In Situ Observations of Tide-Dominated Fluid-Mud Generation and Transport on the Central Jiangsu Tidal Flat

Abstract

Fluid mud (FM), a near-bed layer of high suspended sediment concentration, can be transported offshore in the form of gravity flow under the support of waves and currents, playing a critical role in sediment transport and geomorphological evolution. Wave-supported FM has been extensively studied, whereas research on the transport processes of tide-dominated FM remains insufficient. Here, we conducted four field campaigns on the central Jiangsu tidal flats, revealing that FM events occur frequently during winter, spring, and summer. The FM can be transported offshore as a gravity flow, with gravity-driven velocities ranging from 0.01 to 0.06 m s⁻¹. In situ measurements combined with theoretical modeling indicate that FM generation and transport in the central Jiangsu tidal flats are tide-dominated. On a tidal cycle scale, the tide-dominated FM pattern was divided into four stages. Stage I: during flood tides, fine sediment is transported landward from offshore waters to the tidal flat; Stage II: sediment settles from the overlying water column to the bed during flood slack tide, leading to the formation of FM; Stage III: ebb currents facilitate the downslope transport of FM as a gravity flow; Stage IV: ebb currents disperse the sediment within the FM layer, ultimately causing its dissipation. The tide-dominated FM presented in this study significantly differs from wave-supported FM, advancing the understanding of sediment dynamics on tidal flats and underscoring the importance of observing tide-dominated FM in similar coastal environments globally.