Impact of a water-sediment regulation scheme on the hydrodynamics and sediment conditions in the Sheyang Estuary

摘要

Tidal asymmetry (i.e., unequal ebb and flood intensities and durations) is a dominant factor in the dynamic equilibrium of current-related sediment transport in estuaries. The evolution of estuarine tides and sediment transport is of great importance to the development and utilization of channels in estuaries. Based on field hydrological and sedimentological data collected over multiple years, the hydrodynamic characteristics, suspended sediment concentration (SSC) and grain size, and median grain size of seabed sediments were analyzed to investigate the effects of the construction of a water-sediment regulation scheme (WSRS) in the Sheyang Estuary in China. Our results showed that small grain sizes (fine sand, silt, and clay) dominated and that suspension was the dominant transport mechanism in the area where tidal asymmetry was greatest. Tidal distortion occurred due to the construction of the WSRS. In this flood-dominant system (i.e., before and after the construction of phase I of the WSRS), the flood current velocity was significantly greater than the ebb current velocity, while it also had a shorter duration that caused higher SSCs during the flood current. This likely induced net sediment import to the estuary, which was the main cause of estuary infilling. Furthermore, the net transport of sediment into the estuary caused by the high flood current velocities resulted in the gradual deposition of sediments in the shipping channel of Sheyang Port. Ebb-dominant conditions (i.e., after the construction of phase II of the WSRS) induced net sediment export from the estuary, and sedimentation was significantly reduced. Since the ebb-flood current velocity ratio (R-v) and ebb-flood mean SSC ratio (R-s) could reflect tidal asymmetry and the direction of residual sediment transport with and without the WSRSs, they were used as important and sensitive indices to investigate hydraulic and sedimentological conditions. Results from this study can be used to improve the monitoring and management of navigation channels by providing insights into new methods of preventing or reducing sediment deposition in estuarine channels (i.e., by employing R-v and R-s).