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Data Assimilation
in Climate and Energy
Systems Engineering

 Mt. Umyeon, 
 Landslide in 2011 

우면산 사진.jpg

Overview

  • Due to the influence of Typhoon Kompas, torrential rain fell in the area of Umyeonsan Mountain between September 21, 2010 and September 23, 2010, causing landslides (area 42,000㎡, hereinafter referred to as 2010 landslides) in Umyeonsan Mountain.

  • As a result, as shown in the attached drawing 1, soil and rocks (a mixture of rock, gravel, sand, and soil mixed with water at a relatively high concentration) were formed in the Deokwooam Valley and Yujeomsa Valley, and flowed into the Sindonga Apartment and Deokwooam in Bangbae-dong, Seocho-gu, Seoul

  • In particular, very strong rain was concentrated in Seocho-gu and Gangnam-gu for a short period of time, and residential areas and roads around Woomyeonsan Mountain were flooded along with soil.

  • At that time, precipitation was evaluated as a representative case of localized torrential rain that repeatedly passed through very strong rain clouds in a narrow area.

Scale of damage

  • The landslide of Umyeonsan Mountain caused large-scale soil runoff and flooding in Seocho-gu, Seoul.

  • Due to torrential rain, damage was concentrated in rural villages and areas around roads near Umyeonsan Mountain, followed by traffic paralysis and urban flooding in Gangnam and Seocho areas.

  • The landslide in this case killed 16 people and injured 51 people, and damaged 11 houses, one of which was spread.

Korean Geotechnical Society Report

  • The graph shows the changes in hourly and cumulative precipitation at the Seocho AWS and Namhyeon AWS.

  • Blue bars : 10-minute precipitation

  • Red lines : cumulative precipitation

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  • Precipitation increased rapidly between dawn and morning on July 27, confirming that very heavy rain was concentrated over a short period.

  • In particular, the Namhyeon AWS recorded an extreme downpour of approximately 112.5 mm in one hour, and the cumulative precipitation increased to about 424.5 mm.

  • The Seocho AWS also recorded a cumulative precipitation of approximately 364.5 mm due to the concentration of heavy rainfall over a short period.

  • Due to this torrential downpour, the soil rapidly reached a saturation state, ultimately leading to the landslide on Mt. Umyeon and urban flooding damage.

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AWS/ASOS observation data

  • Maximum hourly precipitation 

       : 112.5 mm/hr (around 7:40 am on July 27, 2011 based on the Namhyeon Observatory)
         85.5 mm/hr (around 7:40 AM on July 27, 2011 based on the Western Observatory)

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  • Cumulative Precipitation (July 26, 2011 to July 27, 2011)

       : 374.5 mm (Seocho AWS)

         424.5 mm (Namhyeon AWS)

Key Causes

  • At that time, the rainy front was stagnant in the central region, and the rain cloud band developed rapidly as the hot and humid lower jet stream passing through the South and East China Sea and the dry cold air settling from the upper low pressure in China met in the central region.

  • The combination of introduced water vapor and strong atmospheric instability formed a very strong convective precipitation zone around Seocho-gu, Seoul, and a train echo-type precipitation pattern appeared in which strong rain was repeatedly concentrated in a narrow area.

  • The geology of Woomyeonsan Mountain was composed of gneiss and boron layers, making it vulnerable to landslides, and torrential rain acted as a decisive cause in a situation where the ground had already reached saturation due to long-term accumulated precipitation.

  • It was evaluated as a case where the damage was aggravated by the combination of natural factors such as torrential rain and human resources factors such as lack of contrast.

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