MCA: Multi-scale considerations of climatic signatures on debris flows and alluvial fans

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Worldwide, communities are experiencing historic changes in storm frequencies and magnitudes that destroy homes and lives. One of the most devastating effects of frequent and/or intense storms is the way in which associated rainfall can destabilized earthen materials and liquefy the very foundation of natural and built infrastructure. Under such conditions, these materials can flow downslope, subsequently entrain additional materials, and increase in dramatically size. Their growth rate and evolution can be alarming as they add mud, rocks, and even meter-sized boulders to become massive rivers of debris flows. These debris flows may abruptly change direction as they flow, and even create their own channel walls, or levees, thus maintaining a high speed as they “super-elevate” relative to their surroundings. The unpredictability of the timing, directions, and magnitudes of these flows can add to their devastation as evident, for example, in the deaths and destruction of the 2018 debris flows in Montecito County, California. For better hazard mitigation scientists need to understand how details such as local materials, moisture, and local climate conditions dictate these behaviors. This project involves research using data from previous flows and their deposits, physical experiments, and computational simulations to help us better anticipate and predict behaviors of likely future flows under varying climatic conditions. This project combines field work, laboratory experiments, granular physics theory, and computational modeling to understand combined effects climate conditions external to specific debris flow events and flow physics embedded in those conditions. This will involve a new framework relating sediment-fluid specifics and boundary conditions as it relates to debris flow behaviors under varying conditions. Experimental work will include: (1) controlled slump-slurry experiments with simplistic basal conditions; (2) erosional channelized experiments, and (3) alluvial fan experiments. Computational work will build on sediment-fluid rheology embedded in a multi-phase discrete-element-method (DEM) model. Field work will include debris flow deposits at sites selected for their distinct climatic and physics-based signals to help identify signals from each: (1) on periglacial deposits in the Richardson Mountains (changing sediment supply with climate changes) with collaborative partner Professor Marisa Palucis of Dartmouth College; (2) on wetter warmer deposits along the Laonong River Valley, Taiwan (high sediment supplies, moist conditions, distinct catchment lithologies); (3) in drier hotter deposits in Owens Valley that contain signatures of distinct climate and lithology differences. Planned work with indigenous communities will contribute to the science with their active involvement and community records. This award is jointly funded by the Geomorphology and Land-use Dynamics Program and the Particulate and Multiphase Processes Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.