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Information in KRIS Big River on Modeling Shallow Landslides

KRIS Web Background Pages: Modeling Shallow Landslides

Note: Geologic information, electronic maps and models within the KRIS Big River project are meant to provide background information only and not as a decision making tool. California requires that licensed geologists be involved directly in decisions related to geologic conditions (see requirement).

Examples below are from the KRIS Big River Map project and show the basin relief, slope steepness and a SHALSTAB Model run. The latter was prepared in 3D Analyst and is available in the ArcView project as an image.

	At left is a Big River elevation map in meters with an elevation grid of 1000 by 1400 cells. Each cell contains an individual elevation value for a10x10 meter location on the ground.  The various elevations are grouped together by color. This map is used to compute steepness and wetness. The highest elevations in the basin are along the eastern and northern boundaries.
	The map image at left shows an artificial 3D landscape with an overlay showing slope steepness, both constructed from the 10 meter DEM. Slope steepness is greatest in the North Fork and Upper Big River. Slopes are generally less steep in the South Fork basin, although some areas in a band running north-south through the Dark Gulch and Leonard Lake Calwater units and extending into eastern Daugherty Creek. Steep slopes in western sub-basins are largely related to the inner gorge area.
	The map image at left shows landslide hazards for the Big River basin. Areas of highest risk have low, negative scores. Dietrich (Dietrich, 1998) requests users of the SHALSTAB model to employ the standard soil parameters he developed in his 1998 validation study to facilitate uniform results. He proposes tentatively a  "high hazard" classification for scores equal to or below -2.8. produced by SHALSTAB with standard soil parameters and 10 meter digital elevation data. There appears to be more high risk areas in the North Fork than in other basins.
	The image at left shows a three dimensional model of the North Fork Big River, showing landslide risks simulated using 10 meter DEMs and running the SHALSTAB model according to Dietrich et al. (1999). Slope shown in yellow is moderate instability (values 2.5-2.8) with higher  instability (>2.8) shown in red. The SHALSTAB results displayed in KRIS are for informational purposes only and should not be used as the only tool in assessing slope instability. The latter task is that of a licensed engineering geologist. Model run by Jan Derksen in ArcView 3D Analyst.

References  

Dietrich, W.E., R.R. de Asua, J. Coyle, B. Orr, M. Trso. 17 June 1998. A validation study of the shallow slope stability model, SHALSTAB, in forested lands of Northern California. Prepared for Stillwater Ecosystem, Watershed, and Riverine Sciences Berkeley, CA.