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Protection of life and properties from landslide disaster is indispensable in creating a safe environment for the society. The national imperative towards safety due to landslide initiation is increasing in view of the higher rate of human settlement in the mountain slope across the country. Landslides are significant amongst those hazards that can easily be disastrous to human life and property. It is estimated that economic loss due to landslides may reach between 1-2% of the gross national product in many developing countries. Evaluating and mitigating the landslide hazard and risk is a major challenge for the technocrats and decision makers in the developing world as 80% of the reported fatalities due to landslide is within the developing countries.

In India, about 0.42 million sq. km or 12.6% of land area, excluding snow covered area, is prone to landslide hazard. Out of this, 0.18 million sq. km falls in North East Himalaya, including Darjeeling and Sikkim Himalaya; 0.14 million sq. km falls in North West Himalaya (Uttarakhand, Himachal Pradesh and Jammu & Kashmir); 0.09 million sq. km in Western Ghats and Konkan hills (Tamil Nadu, Kerala, Karnataka, Goa and Maharashtra) and 0.01 million sq. km in Eastern Ghats of Aruku area in Andhra Pradesh. The landslide-prone Himalayan terrain also belongs to the maximum earthquake-prone zones (Zone-IV and V; BIS 2002) where earthquakes of Modified Mercalli intensity VIII to IX can occur, and thus, are also prone to earthquake-triggered landslides. The most recent example is the aftermath of 18 September 2011 Sikkim Earthquake in the Sikkim-Darjeeling Himalayas.

Regional perspective of landslide prone areas of India

In India, the risk to landslides is high due to ever increasing hill population and growth of hydropower and related infrastructures. Apart from the above, the 21st Century- India is also at the cross-roads of a steep curve of infrastructure development that is continuously focused in connecting remote and morphometrically difficult places by constructing new roads, bridges, railway lines, tunnels, etc. in both the peninsular and the fragile extra-peninsular regions. Despite our great demand of such development, the growing constructional activities in these sectors do bring some unavoidable ecological imbalances in our environment (e.g., landslides and debris flows), which if not mitigated properly, can cause/trigger various geo-environmental hazards and result in obvious loss of lives and property.

Since it is practically impossible to prevent landslides, therefore, task before the scientist, planner and administrator lies with the identification of hazard-prone areas and their zonation in different scales for preparedness and mitigation. The primary contribution of earth-scientists dwells in the area of evaluating the hazards, whereas, the engineers, planners, public officials and social scientists are more concerned with evaluation and mitigation of risk. To combat and effectively minimise the impact of landslide related disaster, need for a rational and objective understanding of the cause and processes of earth system science is very much necessary.

Landslide studies by GSI
GSI’s contribution to landslide studies dates back to 1880 with the study of problem of slope stability in Nainital, Uttarakhand by Sir R.D. Oldham. In 1890, subsequently, C. S. Middlemiss re-investigated the Nainital area. In 1893, T. H. Holland investigated Gohana landslide, a massive rock fall that blocked the river Birahi Ganga at Gohna in Garhwal Himalaya and landslide disaster in Darjeeling town in 1899. In 1945, with the establishment of specialised Engineering Geology and Ground Water Division, GSI started undertaking landslide investigations primarily based on the requests from various stakeholders along with some departmental investigations including R&D. Since 1980, GSI initiated landslide susceptibility mapping following the prevailing systematic approaches. Between 1980 and 2004, landslide susceptibility studies were carried out, as a part of the regular field season programmes, using probabilistic and statistical methods. Since 2005, a semi- quantitative heuristic method indicated in the BIS guidelines and its modified version as proposed by GSI was followed for landslide susceptibility mapping.
GSI’s approach in Landslide Risk Mitigation:
Pre-Disaster study: a) Landslide susceptibility mapping on different scales as per the demand of user’s agencies, b) Landslide inventory mapping.

Post Disaster study: a) Detailed site specific study of landslide for identifying causative factors and most suitable remedial measures, b) Landslide monitoring by instrumentation and threshold modeling for the development of an Early Warning System.
Responsibility of GSI as Nodal Agency:
Government of India has declared the Geological Survey of India as the ‘Nodal Agency’ on 29 January 2004. Geological Survey of India as a Nodal Agency is responsible for undertaking and coordinating landslide investigation and formulation of mitigation measures pertaining to the
  • Formulation of strategy/methodology for any type of landslide investigation in the country
  • Implementation of the proposed action plan on landslide risk mitigation of MHA
  • Formulation of a landslide hazard and risk mitigation code to be followed by all the Govt./non govt. and other user agencies
GSI’s achievements in landslide studies
  • GSI has covered major part of the accessible vulnerable hilly terrain in India through macro scale landslide susceptibility mapping. Till 2013 more than 50,000 km2 area has been covered through landslide susceptibility mapping on 1:50,000 scale
  • GSI carried out research and interaction with national and international institutes for development of terrain specific methodologies for landslide mapping
  • GSI at the request of road maintaining authorities undertakes site specific landslide investigation and provide inputs for formulating both short and long term mitigation measures
  • GSI regularly update the landslide data base of the entire country through landslide inventory work
  • GSI launched National Landslide Susceptibility Mapping (NLSM) programme w.e.f. FS 2014-15 with an aim to produce seamless landslide susceptibility database for the country. Data integration and susceptibility modeling for generation of the desired output in NLSM is to be done in GIS following appropriate methodologies. The national programme was launched with the purpose to prepare a nation-wide landslide inventory and susceptibility database which can be easily retrieved, updated in future in the event of large scale landslide initiation and changes in geo-environmental parameters
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