Schneider - Impact of Largelandslide


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Schneider - Impact of Largelandslide

  1. 1. Impact of large landslides, mitigation measures Jean F. Schneider Emeritus and Senior Geoscientist BOKU University Vienna and Switzerland Vajont 1963-2013: Thoughts and analyses after 50 years since the catastrophic landslide Padova, Italy, October 8-10
  2. 2. Content of the presentation  >Triggering of large landslides  Formation and stability of landslide dams  Mechanisms of landslide dam failure  Mitigation measures  Examples  Synthesis Tangjiashan Lake, China (2008) Photo: courtesy of Chen Zuyu
  3. 3. Triggering of Landslides • Preconditions and processes triggering Landslides: – Slope geology and quaternary history – Slope morphology, inclination and exposition – Precipitation, water content, pore pressures – Active faults, seismological impact – Negative human impact (irrigation, mass balance, undercutting, …) Lake Sarez, Pamir
  4. 4. Area of Landslides (sq. km) Triggering Earthquake Magnitude versus Mass Movement Size 1000000 100000 Large Landslides 10000 1000 Rock Avalanche 100 Rock Slumps Soil Flow 10 Falls 1 LIQUEFACTION 0.1 0 2 4 6 Earthquake Magnitude 8 10
  5. 5. Landslide Hazard Management - Only effective with clear understanding of geology, geometry, volume, dynamics of landslide, run out, hydraulic conditions and seismic ground motion - Today, most efforts are spent on understanding the hydraulic/static and co-seismic trigger mechanism - Also post-disaster failure and long-time behavior of affected slope should be taken into consideration - Back calculation, 3D visualization, and modeling help understanding these processes
  6. 6. Landslide Risk Assessment / Management Dai et al., 2001
  7. 7. Mitigation of Landslides After identification and landslide inventory/maps: • Restricting development (irrigation, infrastructure, construction, mass balance) • Rising awareness, preparedness • Engineering for slope stability (incl. hydraulics) • Developing monitoring and warning systems • But also providing landslide insurance!
  8. 8. Data Collection on Landslide Dams • Types of natural dam (origin, size, composition) – Landslide dam origin, height and volume, lithology – Landslide dam composition and consolidation • • • • • • • Development of retained lake / sediment volume Catchment area, weather conditions Risk of dam to fail, partial or total failure Geometry of the affected valley downstream Characteristics of possible flood wave Entrainment of sediments downstream Vulnerability, land use and elements at risk!
  9. 9. Persistence of Landslide Dams From Debris Flows to Large Landslides Large Landslides Small Landslides 9
  10. 10. Lession learnt: La Josefina, Ecuador 1993 • • • • • • Dam 30 mio qm, H 120 m, 33 days Cuenca, rio Paute, lake 185 mio qm Spillway 18 m deep, 150’000 qm Peak flow 8-10’000 qm/s, 10 hours Sediment entrainment 40 mio qm 14’000 evacuations, but 72 casualties Schuster et al. 2002
  11. 11. La Josefina, Ecuador 1993 Situation today Breach hydrograph after Canuti et al, 1994
  12. 12. Natural Dam Failure Quantifying hazards and risks of landslide dam failures requires again the specification of: – Creation, size, form, composition, age and consolidation of dam, including active faults and aftershocks, – Bathymetry of the impounded lake, accumulation of unconsolidated sediments, flank stability – Weather conditions, forecasting rate of seepage, erosion and time of overtopping, possible breach – Composition and stability of the slopes downstream, size of flood wave and entrainment of sediments
  13. 13. General Causes of Dam Failures 25 per cent 20 15 Overtopping Slope Instability Earthquake Foundation Seepage Structural Erosion Mine Subsidence Unknown 10 05 00 Seid-Karbasi and Byrne, 2004
  14. 14. Risk Mitigation Strategies for Landslide Dams > Each stage in the history of a landslide dam requires its specific risk mitigation strategies immediate (days – weeks) Evacuation QUICK EVALUATION Back analysis Computer Modeling Visualization Awareness, Long term planning Preparedness Training long-term (months – decades) Reduce water table, construction of spillway Monitoring Early warning system
  15. 15. Most used stabilization methods: First: • Observation of piping through dam, damming possible? • Overtopping expected? Determining point of time. • Deviation of water input around dam possible? Then: • Construction of spillway (often not reinforced), or • Drainage by means of syphons or pumping, or • Tunnel outlets and diversions, or • Blasting to open deeper overflow channels
  16. 16. Lake Sarez (Tajikistan, 1911), Earthquake triggered Landslide Usoi dam stability >100 years 16
  17. 17. Lake Sarez/ Usoy Dam Escarpment Mountain sagging HD ~ 700 m Seepage VL ~16 km3 VD ~2.2 km3 Source:
  18. 18. Usoy Dam / Lake Sarez Usoy dam (after Lim, V. et al, 1999) with seepage Possible ways of dam overtopping waves induced by Ways. Scale: approx. 1000 m a right bank landslide (Stucky Interim Report 2003)
