Abstract
After the impoundment of the Three Gorges Reservoir (TGR) in China, water environment problems induced by water temperature stratification in the Xiangxi Bay (XXB, a typical tributary bay of TGR) received wide attention. In this study, a 3-dimensional (3D) hydrodynamic and water temperature coupled model with the z-coordinate in the vertical direction was established with Delft3D software to simulate the continuous hydrodynamic and water temperature process of XXB in 2009, and the static stability and mixing depth were also analyzed. The results show that the upstream inflow is prevented from entering TGR with nutrients enriching and mixing in the upper and middle reach of XXB from winter to early spring, which is the primary cause of spring algal blooms in XXB. Therefore, measures such as improving the upstream hydrodynamic conditions and forcing the nutrients to flow into TGR in winter should be more effective in alleviating spring algal blooms than the artificial tide operation of TGR proposed by previous studies.
Highlights
Large-scale hydropower projects often cause environmental and ecological problems, such as harmful algal blooms [1, 2]
The results show that the upstream inflow is prevented from entering Three Gorges Reservoir (TGR) with nutrients enriching and mixing in the upper and middle reach of XXB from winter to early spring, which is the primary cause of spring algal blooms in XXB
According to the simulated results, the water temperature stratification in XXB can be divided into 3 typical periods: the uniform distribution period, the strong stratification period, and the bottom stratification period
Summary
Large-scale hydropower projects often cause environmental and ecological problems, such as harmful algal blooms [1, 2]. Xiangxi Bay (XXB), 32 km from the Three Gorges Dam, is the nearest and largest tributary bay in the upper reach of TGR, and spring algal blooms have been observed for many years [3, 4]. Researchers suggested that a tide-type operation of TGR would be beneficial in reducing bloom frequencies in the tributary bays [7,8,9], but the operation was restricted by many factors such as flood control, water supply, and power supply of TGR. Transferring the hydrodynamic impact of the tide-type operation to the tributary bays of TGR is difficult, and more operable measures are needed to alleviate spring algal blooms in the tributary bays
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