| Research on the environmental hydraulic characteristic that is the fundament of aquatic environment and ecosystem in bays and the related areas is of importance to better understand the relationship between the physical and ecological processes. As a typical macrotidal and semi-closed bay, the Yueqing Bay's environmental hydraulic characteristic is representative in bays along the coastline in Zhejiang and Fujian province. Considering the horizontal dispersion coefficient, water exchange, tidal prism, and tidal-induced residual flow, the environmental hydraulic characteristic in the Yueqing Bay was studied in this dissertation. The main conclusions are drawn as follows:(1). An expression of the horizontal dispersion tensor was derived theoretically based on the previous methods in literature. By using a well-validated three-dimensional hydrodynamic model, the temporal and spatial distribution of the horizontal dispersion coefficient in the Yueqing Bay was then calculated, which is consistent with the observed data.(2). The analysis of results along the cross sections in the Bay has showed that the relationship between the horizontal dispersion coefficient and water depth can be explained in two ways:a positive correlation between the horizontal dispersion and water depth and a certain correlation between the horizontal dispersion and the significant sea bed variation. The longitudinal and temporal analysis has showed that the horizontal dispersion coefficient has positive correlation with the depth-averaged velocity and is also impacted by the tidal range and the vertical distribution of velocity.(3). Based on the computed results of the three-dimensional tidal current and the horizontal dispersion coefficient, a dimensionless expression was obtained by means of regression analysis as It indicates that the horizontal dispersion coefficient is not only proportional to water depth and the depth-averaged velocity but also has an exponential correlation with the relative tidal range (ΔH/h).In comparison with the often used equation of dispersion coefficient E=5.93u.h, the proposed expression is more meaningful and reasonable to some degree.(4). The spatial distribution of the half-lift-time and the average residence time in the Yueqing Bay was calculated using the convection and diffusion model of conservative substance. The results show that the half-life-time is less than 7 days in the outside of the bay, 7-10 days in the middle of the bay,11-13 days in the inside of the bay, and an average of 8 days for the whole bay. The average residence time was 2-11 days in the outside of the bay, 12-15 days in the middle,15-18 days in the inside, and an average of 11.2 days for the whole bay. The calculated results of the internal exchange capacity coefficient (K) have shown that the most active water exchange appears in the middle of the bay during the neap tide in the spring, while it appears close to the interface of the middle and the inside of the Yueqing Bay.(5). The tidal prism of the Yueqing Bay was calculated based on the hydrodynamic results. Combining with the analysis of the cumulative frequency, we find that the tidal prism is 23.5 billion m3 in the sprint tide with a cumulative frequency of 3.95% and the tidal prism is 10.1 billion m3 in the neap tide with a cumulative frequency of 89.2%. Further analysis also indicate that the tidal prism is larger in the middle of the bay, which leads to the better self-purification and larger exchange capability in this region.(6). The distribution of tidal-induced residual flow in the Yueqing Bay was obtained through the quasi-harmonic analysis of the tidal current calculated by the three-dimensional model. The results show that the depth-averaged residual velocity is mostly less than 15 cm/s inside the bay and increases to 20cm/s close to the bay mouth. The maximum residual flow rates along the east and west normal lines of the cross section at the Xiaomen Island are 15 cm/s and 30 cm/s, respectively.
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