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

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