Study On 2-D Mathematical Model Of Tidal Flow And Sediment In JiaoJiang Estuary

The shallow water area in an estuary, where the depth of flow is insufficient for navigation, restricts the development of the port. Improving the navigable capability of waterway, it is necessary to study the changes of hydrodynamic condition and to predict the amount of sediment deposition in the dredged channel. In comparison with physical model and in situ observation of the dredged channel, mathematical model is characterized by short cycle, low cost and high efficiency. Therefore, it's valuable that mathematical model is used to predict flow variation and river-bed deformation. The sediment-laden capacity is a key parameter to the mathematical model of sediment transport, which is not well understood for the complexity of suspended sediment movement in the tidal estuary, so it's theoretically significant to study further the sediment-laden capacity of tidal flow.Based on the theory of tidal flow and sediment motion, a 2-D depth-integrated mathematical model for the Jiaojiang Estuary is developed by using explicit scheme of finite difference on the triangle elements. The results show that the rotary currents occurring in this area can be simply and effectively simulated by the model. Meanwhile, the suspended sediment concentration simulated is in agreement with the field data.Previous formulas which were set up in light of semi-tidal or tidal-averaged cannot describe the variation of sediment-laden capacity with the tidal flow. According to the concept of sediment-laden capacity, it is considered that the suspended sediment concentration rises with the increasing of the tidal flow velocity and diminishes with the decreasing of the tidal flow velocity. It is more reasonable to set up the formula based on the maximum or minimum sediment concentration and the corresponding hydrodynamic parameter. The coefficient and exponent in the function of sediment-laden capacity can be determined by regression analysis, and the formula of sediment-laden capacity is obtained, which better describes sediment transport in the Jiaojiang Estuary.Flow fields before and after dredging show that the velocity of tidal flow increases in the upstream and downstream areas of the trial-excavation, which arises the erosion in these areas. While inside and two sides of the trial-excavation the velocity of tidal flow decreases. It is obvious that deposition will take place in thetrial-excavation.The calculated results of river-bed deformation indicate that the river-bed in the upstream and downstream areas of the trial-excavation is universally deepened, so is on the outer edges of the trial-excavation. The erosion distribution is like a shell in shape. While obvious deposition occurs inside the trial-excavation. The maximum deposition takes place in the trial-excavation head.It is found from the calculated results that the variation trend of tidal flow velocity and river-bed deformation is the same under various projects. The dredging depth affects the extent of variation. That is, the deeper, the larger.The general principles of the river-bed deformation and flow variation after dredging are obtained, which can be used to direct practical project and avoid the blindness in channel dredging.