Interpreting grain-size trends associated with bedload transport on the intertidal flats at Dafeng, central Jiangsu coast

Abstract

A MIDAS-400 customized data acquisition system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cycles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which indicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30–150 kg·m-1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2 × 104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topography of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the calculated bedload transport, and the grain-size trend vectors for the spring tide are larger than those for the neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.