Distinguishing sediment transport mechanisms in debris flow, hyperconcentrated flow, and streamflow

Abstract:

Debris flows, hyperconcentrated flows, and floods can naturally occur in the mountainous channels and may induce significant dangers to infrastructures and livelihoods on their path. The complexity of flow processes makes it difficult to distinguish them and understand their physical characteristics. Here we combined field observation for debris flows at the Jiangjia Ravine, China, with a dataset that includes streamflows, hyperconcentrated flows, and debris flows from different regions worldwide (China, United States, Switzerland, Italy, Mexico, Indonesia and Colombia) to study the fundamental difference between them. We then used a systematic set of dimensionless groups (q^*; q_s^*; N_Bag; N_Sav; N_fric; N_Rey; N_m) for data processing to assess the general physical mechanisms. Our results show that sediment transport mechanisms vary significantly in different flow types: fluid turbulence and viscous drag force dominate in streamflows and hyperconcentrated flows, but grain collisions control the dynamics of debris flows. Using Support Vector Machines (SVMs), we proposed two boundaries to distinguish debris flow, hyperconcentrated flow, and streamflow in a phase diagram with dimensionless flow discharge and solid discharge. Finally, we applied the proposed boundaries and found that lahars, composed of a slurry of pyroclastic material and rocky debris from a volcano, are mostly transitional flow between hyperconcentrated flow and debris flow.