USING LIDAR TO LOCATE AND ATTRIBUTE LANDSLIDES IN OREGON

In order to improve our ability to reduce losses from landslides in Oregon, areas of landslide hazard must first be located. In 2005, DOGAMI began a collaborative landslide research program with the U.S. Geological Survey (USGS) Landslide Hazards Program to improve our ability to identify and understand landslides hazards in Oregon. Before we began the extensive undertaking of accurately mapping the existing landslide deposits throughout Oregon, a pilot project area was selected to compare remote sensing data/images for effectiveness. LiDAR was overwhelming the best remote sensing data for locating landslides in densely vegetated western Oregon. Two key findings of this pilot study related to the use of LiDAR derived images were the considerable increase in the number of landslides identified and the significant improvement in accuracy of the extent of these identified landslides. In order to create consistent landslide inventories for Oregon, we first developed a Protocol for Inventory Mapping of Landslide Deposits from Light Detection and Ranging (LiDAR) Imagery. The protocol outlines the details of visualizing the LiDAR topographic data, mapping the spatial data, and attributing the spatial data. Because of the high resolution topographic data, we were able to map several features at each landslide including: deposit polygon, head scarp and flanks polygon, and head scarp/internal scarps polylines. Once these spatial components were mapped, we were able to take detailed measurements and classify each landslide directly from the LiDAR Digital Elevation Model (DEM) and derived images such as a slope map, elevation contours, and hillshades. This approach has resulted in a very robust landslide inventory which includes data on type and class of movement, relative age, prefailure slope angle, head scarp height, estimated depth to failure surface, direction of movement, area, volume, and confidence of identification. So far, we have completed landslide deposit mapping in several USGS quadrangles in Oregon and have plans to continue through collaboration with federal agencies (e.g. FEMA and USGS), other State agencies (e.g. ODOT and OEM), counties (e.g. Washington and Clackamas), and cities (e.g. Astoria and Silverton).