| dc.description.abstract | Debris flows are mixtures of water and sediment that flow rapidly down a slope due to gravity
force (Iverson, 1997; Takahashi, 2014). They are destructive to property and often fatal, a single
event potentially killing thousands of people (Iverson, 1997 and 2011; Haas and Woerkom, 2016).
The catastrophe is worsened when the volume of debris flow increases by bed entrainment
caused by the interaction between flowing particles and bed particles (Takahashi, 1981; Pierson
et al., 1990; Haas and Woerkom, 2016). Bed entrainment may result from impact forces and
basal-shear forces and are mainly driven by the debris flow composition. However, it has long
been unclear whether impact or basal-shear forces bear more responsibility in the erosion
process, or it is a combination of both forces. This study shows that impact forces play a critical
role in the occurrence of debris flows, and thereby in the erosion of bed material. Geophone
capable of quantifying impact forces, and load cell capable of measuring flow weight in dry
granular flows (representing debris flows) were used on laboratory-scale simulations. Impact
forces were strongly controlled by debris flow composition (i.e. grain-size distribution) and
moderately by flow properties (i.e. flow depth, flow weight, flow velocity). Thus, impact forces
significantly affect debris-flow erosion, mainly by progressive scour rather than mass failure.
Impact forces possibly result in bed entrainment, which is related to increasing debris-flow
volume. A better understanding of how the debris-flow volume increases will help minimise the
negative impacts of debris flows as well as strengthen hazard mitigation strategies. | |
