Attabad - situation report (Updated 26th June 2010)

Commentary and analysis accompanying this data is provided on Dave's Landslide Blog.

Situation as per 25th June:
Lake depth: 116.7 metres
Change in lake depth in last 24 hours: +0.13 metres (negative number = fall in lake level)
Spillway discharge: 352 cubic metres per second
Estimated seepage: 6 cubic metres per second
Estimated total outflow: 358 cubic metres per second
Estimated total inflow: 419 cubic metres per second

Lake level graphs:
Lake level and rate of filling from time of landslide:

Lake level since 21st May 2010:

Flow through the spillway:

Slowing evolution of the spillway at Attabad

Once again I am grateful for Focus Humanitarian Assistance for sending the latest photos of the spillway at Attabad.  The rate of change new seems to be slowing as flow is being controlled by the large boulders at the head of the channel.  This pair show the downslope side of the channel - the left hand image was taken on 7th June and the right hand image a day later:

Allowing for the slight change in camera angle, there is little indication of major change between the two images.  The large boulder on the left side of the upper part of the channel bank has slipped into the water on the right hand image, presumably indicating that channel widening is continuing.  Of course there may well be some continued erosion of the bed that would is not visible here.

In the upper channel there is comparably little evidence of change also.  The inset image is from 7th June, the main image a day later:

It may be that a more detailed inspection on the ground would reveal a more dynamic system.

It is my intention to stop duplicating posts on the two sites from today, with the Hunza Monitoring Blog being used once again to present data on the state of the dam and the lake, and Dave's Landslide Blog to provide a commentary.  On DLB I will also start covering other landslide events again.

Latest image of the spillway at Attabad

The wonderful people at Focus have provided an image of the state of the spillway at Attabad that is very instructive.  This was taken today:

The current state of play is I think as follows.  Flow appears to be constrained by two blockages but, as a commenter has noted, one is a rock spur out of the channel.  The blockage appears to have formed a small waterfall / rapid.  Downstream of the blockage the channel has widened dramatically - and indeed a section of the track has now been lost.

To me this suggests that the crisis may be far from being over.  In particular, the loss of this barrier could cause a rapid increase in flow rate that could be highly erosive.  It is however important to stress that interpreting the state of play from photos is difficult.

Attabad - an increasingly difficult hazard to manage

Apologies to all who emailed and left messages over the weekend requesting updates. 



FWO data collected at 8 am on Saturday suggests that the rate of flow was 124.6 cumecs, whilst the Pamir Times reported yesterday that it was 131.7 cumecs.  If so, the discharge time graph looks like this:

Thus, the discharge is apparently stabilising.  Various media reports from the site itself suggest that downward erosion of the channel has now reduced, but that some lateral erosion is still occurring.  I have not seen any images to confirm this though.  The lake has stopped rising for now.


It is hard from here to assess the current position with regards to the dam, or to forecast what will happen next.  However, from the start I have held the view that managing this hazard would be somewhat challenging if stable flow became established.  The chronic hazard has not gone away, although the acute hazard may have reduced.  As there is still a vast quantity of water stored in the landscape, the dam remains vulnerable to a series of processes, including:

1. An unexpected increase in erosion rate;
2. Erosion during flood events (the discharge of the Hunza will rise substantially in the next few weeks);
3. A further landslide on the banks of the lake, which could trigger a wave;
4. A seismic event.
   

Thus, NDMA have a huge challenge ahead in deciding when to allow people to move back into the high hazard area.  They will also need to decide whether to initiate erosion through the use of a controlled blast.  This is not an unenviable decision to make.  Inevitably, there are some exerting pressure to initiate a breach to drain the lake, whilst others are happy with the status quo.



Meanwhile, of course those on the upstream side remain isolated, with a huge lake impeding access.  The Karakoram Highway remains closed indefinitely, although the boat service has been resumed.  During summer floods, when inflow may briefly exceed outflow, the lake level could rise again by a small amount, unless progressive erosion of the spillway serves to lower the lake level.  Thus, overall, many challenges remain at Attabad.; it will be interesting to see how NDMA responds to them.

Attabad: spillway flow update of 08:30 this morning

There is a mass of confusing and contradictory information about the state of flow in the Attabad spillway, but the FWO data appears to be consistent at the moment.  The latest data, again via Dr Sadiq,  is that flow was 3700 cusecs (105 cumecs) at 08:00 local time this morning.  This makes the graph look like this:

This suggests that we are still seeing an incremental increase in flow.  However, interestingly, the rate of inflow and the rate of outflow now appear to be balanced, such that the lake level should stop rising (for a while anyway).  If this happens, and spillway flow continues to increase, we will know that erosion is developing.

Photos of the development of the situation at Attabad

Focus have kindly provided a new set of images of the situation at Attabad with respect to the spillway.  I think that these images were taken yesterday.

Most importantly, here is an overview image of the spillway:

It is helpful to compare this with the image of the spillway from 1st June (right hand image):

It is clear that the situation has developed considerably over the last few days.  The flow along the spillway has increased greatly, and the lower part of the channel has widened and deepened.  Flow appears to still be controlled by the large boulder in the middle of the channel, although the lowering of the channel downstream will be steadily undercutting this.The development of the spring on the channel edge is also interesting.


A closer view of the spillway clearly shows how widening is occurring:

The flow is undercutting the banks, which are then progressively failing.  Note also just how much scour is occurring even though the bed of the channel is boulder-strewn - it is clear that at the moment the boulders are not armouring the channel.

A view from the downstream side of the channel is fairly dramatic:

This gives the impression that there is a huge volume of water flowing.  However, a look downstream towards the old landslide deposit at Salmanabad (that is the big pile of debris upper right) shows that this is not really the case:

It is clear that the flow is still rather modest, despite the huge amount of erosion that the water has achieved.

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!