In this study, a three-dimensional model is developed to investigate sediment transport under tidal bores in the Qiantang estuary. The sediment transport is modelled by the advection and diffusion equation, and the exchange of sediment between the riverbed and the flow is determined by a net flux. A new formula of sediment carrying capacity based on recent field data is used and the settling velocity is resolved with an empirical formula accounting for the flocculation of fine sediment. Skill assessment is employed to show the model performance and relatively high predictive skills are demonstrated. The significant rise of sediment concentration under tidal bores is accurately reproduced. Sediment concentration with the arrival of tidal bores increases more than 10 times, and the depth-varying characteristic of suspended sediment is captured. It is concluded that the amount of sediment transport under tidal bores amplifies an order of magnitude, and the reverse sediment transport pattern is documented.

Tidal bores inject large amounts of energy to the estuaries, and the variation of tidal bore is related to its energy distribution. In this study, the temporal and spatial changes of the tidal bore energy are investigated to demonstrate the propagation characteristics of tidal bores in the Qiantang River Estuary. Based on high frequency field data, the characteristics of the potential energy and the kinetic energy per unit area during the passage of tidal bores at Yanguan station is demonstrated. Numerical model employing shallow water equations is established to investigate the tidal bore energy along the estuary. Tidal level, tidal current and tidal bore during spring tides in September, 2019 are verified, and the tidal bore energy and its distribution characteristics along the sections from Ganpu to Wenjiayan are illustrated. The tidal bore energy is significantly decreased in the Daquekou reach but decreased relatively small in the reach from Qige to Wenjiayan. There is the maximum energy loss in the Jianshan reach. The tidal bore energy declines to 15% at Wenjiayan during the passage of the energetic breaking tidal bores, indicating tidal bore disappearance in the upstream reach.

Tidal gates cause adverse effects on the ecological environment through the downstream acceleration of sediment deposition. This deposition process and its quantitative analysis have become a hot topic in marine science. A large-scale physical model experiment of morphological responses to the construction of a tidal gate in an estuarine tributary was performed in this study. The sediment distribution characteristics, morphologic patterns, and further analysis of the adjacent intertidal flats were investigated, triggered by the construction of tidal gates at the mouth of the Nanxi River in Zhejiang, China. The results indicated that the flood and ebb tide velocities change dramatically after the construction of the tributary tidal gates. Large amounts of sediment from the mouth of the estuary could not be entirely carried away from the flood phase to the ebb phase, resulting in downstream deposition in the vicinity of the gates. The ebb tide caused erosion of the tidal flats’ surface in the silted intertidal zone that gradually developed into a tidal channel network. The tidal channel bifurcated in the middle–upper part of the intertidal flats through continuous headward erosion, thus promoting the landward expansions of channels. Applying a set of logistic growth models to the mean sinuosity, Hausdorff dimension, and junction number data indicated that the tidal channel development progressively tended toward a state of morphodynamic equilibrium.