Sedimentary rates driven by laboratory lock-exchange turbidity currents flowing over gravel and vegetated beds

Turbidity currents are key agents in sediment transport and bed reshaping, influencing geological records, organic carbon fluxes and pollutant transport. While extensively studied over smooth beds, their interaction with rough beds, such as gravel or vegetated substrates, remains poorly understood. Existing studies suggest bed roughness slows flow and alters deposition, but a comprehensive understanding of how grain-size affects current dynamics and sedimentation patterns is lacking. In this study, we addressed key knowledge gaps on the influence of bed roughness and vegetation on turbidity current dynamics and sedimentation by conducting a comprehensive series of lock-exchange flume experiments. Six bed grain-sizes, multiple flow depths, and sediment concentrations were tested and compared with previous experiments on simulated and real vegetation. Results demonstrate that increasing bed roughness significantly reduces turbidity current velocity and enhances near-source sediment deposition. Greater deposits close to the source result in more non-uniform sediment distribution, with less deposition along the gravel bed. Conversely, smooth beds facilitate longer sediment transport and more uniform deposition. Flow regimes were observed to shift from inertial to drag-dominated as a function of bed configuration, with vegetated and coarse-grained beds inducing comparable hydraulic resistance. Sediment deposition patterns were closely linked to bed roughness and influenced clogging processes via unimpeded static percolation. Overall, the findings reveal a strong feedback between substrate morphology and turbidity current behaviour, with important implications for turbidite formation, sedimentary structure development, and hyporheic exchange dynamics.