Non-Equilibrium Suspended Sediment Transport on the Intertidal Flats of Jiangsu Coast, China

Accurate modelling of instantaneous sediment transport processes in coastal environments has been a great challenge for many decades. One of the difficulties comes from the existence of time lag between flow and sediment transport, termed as "the non-equilibrium transport effect". To better understand and simulate the sediment transport processes, field observations were conducted on the middle intertidal flats of Jiangsu coast. Water depths, current velocity profiles, wave parameters, stratified suspended sediment concentrations (SSC), as well as grain sizes of both suspended sediment and bed sediment were measured. Results show that suspended sediment has an average grain size of 11.2 pm, the percentage of cohesive suspended sediment can be up to 97%. The bed load has an average grain size of 40 pm, the percentage of cohesive sediment is only 76%. The measured maximum SSC occurs at the beginning and the end of each tidal cycle. It is well-mixed during flood and ebb peak, but stratified during slack period. The vertical equilibrium SSC profiles were calculated based on the advection-diffusion theory. Calculated equilibrium SSC is well mixed during whole tidal cycle and is controlled by the local hydrodynamics. The difference between calculated equilibrium SSC and real ones indicates that the contribution of advection is dominant. Thus the non-equilibrium suspended sediment transport processes should be taken into account for intertidal flat evolution.