Assessing the Influence of Suspended Sediment on Effective Hydraulic Roughness from Tidal Damping Aspect: A Study Based on Yangtze River Estuary

The objective of this project is to assess the influence of suspended sediment on hydrodynamic properties in the study area from tidal damping aspect. Firstly, through conducting tidal amplification factor analysis based on real time measured data, seasonal variation in sloping tendency has been observed. The difference in sloping tendency revealed in tidal amplification factor analysis is a result of flow velocity and water depth interaction. In wet season, the sloping tendency in analysis result suggests that tide with higher amplitude experiences less damping as the tidal wave travels upstream than which with lower amplitude; in dry season, tide with higher amplitude experiences more damping than which with lower amplitude. Secondly, a two dimensional clear water flow model has been set up. By comparing the tidal amplification factor analysis result based on model result and with which based on measured data, a disagreement in sloping tendency has been observed in wet season, which indicates that the pattern of flow velocity and water depth interaction in clear water flow is different from which in the reality. Through extensive sensitivity analyses, the disagreement in sloping tendency in tidal amplification factor analysis result persists. Therefore, the conclusion can be drawn as follows: the suspended sediment which has not been considered in the model does have an influence over the hydrodynamic properties. By performing analysis over tidal amplitude and effective Chezy coefficient, the result reveals that the value of effective Chezy coefficient has a high correlation with the tidal amplitude, as higher tidal amplitude associates with higher value of Chezy coefficient and vice versa. In addition, the analysis result suggests that the value of effective Chezy coefficient for this study area should fall in between 60 for neap tide period to 70 for spring tide period. This finding conforms to the explanation proposed from buoyancy destruction aspect: higher tidal amplitude associates with higher suspended sediment concentration and better mixing, which would induce more buoyancy destruction effect and result in a lower bed roughness. Therefore, through analyses conducted in this project, the buoyancy destruction theory has been indirectly supported. I addition, since insufficient sediment information is obtained, this project fails in predict the future situation in a detailed manner. However, as which has been reported in previous literatures, the concentration of suspended sediment would decrease in the future. Some primitive estimation can still be done. As the sediment concentration drops, the hydrodynamic properties in the study area would be more prone to the clear water flow as presented in the model, such that tide with higher amplitude would experience more damping in Jiangyin-Xuliujing reach and less damping in Zhenjiang-Jiangyin reach.NUS-TUD Double Degree ProgramHydraulic EngineeringCivil Engineering and Geoscience