THE RELATIONSHIP BETWEEN SCOURED CHANNEL WIDTH AND DRAINAGE AREA FOR RUNOFF- AND LANDSLIDE-GENERATED DEBRIS FLOWS

Studies of fluvial systems around the world have demonstrated that river channel width increases with drainage area according to a power law with surprisingly little variability in parameter values. While it is understood that debris flows pose hazards to downslope communities and impact landscape evolution, little work has been done to develop a similar scaling relationship for the uppermost reaches of valley networks where debris flows are thought to be important. Using high-resolution satellite imagery, aerial imagery, and lidar differencing, we measured scoured channel widths of runoff-generated debris flows at four recently burned areas across California, as well as from landslide-generated debris flows in Oregon and North Carolina. When plotting scoured channel width versus upstream drainage area for all study sites with runoff-generated debris flows, we observe a power law relationship with an exponent similar to that seen in fluvial systems. However, while there is variation between study sites, the multiplicative constant is notably larger than that of fluvial systems, indicating that debris flows scour channels that are systematically wider than their fluvial counterparts. For debris flows initiated from landslides, scoured channel width does increase with drainage area, but at slower rate than that seen in runoff-generated debris flows. Our results provide a new empirical description of a key aspect of upper-network channel geometry that will be useful for modeling event-scale hazards and quantitative landscape evolution.