Susceptibility assessment of rainfall induced landslides: A case study of the debris flow on July 27, 2011 at Umyeonsan (Mt.), Seoul, Korea

In Korea-70% of which is covered by mountains-landslides and debris flow hazards are frequently occurring in summer. Most of these hazards have been concentrated around mountainous region. On July 27, 2011, however, a total of 33 debris flows occurred in Umyeonsan (Mt.), around where is densely populated residential areas in Seoul, Korea. The debris flow hazard resulted in 16 fatalities and extensive damage to houses, roads, and other properties. Most of the debris flows were initiated from shallow landslides which were triggered by an intensive rainstorm with a peak intensity of 112.5 mm/h. This paper provides a comprehensive description of the debris flow hazards in Umyeonsan with the morphological, hydrological, and geotechnical features of the watershed. Also, GIS-based prediction methods of landslide susceptibility are highlighted. Based on this, countermeasures by combining elements of engineering solution such as ecological planting, stone channels, soil nailing, and concrete barriers, have been designed and constructed.