Characteristics of Hydrodynamics and sediment transport on flexible vegetated beds under combined wave-current conditions

Coastal vegetation significantly influences hydrodynamic and sediment transport processes in estuarine and coastal environments. Under the constraints of complex hydrodynamic conditions, the response mechanisms of flow and sediment dynamics under combined wave-current forcing remain poorly understood for flexible vegetation. Flume experiments were conducted to examine the effects of flexible vegetation on hydrodynamic structures under combined wave-current flows and to characterize the vertical distribution patterns of suspended sediment concentration (C_SS). Results indicate that, under combined wave-current flows, the wave-damping effect of flexible vegetation intensifies with increasing wave height and is more pronounced under opposing currents. The interaction between waves and unidirectional currents enhances turbulence, with opposing currents further amplifying turbulence by promoting wave breaking and nonlinear wave-current interactions. Near-bed C_SS increases with time-averaged turbulent kinetic energy, particularly under the synergistic influence of waves, opposing currents, and flexible vegetation, where unique hydrodynamic interactions-including enhanced bed shear stress and turbulent fluctuations-significantly promote bed sediment resuspension.