2014 Summer Training Courses on Slope Land Disaster Reduction Hydrotech Research Institute, National Taiwan University, Taiwan August 04-15, 2014

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1 Final Project Report 2014 Summer Training Courses on Slope Land Disaster Reduction Hydrotech Research Institute, National Taiwan University, Taiwan August 04-15, 2014 Landslides in Mt. Umyeon Susceptibility Mapping using GIS and Mitigation Measures August 14, 2014 Dr. Krishna Devkota Asian Disaster Preparedness Center, Bangkok, Thailand Mr. Suh Young Choi Seoul Metropolitan Government, Seoul, South Korea

2 Content of the Report Introduction Objective of the Report Location Map of Mt. Umyeon Landslide in Mt. Umyeon Geology of Study Area Characteristics of Study Area Landslide History of Mt. Umyeon Rainfall in Mt. Umyeon - July 2011 Data Preparation and Sources Landslide Causative Factors Landslide Inventory Map Methodology of Landslide Susceptibility Mapping Mitigation Measures - Drainage System Maintenance Result and Discussion on Landslide Susceptibility Mapping Conclusions

3 Objective of the Report To explore the landslide hazard scenario of Mt. Umyeon, Seoul, South Korea To introduce the Pair-Wise Comparison Method for landslide susceptibility mapping To identify the landslide susceptible area of Mt. Umyeon To explore the landslide mitigation measures in Mt. Umyeon

4 Location Map - Mt. Umyeon Mt. Umyeon is located in the Seocho-gu of the Seoul Metropolitan City in Korea where the mountain peak is situated 10 km south of Seoul and about 5 km northeast of Mt. Gwanak. On July 27, 2011, there were devastating landslides in Mt. Umyeon which killed 16 people (NDMS, 2011).

5 Landslide in Mt. Umyeon - July 27, 2011

6 Study Area is dominated by complex metamorphic rock Geology and its Relation to Landslide granite, metamorphic rock and alluvial deposit. But, all landslides are located on the complex metamorphic rock. The devastating landslides that have occurred are located on the forested area which their moving mass affected the infrastructure as well as community on the downhill. The catastrophic landslides affected two prominent apartments namely, Remain and Shindonga apartment; and two others village known as Jeonwon and Hyeongchon. Mt. Umyeon geological features are composed by metamorphic rock that established lower hill areas which are affected by tectonic movements with faults and strong weathering which makes this area more vulnerable to landslide. Geological Map of the Mt. Umyeon

7 Characteristics of Study Area The hilly part is dominated by forest; the urban area and agriculture land are on the foothill of the mountain. The temperate deciduous forests are dominated in Mt. Umyeon which is composed of nut pine tree forest, broad-leaved tree forest and so on. The major trees are Mongolian oak tree, Dalse Acasia, Quercus Acutissima Carruth (oak tree), black birch and other kinds of pine trees.

8 Landslide History of Mt. Umyeon Table 1: Summary Table of Devastating Landslides Occurred on July 27, 2011 in Korea Devastating Landslides Area Basin and Landslide Area Characteristics Number of Landslide Landslide Basin Debris Flow Landslides Area (m 2 ) Slope ( o C) Slope ( o C) Length (m) Raemian Apartment Shindonga Apartment Jeonwon Village Hyeongchon Village Bodeok Temple Songdong Village Landslide 18 Affected Area 36.0 No. of Death Umyeon Tunnel Location EBS Broadcasting Center 1 3 Raemian Apartment Amsan Village Gangnam Church 2 11 Shindonga 91.20Apartment Daesung Temple 3 15 Jeonwon Village Deoku Temple 4 5 Hyeongchon Village Deotgeol/Angeol Village Total 150 Total number of casualties

9 Rainfall in Mt. Umyeon - July 27, 2011 Rainfall record: July 27, 2011:- 1) Seo Cho Station and 2) Nam Hyun Station Time (hr) Time (hr) Data Source: Korea Meteorological Administration

10 Data Preparation and Sources Seven causative factors have been selected for landslide susceptibility mapping. They are; Slope, Aspect, Elevation, Plane Curvature, Landuse, Soil Depth and Geology All causative factors maps were prepared in ArcGIS 9.3. Digital Elevation Model (DEM) cell size: 20 m by 20 m. Factor Class Topographical Factors Slope, Aspect, Elevation, Plane Curvature Geological Factor Digital Geological/Lithology Map Land Cover Factors Landuse Map, Soil Map Table 2: Data Sources of Landslide Susceptibility Mapping Source Korean National Geographic Information Institute Scale: 1:5,000, Resolution: 20 m Geological Society of Korea Scale: 1:25,000 Korean Ministry of Environment Scale: 1:25,000, Resolution: 20 m

11 Landslide Causative Factors

12 Landslide Inventory Map of Mt. Umyeon

13 Methodology of Landslide Susceptibility In this study, both methods of direct and indirect approaches are used. For the indirect method, the pair-wise comparison method is used to derive the weight of each parameter individually. It compares parameters individually, and generates the degree to which each parameter is more important than the counterpart. The pair-wise comparison of the present study is presented in Table 3. The outcome of the pair-wise comparison presented in Table 4 is used to assign the weight to each parameter Table 5. The total scores are calculated by summing the product of each parameter and its relative importance (Count) rated by using the individual matrix of parameters as shown in Table 4. The total scores for each parameter is normalized based on 1. The calculated weights indicate the degree of individual parameter relative to others.

