Wednesday, December 6th, 2017

Wednesday Seminar

4:10 PM, 55 Roessler
Tea and cookies at 3:45 in the aviary - (2110 EPS)

“Monitoring and modeling post-wildfire debris-flow dynamics”

      – by Dr. Jason Kean, USGS

Debris flows often occur in burned steeplands throughout the western U.S. The size and destructive potential of debris flows presents a major hazard that can last several years after the fire. Fire-related debris-flow erosion can also be an important control on long-term rates of channel incision into bedrock, especially in landscapes with high fire frequency like much of California. I will present an overview of USGS research on post-fire debris-flow processes that are relevant to assessing hazards and understanding long-term geomorphic change. A key part of this research involves establishing monitoring sites in recently burned areas to “catch” debris flows in action. Monitoring includes use of video cameras, geophones, and laser distance meters to quantify flow depth and velocity; rainfall and soil moisture observations to capture triggering conditions; and high resolution measurements of topographic change to document hillslope and channel erosion. I will present highlights of recorded debris-flow events from California and Colorado. I will also describe how we use this data to develop and test (1) physically based models of debris-flow initiation and mobility and (2) more simple empirical models designed for rapid hazard assessment and defining rainfall thresholds for early warning.

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