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5th International Disaster and Risk Conference IDRC 2014 Integrative Risk Management - The role of science, technology & practice 24-28 August 2014 in Davos, Switzerland

5th International Disaster and Risk Conference IDRC 2014 Integrative Risk Management - The role of science, technology & practice 24-28 August 2014 in Davos, Switzerland

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  • 1. Extreme rainfall induced debris flow prediction: Hazard analysis accommodating post event topographic changes in Mt. Woomyun, South Korea Lee, S.R, Vasu, N.N, Kang, S.H, Park, J.Y Geotechnical Engineering Lab Department of Civil and Environmental Engineering,KAIST 5th International Disaster and Risk Conference IDRC Davos 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 2. 1. Extreme rainfall and Landslide types in Korea 2. Hazard modelling 3. Database development and Validation 4. Extreme rainfall event Hazard prediction 5. Conclusion 6. Post 2015 framework for disaster risk reduction August 25, 2014 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2 2014 Davos Switzerland
  • 3. 1. EXTREME RAINFALL AND LANDSLIDES IN KOREA The annual precipitation amount in South Korea is 1,245 mm, two thirds of which occurs during June to September. An increase in frequency and intensity of precipitation has been observed with severe rain storm occurring 20.8 times per year since the late 1990’s ( Cha 2010) Extreme rainfall is defined as unusually severe rainfall and is usually expressed in terms of return period ( 1 in 100 ) or 90th or 99th percentile of the heavy day precipitation 3 August 25, 2014 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland HEAVY RAIN ADVISORY HEAVY RAIN WARNING Rainfall duration (hr) 6 6 Amount of rainfall (mm) >70 >110 Rainfall duration (hr) 12 12 Amount of rainfall (mm) >110 >180
  • 4. Extreme rainfall in mountainous stream areas damage results in landslides of several types with most dangerous being the debris flow Damaged area in Inje County in Gangwon Province, South Korea Damaged area in Woonmyeon Mountain Seoul 2011, South Korea 4 August 25, 2014 EXTREME RAINFALL AND LANDSLIDES IN KOREA 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 5. Varnes(1958) defined debris flow as “Rapidly moving, gravity induced slurries of granular solids, water, and air” Infiltration and wetting depth advancement 5 August 25, 2014 •Lowering of shear strength Shallow translational type landslide •Release of soil mass Liquefaction due to undrained loading •Rapid generation of high pore water pressure Rapid movement of resulting liquid like debris LANDSLIDE stage MOBILIZATION stage DEBRIS FLOW stage EXTREME RAINFALL AND LANDSLIDES IN KOREA 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 6. 2. HAZARD MODELLING  Most of the model available for landslide and debris flow simulation are standalones  There are no criteria’s to determine if the landslide will transform into a debris flow or not. 6 August 25, 2014 Mobilization criteria DEM RAINFALL COHESION SWCC SOIL DEPTH DEM INVENTORY OF DEBRIS FLOW OCCURRENCE POINT VELOCITY Landslide model Debris flow model TRAVEL ANGLE COUPLED MODEL 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 7. TRIGRS-LANDSLIDE MODELLING TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-Stability Model) is a Fortran based program ASSUMPTIONS 1. A well-documented flow field ( initial water table level ) 2. Infinite slope stability condition 7 August 25, 2014 INFINITE SLOPE STABILITY EQUATION HAZARD MODELLING 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 8. FLOW-R: DEBRIS FLOW MODELLING Flow-R, is a distributed empirical model for debris flow assessment on a regional scale THREE CRITERIA’S 1. Terrain slope 2. Water input 3. Sediment availability Source area user defined / inbuilt criteria 8 August 25, 2014 Run out path Susceptible regions Index based approach Grid cells of each input dataset are classified as (1) favourable, when initiation is possible, (2) excluded when initiation is unlikely, or (3) ignored when no decision can be taken on this parameter HAZARD MODELLING Energy based algorithm for run out calculation Velocity threshold is used to limit the debris flow energy to reasonable limit “ A cell is a source area if it was at least once selected as favorable, but never excluded” 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 9. 