Published on May 17, 2011
Attabad landslide crisis in Hunza, Pakistan – lessons for the management of valley blocking landslides: Attabad landslide crisis in Hunza , Pakistan – lessons for the management of valley blocking landslides Dave Petley Durham University, United Kingdom Thanks to: D. Karim, S. Wali, N. Ali, N. Nasab & K. Shaban Focus Humanitarian Assistance, Pakistan http://blogs.agu.org/landslideblog/ Schedule of talk: Schedule of talk Global landslide mortality hazard and risk Landslide mortality hazard and risk along the Himalayan Arc The 2010 Attabad landslide, Hunza , Pakistan Powerpoint file on my AGU hosted blog at: http://blogs.agu.org/landslideblog/ Google: “landslide blog AGU” CRED data for landslide fatalities: CRED data for landslide fatalities 6587 Other disasters 2002-2009 (CRED database) Earthquake: 429,877 River flood : 37,860 Storm: 166,410 Volcano : 221 Slide 4: 81,833 Landslides from the Kashmir earthquake Landslides from the Wenchuan earthquake The (more) true human cost of landslides Global fatal rainfall-induced landslides – 2006 to 2009: Global fatal rainfall-induced landslides – 2006 to 2009 Slide 6: Himalayan Arc Himalayan Arc – 2004 to 2009: Himalayan Arc – 2004 to 2009 Monthly occurrence of non-seismic fatal landslides (NFLs): Monthly occurrence of non-seismic fatal landslides (NFLs) Annual cycle in pentads (five day bins): Annual cycle in pentads (five day bins) Trend in occurrence?: Trend in occurrence? Slide 11: Attabad Slide 14: Slope identified as unstable in 2003 Slide 15: Collapse event: 4 th January 2010 Slide 17: 1. Progressive failure over >7 years, scar height = 1175 m 2. Catastrophic failure event in Jan 2010 with no trigger 3. Emplacement of rockslide onto lake sediments triggered secondary high velocity mudflow event Cross valley runout = 1300 m Deposit height = 120 to 200 m 1858 landslide dam: 1858 landslide dam Wenchuan Earthquake barrier lake risk table: Wenchuan Earthquake barrier lake risk table Yang et al 2010 Data driven flood estimation: Data driven flood estimation Typical values of maximum discharge using this approach: 14,000 cumecs (Costa and Schuster 1986) 12,000 - 26,000 cumecs ( Walder and O’Connor 1997) Management of the hazard: Management of the hazard Initial management response was the construction of a spillway. Original intention: 30 metres deep Actual depth at time of overtopping: 15 metres Final spillway was very narrow and unlined Evacuations: Evacuations After the landslide, Focus installed sirens in 15 villages People in most hazardous areas relocated into camps Boat service established on lake, but enormous hardship upstream One month before overtopping NDMA evacuated 15,000 people downstream of barrier Seepage: Seepage Seepage development: Seepage development Prediction of date of overtopping: Prediction of date of overtopping NDMA consistently predicted the date of overtopping incorrectly (repeatedly predicted overtopping too early) However, final overtopping occurred later than expected because the lacustrine silts deformed, raising the floor of the channel Water level rise: Water level rise Overtopping behaviour: Overtopping behaviour Evolution of spillway discharge: Evolution of spillway discharge Spillway discharge – depth relationship: Spillway discharge – depth relationship Spillway evolution: Spillway evolution Management problems: Management problems Karakoram Highway remains blocked In 2010 floods, Gilgit-Baltistan was cut off to north and south Loss of productive land Loss of cash crop markets Landslide hazard remains Progressive failure GLOF Seismic event Landslide into lake Should the lake level be lowered? FWO attempt through the winter aimed to reduce the spillway elevation by 35 metres, but achieved less than 4 metres 2011 monsoon will start in about six weeks Conclusions: Conclusions Impacts of landslides much higher than conventionally considered Strong component is from the Himalayan Arc Attabad landslide event Long term management problems Should the dam be left alone, strengthened or lowered?