LANDSLIDE HAZARD AND RISK STUDY IN THE CITIES OF EUGENE-SPRINGFIELD, CENTRAL LANE COUNTY, OREGON

The Eugene-Springfield landslide study was undertaken by the Oregon Department of Geology and Mineral Industries (DOGAMI) to create a detailed landslide inventory, landslide susceptibility models and risk assessment for city planners, emergency managers and property owners throughout central Lane County. Lane County has experienced hundreds of landslides in the past 50 years, however no landslide hazard study had been conducted in the most populous portion of the county: the Eugene-Springfield metro area. The cities of Eugene and Springfield are presently experiencing rapid growth and as this is the second most populated metropolitan area in Oregon, understanding landslide hazards and risk is important for citizens and those. The study area is 230 mi² (595 km²) centered on the Eugene-Springfield and Coburg urban growth boundaries with a buffer to include some of the surrounding populated areas of Lane County. For this study we used the landslide inventory protocols established by DOGAMI for 1) mapping existing landslide deposits (Burns and Madin, 2009), 2) modeling deep and shallow landslide susceptibility in order to demonstrate where landslides may occur in the future (Burns and Mickelson, 2016; Burns et al., 2012), and 3) assessing landslide risk through exposure analysis and using the FEMA Hazus-MH model. Our results indicate the following: over 700 landslides have been identified (including historic landslide points), covering ~6% of the total study area; deep-seated landslides pose the greatest risk with ~$476 M worth of buildings located on them and ~4,500 residents (~2% of local population). Compared with other studies in Oregon, these results suggest that the study area is exposed to moderate hazard and risk, with the largest risk associated with exposure of existing structures to deep landslides. These results are expected to be incorporated into new land use planning efforts that are being developed by the communities of Eugene and Springfield.