The International Geotechnical Societies’ UNESCO working Party on World landslide inventory defined landslides as “the movement of a mass of rock, debris or earth down a slope”. (Sassa et.al., 2007). Landslides as described by the Dahal (2006) are a downward movement of rock materials or debris or soil along the slope, when shear stress exceeds shear strength of the material. Many classification of landslides have been found in literature among them are the classification given by Shape (1938), Hutchison (1968), D.J Varnes (1978) and fundamentally all these classification are based on the factors such as types of material, soil moisture, climate, geomorphic attributes (like Slope forms, weathering topographic profile), landslide morphology, type of movement, triggering mechanism and the speed of the movement. Nepal is a country comprised of 83 precent hills and mountains, and steep terrain , fragile geology, and seasonal monsoon rainfall contribute the landslide potential (Dhakal et al., 2000). The construction of roads through the steep slope cutting has been another reason of the high landslides hazards along transportation line in Nepal. According to Dahal and Kafle (2003), in the year 2003, Muglin – NarayanGhat road of central Nepal was extensively damaged by rainfall triggered landslides. Likewise, a total of 213 landslides were noticed along this road section only on the same year. Among the many highways in Nepal, most are in the hilly areas except the east west Mahendra highway. Landslides during the monsoon season cause severe damage along these highways obstructing the traffic. Most major and severe are Krishnabhir landslide on prithvi Highway, Siddhababa landslide and Kerabari landslide on Butwal –Palpa section of the Siddhartha Highway along with many others. The economic losses due to these landslides are not quantified but the loss incurred may be much higher than ones’ imagination. Every year, DOR has to invest a lot of money and manpower to maintain the roads damaged by landslides. At the times when we are not been able to stop the damages due to landslides along the major national highways of significance importance, we can imagine how affected are those unplanned rural roads which are being constructed without any prior survey and planning. LHA is a very significant and critical step towards avoiding and mitigating the landslides hazards. It is assumed that the forthcoming landslide occurs under the similar condition of the past occurring landslide (Gugetti et al., 1999 cited by Ayalew et al., 2004). A detail inventory of the landslides of the area under the mapping must be carried out to draw a picture about the condition under which landslides occurred. GIS aided landslide hazard assessment techniques have helped increased the accuracy of the Hazard map. LHA are primarily aimed at identifying the potential landslide occurring area and these maps are of great use to planners, supervisors and managers and also may serve transportation officers, foresters and emergency planners and agencies concerned(Chauhan et al., 2010). If we can produce the high accuracy hazard map, (accuracy of the hazard map are controlled by different factors as method implied, precision on field work and spatial and temporal distribution of factors affecting the landslides), country like ours facing great economic loss along with the fatalities from landslides are likely to benefit in minimizing the risk by implementation of the appropriate remedial measure.
1.2. Statement of Problem
Most of the highways and roads in hilly region of the country have been constructed with slope cutting even in very steep and previously unstable slope. The fragile geology due to continuously upliftment( as result of the plate collision), the unevenly distributed rainfall pattern basically at temporal scale along with the high rate of deforestation and improper land use practice are the major reasons for the...
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