Contribution of sediments to stratification in a fluvial estuarine system during a low-discharge period

Abstract Changjiang River Estuary (CRE), as one of the largest fluvial estuarine systems worldwide, experiences great changes in river discharges, sediment loads and geomorphology, due to heavy anthropogenic activities. The contribution of sediments to stratification in CRE was examined by analyzing the field data of sea surface level, current, salinity, suspended sediment concentration (SSC) and sediment grain size. The data were simultaneously observed at 1-h intervals and six vertical layers at 10 stations during the low-river discharge period from January 11 to 19, 2016. During this winter period, the asymmetric tides at all the field stations had longer ebb durations. The tidal range in the north branch became the largest among all the stations. The tidal phase inside the north branch was more delayed than that in the south branch, due to the effect of the local bathymetry and coastlines. Currents and bed sediments impacted SSC through changing bottom friction and viscosity, and then impacted water stratification subsequently through modulating water density. Net sediment flux was mostly seaward during the entire spring-neap tidal cycle, because of the Eulerian velocity and tidal pumping effect. Turbidity-induced stratification accounts for more than 50% of the total stratification during spring tides.