have been various comments on the blog that the dam is not behaving as expected - i.e. erosion is not initiating - and that as a result measures should be taken to encourage erosion.  I want to stress that this is not correct - from the start we knew that it could be that it could take some time for erosion to initiate.  So far I see nothing surprising in the behaviour of this system, and nothing to suggest that erosion will not allow a lowering of the lake level in the next few days.  At the same time, it is important to emphasise that the probability of a rapid breach has not diminished, and may in fact have slightly increased due to the headward erosion of the lower gully.  

There is no need to panic, but at the same time there is also no justification for lowering the alert status.  We all need to be patient and alert - this has a long way to go yet.   If you are in the area please pay attention to the local alert system.