This may be a Long Walk Home

Attabad Land slide captured by a passerby

The Spill way which is not steep enough to assist an expected erosion

 By A Khokar  May 31, 2010

This was expected that under the present plan the subject spillway/ barrier of Hunza River at Attabad will be eroded and major water out flow of the lake may start soon but unfortunately this is not happening as expected.

 Keeping in view the long length of blockage of the barrier and nature of the surrounding hills, that by attempting any mechanical blasting to reduce the barrier; it is feared that hills prone to triggering further land sliding will start refilling the blocked mouth.

 Reportedly, the fresh water pouring in the lake is much higher than the small drain at spill way point. The expected erosion of 4 to 5 seepage point is also not working; thus the water in the lake keep on rising; engulfing more and more of upstream houses and villages.

 But it is most important that mechanical measures be under taken to induce the drainage of the water to at least purge the increase of fresh water level pouring in from the melting glaciers.

 Blasting of the barrier may be out of the question as it may trigger the further landslides and result in adding in the blockage. As suggested earlier artificial siphoning through large hoses may be the only solution to remain in control of the situation.

 At the same time effort for a secure excavation of barrier as well as enhancing the seepage point to facilitate the main drain of lake may be carried out to achieve the required results.

Attabad Dam out Burst; Red Alert

By A Khokar   May 28.  2010

 Reportedly the expected over topping (over flowing) of the spillway have started at a very low rate and hopefully all the access glacial water pouring into lake at its tail which is extended to some 8 to 10 mile upstream—- will result in a move of water in the lake. This move may result into more erosion along the length of lake.

At the spillway it’s soil is not compact but is loose in nature and once the loose clay found in between the big boulders stuck in the blockages is eroded by the water flow—-more water will start flowing through them which may result in shifting of boulders as well as debris thus causing an exceptional sudden outburst any time soon.

Even at this stage in order to control the drainage of lake it is highly recommended that
to prevent the downstream destruction by sudden outburst of lake dam; an adequate water draining arrangements by laying the mega poly pipes or other flexi hose artificial Siphons System along the spillway may be the only solution to avail a controlled drain of the lake as well as prevent the downstream damages that it may cause to the life and properties of people including the mega structure of Tarbela Dam.

New images and maps of Attabad

Report compiled by  A Khokar 

Whilst we wait for news from Pakistan, here are two new resources that readers may find useful.  First, NASA have released a new Aster image of the lake site, collected in the last few days.  This is available here, with a link to my blog (thanks to them for this).  The image shows the manner in which the lake has extended in the last few weeks – NASA have helpfully provided an image with the previous extents shown:

 The unannotated image, this time orientated north-south, is also rather fine:

 

Alonside this, UNOSAT have released another map of the areas inundated by the flood.  This is available here, and looks like this:

We may see some landslides along the banks of the lake as the water level is drawn down by the breach, so this imagery may prove to be very useful.

Posted by Dr Dave at 13:02 2 comments  

Labels: Attabad, barrier lake, Hunza, landslide dam, pakistan

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Attabad: Overtopping is now likely to be imminent

It is unfortunate timing that the likely day of overtopping has fallen on a Friday, the holy day in Pakistan, meaning that flow of information is impeded.  As a result I have not yet had an update for today on the lake level.  Jean Schneider of BOKU visited the site yesterday by helicopter and measured the freeboard at 2.25 feet, which is about 70 cm.  I am not sure what time this measurement was made.  Based upon the rate of rise of water level, that should put the time of overtopping at some time today.  However, this will depend upon the continued rise of the water at a similar rate, no further heave of the floor of the spillway and, perhaps most importantly, no further collapse of the walls of the spillway.

Meanwhile, the continued mixed messages from the Pakistan administration has been illustrated by an article in The News today:

“Zameer Abbas, Assistant Commissioner and in charge of relief camps in Hunza Nagar, told this correspondent that the Karakoram Highway had been closed for every kind of vehicular traffic as the lake water was expected to reach spillway today (Friday) after which the overflow would begin, paving the way for controlled release of water.  Dismissing the chances of water outburst, he said the landslide blocked some one-and-a-half portion of the Hunza River and it was apparently out of question that water would force out of this huge amount of mud and debris.”

