As one of the most important influencing factors, inter-basin water resource development has been exerting an increasingly evident impact on the hydro-environment of river basins. The Han River was selected as a case study to reveal the hydro-environmental response to China's inter-basin water resource development. The hydrological changes and water-quality variations resulted from the middle route of the South-to-North Water Transfer Project (SNWTP) and the Three Gorges Reservoir (TGR) operation were examined based on a hydro-environmental model. The results indicated that the runoff reduction is obvious after the SNWTP operation, and the low-flow duration significantly increased by 4–5 months. Consequently, the flow decrease significantly contributed to the water quality deterioration in the middle and lower Han River, while the Yangtze-Han Water Diversion Project (YHWDP) can not alleviate the situation completely. Moreover, the nutrient assimilative capacity decreased after water diversion, which agrees with the hydrological changes along the middle and lower Han River. The quantitative analysis performed in this study distinguishes the spatiotemporal variation in water quality variables using the integrated model. It provides insights into water quality management under the influences of inter-basin water resource development.
The evolution mechanism of meandering river is one of essential references to predict the evolution disciplines of meandering river. Jingjiang curved reaches are the typical meandering river; more specifically, they are located downstream the gigantic hydraulic project named Three Gorge Project (TGP). Because the incoming water and sediment condition have been changed by the gigantic project, the evolution behavior of Jingjiang curved reaches changes a lot, making the evolution behavior unpredictable. However, traditional two-dimensional (2D) hydrodynamic model could not simulate the transportation characteristics of unbalanced and suspended sediment, leading the predict results of 2D model are far from the measured data. This paper presents a theoretical and numerical approach that explores the evolution mechanism of meandering river downstream gigantic hydraulic project. Firstly, the evolution behavior and evolution disciplines of Jingjiang curved reaches were classified before and after the hydraulic project implement respectively. Secondly, a 2D hydrodynamic model was set up and verified according to the measured data. And then a superior three-dimensional (3D) numerical model, whose boundary conditions were simulated by the results of the 2D numerical model, considering the unbalanced water and sediment transportation properties, was developed and verified by the measured data. Research results show that the 2D model displayed a reasonable accuracy in predicting the water level, branch diversion ratio, and flow velocity; the 3D model displayed a better accuracy in predicting the water lever, vertical flow velocity, longitudinal flow velocity, sediment concentration, and sediment variable quantity. Both 2D and 3D models could be applied to study the evolution mechanism of meandering river; especially the proposed 3D model considering the sediment transport in longitudinal, transverse, and vertical directions will improve the accuracy of behavior prediction and will help decision-making for the river regulation.
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