SEACAP 21. Landslide impacts on the road network of Lao PDR and the feasibility of implementing a slope management programme

Abstract

The Peoples' Democratic Republic of Lao is a landlocked country bordered by Vietnam to the east, Thailand to the south and west and China to the north. It is predominantly hilly or mountainous, and experiences a sub-tropical climate defined by a distinct rainy season during the summer. Annual rainfall varies in the mountainous regions of the north between 1.5m and 4m per year, most of which falls during the summer months, sometimes in association with typhoons developed in the South China Sea. Forest occupies the majority of slopes that neighbour the road network. The road network of Laos is impacted upon by landslides. These landslides occur most frequently as shallow and localised slope failures in roadside cuttings, though below-road slope failures are also common and deep-seated hillside failures less so. The majority of landslides result in temporary partial or complete blockages to short sections of road. These failures can give rise to several hours of delay to traffic and also require ongoing investment in debris clearance, repairs to walls and roadside drains and road pavement. Although the risk posed by landslides to mountain roads in Laos appears to be relatively low when compared to some other countries in the Asian region, there are both technical and economic justifications for the development of an enhanced slope management programme. An evaluation of landslide costs in engineering terms concludes that the economic justification for investment is marginal. However, when the costs of traffic delays are taken into account the case for increased investment in enhanced slope management becomes strengthened. The proposed programme for this investment combines capacity building through training with the implementation of pilot slope improvement projects. Improved data collection and monitoring systems are also proposed