14 Table 3: Pair-wise comparison method Methodology: Pair-wise Comparison Method Attribute Slope (A) Aspect (B) Elevation (C) Plane Curvature (D) Landuse (E) Soil Depth (F) Geology (G) Slope (A) - A1.5 A1.5 A1.5 A1.5 A1.5 A1.5 Aspect (B) B1 0.5 B1 Elevation (C) C1 0.5 C1 Plane Curvature (D) D1 0.5 D1 Landuse (E) F1 0.5 Soil Depth (F) F1 Geology (G) Note: 1 = important, 1.5 = very important, 0.5 = equivalent

15 Calculated Weights Table 4. Calculated weights based on pair-wise comparison method Attribute Parameter Count Sub-total Total Weigh Slope Aspect Elevation Plane Curvature Landuse Soil Depth Geology

16 Subclasses of Each Parameter and their Consequent Weights Table 5. Subclasses of each parameter and their consequent weights Parameter Subclass (degree) Weight Slope >45 1 Aspect Flat 1 North 2 Northeast 1 East 2 Southeast 2 South 2 Southwest 3 West 2 Northwest 2 Elevation < 50 m m m m 4 > 200 m 2 Parameter Subclass (degree) Weight Plane Curvature < > Landuse Agriculture 1 Forest 3 Hydrology 1 Urban 1 Soil Depth Very Low 1 Low 2 Medium 3 High 3 Very High 2 Geology Granite 1 Complex Metamorphic Rock 3 Metamorphic Rock 1 Alluvial 1

17 Calculation for Landslide Susceptibility Map Finally, the total hazard score is the sum of the product of the weight of each parameter and subsequent weights of subclasses (Tables 4 and 5). From this analysis the landslide hazard can be proposed based on seven parameters and their subclasses as follows: Landslide Hazard = 0.375(VS) (VA) (VE) (VP) (VL) (VS) (VG) (Eq. 1) Where, VS, VA, VE, VP, VL, VS and VG are the weight of subclasses of the slope, aspect, elevation, profile curvature, landuse, soil depth, and geology of the study area, respectively.

18 Landslide Susceptibility Map of Mt. Umyeon

19 Mitigation Measures - Drainage System Maintenance

20 Mitigation and Recovery - Mt. Umyeon Landslide Recovery of Landslide affected Area in Mt. Umyeon Raemian Apartment Imgwang Apartment: It located in the northern part of Mt. Umyeon. The large amount of water with sand driftwood and debris moved towards South Circular Road (Nambusunhwan) which damaged apartment and killed 3 people at 8:30 AM on July 27, 2011.

21 Mitigation and Recovery - Jeonwon Village Recovery of Landslide affected Area in Mt. Umyeon Jeonwon Village: Located on Western part of Mt. Umyeon which experienced severe landslides and killed 4 people

22 Mitigation and Recovery - Shindonga Apartment Recovery of Landslide affected Area in Mt. Umyeon Shindonga Apartment: It was also affected by landslides causing death of 3 people. The landslide induced debris was entered into the Buddha Television Network (BTN) building along with apartment and killed one person in BTN and 2 in apartment.

23 Mitigation and Recovery - Hyeongchon Village Recovery of Landslide affected Area in Mt. Umyeon Hyeongchon Village: It is located in Ecological Park of Mt. Umyeon where many household were damaged and 6 people was killed due to unexpected debris produced by rainfall-induced shallow landslides in the region. This village is located in southern part opposite from South Circular Road (Nambusunhwan-ro). This area has valley and small scale monsoon streams.

24 Result and Discussion on Landslide Susceptibility Mapping The final landslide susceptibility map based on Eq. 1 is divided into 5 classes as very low, low, moderate, high, and very high susceptible respectively. In order to validate the result, five locations of landslides identified on July 27, 2011 are also presented in the landslide susceptibility map. It is observed that four landslides were fallen into the high and very high susceptible zones while the other was enclosed by the moderate susceptible zone. It is also found that slope, aspect, elevation, soil depth and plane curvature of the study area have a significant role in triggering landslides compared to other factors such as geology and landuse. This highly dependence on specific factors may lead to unexpected results in identifying the susceptible areas. As assigning weights of causative factors and their subclasses are somewhat arbitrary, the relative landslide susceptibility is expected rather than absolute.

25 Conclusions In this study, approximate areas of Mt. Umyeon are identified based on relative importance of parameters and their inherent subclasses. Drainage management is fundamental measures to prevent future landslides in Mt. Umyeon. The pair-wise comparison method is employed to reduce the subjectivity which might happen in deciding weights of parameters. Based on the findings of this study, the landslide susceptibility map could be beneficial to identify the most susceptible areas. Increasing population has forced the Seoul Metropolitan to concentrate their development activities on downhill of the mountain where the possibilities of landslides are relatively high. Thus, to save the life and properties from landslides, the susceptibility map can be used as a basic tool in land management and planning future construction in this area.

26 Nothing can Stop Disaster but can be Avoided! Thank You!