11 June 2010
The continued threat posed by landslides at Attabad
Posted by Dave Petley
Attention continues to be focused upon the state of the spillway at Attabad, and in particular the likely impact of the increase in flow we might see over the next few weeks. Yesterday’s images from Focus showed that slow evolution of the spillway continues, with the lake level reported to have dropped only by a:n inch (2.5 cm):
However, we must not lose sight of the potential for other failure mechanisms. Given that seepage appears to now be constant, the greatest concern may well be associated with the potential for a further landslide into the lake. The high water levels and (comparatively) warm temperatures render this a possibility (but not in any way a probable event). This remarkable set of images, taken at 6:14 to 6:16 pm last night (10th June) by the Focus geologists, clearly illustrates the ongoing threat:
Thanks for the update.The pics are showing that there is lot of instability.Do you think a landslide like this can trigger a wave and ultimately the dam would be broken?
From the pics it looks like this landslide is at the mouth of spillway. Do you think this could cause blockage of spillway and dam would remain intact?
FOCUS helicopter video over spillway uploaded June 11. Fallen boulder clearly has water flowing on both sides. Gives good sense of the spillway's profile, especially in the first 15 seconds.
Here is another news update:http://www.samaa.tv/News21037-Outflow_in_Attabad_Lake_on_the_rise.aspx
The longitudinal profile of a landslide dam is an important facter to determine flood discharge from the landslide dam. Do you have the data?Long landslide dams (along the flow direction)and one with mild gradient of its downstream slope do not generate large flood. The length of a landslide dam controls flood dischrge than its height or storage water volume.http://www.fujipress.jp/JDR/DSSTR00050003.html#pagetopPrediction of Floods Caused by Landslide Dam CollapseYoshifumi Satofuka, Toshio Mori, Takahisa Mizuyama, Kiichiro Ogawa, and Kousuke Yoshino, pp. 288-295Takahisa MizuyamaKyoto University
Damn! CNN showed here in Europe a nice report from Attabad but I was half asleep and could not assess the state of the spillway. I seem to remember large flow with a big boulder really holding the flood together.I could not find the video on cnn site either! 🙁
http://interceder.net/news/hunzavideo June 12 of spillway
Dave posted a link to a report on the flow rates of the Hunza during the year:http://iahs.info/redbooks/a190/iahs_190_0139.pdfSee Dave's entry here:http://daveslandslideblog.blogspot.com/2010/05/inflow-to-landslide-lake-at-attabad.htmlAccording to the observations of the author, the Hunza's peak flow (cubic meters) will happen in July, with the flow going down starting around August 1. While there are many more forces than just flow at play, it should be noted that the lake's inflow is still increasing, so for the lake to remain at its current level, the spillway flow would also need to increase. Obviously this is about averages, not a specific day. There could be cold upper elevation temperatures that slow the glacial melt, and thus, the inflow could slow.According to the report, the flow rate can be expected to go down greatly in August, so if the dam holds until mid-August, it's my guess that we will be clear of flow issues until next year.This month, June, the inflow into the lake is still increasing.Yes, I know I've made some assumptions, including one about flow rates at the observation point and the dam location.
This area as active landslides as shown in these pictures. I always thought that NDMA/FWO is not working hard and fast to prepare the spillway. The other day I saw an interview of Chairman NDMA from a helicopter and there were active landsliding happening when he was in the chopper. There he said that these landslides made their work difficult and very risky. And his reply to all the people criticizing the pace of work was that the workers put their lives on the line to prepare the spillway.Probably now I understand their situation a little better.
Useful video of the lake and spillway: http://www.youtube.com/watch?v=oRvp1Eo7s6IRobert
Dave plz read the news on the link below. Its about another lake forming in Shamshal area some where 60km from Attabad.http://www.adailynewspaper.com/glacier-melting-spawns-another-lake-at-shamshal-9307