Landslide Susceptibility Mapping, Vulnerability And Risk Assessment For Development Of Early Warning Systems In India

Landslide or the landmass movement is a geomorphic hill slope physical process of mass-wasting resulting in downslope rolling of large mass of debris, regolith and soil under influence of gravity. It is caused by a combination of particular geo-factors that are region or territory specific. Landslides are generally triggered and activated by substantial precipitation and/or earthquake tremors and other anthropogenic interventions such as over the top cutting of slant for development of mountainous roads/streets and other excavations for civil structures, etc. The relatively young entire Himalayan hilly tract, mountainous steep slopes in sub-Himalayan landscape of North-east India, Western Ghats, the Nilgiris in Tamil Nadu and Konkan ranges are susceptible to landslides or debris flow.In order to formulate strategies to minimize societal impacts of landslides, a systematic approach would entail preparation of Landslide Susceptibility Maps linked to landslide incidence inventory and making them available to the concerned stakeholders for necessary preparatory and mitigation measures. Geological Survey of India (GSI) being the nodal agency for landslides studies in India formally launched on February 05, 2014 the National Landslide Susceptibility Mapping (NLSM) programme which has been a geoscientific exercise on 1: 50,000 scale on GIS platform in making both quantitative or qualitative estimates of spatial distribution of landslides which either exists or has the potential to occur in a given area. GSI has formulated a set of standard operating procedures that emphasize on geo-parametric data collection (as per standard and devised formats) for landslide inventory. These data sets are synthesized with relevant spatially-distributed causative thematic maps into susceptibility zonation which represents geospatial information indicating intensity and propensity of landslides. Such baseline data will ultimately lead to the collation and evaluation of landslide hazard and risk and mitigation plans. It will also help in disaster preparedness of the country and to indicate areas critical for landslide monitoring and developing early warning system (EWS).It is aimed to demarcate and facilitate prioritization of areas for further detailed studies (Meso- and Micro-scales) and help in Regional Land Use Planning and provide the scientific basis for framing the Land Use Zoning Regulations. Several lessons were learnt from Uttarakhand disaster of June 2013 in India that compelled re-evaluation of the existing methodology of conducting geosurveys of macro scale landslide susceptibility maps. Additional geofactors that also need to be considered include: effect of toe erosion by higher order streams; effect of long runouts of the debris flows and drainage morphometry; nature and size of clastic components, etc. It is intended to elaborate here a synthesis of various approaches and constraints on continuing research on such country-wide programmes on landslides related geohazards characterization and its implications on evolving EWS for the societal preparedness and resilience for mitigating impending disasters. However, any method of predicting landslide susceptibility needs validation which sometimes may be difficult in areas having no land sliding history. Besides, EWS need also to highlight mitigation efforts/remedial measures through geotechnical and engineering solutions as suited to Indian conditions on case to case basis, delineation of safe escape routes in the event of a landslide/debris flow/flash floods, and for optimum utilization of available resources.