Turbulent mixing and sediment induced stratification in macrotidal Qiantang Estuary (China)

Physical processes is fundamental to understanding how estuaries change under the impact of human activities. In this paper, time series of in-situ measured velocity and suspended sediment concentration from Qiantang Estuary (China) and estimates of turbulence and sediment stratification parameters are presented. The data span a period of nine days and after phase-averaged, they are used to explore spring-neap tidal variations in flow, turbulence and sediment stratification. A local balance between shear production, sediment-induced buoyancy flux and dissipation is found to hold during ebb for both neap and spring tides. During flood elevated turbulence dissipation rates are observed, attributed to non-local turbulence, most likely due to horizontal advection. Our results show that the effect of sediment stratification is successfully parameterized by adding the Monin-Obukhov length scale to the classical logarithmic layer theory. Flood-ebb asymmetry in both Ri_g and R_f is observed, with higher values attained during flood due to the higher sediment concentrations and the corresponding weaker velocity shear found at these times. Our findings might shed new light on understanding estuarine processes and management in the Era of the Anthropocene, such as estuarine regulation and coastal engineering.