Variations of suspended sediment concentrations and transport in response to a storm and its dynamic mechanism - A study case of Nanhui tidal flat of the Yangtze River Delta

Suspended sediment concentration (SSC) is an important environmental index of muddy coasts. To understand the response of the suspended sediment concentration and suspended sediment transport on tidal flat to a certain storm event, we carried out in situ measurements of water depth, wave height, near-bed velocity and SSC profiles in high resolution on an intertidal mudflat of Nanhui Spit, which is on the delta front of the Yangtze River, China. The measurements last for 9 tidal cycles, covering pre-, intra-and post-"Fung-wong" typhoon. The results show that: (1) mean and max wave heights, bed shear stress , SSC and suspended sediment transport rate during storm condition were several times higher than those in calm weather; (2) in storm condition, a fluid mud layer (SSC >10 g/L) in the thickness of tens of centimeters developed during slack water at high tides, resulting from settling of suspended sediment. We conclude that the drastic variation of suspended sediment concentration in muddy coastal areas is caused by enhanced energy in the water column caused by storm, leading to increasing combined wave-current bed shear stress, which leads to bed sediment resuspension.