Intra-tidal sedimentary processes associated with combined wave–current action on an exposed, erosional mudflat, southeastern Yangtze River Delta, China

Numerous deltaic coasts in the world are eroding in response to a decline in sediment supply as a consequence of river damming. Near-bed sediment dynamics are key mechanisms of erosion and deposition. To understand the sediment dynamics of an exposed, erosional mudflat on the delta front of the Yangtze River, China, we measured wave parameters, near-bed current profiles (for 30 layers located up to 50 cm above the seabed), suspended sediment concentration (SSC) profiles (at 6, 15, 35, and 75 cm above the seabed), bed-level changes, and sediment properties, at a low flat site. We found that bed shear stresses induced by waves can be important to sediment dynamics on the mudflat, even in periods of offshore winds. SSC-measurements close to the seabed revealed the presence of a highly dynamic fluid mud layer. At the high tides, SSC at the near-bed 6-cm layer increased to > 8 kg/m3, as a result of sediment deposition from the overlying water column. During the ebb tides, however, an increase in hydrodynamic variations resulted in resuspension, and the near-bed SSC was reduced to