Landslides in relation to terrain parameters - A Remote Sensing and GIS approach
Landslide and lineament density
In a similar way, lineament density map is also prepared by computing density for each 250 m cell. The density values which range from 0 to 13 km/km2 is classified into three classes of low, moderate and high. The lineaments superimposed on density map are shown in the Fig.3. These density classes are then integrated with the spatial distribution of landslide to determine the landslide frequency in each lineament density class. The data are given in Table 2. This shows a direct relationship between landslide and lineament density which complements the fact that areas with more fracturing and faulting are always prone to landslide occurrence. Landslide and proximity to road As we all know that road construction most often causes slope instability, a distance of 150 m from the road on the uphill and downhill side is considered to study the influence of roads on landslide occurrence. For this, a road buffer map with 150 m interval is generated in GIS (Fig.4).  Fig. 4: Road Buffer Map The number of landslides in each class of road buffer obtained by integrating the two layers is shown in the Table 3. It can be inferred from the table that maximum number of landslides is in the class of 150m and it decreases as the distance from road increases. However, it is observed that there is no significant change in landslide numbers after a distance of 450 m. Conclusions Landslide in relation to terrain parameters in Darjeeling Himalaya has been studied to decipher the influence of these parameters on landslide occurrence. It has been found that high spatial resolution satellite image (IRS PAN) and the merged product of PAN and LISS III are quite useful for terrain feature extraction. GIS is found to be a useful tool for preparation of thematic layers and spatial data analysis. The results obtained from the study has shown an inverse relationship between landslides and drainage density which may be due to high infiltration in weathered gneisses causing more instability in the area. Landslide frequency has been found to be maximum in high lineament density which indicates that the areas with more morpho-tectonic lineaments are more susceptible to landslides. The maximum landslide frequency within a 150m distance from the road strengthens the fact that the road is one of the important anthropogenic factors associated with landslide occurrence. Such type of study is useful for determining the relative importance of the terrain parameters and their categories for landslide hazard assessment. Acknowledgement Authors are grateful to the Director, CBRI for his kind permission to publish the work. The financial support from Ministry of Environment & Forests, New Delhi is acknowledged.
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