Sediment Dynamic Process Of Intertidal Flats, Dafeng, Northern Jiangsu, China

The thesis deals with the sediment dynamic processes of intertidal flats at Dafeng, northern Jiangsu, in terms of. sediment grain-size variability, benthic boundary layer properties and suspended sediment concentration profiles, sediment transport rate, on the basis of in situ measurements and laboratory analyses.Grain size distributions of the seabed sediment have marked spatial variations on the intertidal flat, with the sand content decreasing and silt and clay contents increasing from the lower part towards the upper part of the intertidal zone. On the Sueada salsa and Spartina alterniflora flats, materials from settling of suspended sediment are the main source for seabed sediment; hence, the grain size distribution of seabed sediment is determined by the characteristics of suspended sediment. On other parts of the flat, the seabed sediment originates largely from bedload transport.Near the lower part of the fine sandy flat, the tidal current rotates in an anticlockwise manner during the flood phase of the tide, whereas during the ebb the current rotates in a clockwise pattern; the range and rotation during the flood is larger than during the ebb. Ebb duration is longer than flood duration, but the ebb current velocity is stronger than the flood. Net water transport during the ebb is stronger than during the flood; net water transport direction during the flood is parallel to the shoreline, but it is towards the sea during ebb (perpendicular to the shoreline). Such hydrodynamic patterns result from the influences of the presence of tidal creek systems and/or the residual circulation over the intertidal zone. During the entire tidal cycle, there is only one current velocity peak that occurs at the middle ebb, and there is almost no slack water (i.e. zero current velocity) during the high water periods.On the intertidal flat, suspended sediment concentrations (SSCs) vary considerably during the tidal cycle; time averaged SSCs during the flood are higher than during the ebb, with remarked temporal and spatial variations in the SSC and its vertical gradient. Based upon the information on current velocity, SSC and variations of grain size distribution of suspended sediment, there is no intensive resuspension and settling at the measurement station during the survey period. Advection and spatial gradient of SSC is the main reason of CCS changes in the tidal cycle; in this case, the temporal variation in the SSC is a reflection of the spatial variation. Resuspension and settling...