Lessons learnt from landslides of Uttarakhand Disaster (June 2013) A. Sundaramoorthy Director General Geological Survey of India
Lessons learnt from landslides of
Uttarakhand Disaster (June 2013)
A. SundaramoorthyDirector General
Geological Survey of India
• Rugged mountain chain with high relief
• Varied geomorphic landforms: Glacial/ glacio-fluvial and fluvial
• Dominance of erosional & gravitational processes
• Lies in Zone IV & V of Seismic Zoning map of India
• Known to be one of the most landslide prone states in India
• Rainfall & Earthquake are the main triggering factors for slope failures
Uttarakhand Landscape
400
7000
• Active tectogene – the Himalayan Fold-Thrust-Belt (FTB)
• Varied litho-assemblages of Proterozoic to Holocene Age (Sedimentaries to Crystallines):
Folded, fractured and weathered
• Colluviums, Scree and terraces of variable thickness
• Suffered multiple stages of deformation and metamorphism
• Traversed by major thrusts like Main Central Thrust (MCT), North Almora Thrust (NAT) besides
many other faults/shears
Geological set up
Sequence of events culminating into the June 2013 disaster
• Heavy precipitation in the upper reaches of Uttarakhand (15th– 17th June)
• Bursting of glacial lakes
• Increased debris laden discharge in trunk streams
• Rising of water level upto 5-7 m
• Heavy toe erosion and flooding
• Fresh landsliding along steep river banks & slopes
• Colossal loss of properties and lives & road links
Heavy incessant rainfall – a trigger for Uttarakhand Disaster
• Heavy rainfall in the higher altitude areas
• 325 mm in 24 hours between 5 PM 15th June and 5 PM 16th June at
Chorabari Lake (3960 m asl) as against 272 mm in 3 days (15-17 June) at
Ghuttu (~1430 m m asl) (Dobhal et al, 2013)
• Sudden increase in daily rainfall in the month of June 2013 as compared to
total rainfall of June for last 5 years
0
20
40
60
80
100
120
140
160
180
5.6615.28
113.25
180
18
0
Rai
nfa
ll (m
m)
0
100
200
300
400
2008 2009 2010 2011 2012
148.9
17.8
166.6
369.6
95.4
Rai
nfa
ll in
Ju
ne
(m
m)
Increase & pattern in river discharge – a trigger for bank erosion and landslides
0
20
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60
80
100
120
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0
500
1000
1500
2000
2500
14.06.13 15.06.13 16.06.13 17.06.13 18.06.13 19.06.13
Rai
nfa
ll (m
m)
Dis
char
ge (C
um
ecs
)
Discharge (Cumecs) Rainfall
Bhagirathi Valley
(Uttarkashi)
River discharge is mixed with huge supply of debris from upper reaches:
yielding tremendous momentum & erosive power
Nature of damages (Along river courses and on neighbouring hill slopes)
• Damages within active flood plains
• Erosion caused by the debris-laden flood discharge in trunk streams
• Damages on banks of trunk streams
• Erosion caused by toe cutting
• Damages along hill slopes
• Caused by headward and channel erosion
• Debris flows with longer run outs
• Shallow translational landslides on slope
Damages within flood plains(an example from Kedarnath)
Source: Bhuvan Portal, ISRO
Damages within flood plains
Kedarnath
Landslides on banks due to toe erosion
Debris slides & flows on banks
GSI’s immediate response … 1
• Preliminary assessment of disaster affected areas in
close association with Uttarakhand Government &
NDMA officials
• Immediately constituted a team of 10 Geologists and
deployed in field for reconnaitory survey of damage &
causative geo-parameters
• Studied landslides and slope instabilities at several locations
in Mandakini, Alaknanda, Bhilangana and Bhagirathi valleys
• Carried out preliminary geoscientific assessment of
Kedarnath Temple & township
• Identified areas of extreme vulnerability for further detailed
surveys
GSI’s immediate response … 2
• Preliminary assessment of disaster affected areas in close
association with Uttarakhand Government & NDMA officials
• Formulation & initiation of five formal programs (involving 20 field
geologists) of geological investigations in five worst affected districts –
Rudraprayag, Chamoli, Uttarkashi, Bageshwar & Pithoragarh
• Consultation of existing literature & database
• Landslide inventory mapping using Geo-parametric format
