2-D Suspended Sediment Numerical Simulation Under Waves And Currents In Yangtze Estuary

In order to calculate depth-averaged two-dimensional (2-D) suspended sediment transport under waves and currents in the Yangtze Estuary, a numerical model system is developed. Four models, a 2-D compound fluid model including wind, waves, tides and river runoff, a SWAN wave model, a wave-current bottom boundary layer model and a 2-D suspended sediment transport model are integrated. Three different calculating regions, East China Sea region, Yangtze Estuary and Hangzhou Bay region and Yangtze Estuary region, are defined for nesting computation.The model system is in the generalized curvilinear coordinates, using high precision self-adaptive grids to fit the complicated topographies and coastal shapes. The effect of wave radiation stress is considered in the compound fluid model. The value of bottom friction is offered by the wave-current bottom boundary layer model. Seven main constituents are added to the open boundaries for perfectly simulating astronomical tides. Under the typhoon weather, residual elevations at the open boundaries of the Yangtze Estuary and Hangzhou Bay region can be obtained by interpolating from the elevation varieties induced by wind in the East China Sea region. In this way, the local wind and the non-local wind can be taken into account simultaneously.In the suspended sediment transport model, the method of shear stress is adopted to determine the source function in the suspended sediment diffusion equation. Through a series numerical experiments and statistical analyses of observed field data, a local coefficient, which can reflect the bottom material and consolidation, is introduced into the classic critical erosion velocity of the sediment. In calculation, the bottom shear stress under the effect of waves and currents is supplied by the wave-current bottom boundary layer model. The floe settling velocity of sediment particles is taken as the function of current velocity, salinity and suspended sediment concentration.The model system is verified by lots of observed data when applied to the Yangtze Estuary. Observed tidal harmonic constants in many stations are used to verify the astronomical tides in the compound fluid model. The wave model is testedby a set of wave flume data at first. Then the results are compared by the actual processes of significant wave height in gauging stations. The processes of surface elevation, current velocity in the compound fluid model and suspended sediment concentration in the suspended sediment transport model are verified by observed data of many stations in flood/dry season and in spring/middle/neap tide. The analyses of the calculated current fields, wave fields and suspended sediment distributions under normal or typhoon weather show that the model system can preferably reflect hydrodynamic fields and sediment distributions in the Yangtze Estuary.