Numerical modelling of wave-current induced turbidity maximum in the Pearl River estuary

The dissertation describes a study of the hydrodynamics and sediment transport characteristics as well as the formation and development processes of turbidity maximum in the Pearl River Estuary (PRE) under the interaction of both wave and current through field data analysis and numerical modelling.; Field data analysis results show that turbidity maximum widely exists in the PRE and is not only related to the intrusion of salt water, but also to the freshwater runoff from the three western river outlets. Gravitational circulation and tidal trapping are the main causes to form the turbidity maximum in the West Channel. However, turbidity maximum in the East Channel is mainly caused by the sediment resuspension and deposition processes. The general characteristics of hydrodynamics and sediment transport in the PRE are studied by using a vertically integrated two-dimensional model.; With the background knowledge obtained from the data analysis and 2D modelling, a 3D hydrodynamics and sediment transport model is improved based on the work by Wai and Lu (1999 and 2000), and is used to study the turbidity maximum in the PRE. Modelling results show that turbidity maximum occurs during spring tides, disappears during neap tides and fully develops when ebbing during a spring tide in the wet season. Gravitational circulation, tidal pumping and resuspension are the main factors in the formation of turbidity maximum in the wet season. However, local resuspension is the main cause in the dry season.; To study the wave effect, a wave propagation model, developed by Chen (2001), is coupled with the present 3D hydrodynamics and sediment model. The wave-current integrated modelling results show that the island sheltering and shoaling factors significantly influence the propagation of wave into the PRE. The combined wave-current interaction increases the sediment concentration mainly near the sand bars and in shoals, resulting in a broader and thicker turbidity maximum with higher sediment concentration.