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!