Waves and vegetation shape near-bed turbulent kinetic energy in coastal marshes

Turbulence plays a key role in sediment mobilization in intertidal zones. Prior laboratory studies have explored turbulent kinetic energy (TKE) under the influence of waves and currents, but the extent to which an idealized laboratory setting translates to natural environments remains unclear. Key questions persist in application to field conditions, including the relative contributions of waves and currents to TKE, and the impact of vegetation flexibility. To address these gaps, this study made field observations of waves, currents, and TKE across the intertidal zone of Chongming Dongtan Wetland in the Yangtze Estuary. Hydrodynamic conditions differed between the mudflat and salt marsh, with the magnitude of current velocity exceeding wave velocity on the mud flat, but the reverse being true within the marsh. As a result of this shift, on the mudflat, TKE was mainly generated by currents, and in the marsh, TKE was mainly generated by waves. Additionally, TKE on the mudflat was associated with bed shear production, but within the salt marsh was mainly produced through the interaction between waves and vegetation. Finally, the influence of vegetation flexibility on vegetation-generated TKE was described by a new model that incorporated the plant Cauchy number ((Formula presented.)) and vegetation-to-wave-excursion length ratio ((Formula presented.)) as descriptors for vegetation motion. The inclusion of vegetation motion significantly improved the prediction of TKE within the salt marsh canopy, which can contribute to more accurate coastal modeling, improving coastal zone management and research.