Medium-scale landslide susceptibility mapping along the strategic National Highway corridor of Bomdila-Tawang sector, Arunachal Pradesh, North East India, through heuristic approach

摘要

The study highlighted the landslide susceptibility status of approximately 200 line km of the strategic communication corridor between Bomdila and Tawang of western Arunachal Pradesh which has been brought out through medium-scale (1:50,000) landslide susceptibility mapping. The slope mass along the road corridor was categorized into five susceptibility classes based on a heuristic approach proposed by BIS (modified by GSI, 2005) considering relative weightage of a set of causal factors. The thematic maps on each of the causative factors and landslide incidence map of the studied corridor were prepared through augmentation of field data and baseline information. The Landslide Susceptibility Map (LSM) of the specified road corridor was generated through facet-wise integration of the generated field data in GIS platform pertaining to the lithology, structure, slope morphometry, relative relief, land use, land cover, slope erosion, hydrogeology, landslide incidences and rainfall parameters. Analysis of the generated landslide susceptibility map reveals that 1.8% of the total area studied may be categorized as "Very High" and "High" susceptibility classes. The various other susceptible classes, viz. "Very Low", "Low" and "Moderate" account for 0.1%, 47.91% and 33.89% respectively of the total studied area.Spatial correlation of the various thematic maps with that of the landslide incidence map and LSM of the area indicates that: a) overburden/soil-covered slopes are more prone to failure than that of slopes with bedrocks b) a significantly higher concentration of landslide incidences has been recorded in the vicinity of the prominent regional thrust (MCT) c) a relatively higher concentration of the landslide incidences categorized as "Moderately steep slopes" d) a significantly higher concentration of landslide incidences in the slope "Barren" and "Sparsely vegetated" land cover category e) an overwhelmingly high percentage of landslides/slope failures being initiated due to the extensive slope excavation for widening of the road corridor f) the very high landslide susceptibility in the higher altitude areas of Baisakhi-Se La-Nuranang-Jaswantgarh can be attributed to seasonal and diurnal thawing and freezing effects, snow melting, high anomalous snow and rainfall, wind action, ground vibrations, etc. g) Landslide initiation in the study area has been found to be influenced by both natural triggering factors as well as anthropogenic interferences. The above observations are further corroborated from the spatial distribution of different Landslide Susceptibility (LS) categories vis-a-vis the said related parameters. The generated susceptibility map as such is not static in nature and warrants periodic upgradation in the event of large-scale modification in the slope, unprecedented rainfall (cloudbursts), high magnitude seismic activity (>5.0 on Richter scale), etc. The same may be utilized by the planner/road-maintaining authorities for i) perspective planning and estimation of hazard and risk (when combined with temporal database on past rainfall, earthquake, slope failures) ii) taking up environmental regeneration programme in the identified unstable, highly susceptible areas iii) target areas for meso-zonation (1:10,000/1:5,000) and site-specific studies (1:1000/1:2000) iv) a significant contributing parameter for the geo-hazard assessment of the area.