Landslide hazard and risk assessment along a transportation corridor in India

Landslide hazard and risk assessment is a complicated process which requires a large
amount of data. One of the most essential data types consists of historical landslide
information. This paper presents a quantitative approach for landslide risk assessment
for a road and a railway alignment in parts of Nilgiri hills in southern India. The method allows estimating direct risk affecting the alignments, vehicles and people. The method uses three basic parameters to quantify direct risk: hazard, vulnerability and value of exposed elements. Hazard in a given return period is expressed as the number of landslides of a given magnitude per kilometer per annum obtained using Gumbel distribution and magnitude-frequency statistics. A total of 1040 landslides were collected from historical records, of which 95.5% occurred in cut slopes along the railway and road alignment. All landslides were grouped in different magnitude classes. In total 18 hazard scenarios were generated using three magnitude classes (class I to III) and six return periods (1, 3, 5, 15, 25 and 50 years). The assessment of vulnerability of the alignment was based on the damage records, combined with expert opinion. Direct specific losses for the alignment (railway line and road), vehicle (bus, lorry, car and motorbike) and train were expressed in monetary values, and direct specific loss of life of commuters was expressed in annual probability. The detailed estimation of direct risk will facilitate to develop landslide risk mitigation and management strategies for transportation lines in the study area.