This coverage is a predictive data layer of shallow-rapid slope stability using one or more calibrated GIS-based models. This grid covers all forested watersheds of western Washington State. This data layer is an anticipated outcome of the Forestry Module negotiations as outlined in the Forest and Fish Report (1999) and legislated in the Engrossed Substitute House Bill 2091 (1999).
The purpose of this dataset is to be a screen for determining shallow-rapid landslide potential. It is intended to be used for pre-classification screeening of forest practices applications and screening for slope stability concerns on managed timberlands.
This data is derived from calibrated algorithms (models) that use DEMs to generate slope and curvature information. The models used are SMORPH and SHALSTAB. The stated resolution of the data is tied to the resolution of the DEM available in the area. Additionally, other information, such as landslide inventories, soils, mass wasting units, geology, and precipitation amounts are used in the calibration of these models to a specific area. These landslide data were collected at a variety of scales, over a large period of years. The horizontal accuracy of the grid coverage is dependent on the resolution of the Digital Elevation Model (DEM) from which it was derived. Better information is obtained with higher resolution DEMs. In those areas where a 10 meter DEM was available, the accuracy is +/- 35 feet. At present, 10 meter resolution data are available for most of western Washington. As better DEMs become available, the model may be rerun in those areas and will update the existing coverage.
1111 Washington St. S.E.
P.O. Box 47012
Forest Practices Division
modeled shallow rapid slope stability: tests (Shaw & Vaugeois, 1999) show that 93% of shallow rapid type landslides occur in areas modeled with a high (value = 3) probability of instability. no model accurately predicts where deep seated landslides are going to occur
data is based on USGS 10 meter dems. as such, it has a horizontal accuracy of 40 feet
data is based on USGS 10 meter dems. as such, it has a vertical accuracy of 50 feet
Internal feature number.
Modeled probability of slope instability
Low expected probability of slope instability
Moderate expected probability of slope instability
High expected probability of slope instability