Slope stability analysis in a part of East Sikkim, using Remote Sensing & GIS

Abstract

The whole state of Sikkim is very vulnerable to landslide because of structurally controlled extremely scrutinized undeveloped geography, delicate rock condition, high rainfall escorted by occurrence earth trembles. Sikkim Himalaya in the eastern Indian Himalayan Region also experiences the landslide troubles because of geologically brittle host terrain coupled with heavy rainfall as well as other natural and anthropogenic factors. Mountain highways/roads are the single most important infrastructure, that suffers efficiently because of landslides and therefore, affecting the regular traffic in the hills. Such events lead to problems of road and other communications particularly during monsoons with adverse impacts on economic/commercial as well as development related activities. Survey of India toposheet, cloud free satellite data and field survey with the help of handheld GPS were carried out along major road of Sikkim for landslide investigation. Landslide phenomena increasing day by day in Sikkim particularly along the roadside. Mostly landslide occurred in Sikkim during prolonged rainfall. Landslide occurrence increasing due to anthropogenic activities in the region, i.e. road cutting, building construction and unplanned agricultural activities in the region. The present paper has been covered the part of the east district of Sikkim and it has covered the 133.80 sq.km. A detailed landslide inventory carried out in and around the part of the east district of Sikkim. Survey of India toposheet 78A/11 1962-63 has been used for historical landslide as well as base map preparation. A total 50 landslides have been identified from the SOI. Major and minor landslides were interpreted from Remote Sensing data using Cartosate-1(2008), IRS 1C/1D LISS-III (2009) and LISS-IV (2008). A total 43 landslides identified in the field survey incorporated in the map. Out of 43 landslides 13 were considered as significant having direct impact on roads. These slides are 6th Mile, Amdogolai landslide, Chandmari landslide, 5th Mile Landslide, 8th Mile landslide, 17th Mile landslide, Kyongnosala landslide, Bakthang landslide, Amdogolai landslide and Manbir Colony slide etc. A remote Sensing & GIS technique has been used for creating thematic layers for landslide hazard zonation. The appropriate weightage system used for ranking system on the basis of role in inducing landslide activity in the region. Each of the layers was assigned rating 1 to 9 maximum. The following parameters have been used for final landslide hazard zonation i.e. Geology, Drainage Density, Landuse, Soil, Geomorphology, Slope, Aspect, Relative Relief, Ruggedness' number, Dissection Index, Thrust, Fault, Lineament Density and Rainfall etc. Although the factor planned under topographic parameters hase been measured as basic inputs for Landslides Hazard Zonation study. Final Hazard Zone divided into five zones from very low landslide hazard to very high landslide hazard zone. Finally, model has been validated in the field based information.