Deposition morphology in large-scale laboratory stony debris flows

Abstract

Debris flows affect vulnerable areas by unloading their destructive impact and depositing sediments in debris-flow lobes in the runout area. The debris flow deposition morphology characteristically displays a complex process and is of particular interest for hazard mapping, economic activities planning, construction of civil structures, and settlements in vulnerable areas. This laboratory study is based on large-scale stony debris flow experiments, focusing on the runout distance, mobility, and inundated area. The experiments were conducted under different initial and boundary conditions like particle size, solid volume fraction, and basal roughness. Our experimental results reveal that runout distance and lobe shape change dramatically under different solid volume fractions and are highly dependent on basal roughness. On the contrary, the particle size has a marginal effect on deposit morphology. The newly introduced dimensionless runout capacity allows the evaluation of the momentum transfer of the debris flows to the end of the flume into a runout distance. The experimental results show that the runout capacity is inversely proportional to the Froude number of the stony debris flow. We deduce a relationship for the runout distance from this concept, which reveals that flow velocity contributed to the runout distance on a par with the flow depth. A weak velocity can be counterbalanced by an increased front depth to achieve a similar runout distance. Furthermore, we evaluate flow mobility, deposited volume, as well as the inundated area, and compare our results with other experimental and field data. The presented data match existing hypermobility models in-between small-scale laboratory and field-scale events. Consequently, this study complements missing data to the previous dataset of runout distance, elevation difference, mobility, and inundated area, contributing to better understand debris flow dynamics.