Characterization of Stream, Hyperconcentrated and Debris Flows from Seismic Signals: Insights into Sediment Transport Mechanisms and Flow Dynamics

Sediments in steep channels can be mobilized to form stream flows, hyperconcentrated flows and debris flows, which can cause damage to downstream communities. However, the understanding of the sediment-transport mechanisms that control these processes remains incomplete due to the lack of effective monitoring methods. In this study, we utilize seismic data captured during these sediment-laden flows through field experiments and in situ monitoring to offer insights into flow mechanics and sediment transport mechanisms. Results show that sediment transport in stream flows and hyperconcentrated flows is primarily supported by viscous shear and turbulent stresses, whereas grain collisional stresses play a significant role in debris-flow dynamics. By characterizing impact rates, basal impulses and flow discharge, seismic monitoring can reveal the internal flow dynamics and bulk flow characteristics as well as the characteristics of sediment transport. Increasing solid concentrations can elicit positive nonlinearities in the frequency-based scaling relationships between seismic power and hydrographs, indicating transitions in the seismic signal from turbulence-bedload-dominated to bedload-dominated, and grain collisional-dominated regimes. By introducing the ratio of the real shear stress to the critical shear stress, we refined the phase space for sediment stability. Combining this criterion with the absolute seismic power enables us to establish ground-motion thresholds for distinguishing different flow types. Our results highlight opportunities to use seismic data for the quantitative inversion of these fluvial processes and debris flows as well as early warning strategies. In steep channels, runoff from intense rainfall transports mud and rocks downstream, resulting in the formation of a dynamic mixture of sediment and water. They not only alter the landscape but also present a significant threat to human life. Understanding the mechanisms of sediment initiation and transport is crucial for the accurately predicting and effectively mitigating these processes. In this work, we employ seismic equipment to quantify ground vibrations generated by diverse channel activities, which provide insights into the internal flow dynamics that are difficult to assess via traditional methods. Based on the ground motion caused by the moving solid-liquid mixtures, we classify sediment-laden flows into three types, each exhibiting distinct sediment transport mechanisms. This classification aligns well with the three field experiments and 11 in situ observations as well as previous observations, and can explain the nonlinear relationship between the seismic energy and flow discharges. Our findings demonstrate the potential of seismic monitoring in acquiring precise data on various channel activities as well as providing early warning signals. Seismic observations and analysis reveal distinct sediment-transport mechanisms of stream, hyperconcentrated, and debris flows Scaling seismic power with hydrographs isolates the bedload-generated ground motion and gives insights into the temporal dynamics of bedload We propose a ground-motion-based criterion for distinguishing different sediment-laden flows that aligns well with our monitored data