713 / 2024-09-19 09:55:03

Hydroacoustic Measurements Highlight Channel Impact on Macrotidal Mudflat Morphodynamics

Intertidal mudflats; Tidal Channels; Tidal asymmetry; Sediment transport; Hydroacoustgic

Unvegetated tidal mudflats are typically dissected by networks of channels that arguably exert a prominent role in the ecomorphodynamic evolution of these environments. However, the intricate processes of tidal flows propagating through tidal channels and across mudflat platforms remain inadequately understood, particularly concerning the localized hydrodynamics occurring at the interface between channels and mudflats. In this study, we report the results of in-situ hydroacoustic measurements carried out in the macrotidal Yangkou tidal flat (Jiangsu coast, China), where we synchronously assessed the three-dimensional flow fields and suspended sediment concentrations at three distinct sites—namely, the channel thalweg, channel bank, and distant mudflat platform—over the course of 8 semidiurnal tidal cycles. Whereas mudflat areas typically exhibit an overall flood dominance, tidal channels feature ebb-dominated flows and higher concentrations of suspended sediments. In contrast to vegetated tidal settings, where in-channel flow velocities are systematically higher than across the frictionally dominated intertidal plains, hydrodynamics of bare mudflat systems is controlled by flow inertia and sheet-flow conditions whenever water levels exceed the channel bankfull threshold. At bankfull, pronounced changes in tidal flow orientation are observed, which critically enhance both cross-sectional velocities within the channel and bottom shear stress near channel banks. Our results support earlier suggestions that the hydrodynamics of bare mudflat systems are strongly influenced by the interactions between in-channel and overbank flows. Therefore, we propose that future modeling works related to accurately reproducing morphodynamic processes occurring in unvegetated coastal environments should take into account the localized three-dimensional flow interactions near the channel-flat interface.