LANDSLIDE HAZARD AND RISK EVALUATION OF THE US HIGHWAY 30 CORRIDOR, CLATSOP AND COLUMBIA COUNTIES, OREGON

Cutting through the northern Oregon Coast Range, the US Highway 30 Corridor is prone to slope instability. In December, 2007, two storms caused significant damage to 10 counties in western Oregon and several landslides impacted the Highway 30 corridor, causing lengthy road closures. Disaster funding provided by FEMA was used to perform landslide hazard evaluation along this corridor in Clatsop and Columbia Counties. The primary purpose of this project was to provide detailed information about the landslide hazards and the assets at risk. The four main objectives were to make a detailed landslide inventory, to create shallow and deep landslide susceptibility maps, to compile and/or create a database of assets, and to perform exposure and a Hazus-MH based risk analysis. Lidar-derived datasets were used to map both the landslide hazards and asset data, including roads, transmission corridors, and buildings. The completed landslide inventory has a total of 581 landslides mapped within the 90 mi² study area. Two-hundred and ninety-eight deposits were classified as deep and 140 as shallow. One-hundred and fifty debris flow fans were mapped, accounting for 25% of all mapped deposits. The completed susceptibility maps show that this area is susceptible to both shallow and deep landslides. Results of the shallow susceptibility map show that the high susceptibility zone covers 15% and the moderate covers 32%. Results of the deep susceptibility map are that the high susceptibility zone covers 28% and the moderate covers 15%. The exposure and Hazus-MH based risk analysis estimated potential losses and damages from landslide hazards. The results of these analyses showed that residential buildings are the most exposed asset. The primary infrastructure, mainly the highways and electric corridors, are also at-risk. Sixty-eight percent of the electric corridor and 57% of the electric towers are currently routed on landslide deposits making the entire system vulnerable if a failure was to occur. The conclusions from the risk analysis are important since they allow planners and first responders to understand where resources should be directed. The results of the study show that lidar data can be used for a variety of applications including hazard and susceptibility mapping, asset collection, and emergency management.