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

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5.6615.28

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Increase & pattern in river discharge – a trigger for bank erosion and landslides

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14.06.13 15.06.13 16.06.13 17.06.13 18.06.13 19.06.13

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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)