Sediment transport in turbidity currents: internal structure and flow energetics

This project investigates the material-transport dynamics of natural-scale turbidity currents. The sediment-laden gravity-driven flows are a dominant control on the sediment transport between continents and deep marine systems. The resulting sediment architectures are expected to record the previous millennia of environmental events such as tectonic events or relative sea-level changes. In spite of their importance as paleo-environmental record, and a key geohazad, their dynamics are still poorly constrained due to the limitations of observation, computational costs, and the destructive nature of turbidity currents. Indeed, key knowledge gaps include the internal structures and flow energetics of turbidity currents, which dictate the dynamics and thus sediment transport mechanics and deposits of such flows.Data compilation and laboratory-scale experiments of turbidity currents, on which this work is based, have been conducted. The velocity and density profiles of pseudo-steady flows were gathered from laboratory experiments and natural-scale events to investigate the key factors that control the vertical flow structure. Laboratory experiments were designed to fill the gaps between the compiled data from the past literature and provide high-resolution observations.The statistical analysis of pseudo-steady turbidity currents’ compiled velocity and concentration profiles provides valuable insights into the material-transport dynamics. The empirical models for predicting flow velocity and concentration profile of turbidity currents are developed using machine learning techniques. Implications of the analysis and the developed models are that the internal structures of turbidity currents enhance their material-transport efficiency as the flow is decelerated.The theoretical analysis of the energetics of turbidity currents revealed that the previous fluvial-based energetics theory significantly underestimated the sediment-load capacity of turbidity currents. The direct implication is that the traditional micro-scale turbulent energy production cannot explain the energetics ofgravity currents.To conclude, the findings of this thesis contribute to a better understanding of the material-transport dynamics of turbidity currents, identifying useful research areas for future works.