Attabad: Overtopping is now likely to be imminent

 

It is unfortunate timing that the likely day of overtopping has fallen on a Friday, the holy day in Pakistan, meaning that flow of information is impeded.  As a result I have not yet had an update for today on the lake level.  Jean Schneider of BOKU visited the site yesterday by helicopter and measured the freeboard at 2.25 feet, which is about 70 cm.  I am not sure what time this measurement was made.  Based upon the rate of rise of water level, that should put the time of overtopping at some time today.  However, this will depend upon the continued rise of the water at a similar rate, no further heave of the floor of the spillway and, perhaps most importantly, no further collapse of the walls of the spillway.

Meanwhile, the continued mixed messages from the Pakistan administration has been illustrated by an article in The News today:

“Zameer Abbas, Assistant Commissioner and in charge of relief camps in Hunza Nagar, told this correspondent that the Karakoram Highway had been closed for every kind of vehicular traffic as the lake water was expected to reach spillway today (Friday) after which the overflow would begin, paving the way for controlled release of water.  Dismissing the chances of water outburst, he said the landslide blocked some one-and-a-half portion of the Hunza River and it was apparently out of question that water would force out of this huge amount of mud and debris.”

Attabad Water Bomb: Siphon the water out and Drain the lake

Reportedly the lake level continues to rise. The estimates from satellite imagery suggest that the volume may have now exceeded 500 million cubic metres into Attabad Lake as weather is getting warmer and glaciers are melting fast. But the expected decrease of freeboard is not being achieved to facilitate the overtopping (over flow) of water from over the spill way as was expected to top over by May 24/25th.

A caveat certainly applies that estimated volume of some 500 million cubic meters of water is contained in such a narrow Attabad lake of loose eroding soil which is highly dangerous. Daily increase of water into lake is not attaining the rise in the water level and is not automatically translated into reduction of freeboard. Keeping the nature of soil the deformation and swelling of lake bed may give the way to water to travel within the lake to multi burst points.

Reportedly the spill way made of debris from the slides is weak in nature but being at the turning point of the River is sufficiently strong at least to block the water as the mass of water is seemingly contained by the curved sides near the mouth of the lake. The subject blockage expected to serve as spill way is made of lose clay debris and already many seepage holes are discovered in it. There is likely hood that massive volume of water is already pushing out and up lifting the lake floor on to the sides and loosening the weak clay deposit under the spill way; it may collapse and lake may bursts out.

The expert may tell us better but to keep the spill way intact in order to prevent the downstream wide spread disaster and devastation, it is but necessary that an adequate water draining arrangements by laying the mega poly pipes or other flexi artificial Siphons System over the spill way may be the only solution to drain the lake as well as save the situation and its sudden outburst which may damage even the downstream Tarbela dam is prevented.

Attabad: the freeboard is now reportedly about 1,3 metres

Thursday, 27 May 2010

 The latest NDMA figures suggest that the freeboard is down to about 4.3 feet (1.31 metres) as of 3 pm today.  That is a reduction of about 70 cm on the day, meaning that we are probably less than two days from the point of overtopping:

 I am reasonably confident of these values as the Focus geologists took this picture yesterday of the spillway:

 

 The circled boulder is the crest of the spillway, so water flow will start when this point is reached.  Of course the one potential problem is a slope failure on the spillway walls, which could block the channel.  This is a real possibility, but we won’t know until tomorrow.

Close up the channel at this point looks like this:

 

Unfortunately the large boulder will resist lateral cutting, initially at least, which is likely to increase the rate of down-cutting.  This is unfortunate.  Once the water reaches the top it will initially flow down this channel, crossing the summit of the dam:

And then will flow down here:

The disturbance here is from collapse of the banks induced by the seepage.  Finally, it will flow down the main river channel:

The terrace in the centre left of the image is at 60 metres above the river level.  Previous (comparatively recent) floods have not reached this level, which is half the height of the dam.  This is the level that we believe is comparatively safe from the flood.

———-

Source:  David Petley Wilson Professor, Department of Geography, Durham University

 

HUNZA IN FULL BLOOM in Video

 

 

By A Khokar

While River Hunza is partially blocked at Atabad due to massive land slide and up stream it has formed a huge lake resulting in numerous village submerged in water and displacement of  thousands of people.