3. DATABASE DEVELOPMENT AND VALIDATION STUDY AREA: WOOMYEON MOUNTAIN 9 August 25, 2014 2010.8 2011.8 2010.8 2011.8 • Landslide initiation point / Debris flow scar • Available datasets - Topographic maps: 1:5,000 - Aerial photographs: 25 cm × 25 cm - Satellite images: 1 m × 1 m - Field investigation: Official archive (KGS, 2011) - Landslide inventory: Official archive (KSCE, 2012) • Procedures of mapping (1) Collection / Preparation (2) Mapping / Digitizing (3) Comparison / Verification 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 10. DATABASE FORMAT 10 August 25, 2014 DATABASE DEVELOPMENT AND VALIDATION Database Format GIS data type Scale Source Study area Hazard data Landslide inventory Point coverage 1:5,000 Korean Society of Civil Engineers 1 / 2 Damageable objects Buildings, roads, facilities Line and polygon coverage 1:5,000 National Geographic Information Institute 1 / 2 Image data Aerial photographs GRID 25 25 cm National Geographic Information Institute 1 Satellite images GRID 1 1 m Commercial company 1 Satellite images GRID 5 5 m Commercial company 2 Hydrologic data Precipitation Point coverage 1:5,000 Korea Meteorological A dministration 1 / 2 Basic data Topographic map Point and line coverage 1:5,000 National Geographic Information Institute 1 / 2 Geotechnical map Point coverage 1:5,000 Field investigation reports 1 Forest soil map Polygon coverage 1:25,000 Korea Forest Service 1 / 2 Geology map Polygon coverage 1:50,000 Korea Institute of Geoscience And Mineral resources 1 / 2 Forest map Polygon coverage 1:25,000 Korea Forest Service 1 / 2 Landuse map Polygon coverage 1:50,000 National Geographic Information Institute 1 / 2 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 11. DATABASE DEVELOPMENT: TRIGRS 11 August 25, 2014 18 borehole database → 5 zones (Catchment and engineering properties) Parameter (units) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Friction angle, (°) 25.3 28.5 37.6 30.9 28.2 Cohesion, c (kPa) 9.6 5.8 7.7 7.6 6.3 Total unit weight of soil, ( 18.1 17.7 17.0 17.3 18.2 KN/m3) Hydraulic conductivity of saturated, Ks (m/s) 7.15×10-6 3.37×10-6 1.80×10-6 9.70×10-6 3.69×10-6 Saturated volumetric water content, 0.50 0.50 0.51 0.51 0.51 Residual volumetric water content, 0.20 0.20 0.19 0.19 0.19 Hydraulic diffusivity, D0 (m2/s) 200 Ks Steady infiltration rate, Iz (m/s) 0.01 Ks GEOMORPHOLOGICAL+RAINFALL DATABASE GEOTECHNICAL DATABASE HOURLY MAXIMUM RAINFALL Namhyun: 114 mm/hr (07:44~08:44 27th July) Seocho: 87 mm/hr (07:41~08:41 27th July) DATABASE DEVELOPMENT AND VALIDATION SLOPE 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 12. MODEL VALIDATION: TRIGRS DATABASE DEVELOPMENT AND VALIDATION 12 August 25, 2014 5th International Disaster and Risk Conference IDRC 2014  For the quantitative validation of the landslide susceptibility mapping for each scenario, the cumulative frequency applied.  Validation was performed through comparing the known landslide location data from the inventory with the landslide susceptibility simulation result of TRIGRS model.  Used a landslide susceptibility index rank (Lee et al., 2007) to compare relative accuracy.  Higher susceptibility rank contains more landslides ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland for a good model.  The graph shows area under the curve (AUC) for several statistical models along with TRIGRS.  TRIGRS has an AUC =0.9574 meaning , the prediction accuracy is 95.74%.
