Landslide induced disaster is a serious problem in the mountainous terrain of Nepal. The landslides and debris flows cause losses of lives and properties, damage the nature and other infrastructures in the monsoon every year. The risk evaluation of landslides is to be most important for landslide hazard reduction . This paper is to focus on evaluating the potential landslide topography of Shrawan danda landslide which lies on the southern slopes of the Siwalik Hills and has created serious problems in Butwal, Nepal. The series of the investigation methods have been carried out to identify the characteristic of each factor of the micro landform of the landslide through interpretation of aerial photographs incorporated with the information of field survey and historical records. The maps and related tables were converted to digital format from the database that was the part of the geographical information system (GIS). The information of aerial photo interpretation has been used for risk evaluation of the landslide based on the AHP method.
Firstly, Shrawan danda landslide was divided into three landside bodies (A, B and C) based on the geomorphological features of the landslide area. Secondly the distribution maps of the micro landform features were prepared by using GIS. Thirdly, the length, area and density of the micro landform features (scarps, blocks, bare lands and cracks) of the landslide bodies were calculated. After that, the detailed information of instability of the landform features of the landslide bodies were analyzed for risk evaluation. Finally the weight of risk value of the micro landform features produced by the AHP method were used for classifying the landslide bodies as one with high, moderate or low risk.
The results show the weight of risk value of the landslide body A=44, B=90.4, and C=76.4 points. The weight of risk value of the landslide body B and C were found more than 70%. These landslide bodies are highly contributed by the number, length and density of the micro landform features which are perceived as high risk . The weight of risk value of the landslide body A was found between 30 to 70% which is moderately controlled by the number, length, area and density of the micro landform features that is perceived as moderate risk. Thus results of qualitative and quantitative estimation of the micro-landform features led by using GIS and numerical function, and the weight of the risk value of the micro landform features led by using Analytical Hierarchy Process (AHP) method synthesizing information of the aerial photo interpretation (API) provide a precise contribution to evaluate risk of a landslide in various environmental conditions.