Hydrodynamics of Meander Bends in Intertidal Mudflats: a Field Study
From the Macrotidal Yangkou Coast, China
Luca Carniello
Department of Civil, Environmental, and Architectural Engineering, University of Padova, Department of Civil, Environmental, and Architectural Engineering, University of Padova, Department of Civil, Environmental, and Architectural Engineering, University of Padova
Author ProfileAbstract
Meandering channels are ubiquitous features in intertidal mudflats and
play a key role in the eco-morphosedimentary evolution of such
landscapes. However, the hydrodynamics and morphodynamic evolution of
these channels are poorly known, and direct flow measurements are
virtually nonexistent to date. Here, we present new hydroacoustic data
collected synchronously at different sites along a mudflat meander
located in the macrotidal Yangkou tidal flat (Jiangsu, China) over an
8-day period. The studied bend exhibits an overall dominance of flood
flows, with velocity surges of about 0.8 m/s occurring immediately below
the bankfull stage during both ebb and flood tides. Unlike salt-marsh
channels, velocities attain nearly-constant, sustained values as long as
tidal flows remain confined within the channel, and reduce significantly
during overbank stages. In contrast, curvature-induced cross-sectional
flows are more pronounced during overbank stages. Thus, a phase lag
exists between streamwise and cross-stream velocity maxima, which limits
the transfer of secondary flows and likely hinders the formation of
curvature-induced helical flows along the entire meander length. Our
results support earlier suggestions that the morphodynamics of
intertidal mudflat meanders does not strongly depend on
curvature-induced helical flows, and is most likely driven by high
velocities and sustains seepage flows at late-ebb stages, as well as by
other non-tidal processes such as waves and intense rainfall events. By
unraveling complex flow structures and intertwined morphodynamic
processes, our results provide the first step toward a better
understanding of intertidal mudflat meanders, with relevant implications
for their planform characteristics and dynamic evolution.