Impacts of wildfire on debris-flow hazards in Oregon’s western Cascade Range

In this talk, we'll summarize what we have learned about postfire debris-flow hazards in Oregon's western Cascade Range.
In the steep and mountainous environment of western Oregon, debris flows pose a significant threat to property, infrastructure, and life. Wildfire increases the susceptibility of steep slopes to debris flow. The USGS estimates postfire debris-flow likelihood and triggering rainfall thresholds using the M1 postfire debris-flow likelihood model.
This model was calibrated with data from southern California, where postfire debris flows typically initiate from distributed runoff and erosion. Due to a lack of available data, the likelihood model has not been tested in western Oregon, or in locations where postfire debris flows initiate via other mechanisms (e.g., shallow landslides or in-channel failures). Using repeat field observations and aerial imagery, we developed two new debris-flow inventories within, and adjacent to, the perimeters of five 2020 wildfires in western Oregon: Archie Creek, Holiday Farm, Beachie Creek, Lionshead, and Riverside.
The first inventory focuses on debris flows prior to fires (1995-2020); the second focuses on postfire debris flows (2020-2022). Using these pre- and postfire inventories, we investigate how wildfire alters the initiation and frequency of debris flows. We additionally test the performance of the postfire debris-flow likelihood model.
USGS video: www.usgs.gov/m...