Modelling Of The Three-dimensional Flow And Sediment Transport Processes In Estuaries

According to the water flow and sediment transport properties in the estuary, an integrated 3-D numerical model study is conducted to investigate the interaction between the hydrodynamic, morphological and sediment transport processes occurring in the estuary. The numerical model is established based on the widely used in environmental sediment transport studies worldwide model- namely ECOMSED, which is modified to facilitate for the study of the hydrodynamic, morphological and sediment transport processes occurring in the estuary. Major innovations are as follows,1) For large-scale simulations, the influence of the shear-stresses along closed boundaries can be neglected. Free slip is then applied for all closed boundaries. For simulations of small-scale flow (e.g. laboratory scale), Partial slip is set for the influence of the side walls on the flow may no longer be neglected. 2) A wetting and drying scheme is proposed and applied to the model, which defines'dry'cells as regions with a thin film of fluid O(cm). The primitive equations are solved in the thin film as well as in other regular wet cells. 3) A model for the bed load transport is included in the code to account for the dynamics of the mobile bed boundary. The bed evolution due to bed load transport is obtained by solving the sediment mass-balance equation.The model is validated by the trench flume flow, the spur dyke flume flow, sediment suspension over a loose sand bed and a water level over parabolic bed with free oscillations, which show that the model can be used in a wide range.The bed form development processes in an estuary-related laboratory flume experiment are concerned to study the bed roughness height distribution based on the Coleman method, which is included in the numerical model to simulate the water flow and sediment transport processes in the flume experiment. The comparisons between the numerical results and measured data of water velocities, turbulence energies, bed shear stresses, sediment concentrations in the water column and the bed level change processes show good agreements.The 3-D numerical model then is used to predict the sediment transport processes in a macro-tidal estuary with parameters of the model are calibrated first based on the field measured data of morphology, hydrology and tide cycle. The numerical results show the water velocities, water levels and bed level changes during the tide cycle. Tiny bed erosion is occurred in the estuary, most serious place is in the upper narrow river, and the tidal flat in the estuary is stable. The salinity distribution and sediment transport are significantly influenced by the tidal level change. The study can provide technical support for the water environmental management in estuaries.