Investigation of urban landslide characteristics by summer heavy rain

Climate anomaly by global warming due to climate change, - typhoon, flooding, drought and landslide etc. - intensifies the degree and magnitude of natural disaster on human environments. Summer heavy rainfall results in many landslides in Korea. Landslides commonly occur in mountainous areas after intensive rain, often leading to topographic changes. They constitute a potentially costly risk for human life and the built environment. And landslide is a phenomenon that rock loses balance to external force such as an earthquake or rainfall to weaken the unity of the soil, crumble under a time by the action of gravity. In most parts of Korea, including Seoul, the thickness of the colluvium is generally less than 2m because of the relatively shallow depth of the bedrock, and hence shallow landslides are frequent. Furthermore, the climate of Korea shows typical summertime Monsoon with concentrated rainfall. In Korea, about 70% of the land area consists of mountains, and the average annual precipitation reaches 1,200 mm~1,500 mm. During 26-27 July 2011, in particular, a heavy rainfall occurred in Seoul, an amount approximately 30% of the total annual rainfall for that region. It was the worst flooding in urban areas since the meteorological data have been recorded from 1907. Especially, the landslide debris and flooding from Mt. Woomyeon in Gangnam, Seoul resulted in death of 17 people on July 27, 2011. However, no landslides occurred at Mt. Daemo in Gangnam, Seoul whose precipitation is more than that of Mt. Woomyeon. So, landslide does not occur only due to the amount of precipitation. In addition, there is a tendency of increasing frequency of local heavy rainfall; landslide damage like Mt. Woomyeon will be more probable in the future. So the purpose of this study is to investigate the topographic and meteorological characteristics of both mountain cases to minimize the property damage and casualties caused by urban heavy rainfall.