Sediment transport provides a critical bridge between hydrodynamics and morphodynamics. Sediment transport behaviour has obvious impacts on morphodynamic development. Long-term morphodynamic modelling enables examination of large scale morphological patterns, such as channel-shoal patterns in estuaries and deltaic channel structures. Non-cohesive sand is mostly used as the material in shaping morphology. However, most of estuaries and deltas in nature are partly or fully dominated by cohesive sediment or mud. There are researches on sand-mud interactions and their implications on total sediment transport (van Ledden, 2003). It is increasingly aware that adding mud to the system can make a big differences on the large scale morphodynamic development behaviour (Edmond and Slinger, 2009; Gelynese et al., 2010; Caldwel and Edmond, 2014). However mud transport is notoriously difficult to be defined properly in the model given the combined sensitivity to a few fundamental parameters (Partheniades, 1965; Mehta, 2014). It is thus not clearly known how mud have controls on development of large scale morphodynamics and the sensitivity to the mud property. @en

The flocculation process and modelling of suspended sediment transport in estuarine regions is a hot topic in estuarine science[Winterwerp, 1999]. The flocculation is greatly influenced by biochemical parameters[De Lucas Pardo, 2014]. In this paper, we analyse the impact of algae on the processes of flocculation in the Yangtze Estuary, and we identify the mechanisms which are responsible for their changes. The amount of algae (phytoplankton biomass) is linked to the chlorophyll α concentration which we measured[Uncles et al., 1998]. The measurements were performed in the maximum turbidity zone. The seasonal variations of phytoplankton lead to changes in the flocculation dynamics and the composition of suspended particle matter. We recorded the floc size changes in the Yangtze Estuary and we found that: (1) the flocs are significantly influenced by tidal dynamics, as the floc size during slack water is larger than ebb tide and flood tide, (2) there is a correlation between the Chlorophyll concentration and sediment concentration, (3) the floc size is correlated to the algae-sediment mass ratio, (4) in winter, with high salinity and small river discharge, the region has a significant stratification and the floc size was smaller than the one in summer@en

Model results suggest that 1) varying lateral bed-slope factor has strong impacts; larger value leads to gentler channel-shoal interface or smaller lateral channel bedslope. 2) Different sediment transport formulas lead to considerable differences in morphodynamic patterns. 3) Sediment transport formulas considering both suspension and bed load transport tolerate a smaller morphological acceleration factor and requires a larger bed-slope factor.@en

Estuarine morphodynamics undergo significant changes due to declined sediment supply from river, rising sea-level, and human interferences (Syvitski and Saito, 2007; Syvitski et al., 2009). The Yangtze Estuary is such a case whose decadal morphodynamic evolution was broadly examined. It was documented that the subaqueous delta shifted from deposition to erosion since the early 2000s due to sediment supply reduction after the Three Gorges Dam (Yang et al., 2015) while some others reported that the estuary mouth bar area sustains accretion until 2010 (Luan et al., 2016; Zhu et al., 2016). The mouth bar area of the Yangtze Estuary is where the turbidity maximum exists. To clarify the morphodynamic changes therein, we examine the two large scale shoals, i.e. the Hengsha flat and the Jiuduan shoal, based on bathymetric data between 1958 and 2016 and satellite images since 1985.@en