Collaborative Research: Leveraging seismic data to unravel postfire debris flow dynamics

As the occurrence and severity of wildfires increases across the United States, post-wildfire debris flows and flooding represent an increasing threat to communities. This work focuses on using ground vibrations, produced by debris flows and floods and recorded by seismic instrumentation, to better understand the conditions that trigger flows from within recently burned areas. Using this approach will allow the investigators to monitor a burned area with higher spatial resolution than traditional monitoring equipment, allowing them to record and characterize small-scale changes in flows and the rainfall conditions that trigger them. By monitoring for years following the fire, this work will also allow them to assess how post-wildfire flow hazards evolve with time. This work will improve models of debris flow and flood triggering, which will allow for better assessment of post-wildfire risks to communities downstream from burned areas. Better understanding these hazards and triggering thresholds will lead to improved models of landscape evolution and more-accurate early warning for downstream communities. This project will lead to a better understanding of debris flow processes and will enhance tools to study them using seismic data. Leveraging recent advances in seismic instrumentation will allow the investigators to generate in-situ observations of post-wildfire debris flows using a network of nodal seismometers installed in a recently burned area. Specifically, the investigators will test the following hypotheses: a) debris flow initiation locations will migrate downstream over time as the landscape recovers, b) the timing and location of debris-flow initiation can be predicted using a slope-dependent dimensionless discharge threshold, and c) debris flow surge magnitude and frequency are influenced by drainage area, rainfall intensity, and sediment supply. Using data from ~100 seismic instruments, validated with additional instrumentation, the team will produce a comprehensive catalog of post-wildfire debris flows within the study area, including the location and timing of initiation, velocity, and changes in grain size as they move downslope. These data, which will provide a more spatially and temporally complete picture of the lifecycle of post-wildfire debris flows relative to traditional monitoring methods, will enable the investigators to better understand the behavior of these flows. Results will advance fundamental understandings of debris flow processes and the ability to extract information about environmental phenomena from seismic data. 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.