REALTIME FORECASTING OF SHALLOW LANDSLIDES USING RADAR-DERIVED RAINFALL Ryohei Misumi, Masayuki...
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Transcript of REALTIME FORECASTING OF SHALLOW LANDSLIDES USING RADAR-DERIVED RAINFALL Ryohei Misumi, Masayuki...
REALTIME FORECASTING OF SHALLOW LANDSLIDES USING RADAR-DERIVED RAINFALL
Ryohei Misumi, Masayuki Maki, Koyuru Iwanami,
Ken-ichi Maruyama and Sang-Goon Park
National Research Institute for Earth Science and Disaster Prevention, Japan
By
Shallow landslide at Izumozaki-town, Niigata Prefecture on 13 July 2004
Outline
X-band polarimetric radar
Distributed rainfall-runoff model
Real-time forecast of landslides
Soil water
Rainfall estimation in high accuracy and resolution
WeightBed rock
Soil layer
Slip surface
Sliding force
Shear resistance
Normal situation
What is shallow landslide ?
Bed rock
Soil layer
Saturated Zone
Soil particles
Water During heavy rainfall
Increase of pore pressure
Decrease of normal stress
Rain
Estimation of rainfall intensity using the specific differential phase (KDP)
not affected by rain attenuation
immune to beam blockage
less sensitive to beam filling and drop size distribution
++
Z KDP
Disdrometer
+
R-KDP
R-Z
R-Z (corrected)
Catchment50m grid
Rainfall
Distributed rainfall-runoff model
Evaporation
Infiltration
Direct runoff
Base flow
Maximum storage capac
ity
SmaxWater
storage
S
50m grids
tan
'tan)])((1[
cossin
' w
z
h
z
cF
γγ
γ
Infinite slope stability analysis
F: Factor of safety
γ, c', Φ': Soil properties
γw: Density of water
h: Level of groundwater
z: Depth of soil
β: Inclination of slope
maxS
S
z
h
80km
Tsurumi river basin
MP-X radar
Real-time evaluation
Meso-β scale depression on 9 July 2005
22:59
Rainfall rate
Water storage
Predicted landslides
Meso-β scale depression on 9 July 2005
23:29
Rainfall rate
Water storage
Predicted landslides
Meso-β scale depression on 9 July 2005
23:53
Rainfall rate
Water storage
Predicted landslides
3 km
Actual landslide
Predicted grid
Landslide on 9 July 2005
Evaluation with past events
Upper Abukuma River basin (151.07km2)
Rainfall event in August 1998
0 4321 5
02JST on 27 August
(2 hours before severe landslides)
Distance (km)
Dis
tanc
e (k
m)
Slope failure
Predicted grids
Welfare facility
Predicted factor of safety (F) and occurrence of landslides
Factor of safety
Occur Not occur
F < 1 205 grids 1809 grids
F > 1 56 grids 5318 grids
Correct forecasts: 74.8 %
False alarm ratio: 89.8 %
Conclusions
An accurate forecast of shallow landslides is still difficult.
Increase of landslide potential in a few-km scale may be predictable using rainfall observation with the X-band polarimetric radar (lead time is about 2 hours).
The lead time would be greatly extended if a reliable QPF is available.