Particle motion on burned and vegetated hillslopes.

Area of Science:

• Geomorphology
• Environmental Science
• Sediment Transport Dynamics

Background:

• Wildfires in the western US are increasing, leading to significant geomorphic changes.
• Existing sediment transport models fail to capture rapid sediment movement post-wildfire, crucial for debris flow prediction.
• Nonlocal, particle-based models show promise but require empirical data for landscape application.

Purpose of the Study:

• Validate a generalized Lomax model for particle travel distance distributions using field data.
• Investigate the role of surface roughness in post-wildfire sediment transport.
• Develop a framework linking particle motion statistics to surface characteristics.

Main Methods:

• Conducted field experiments to collect data on particle travel distances.
• Validated a generalized Lomax model to describe particle travel distance distributions.
• Measured surface roughness of burned and vegetated slopes.

Main Results:

• Burned slopes are measurably smoother than vegetated slopes.
• Smoother surfaces lead to reduced particle disentrainment and increased runaway motion.
• The Lomax model successfully describes the transition to heavy-tailed travel distances with increasing particle size and decreasing slope roughness.

Conclusions:

• Surface roughness is a critical factor controlling sediment transport on steep slopes, especially after wildfires.
• Smoother post-wildfire surfaces can lead to preferential delivery of coarse sediment to channels, initiating debris flows.
• The validated Lomax model advances nonlocal sediment transport theory and provides insights into hillslope mechanics.