  19. 19. Lake Sarez: Flood Wave Simulation, triggered by Mountain Sagging Landslide Stucky Interim Report 2003
  20. 20. Flood risk: prevention and mitigation Lake Sarez- Bartang Valley ? Lake Sarez, Pamir
  21. 21. Hattian Bala (Kashmir Earthquake, 2005) Landslide Dam, Karli-/Tang-Lakes Quickbird II, 10_27_2005 21
  22. 22. Hattian Bala Dam Breach (05/2005 – 01/2009) Landsat TM 22
  23. 23. Hattian Bala Dam 2005 Spillway excavation Spillway after overflow Photo FWO Karli Lake under formation
  24. 24. Hattian Bala, failed dam (January 2009)
  25. 25. Both Flanks of Karli Lake failed
  26. 26. Hyperconcentrated Flow in Pjanch River after Dam Breach
  27. 27. Hattian Bala Dam after Breach 01/2009
  28. 28. Attabad Rock-Slide and Dam (Hunza Valley Pakistan, 04-01-2010) 28 Photo Pamir Times
  29. 29. Geological Map Hunza Valley PakGS
  30. 30. Attabad Rock-Slide, Dam, Lake 3/19/2010 Partly destroyed Attabad Hamlet Landslide (continuous Rock-fall/slide) Eroded 1858 Slide Dam Debris Flow Dam Spillway Construction
  31. 31. Cross-Section Attabad Slide Lake Sediments Data NESPAK, 2010 (not to scale)
  32. 32. View from Attabad Hamlet looking to View from Attabad Ls dam looking to downstream Part of Dam/Debris Flow partially eroded 1858 dam downstream
  33. 33. Attabad, Hunza Lake 2010 Imagery: EO1
  34. 34. Atabad Dam Breach: flood hazard indication map Attabad Dam 80 km upstream Confluence with Gilgit River (this slide) PAMIR Kickoff meeting Dushanbe March 14 – 16, 2011 Remote geohazards in Central Asia 34
  35. 35. Attabad Dam-Break Study, Flood Wave Propagation HEC-RAS, Flow 2D Danger! Safe Safe NESPAK 2010, IAG-BOKU
  36. 36. Attabad Dam: Seepage before Overflow spillway seepage point Photo: Pamir Times 36
  37. 37. Location and blasting of temporary coffer Excavation reduce water flow for work dams built toof Spillway Channel under high Risk! Following photos by FWO Pakistan, Pamir Times
  38. 38. Siachen-Gayari Ice/Rock Avalanche, April 7, 2012 Pakistan
  39. 39. Siachen-Gayari, Situation before Incident Glacier Moraine/Debris Cone Military Camp
  40. 40. Gayari Debris Cone, 19. 04. 2012 Siachen-Gayari, Proposed Spillway (with fresh Snow) Capped Moraine Military Complex Proposed Cut
  41. 41. Siachen_Gayari ice/rock avalanche April 6, 2012 Siachen_Gayari ice/rock and Clearence Efforts Siachen-Gayari, Rescueavalanche April 6, 2012, lateral moraine wall capped! Upper glacier, post disaster image. Avalanche! Upper glacier, pre disaster image. Seracs! c Digital Globe 2012
  42. 42. Georadar carried out by Norvegian Red Cross Thickness of Debris Proposed Water Channel
  43. 43. Siachen-Gayari One Month later! Disaster (5 days later) Center Coordinates: 76°49'46.10"E 35°13'7.53"N c Digital Globe, 2012
  44. 44. Water management/Clearing efforts at Gayari Water started draining April 2012 => quick lake level reduction of 20 meters. Excavation work / clearance efforts continued Summers 2012/13, despite difficulties posed by seepage of water to the sites, hazards of crevasses / erosion by water and sinking of equipment. Artificial channel Summer 2012: >300 persons were working , with 10 Dozers, 11 Excavators, 18 Dump trucks and 9 FE loaders to recover the buried bodies. Meanwhile, all 140 bodies and some destroyed equipment are excavated.
  45. 45. Challenges for risk mitigation <5 years< >? Hattian Lake! Lake Attabad, others ? after Costa and Schuster (1988) 45
  46. 46. Understanding Dams / Lakes created by Landslides, Problems – Numerous cases known, yet data incomplete and of varying standard. However, known cases provide empirical benchmarks for regional comparison – Analyses are static and do not account for process-induced changes. Very little information on geotechnical behavior. – Few data on sediment retention due to infill in lake behind landslide dams as well as on dam outburst floods, availability of soils, and / or post-failure sediment delivery – Hazard assessment of landslide dams should integrate geology/geotechnics as well as process dynamics.
  47. 47. Synthesis > Landslides commonly form dams impounding lakes! The impact areas of these geohazard events are often located far away from the source areas > These events occur at low frequencies (long intervals) > Therefore, the levels of awareness of and preparedness for such events are generally low > Furthermore, the predictability of such events suffers from insufficient knowledge of the conditions and changes in the high-mountain areas > Therefore, the sensitivity of population and stakeholders, the capacity of understanding processes needs to be increased > Comprehensive research and monitoring as well as awarenessraising and preparedness-building in the local communities are therefore key activities for risk reduction and mitigation 47
  48. 48. Thank you for your attention ! Jean F. Schneider Emeritus and Senior Geoscientist BOKU University Vienna and Switzerland Vajont 1963-2013: Thoughts and analyses after 50 years since the catastrophic landslide Padova, Italy, October 8-10