Assessing Spatial Vulnerability for Landslide Threat in Hilly Areas of The Nilgiris, Tamil Nadu, India

Transcription

1 Assessing Spatial Vulnerability for Landslide Threat in Hilly Areas of The Nilgiris, Tamil Nadu, India by G.P.Ganapathy, Centre for Disaster Mitigation and Management, VIT University, Vellore , India, Dharma Rao, Director-National Intelligence Grid, Ministry of Home Affairs, Govt. of India, New Delhi , India, Sekar S.K, Centre for Disaster Mitigation and Management, VIT University, Vellore , India

2 Landslide Hazard Zonation Map of India 3% 7% 30% 60%

3 Agencies involved 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.

4 Study Area

5

6 The Nilgiri s Revenue Taluks

7 Population growth in Nilgiri District Area 2500Sq.km Lakhs 7.62 Lakhs

8 General causes of Landslides Addition of Moisture (Extensive Rainfall) Removal of Vegetation (Timbering) Addition of Weight (Buildings in Top) Over steepening Vibrations These factors will act either individually or in combination.

9 Landslide Occurrences Since 1865 in Nilgiris 300 LS

10 Landslide Occurrences Since 1865 in Nilgiris

11 Geological Map

12 Geomorphological Map

13 Topography - Coonoor to Ooty

14 Aerial view of Coonoor to Ooty

15 Monthly Normal Rainfall in Nilgiri District

16 November 2009 Landslides 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

17 Spatial Distribution - November 2009 Landslides RF: 19cm RF: 82cm RF: 31cm

18 Daily Rainfall from November 2009

19 November 2009 Landslides Lessons Learned 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.

20 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

21 Lovedale Road view from Coonoor Road Increase of Head Load Toe Removal Water

22 Closer View

23 Closer View

24 Closer View

25 Lovedale Road View from Coonoor Road Landslide Scenario

26 Zone of Crack Lovedale Road at Thalayattu Mandu on top and bottom side showing the Zone of Crack and Zone of Failure Zone of Failure

27 Houses built in the Stream Channel Severe Damage at Naduhatti

28 Debris covered at Naduhatti

29 Severely Damaged Road - Ooty Coonoor Road near Thalayattu Mund Junction.

30 Ooty Coonoor NH. 2 kms from Valley View point. No way beyond this point.

31 Near Sagar Holiday Resorts, Valley View.

32 Unplanned colonization

33

34 Lessons for the Planners and public 2009 landslides Severe to High Landslide Areas identified by GSI in 1982

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

36 Tourism in Nilgiris 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 persons per day is noted. The tourists visiting the town present a cross section. The foreign tourists account for about persons in a year.

37 Tourist Places

38 Landslide Inventories

39 Spatial Vulnerability Analysis 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

40 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

41 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.

42 Critical Facility/Life line Inventory Analysis 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 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.

43 Landslide Hazard

44 Vulnerable facilities of Nilgiris Sl.No Facilities Total Falls Under Percentage High to Moderate Hazard Areas 1 Essential % 2 Lifeline % 3 Transportation % 4 Village/Towns %

45 Recommendations/ Conclusions

46 Dangerous Slopes

47 Blocking the Natural Draines

48 We Don t Bother

49 Recommendations/Conclusions 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, Small scale maps typically represent extensive areas, but they offer only a gross perspective on details.

50 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.

51 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.

52 Monitoring Additional rain gauge stations may be installed in close interval and monitor the intense rainfall as well as the existing unstable slopes.

53 Destination- Disaster Free India