Use of a Slope Stability Index Based Predicting Tool for Landslide Hazard Mapping in Sri Lanka

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Use of a Slope Stability Index Based Predicting
Tool for Landslide Hazard Mapping in Sri Lanka
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Study Area Ratnapura Town Area
Ratnapura Town Area
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Objectives

• To produce a landslide hazard map of Ratnapura
  area utilizing a index based slope stability
  model.
• To compare the model based landslide hazard map
  with NBROs existing probabilistic landslide
  hazard map.
• To propose modifications, if necessary, to make
  the product more meaningful to the end user.

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Methodology SINMAP
Soil Lab Test/Reports on previous landslide
studies
Soil Overburden Map
Rainfall Data
Topographic Map Scale 110,000
Soil Strength Parameters (cohesion, friction
angle, soil density, transmissivity)
DEM 10m x 10m Grid
Recharge
Calibration Regions
Landslide Points Theme
SINMAP MODEL
CALIBRATION
STABILITY INDEX MAP SINMAP Based Landslide Hazard
Map
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Methodology
Landslide hazard map based on SINMAP model
Landslide hazard map of NBRO
Comparison giving due consideration to land use
and geology of the area
Map of Geology/Land use
Recommendations
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Data Collected

• Contour map of yr. 2000, Scale 110000, Source
  Survey Dept.
• Landslide inventory as of yr 2002, Source NBRO.
• Geotechnical data, for part of the study area,
  from reports on previous landslide studies,
  Source NBRO.
• Daily rainfall data, from 1996 to 2006, Source
  Meteorological Dept.
• Map of geology as of 1998, Scale 110000, Source
  NBRO.
• Map of land use as of 1998, Scale 110000,
  Source NBRO.
• Map of overburden as of 1998, Scale 110000,
  Source NBRO.

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Data Collected through Field Visit

• Updating the landslide inventory for the period
  from 2002 to date
• Collection of soil samples
• Collection of ground truth data for image
  interpretation

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SINMAP Inputs
Digital Elevation Model of the study area
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SINMAP Inputs
Landslides Initiation Points
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SINMAP Inputs
Calibration Region Theme A polygon coverage of
soil overburden thickness distributed over the
study produced by NBRO reflecting the different
soil types and thickness was used as calibration
region.
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Model Parameters
SINMAP Inputs
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SINMAP Results
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SINMAP Results Statistical Summary for the
Study Area
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Landslide Hazard Map of NBRO
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Reclassification Methodology
The adopted methodology to reclassify the SINMAP
Stability Index Map for the purpose of comparing
it with the NBROs landslide hazard zonation map.
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SINMAP based Hazard Zonation Map
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A Comparison of Maps
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Conclusions

• Analytical results of SINMAP shows that 65 of
  the study area is stable while the remaining 35
  of the area is quasi-stable and unstable. 79 of
  the recorded landslide points fall in the latter
  area, giving credence to the model.
• The output of SINMAP model could have been
  improved had there been very high resolution
  satellite imagery such as those of ALOS/PRISM for
  producing a precise DEM.
• Comparison of the hazard zonation map produced by
  the SINMAP model and NBRO map indicates that the
  SINMAP has a better reliability in predicting the
  slope instabilities of the selected study area.
  SINMAP model can be expected to be used in other
  areas for landslide hazard zonation cost
  effectively.