Assessing Spatial Vulnerability for

Landslide Threat in Hilly Areas of

The Nilgiris, Tamil Nadu, India

G.P.Ganapathy, Centre for Disaster Mitigation and Management, VIT

University, Vellore 632014, India, E-mail: seismogans@yahoo.com

Dharma Rao, Director-National Intelligence Grid, Ministry of Home Affairs,

Govt. of India, New Delhi - 110 011, India,

Sekar S.K, Centre for Disaster Mitigation and Management, VIT University,

Vellore 632014, India

by

Landslide Hazard Zonation Map of India

3%

7%

30%

60%

•Geological Survey of India (GSI)

•Central Road Research Institute (CRRI)

•Central Building Research Institute (CBRI)

•Indian Institute of Technology, Roorkee (IIT-R)

•Wadia Institute of Himalayan Geology (WIHG)

•Department of Space (DoS)

•National Remote Sensing Centre (NRSC)

•Defence Terrain Research Laboratory (DTRL)

•Bureau of Indian Standards (BIS)

•some academic institutions, and individual experts.

Agencies involved

Study Area

The Nilgiri’s Revenue Taluks

2001 1901

Population growth in Nilgiri District

Area 2500Sq.km

0.37 Lakhs 7.62 Lakhs

• Addition of Moisture (Extensive Rainfall)

• Removal of Vegetation (Timbering)

• Addition of Weight (Buildings in Top)

• Over steepening

• Vibrations

General causes of Landslides

These factors will act either individually or in combination.

Landslide Occurrences Since 1865 in Nilgiris

300 LS

Landslide Occurrences Since 1865 in Nilgiris

Geological Map

Geomorphological Map

Topography - Coonoor to Ooty

Aerial view of Coonoor to Ooty

Monthly Normal Rainfall in Nilgiri District

• Heavy rains triggered a series of

landslides in Ooty, Coonoor and

Kotagiri regions of the Nilgiris

• Killed 42 people within 48 hours. Total

Deaths 80.

• Estimated loss about 300 Crores

November 2009 Landslides

Spatial Distribution - November 2009 Landslides

RF: 19cm

RF: 82cm RF: 31cm

Daily Rainfall from 01 – 15 November 2009

• Many slides have taken place in

areas of intense cultural activity.

• agricultural operations,

• construction of buildings and roads

• removal of earth and rock

• levelling of slopes

• deforestation and

• blocking of natural drainage.

November 2009 Landslides Lessons Learned

Considering all these evidences the following factors

appear to have been involved, singly or in

combination, in inducing the landslides.

• Water (Heavy rainfall)

• Toe Removal

• Increase of Head Load

November 2009 Landslides Lessons Learned

Lovedale Road view from Coonoor Road 10.11.2009

Toe Removal

Increase of Head

Load

Water

Closer View

Closer View

Closer View

Lovedale Road View from Coonoor Road Landslide Scenario

28.11.2009 10.11.2009

Lovedale Road at Thalayattu

Mandu on 10.11.09 top and

bottom side showing the Zone

of Crack and Zone of Failure

Zone of Crack

Zone of Failure

Houses built in the Stream Channel –

Severe Damage at Naduhatti

Debris covered at Naduhatti

Severely Damaged Road - Ooty Coonoor Road near

Thalayattu Mund Junction.

Ooty Coonoor NH. 2 kms from Valley View point.

No way beyond this point.

Near Sagar Holiday Resorts, Valley View.

Unplanned colonization

Lessons for the Planners and public

2009

landslides

Severe to High

Landslide Areas

identified by GSI

in 1982

Landslide hazard zonal significance (BMTPC, Landslide Hazard Zonation Atlas of India 2003)

• Nilgiris District has tremendous potential for tourism.

• Several places in this district like Ooty. Coonoor and the

Mudumalai sanctuary are well known to tourists all over

India and the world.

• The district is blessed with abundance of natural beauty

and a variety of wild life. The salubrious climate is a

major attraction to the tourists.