But the nature never stops blooming for any hazzards or  the invirone disruptions.

The other parts of Hunza are in full Bloom

[youtube]http://www.youtube.com/watch?v=GX2XSG-oP-I&feature=player_embedded[/youtube]

Attabad: update report for 26th May

 Wednesday, 26 May 2010

The combined monitoring effort appears now to be providing consistent measurements of the remaining freeboard, and these are now being used in the media, which is helpful.  As of late last night the reported freeboard was 8.8 feet, which is 2.56 metres.  This provides a freeboard – time graph that looks like this:

 

 This suggests that we are still on course for overtopping on about 27th or 28th May, although clearly this remains a moving target for all the reasons previously outlined.

 Meanwhile, the media in Pakistan have now picked up on the inconsistencies in the measurements reported by NDMA, and in particular their incorrect measurements of freeboard.  This article is strongly critical of the error by the government agencies.

The state of the spillway is also a concern now within Pakistan.  From the same article:

The engineers said the 25-metre-deep spillway was too narrow to accommodate outflows of more than 2,400 cusecs from the lake, which held an estimated 1.2 million cusecs on May 17. A cusec is a unit of water flow equal to one cubit foot per second. “There is a serious possibility that the entry of water into the spillway could trigger a collapse of debris that would block it altogether,” an engineer said.

Several people have asked why the slopes on the sides of the spillway are failing given that the weather is dry.  The answer I think lies in the material – which dries on the surface but remains wet and very weak just below – and the loading from the excavated materials on the slopes above the spillway:

 

 

The Sinking Paradise-Video

[youtube]http://www.youtube.com/watch?v=B1wcdhoimys&NR=1[/youtube]

Attabad – a bizarre race between two processes

 

 Tuesday, 25 May 2010

Water filling the lake is continuously rising in  the newly formed lake. It was expected that soon the water will start over flowing the spillway. But as soon as the water freeboard level[1] is over come and water may move for the spillway and start draining the lake excess water; spillway starts filling up agian by the falling mountains debris.

 Mean while seepage at various place down the spillway which is very porous in nature from small openings and holes  is said to be most dangerous that it may cause a sudden breach of dam so formed and there may be sudden outburst.

 National Disaster management authority(NDMA) along with the local administration with the help of Pak army have managed to evacuate the population from the downstream areas.

Yesterdays “coalition” resurveys of the spillway and water level now appears to provide a definitive freeboard* value.  As of 8 am this morning the freeboard was 3.027 metres, representing an increase of water level of 1.09 metres in the last 24 hours.  This elevated rate of water level rise probably reflects the warmer weather in the area in the last few days, which will be driving snowmelt.

I have recalculated the freeboard values assuming that the official numbers released today are correct, meaning the early figures under-estimated the true freeboard figure.  The resulting graph is as follows:

At the current rate of increase the freeboard will be lost in two to three days, but as before we are reliant upon these figures being correct.  This episode of incorrect freeboard measurement does not reflect well on NDMA, given the importance of these numbers.  Of course, the fact that the saddle is located at a higher elevation means that the lake volume will be larger – i.e. it increases the size of the potential flood.

Of great concern to me though is the continued problem of closure of the spillway.  It is clear that the banks of the spillway are failing in multiple locations.  These failures are progressively closing the spillway, as this Focus image, taken of the spillway banks yesterday morning, shows:

 The concern would be that the spillway closes completely before the water level reaches this level, which would effectively increase the freeboard once again, albeit probably briefly.  In effect we are in a high stakes race between the rate of water level rise and the rate of closure of the spillway.  The strength of the clay material forming the spillway banks is clearly low, as we believed from the start.  Either way, the spillway is clearly completely incapable of handling the flow, so erosion is inevitable.  The one bright spot is that the failed banks may erode preferentially, allowing the channel to widen more rapidly than it down-cuts, as happened at Tangjiashan. 

 Finally, let’s not forget the hardship that this crisis is imposing on the local people.  The Pamir Times today published this image of a camp for Internally Displaced People (IDPs):

 Notes

 [1]Freeboard: Vertical distance from the normal water surface to the top of a confining wall….i.e. spillway height of Attabad Lake left to be filled that water will start over flowing after its filling.