3D Numerical Simulation And Analysis Of The Transportation Of The Fresh Water And Sediment In The Huanghe Estuary During Flood And Drought

In this paper, the survey data in the Huanghe estuary area are fully analyzed and discussed. Then the ECOMSED numerical model is applied to the Huanghe estuary. A 3D transportation simulation model with the orthogonal curvilinear grid which is based on the coastal line and terrain of Huanghe estuary is built up. With this model, the transportation processes of the fresh water and sediment in the Huanghe estuary during flood and Drought are successfully simulated. Then the basic dispersing character of the fresh water and sediment during flood and drought is analyzed based on the survey data. There are some particular depositional dynamic phenomena, such us maximum turbidity zone, hyperpycnal flow, which are found during the simulation. The shape character and the dynamic mechanism of these phenomena are discussed in this paper. The following results are obtained throughout the work:The simulation result of ECOMSED model about the transportation process of the fresh water and sediment in the Huanghe estuary with the effect of the tide current is believable. In the paper, the tide current of Bohai and then the current, salinity, sediment concentration in the Huanghe estuary are simulated. The result complies with the survey data after verification.During drought, the fresh water and the sediment disperse into the sea as the hypopycnal flow. The salt water intrudes into the channel like a wall and stops the dispersing of the fresh water at the flow time. During flood, the fresh water and the sediment disperse in the shapeof both hypopycnal flow and hyperpycnal flow. And the hypopycnal flow is also a important factor of their dispersion. The salt water which traces upward along the sea bottom can only trace a shorter distance because of the impact of the hyperpycnal flow.The estuarine maximum turbidity zone occurs at the time when ebb and flow alternates and the tide speed is relatively low. It is located at the stagnation point on the river bottom where the land-ward density induced current and the river current meet. Both the upstream and downstream currents convey sediments to the stagnation point that induces the convergence of sediments, and the upwelling current here makes sediment difficult to settle down. As a result, the sediment concentration near the stagnation point is larger than the other area, then the maximum turbidity zone occurs.Hyperpycnal flow occurs during the transportation of the high sediment concentration flow into the sea when the sediment concentration of the river flow is layered. Hyperpycnal flow can only carry the sediment to a short distance where the water is not deeper than 6 rn. At the ebb, the sediment concentration of the hyperpycnal flow reduces as more sediment disperses with the hypopycnal flow.