• It is estimated that during loan season an average

inflow of about 15000 persons per day is noted.

• The tourists visiting the town present a cross section.

The foreign tourists account for about 29000 persons in

a year.

Tourism in Nilgiris

Tourist Places

Landslide Inventories

• Establishing the degree of vulnerability of buildings and

lifeline utilities, one can obtain an estimate of risk.

• Vulnerability analysis is, therefore, an intrinsic aspect of

disaster mitigation and one of the linkages in the

assessment process.

The Nilgiris district spatial vulnerability is assessed in three

categories viz.,

•built environment,

•critical facilities (essential and high potential loss),

•and transportation & lifeline utilities. The details are

Spatial Vulnerability Analysis

Critical Facilities

1.Essential facilities

hospitals, medical clinics,

schools/educational institutions, fire

stations, police stations and emergency

operations facilities

2.High potential loss facilities

dams, levees, military installations,

nuclear power plants and hazardous

material sites

Lifeline Inventory

1. Transportation

highways, railways, bus, ports, ferry and airports

2. Lifeline Utility

potable water, wastewater, natural gas, crude &

refined oil, electric power and communications.

• The Ooty town has, two colleges, one Polytechnic 12

primary school and 9 secondary schools.

• The town has 2 Government Hospitals, 4 private hospitals, 3

municipal dispensaries and an eye hospital.

• The roads, lanes and by lanes constitute predominant land

use. This is inevitable as the palaces, bungalows are

scattered and the topography demands the type of roads.

• The Ooty town has partial underground drainage which was

laid 100 years ago. This covers an area of 12.94 sq.km. Out

of a total corporate area of 30.94sq.kms.

• There were 5165 service connections which have been

provided under sewerage scheme.

• Out of 36 utilities in the study area about 65% critical

facilities and 36% of transportation and life line utilities are

vulnerable to severe landslide threat.

Critical Facility/Life line Inventory Analysis

Landslide Hazard

Sl.No Facilities Total Falls Under High to

Moderate Hazard Areas

Percentage

1 Essential 114 24 21%

2 Lifeline 96 7 7.3%

3 Transportation 20 6 30%

4 Village/Towns 42 7 16.7%

Vulnerable facilities of Nilgiris

Recommendations/

Conclusions

Dangerous Slopes

Blocking the Natural Draines

We Don’t Bother

1. In order to reduce the enormous destructive potential of

landslides and to minimise the consequential losses, it is

necessary that Risk should be calculated.

2. Most of the topographic maps of hilly terrain of Nilgiris

which are used as base maps for carrying out various

studies including landslide investigation and mapping are

available in small scale of 1:50,000 and a very few in

1:25,000.

3. Small scale maps typically represent extensive areas, but

they offer only a gross perspective on details.

Recommendations/Conclusions

3. The potential for accuracy drops as the

area mapped grows larger and the scale

grows smaller. Such scaled maps are not

suitable for in-depth and accurate

landslide investigations and

instrumented monitoring.

4. A large-scale map, which shows a limited

amount of space and provides a

considerable amount of detailed

information about that space can only be

used for detailed landslide

investigations, mapping and monitoring.

5. From the study it has been found that

the eastern part of the study area is

more prone to landslides. The historical

landslide inventories very clearly reveal

most of the landslides are trigged by the

human and cultural activities.

6. Strengthening of buildings and infrastructure should lead to

reduction in Vulnerability. The vulnerability of the buildings,

critical facilities, lifeline structures should be studied

thoroughly for further planning purposes.

7. The present vulnerability study is based in spatial distribution

and relative risk based. However the likely damage to

structures should be categorised in different grades

depending on their impact and landslide types.

8. The out put of the present study can be used as first hand

information for the decision makers and planners and also

helpful for the further developmental activities in the

landslide prone areas of Nilgiris District of India.

Additional rain gauge stations may be installed in close interval and

monitor the intense rainfall as well as the existing unstable slopes.

Monitoring

Destination- Disaster Free India