LANDSLIDE HAZARD MAPPING BASED ON GEOLOGICAL ATTRIBUTES

A landslide susceptibility zoning technique is proposed and has been tested in a catchment area of 317 km2 along the Aglar River, a tributary of the River Yamuna in the Himalayas. The Aglar catchment is characterised by varied rock types, mostly sedimentary, an active fault, landslides, moderate to intense seismic activity and moderate human influence. Very little is known about this terrain except for one previous study. This study focusses on the relationship between the terrain parameters and landslide hazard mapping. A landslide susceptibility map is presented which can serve as first generation map on which subsequent detailed information can be incorporated. It is the first map of this kind from the Himalayas based on quantitative evaluation of geomorphological and geological parameters on a classified terrain database map. The study is in two stages: first, the terrain has been classified into several homogeneous patterns, followed by small physiographic units which are uniform in their characteristics throughout. Second, each unit acquires a score, from a rating system based on the degree of mutual relationship between landslides and geological attributes such as slope, distance from fault, relief, dip-slope relationship, etc.; each of which has been given weighting according to the strength of this relationship. The aim is to frame a practical database system rationally, which can be imported into a Geographical Information System for rapid digital handling of the data. A positive relationship, established between landslide and sediment yield, indicates that long term sediment production in the catchment area comes from the ongoing geological and geomorphological activity. The work may have applications in various parts of the Himalayas, especially the ungauged and unknown catchments falling in similar geological areas and latitudes.