Experiments on debris-flow initiation from runoff

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In steep mountain terrain, debris flows can dominate sediment transport and bedrock channel incision, and drive landscape change. Although debris flows are often generated from landslides that fluidize upon failure, there is increasing evidence for the importance of debris flows generated from runoff and overland flow, especially in steep alpine landscapes and following wildfire where dry, loose sediment collects in channels and chutes prior to failure. The initiation mechanisms for debris-flow generation from runoff are not well understood. To address this, a series of experiments that will form the baseline to test and develop theory for debris-flow initiation in mountain channels will be conducted. The experiments will take place in a new state-of-the-art facility at the California Institute of Technology designed specifically to investigate sediment transport processes on very steep slopes. The proposed work will test four hypotheses concerning the onset of debris flows over a wide range of channel slopes and sediment sizes. The expected outcome from this work is new insight into the underlying mechanics that control debris-flow initiation from within channels, and the development of predictive models that link debris flow initiation to topography, such as channel slope, and environmental perturbations, such as floods and wildfires. Debris flows are one of the most dangerous and costly hazards of mountainous terrain worldwide. This work will improve our understanding of debris flow initiation and aid in our ability to forecast hazards and develop better land-use strategies. The results will have applications for the Los Angeles area where runoff-generated debris flows are common following wildfire, in cases resulting in loss of life and property damage. These results will be made available to the public through journal publications and to the scientific teaching community through the GeomorphLectures Wiki, designed to be a resource for young educators. Educational and outreach activities include training scientists at the undergraduate, PhD and postdoctoral levels, and volunteer classroom presentations and laboratory tours through collaborations with the Pasadena Unified School District, CA.