CSDMS 2015 annual meeting poster LukeMcGuire
High resolution modeling of overland flow and sediment transport following wildfire
Jason Kean, USGS Golden, Colorado, United States.
Dennis Staley, USGS Golden, Colorado, United States.
Francis Rengers, USGS Golden, Colorado, United States.
Mountain watersheds that have been recently burned by wildfire often experience greater amounts of runoff, increased rates of sediment transport, and a significantly higher risk for debris flow generation relative to similar unburned areas. Previous work suggests that the redistribution of sediment within hillslope-channel systems by overland flow may play a key role in producing runoff-initiated debris flows, but the physical mechanisms by which water-dominated flows transition to a debris-flows are not well understood. In order to examine the connections between runoff, sediment transport, and debris flow initiation, we developed a numerical model that couples overland flow with sediment transport processes. We applied the model to study erosion from a single rainfall event that produced numerous debris flows within a small, recently burned drainage basin in the San Gabriel Mountains, CA. Input data for the numerical model was constrained by rain gauges, stage measurements at the basin outlet, soil moisture sensors, and soil particle size distribution analyses. Pre- and post-storm basin topography was obtained using high-resolution terrestrial laser scanner data. Numerical model results are quantitatively compared to post-event terrestrial laser scanner data and stage measurements recorded during the event. Our preliminary results show that the magnitude and spatial pattern of model-predicted erosion/deposition compare favorably with the measured topographic change throughout the study area. Additionally, the model predictions suggest that rain splash induced sediment transport was the dominant form of erosion throughout much of the watershed. Based on numerical model predictions, the failure of sediment piles that were generated by preferential deposition within the channel system likely contributed to repeated debris flow initiation throughout the event.
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