2. Evaluating and Mapping the Stability of Slopes in Napa County with a GIS-based Model Dongyuan Wang Ph.D candidate in geotechnical engineering The University of Texas at Austin December 7, 2000

3. Outline  Objective  Background  Data Preparation  SINMAP Model  Implementing SINMAP  Outputs of SINMAP  Discussions  Acknowledgement

4. Objectives  Make the evaluation results visualized and accessible to the people.  Through this showcase, explore the feasibility of applying GIS in geotechnical engineering;  Show how to evaluate and map the stability of slopes with SINMAP, a GIS-based model.

5. Background  Why Napa County? Development require more Lands; Landslide is one of main natural disasters plaguing the people in every country.  Why slope stability?  Why GIS?

6. Landslides in USA

8. Data Preparation(1)  DEMs: from USGS website Only part of Napa County SDTS Grid Scale:1:24000 UTM projection  Soils: from USDA website SSURGO Useful files: comp,layer, mapunit “Unifiled” field in “layer”

9. Data Preparation (2)  Landslides: from USGS website In geographic coordinates system Convert it to UTM; Landslide Points Add “type” filed to the shapefile

10. SINMAP  An ArcView extension to calculate and map stability index of slopes based upon geographic information, primarily on DEMs.  Theoretical Basis Infinite slope model Topographic wetness index, R/T ratio Distribution: Uniform

11. Implementing SINMAP (1)  Model Parameters Gravity constant: 9.81 m/s 2 Soil Density: 2000 kg/m 3 Water Density: 1000 kg/m 3· Number of points in SA Plot: 2000  Calibration Parameters T/R ratio: 2000-3000 m Dimensionless cohesion: 0.0-0.25 Angle of internal friction: 30-45 degrees Lower wetness line percentage: 10%

12.  Select DEM Grid  Calibration area Use “comp” file in soil date to create a calibration area; Clip “unifiled” field in “layer” to “comp” manually. Add landslide points;  Analyze Stability by adjusting calibration parameters Implementing SINMAP(2)

13. Outputs (1)

14. Outputs(2)

15. Discussions 1.Can we apply GIS in geotechnical engineering ? 2. Does SINMAP work well ? 3. Future work ?

16. Acknowledgement  Dr. Maidment at UT  Dr. Tarbonton, Bob Pack and Craig Goodwin at USU