• Preliminary identification of areas for relocation/ rehabilitation &
selection of sites for detailed investigation
• Identification of NH/SH road stretches needing restoration
• Identification of damaged road stretches needing detailed
investigations
• Extreme event of this nature in the Himalayas is imminent if
heavy and very heavy rainfall occurs in the upper
reaches, where loose unconsolidated glacial/ glacio-fluvial
material is the predominant slope forming material
(Kedarnath area)
• Moraine- dammed Lakes (e.g. Gandhi Sarovar) pose high
vulnerability to lake-burst or breach during such heavy rains
• Core-zones of Flood plains, Outwash plains are the most
hazard-prone areas for flash floods and deluge
(e.g., Mandakini, Bhagirathi river courses)
Lessons learnt … … 1
• Encroachment immediately below and above the high flood
line of the trunk streams and areas in the immediate vicinity
of prominent depressions on slopes - extremely risk prone
• Damages by mass wasting not only restricted to the zone of
depletion of material but also observed along its long run
outs and in its depositional zones
• Tehri Dam stood as a real saviour in storing about 22 m
increase in water level in its reservoir saving many
settlements in lower reaches from inundation (Source: THDC Ltd.)
Lessons learnt … … … 2
• A robust and strong Disaster Preparedness including increased awareness
amongst all the stakeholders during planning and management in hazard-
prone areas is essential
• More stress on identification of landslide susceptible areas on macro scale
(1:50,000/25,000) needs to be given.
• Codes for landslide zonation should also take into account the domino
effects of flash flooding and effects of landslide run outs
• Creation of norms, regulatory mechanisms and strict compliance of land
use zoning regulations in the mountains based on landslide zonation maps.
Constructions should be restrained from entering into active river regime
and fluvial geomorphology.
Lessons learnt … … … 3
• New land use development including road construction in
Himalayan mountains should mandatorily consider the geological
and geotechnical slope stability conditions and landslide
susceptibility zones
• Excavation or slope modification and protection measures for
modified slopes should go hand in hand for ensuring slope stability
• All moraine-dammed lakes in the Himalayan catchments be mapped
and their geotechnical stability be assessed
• Weather forecast in the landslide prone areas of the country to be
improved by IMD through installation of more number of state-of-
the-art AWS and closely spaced Doppler instruments for regular
monitoring & developing Early Warning system
Action to be taken
• Being nodal agency on landslide studies, GSI is committed to assist TAC
(MoM) & NDMA and help other Organisations / Universities for capacity
building on vulnerability zonation and other related landslide studies
• GSI recently constituted a Geohazards Research & Management Cell at CHQ
to launch specific R&D Projects, co-ordinate and spearhead all the above
activities
• Can share a substantial quantum of work-load on multi-scale landslide
zonation with a priority to cover the risk-prone areas and important locales
including site specific studies, road alignments, updating of
inventory, developing early warning system, and related research activities
• GSI is wiling to collaborate based on its available resources employed in this
field with other government agencies engaged in such studies including
research based investigations
How GSI is contributing
GSI’s commitments in Uttarakhand
• On-going assignments (FS 2013-14)
• Preliminary investigations in five worst affected districts
(Rudraprayag, Chamoli, Uttarkashi, Bageshwar and Pithoragarh)
with an objective to prepare the inventory of landslides, to
assess the vulnerability of 24 villages for restoration/
resettlement and geoscientific work in Kedarnath areas (20
Geologists are presently engaged in Uttarakhand)
• Future planning (FS 2014-15 onwards)
• Detailed investigations as envisaged and proposed in the
preliminary investigation will be taken up from April 2014
onwards (FS 2014-15)