  • 13. DATABASE DEVELOPMENT FOR PREDICTION 13 August 25, 2014 DATABASE DEVELOPMENT AND VALIDATION POST EVENT DEM ( 5m ) Removed previous event scars where counter structures and drainage path were constructed Introduced zone soil properties at the Air force base ( High cohesion value) SLOPE (5m) 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 14. MOBILIZATION CRITERION 14 August 25, 2014 DATABASE DEVELOPMENT AND VALIDATION Criterion was developed using 300 events ( debris flow, slides) in Gyeong-gi province. RED LINES ARE THE DEBRIS FLOW POTENTIAL SOURCE SLOPE CRITERION TWI ELEVATION PLAN CURVATURE -2/100 m-1 ELEVATION SLOPE TOPOGRAPHIC WETNESS INDEX (TWI) 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 15. FLOW-R DATABASE DEVELOPMENT 15 August 25, 2014 Holmgren’s modified algorithm controls degree of spreading exponent of 4 selected Gamma (2000) 28 m/s travel angle= 130 ( Choi and Paik, 2012) DATA WAS OBTAINED FROM LITERATURE AND BACK CALIBRATION DATABASE DEVELOPMENT AND VALIDATION Back calculation using the 2011 debris flow event scar 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 16. 16 August 25, 2014  A constant rainfall intensity of 100 mm/hr (200 year return period ) for a duration of 48 hrs was applied.  Spatial variation of landslide initiation area corresponding to time duration of 1 hr, 6hr, 12 hr, 24 hr and 48 hr is as shown. 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland 4. EXTREME RAINFALL EVENT HAZARD PREDICTION INITIAL 6 HR 24 HR 1 HR 48 HR 12 HR
  • 17. 17 August 25, 2014  Variation of pressure head with soil depth.  Initial condition considers –ve pore pressure until the water depth at 2m.  Water table rise with time progression is seen  Pressure head is limited using equation EXTREME RAINFALL EVENT HAZARD PREDICTION STRENGTH REDUCTION RATIO ( Yunki kim, 2009)  Sensitivity analysis shows cohesion to be the most influential followed by slope angle ( 23-42) and friction angle.  The above chart for reduction ratio of factor of safety shows, for given range of ks/i , that there is no significant reduction of FS . Thus zone 5 and zone 2 has higher % landslide initiation areas even with relatively low Ks. ZONE ks/i 1 0.257 2 0.112 3 0.064 4 0.349  (Z, t)  Z 5 0.133 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland RESULTS AND DISCUSSION
  • 18. RESULTS AND DISCUSSION 100 mm /hr for 48 hrs 18 August 25, 2014 2 mm /hr for 24 hrs 100 mm /hr for 96 hrs EXTREME RAINFALL EVENT HAZARD PREDICTION  Mobilization criteria applied on the TRIGRS generated landslide areas.  2 mm/hr rainfall for 24 hrs resulted in debris flow initiation zones mainly in zones 2 and 5.  Increase in duration of 100 mm/hr for another 48 hrs results in small increase in area of initiation zones.  Significant number of debris flows on revised DEM are initiated in zone 5 ,4 and 2. Number of them flow into the path with countermeasures 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 19. 5. CONCLUSION 1. Prediction of debris flow initiation and run out path was done in Woonmyun San under different rainfall condition. 2. Landslide model, mobilization criterion and debris flow run out model was validated using 2011 event in the region. 3. We see a spatio temporal distribution of landslide areas for an extreme rainfall in different zones due to spatial variability of cohesion , while the variation of ks/i doesn't result in a significant factor of safety reduction. 4. The final debris flow run out areas on a regional scale helps us to delineate the areas of high risk. 19 August 25, 2014 Debris flow event under extreme rainfall of 100mm/hr for duration of 4 days 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 20. 20 6. POST 2015 FRAMEWORK FOR DISASTER RISK REDUCTION MINISTRY OF SCIENCE, ICT AND FUTURE PLANNING REPUBLIC OF KOREA PROJECT TITLE: Core Technology Development Of Real Time Prediction And Counterplan For Extreme Rainfall Induced Landslide Disaster TOTAL BUDJECT: 6 Billion won ( 1.17 million USD) TIME PERIOD: 2012-2017 RESEARCH PARTICIPANTS: 5 CONTRIBUTION: 1. Buildup and operation of advanced level national safety system. 2. Development of practical and marketable disaster prevention technology ( Geotechnical-geology models, real time monitoring system and early warning system ). 3. Developing education material and training experts , young researchers. 4. Development of strategy for sustainable and continuous maintenance of risk reduction facilities Real time monitoring system Expert training and education material CORE TECHNOLOGY Debris flow mobilization criterion Hazard model Database system Risk model August 25, 2014 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland
  • 21. 21 REAL TIME MONITORING DATABASE SYSTEM EXPERT TRAINING AND EDUCATION MATERIAL RISK MODEL HAZARD MODEL DEBRIS FLOW MOBILIZATION Integrated Landslide Management System 5th International Disaster and Risk Conference IDRC 2014 ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August August 25, 2014 2014 Davos Switzerland
  • 22. 22 August 25, 2014 5th International Disaster and Risk Conference IDRC 2014 THANK YOU ‘ Integrative Risk Management- The role of science, technology and practice ’ 24-28 August 2014 Davos Switzerland

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