DEVELOPMENT OF A LIDAR-DERIVED SHALLOW LANDSLIDE SCREENING TOOL FOR FOREST MANAGEMENT

Shallow landslides are a significant source of sediment on managed forestlands in the Pacific Northwest. The Washington State Department of Natural Resources currently utilizes the spatially distributed slope stability model SMORPH as a screening tool to identify areas of potential shallow landsliding in areas where timber harvesting and road construction activities are proposed. SMORPH employs a 10-m digital elevation model (DEM) and tends to over-predict areas of potential shallow landsliding. Additionally, the resolution of the 10-m DEM grid is not capable of detecting subtle landforms such as colluvium-filled hollows and small inner gorges that are often source areas for shallow landslides. In contrast, 2-m Light Detection and Ranging (LiDAR) DEMs can be used in the GIS environment to reliably identify shallow landslide source areas by calculating plan curvature and slope angle. Plan curvature, the measure of the radius of the ground surface in a horizontal plane, is a surrogate for slope convergence. Combining plan curvature and slope angle data sets shows great promise as a means of remotely identifying colluvium-filled hollows and inner gorges. The goal is to produce a screening tool that allows natural resource managers to identify these landforms during the early stages of the forest management planning process. The screening tool has the potential to significantly decrease the occurrence of “false negatives” and, as a result, the rate of shallow landsliding associated with forest management activities.