High-resolution data collection for analysis of sediment dynamic processes associated with combined current-wave action over intertidal flats

Abstract

An MIDAS-400 Customised Data Acquisition System was deployed to obtain current velocity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same time, seawater temperature, conductivity and pressure were measured. Using a data sampling rate of 4 Hz, the high-frequency pressure signals in response to water surface fluctuations were recorded and subsequently transformed into wave parameters. The analytical results show that the apparent bed roughness length has a magnitude close to the height of sand ripples, which is much larger than the grain size diameter. The bottom shear stress associated with current-wave interaction is higher than the tidally-induced stress and intensified turbulent mixing and resuspension. Furthermore, several suspended sediment concentration peaks occurred during a tidal cycle, which can be related to strong turbulence near the bed caused by frontal tidal currents and the enhanced resuspension; advection and extreme weather conditions (e. g. storms and strong winds) also played an important role. Finally, large net suspended sediment fluxes were observed to present when the flood or ebb currents prolonged, i.e. the flow became quasi-unidirectional during a tidal cycle. In general, the MIDAS-400 is a suitable tool for high-resolution data collection for the situations of combined current-wave action over intertidal flats; the data obtained can be used to analyze the processes and mechanisms of material transport.