DEBRIS FLOW MAPS FOR WESTERN OREGON

A valuable map tool for evaluating rapidly moving landslides in western Oregon is being developed. The mapping project was initiated by Oregon Senate Bill 12, which outlined cooperative, proactive policies to address life-threatening landslides. The development of the hazard maps has been a collaborative effort involving the State Departments of Geology, Forestry, Land Conservation and Development, the Earth Systems Institute, and many landslide researchers and practitioners throughout the state and beyond.

The steps used to create the maps have included iterative combinations of GIS modeling, field evaluations, and landslide inventory comparisons. The primary objective of the iterative process has been to utilize each possible source of information to overcome the limitations inherent in each individual method of evaluation.

The final maps will be based on a newly-developed and rigorous GIS program that covers the full range of debris flow hazards, including initiation, transport, and deposition. The output map will cover all of western Oregon and be released in flexible GIS formats later this year. The intended scale is 1:24,000 (based on USGS 10-meter DEM grid-spacing), and the range of hazards will be separated into zones from low to extreme relative hazard. A report accompanying the maps will provide background on debris flows, details on the mapping methodology, and highlight important limitations for use of the maps. The results are showing good agreement with historic slide locations thus far, and the final product is expected to be quite valuable for a wide range of users.