29 May 2010
Attabad: overtopping has begun
Posted by Dave Petley
The media are reporting that water has now “entered the spillway” – i.e. that overtopping has begun. The report, which is from the Chinese Agency Xinhua, carries a rather strange quote from an official from NDMA:
“The next 12 hours could be crucial as the water flow would reach its maximum intensity,” commented an official of the National Disaster Management Authority (NDMA), the organization mainly responsible for the overall rescue and damage control operation.
Maybe this is a misquote? The next twelve hours are crucial of course, but there is a good chance that a breach won’t develop in this time. The water level will continue to rise until outflow (seepage + spillway flow) = inflow. As some of the water is being released, this may well take much more than 12 hours to develop. In addition, a breach will only start when erosion of the base occurs at the highest point of the saddle. This may well take time to occur.
So, I would like to make two points:
1. The development of a breach in the next 12 hours is very possible; the failure of a breach to develop does not mean that one won’t occur. At Tangjiashan the breach took several days to start, but was then rapid;
2. It is also possible that an initial small flood will happen, but that this will then cease. For example, this could be the case if the sides of the channel collapse, blocking the flow. We must be clear that if there is a small flood that then declines then the situation is certainly not over. People must not go back into the danger zone until we know that the threat has passed.
Of course what we are hoping for now is slow erosion and the release of the water over the next few days. Such a scenario is certainly not beyond the bounds of possibility.
I will post again as more information becomes available, but don’t be surprised if this takes a few days to develop.
thanks David for the latest update at last water started to flow the spill way and we can hope there will be smooth flow of water in next few days.
Hi Dave, Thank you. I hope everyone will heed your words – it is not safe to go into the danger area just bcos of some small flood! I wish for everyone to be cautious and stay on high ground until the dam erodes and water is released. No lives need be lost.
Hi David,thank you very much for up-dating us about the attabad situation, water started to flow but the results are expected in next 12 hours, you are doing a wonderful job, as i belong to that area but sitting very far, you updates enable me to see the possible circumtances, thanks you once again
We are fortunate to have a village house well above the 60 meteres and with a good 3 kilometres between us and the river. I have a good job and have been aware this was coming for weeks ( thanks to your blog)and we have been trying to get the extended family out of Gilgit for over a week. Finally yesterday 12 people joined our house. We are busy keeping them entertained so they don't want to go home – people are not really aware of the worst case scenario- south of Hunza and in Gilgit – and reluctant to move from their homes. I am praying for a slow but steady release as people will get resless and may want to go back before the danger is over
I find it extraordinary that the authorities are making statements such as this. Why on earth don't they ask an expert – ie you? You clearly have a very good idea, based on years of academic study and fieldwork experience. Are they too proud to ask? Are they willing to put people's lives at risk by giving them misleading and inaccurate information, rather than 'lose face' by asking for good, reliable information from a foreign expert?
Hi Dave,Thanks for keeping us informed of this major event. As you say there may be some days to run before the danger is truly passed. Based on the Unosat map, on 21st May the surface area of the lake was 829hectares i.e. 8.3M sq.m not including the original area of the river. A current surface area for the lake would therefore seem to be about 10M sq m. Your plot indicates a rate of lake level rise of about 0.7m per day, suggesting an inflow to the lake of around 7M cu m or about 80 cu.m/sec (plus any seepage through the landslip). Assuming a flow velocity through the spillway of 10m/sec, this would suggest a cross-section of 8 sq m of water. For a 90 deg V-notch channel this would imply a depth of water of about 2.8m. At the original rate of lake rise this would take 4 days to achieve this depth of flow, and it would take longer because of the partial discharge through the spillway. All very approximate, but it suggest some days before a safe steady state would be achieved. Any shorter period and this would imply erosion of the spillway, which as you suggest with the grading of the material, probably would lead to an accelerating breach.
I would like to thank you and the focus team working in such a remote area. I read your blog for the first time today it gave me quite an insight on the current happenings at attabad and what to expect. Hope there is minimal damage.Once again thanks for your work and thuumbs up to team FOCUS.
why does not the pak army make suicide bombers out of the displaced folks… and then these suicide bombers could go and blast the rubble and increase the size of the spillway… pakistan will be saved.
NDMA update for 29 May is now online, reporting outflow at 300cusecs.
Dave, you are doing an excellent service to the people of the affected area, as well as students of the science such as myself. Many thanks on behalf of them, myself, and everyone else.
You will find the NDMA update there: http://www.ndma.gov.pk/AttaHunzaLandslide.htmlG. Thiem, Stuttgart, Germany
Attabad Dam out Burst; Red AlertReportedly 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 thatto 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.
mega poly pipes… madrassa logic.
Some mainstream media coverage: the LA Times has a new piece here, which mentions your March report on the situation. Fingers and toes crossed …
I've had the same idea as A. Kohar for a few weeks. I think it is much safer to siphon the water because there is more control, less unknown.Allowing the water through the spillway and hoping for the best is not a guarantee that the best will happen. Anything could go wrong and cause more damage. If siphoning had taken place right after the landslide happened the lake would not have grown so big and so many villages and fields and bridges been submerged. I don't see the "madrassa logic" in this. I am not a Muslim and the flexi-hose is best to adapt to the landslide profile. Once the siphon is started the water goes up the slope by virtue of the law of physics, not power is needed.I think all villages in landslide-prone areas should get equipped with large diameter flexi hoses (or buy one set of equipment to own communally and use where needed) so that as soon as an event similar to this occurs, the material owned by the villagers is set to work immediately, without need to call on the federal government and suffer costly and tragic delays.
and the faithfull will congregate after friday juma prayers and suck on the mega poly pipes to create the suction !!!! vow.
kamo, do u have any idea about the inflows into the lake and the suction power of your mega poly pipes… so are you next planning to get flash gordon on the site??
Dear all, I dont think that the siphon / pump idea was ever practicable at this site, and certainly is not now. The height of the dam was too large, the location too remote, and the inflows too high. This was always a red herring – a sensible approach was always to either build a proper (armoured) spillway or to allow overtopping with a decent level of preparation.D.
Dr dave.. i compliment you for drilling some sense into these delusional pakis. Even the most educated of pakis will show a delusional, idotic and streaks of primitibe medivalism. the only thing that they do well is suicide bombing… i could not laughing the whole night visualizaing pakis sucking at poly pipes with cries of 'allah oh akbar'even building a armoured spillaway was very difficult since you could not get the anchor/foundation into something solid.
dave, even the level of competence of 'expert' pakis is astounding. there were paki hydrology experts at our simulation model at roorkee university ( bahlihar dam dispute) .. and the paki clowns were totally lost with our calculations and model… they could not understand the simulation model. i feel sorry for these jokers.
well 'Mr. anonymous' your observation might be correct about the incompetent so called hydrology experts who make it thus far due to unfortunate scrutiny procedures and corruption involved in the society, but you should realize that people commenting here are no experts they might have no idea of what a practical solution should be, they just posted their ideas. Dr. Dave here gave a very good answer that can make everyone understand.You on the other hand have started mocking them, of course the idea is ridiculous but your comments are a bit harsh targeting the whole country. Please don't start judging the whole country by interacting with few individuals.
To Blog Administrator, I thankyou for removing the last two comments from 'anonymous' and would be grateful if you would do so re the others that are littering an otherwise inspiring inspired and positive collaboration. 'Anonymous' reeks evil and is anathema to this site.