Analysis of hydrodynamic features of the north passage in the turbidity maximum, Changjiang estuary

Based on the observations of full depth in the North Passage (NP) during the flood season in 2015* an analysis of horizontal flow, residual flow structure and boundary layer features in the middle-lower sections of NP was further conducted. The research reveals that the tidal current vectors during spring tide shows clear vertical variations. A lateral water transport to the north of the channel appears in the study site. The lateral flow velocity (depth-averaged) varies from-0.10 m/s to 0.39 m/s during spring tide while-0.13 m/s to 0.25 m/s during neap tide. Lateral advection plays an important role in the longitudinal mass transport and hydrodynamics. There is a significant variation in the residual flow vertical distribution, with an approximately zero value at the bottom. The residual flow is stronger in the neap tide. Suspended bed sediments can be seen as a supply for the turbidity maximum. There are great errors in the logarithmic velocity fitting law based on the traditional “six points” method. To gain the precise bottom boundary layer parameters, we need to focus on the high-resolution velocity profile in the 1 m water column above the bed.