Assessing the dynamic influences of slope angle and sediment composition on debris flow behaviour: An experimental approach

Abstract

Debris flows are hazards that can inflict significant infrastructural damage and loss of life. Their rapid and unpredictable onset in isolated locations means that field studies are limited. Laboratory studies are therefore necessary for understanding debris flow behaviour. Despite this, fundamental uncertainties remain. This study set out to explore debris flow dynamics with an assessment of the influence of slope angle and mixture composition on flow behaviour. A novel dual-scale approach was taken, leading to an evaluation of the extent to which two different flumes (2 m and 10 m long) produced comparable results.

Results produced in the two flumes were comparable with each other. They were also comparable with natural flows, and with other experimental studies. There was some evidence of limitations imposed by rigid channel boundaries, particularly in terms of flow development. Channel slope was shown to have a significant influence on flow behaviour, particularly flow velocity; and a clear link was demonstrated between mixture composition and flow behaviour. A three- fold flow classification was developed, with flows being classified as granular, viscous or muddy. The importance of internal morphological interactions was also demonstrated, with relationships varying in strength and direction dependent on flow type. Flow velocity was influenced by both mixture composition and channel slope, while flow morphology was influenced by velocity and internal feedbacks. Conceptual diagrams were produced, demonstrating the influences and feedback dynamics relevant to each flow type.

Although limited by experimental constraints, this study has important implications for understanding the link between local environments and debris flow behaviour. The understanding of debris flows would benefit from further research examining a wider range of slope angles and sediment types, and the
use of larger flumes to further explore the comparability of experimental results.