LANDSLIDE MAPPING WITH LIDAR IN THE WEST HILLS OF PORTLAND, OR

Landslides present a substantial risk to the residents and businesses in the West Hills of Portland, Oregon. The area is prone to landslides because of steep slopes with weak geology of loess-overlaying basalts coupled with the high levels of precipitation that occurs during the winter months. The area is densely vegetated, so landslide indicators have been hard to identify, making landslide mapping problematic. However, LIDAR (light detection and ranging) can be used, as its ability to penetrate the ground through vegetation provides a more detailed view of the ground morphology. The goal of this project is to identify a procedure for using LIDAR to map landslides and evaluate the accuracy of the findings. The LIDAR data was acquired by Portland State University from the Puget Sound LIDAR Consortium (PSLC) which flew the West Hills area in winter of 2004. The project area is contained in the Northeast corner of the West Hills, where 55 landslides were identified from the LIDAR data. Based on road accessibility, we chose 12 to field check, and of these 11 were confirmed during ground reconnaissance. Depositional features were the most recognizable features on the LIDAR. Landslides that had been repaired with gabion walls and buttresses were interpreted as scarps on the LIDAR. Houses and human-made structures created slope disturbances in the data that made it hard to identify landslides in populated areas. Moderate volume slides (~953 cu. yards) were the most evident slides on the LIDAR. Based on these initial findings LIDAR proves to be a valuable tool for identifying landslides in highly vegetated areas.