Landslide modelling and susceptibility mapping using AHP ...
Landslide Susceptibility Evaluation Techniques
description
Transcript of Landslide Susceptibility Evaluation Techniques
Interpreting Landscape to Predict Landslide Vulnerability
A brief overview of the techniques involved to evaluate the conditions
for a landslide
Christopher BrideGEP635Spring 2012Prof. Yuri Gorokhovich Photo courtesy of Riverkeeper.org
Study Site: Milton, NY
Milton Landslide into the Hudson River
Slope Profile via Google Earth
Parameters to Study
• Slope • Soil type• Tree/vegetation cover• Many others outside the scope of this class– Hydration– Impermeable surface– Other man-made factors
GIS• DEM files: Digital
Elevation Model• GIS Clearinghouse• County boundaries• Hudson River
shoreline shapefile
Data acquisitionGrid enables easy location of the tiles needed to acquire for this project
Also can be done by town name.
Download, unzip, add to map, symbolize via “stretched value”, “discrete colors”, or “classify”
Digital Elevation ModelColored to indicate elevation in feet
This is actually 4 grid tiles
Analyze slope: Geoprocess/Slope
Soil Analysis
Simplified: Dangerous types vs. everything else
Slope & Soil Type
Slope & Soil Type
Orthophotos: Tree/Vegetation cover
Data Acquisition
Download Ortho-index grid
Input Ortho-grid into GIS
What tile do I need?Choose “ID” tool in ArcGISSelect the grid position you needRecord or memorize the grid number
Find tile coordinate in list, download/unzip, and add to map
Start combining layers• Ulster County Orthophotos underneath Slope
Analysis
Milton Landslide & Slope
Landslide Area
Landslide Site & Soil TypeGlacial Deposits
Bedrock (type “r”)
“other”
Landslide Area
Slope & Soil Type
Landslide Area
Index/Model
• Landslide susceptible soils categorized into one class • Landslide susceptible slopes categorized into one
class (slopes >30 degrees)• Vegetation coverage was not on hand, but would
have otherwise been given a classification as well • For now, we will look at where soil type and
landslides overlap/intersect.• Then use GoogleEarth or orthophotos to evaluate
vegetation coverage.
Union of Slope and Soil Type LayersNeed to convert slope raster into a polygon so that a Union geoprocess can be performed with the Soil layer
Slope Raster to PolygonSlope Raster from DEM Slope polygon file >30o
Union these two layers for Landslide susceptibility analysis
Slope polygon Soil polygon
Soil and Slope UnionAfter “Union” geoprocess, the areas with >30 degree slope that overlay the landslide susceptible soil types are indicated in red. All other areas, soil and slop alike, are indicated in green.
Ulster Landslide Area Analysis
Landslide site, 2011
Final map
Potential Problem AreaResidential, tree removal apparent, strong slope and soil type correlation to landslide conditions.
Advice? Don’t remove the trees or vegetation in these areas.
GoogleEarth Photo of Potential Landslide Area
References
• Orthophotos and Soil Data: http://gis.ny.gov/ (NYState GIS Clearinghouse)
• Digital Elevation Models: http://cugir.mannlib.cornell.edu/datatheme.jsp?id=23 (CUGIR: Cornell University Geospatial Information Repository)
• Opening photo: http://hudsonriverkeeper.blogspot.com/2012/04/landslide-into-wetland-at-residential.html
Thank You!