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. 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. 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. 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. 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. Landslide Risk Assessment /
Management
Dai et al., 2001

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. 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. Persistence of Landslide Dams
From Debris Flows to Large Landslides
Large Landslides
Small Landslides
9

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. La Josefina, Ecuador 1993
Situation today
Breach hydrograph after Canuti et al, 1994

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. 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. 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. 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. Lake Sarez (Tajikistan, 1911),
Earthquake triggered Landslide
Usoi dam stability >100 years
16

17. Lake Sarez/ Usoy Dam
Escarpment
Mountain
sagging
HD ~ 700 m
Seepage
VL ~16 km3
VD ~2.2 km3
Source: earthobservatory.nasa.gov

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. Lake Sarez: Flood Wave
Simulation, triggered by Mountain
Sagging Landslide
Stucky Interim Report 2003

20. Flood risk: prevention and mitigation
Lake Sarez- Bartang Valley
?
Lake Sarez, Pamir

21. Hattian Bala (Kashmir Earthquake, 2005)
Landslide Dam, Karli-/Tang-Lakes
Quickbird II, 10_27_2005
21

22. Hattian Bala Dam Breach (05/2005 – 01/2009)
Landsat TM
22

23. Hattian Bala Dam 2005
Spillway excavation
Spillway after overflow
Photo FWO
Karli Lake under formation

24. Hattian Bala, failed dam (January 2009)

25. Both Flanks of Karli Lake failed

26. Hyperconcentrated
Flow in
Pjanch River
after Dam Breach

27. Hattian Bala Dam after Breach 01/2009

28. Attabad Rock-Slide and Dam
(Hunza Valley Pakistan, 04-01-2010)
28
Photo Pamir Times

29. Geological Map Hunza Valley
PakGS

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. Cross-Section
Attabad Slide
Lake Sediments
Data NESPAK, 2010
(not to scale)

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. Attabad, Hunza Lake 2010
Imagery: EO1

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. Attabad Dam-Break Study,
Flood Wave Propagation
HEC-RAS, Flow 2D
Danger!
Safe
Safe
NESPAK 2010, IAG-BOKU

36. Attabad Dam: Seepage before Overflow
spillway
seepage
point
Photo: Pamir Times
36

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. Siachen-Gayari Ice/Rock Avalanche,
April 7, 2012 Pakistan

39. Siachen-Gayari, Situation before Incident
Glacier
Moraine/Debris Cone
Military Camp

40. Gayari Debris Cone, 19. 04. 2012
Siachen-Gayari, Proposed Spillway
(with fresh Snow)
Capped Moraine
Military Complex
Proposed Cut

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. Georadar carried out by Norvegian Red Cross
Thickness of Debris
Proposed
Water
Channel

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. 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. Challenges for risk mitigation
<5 years<
>?
Hattian Lake!
Lake Attabad,
others ?
after Costa and Schuster (1988)
45

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. 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. 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