Influence of Thermal Density Flow on Hydrodynamics of Xiangxi Bay in Three Georges Reservoir, China

Abstract

Hydrodynamic conditions play an important role in formation and disappearance of spring algal blooms in the Xiangxi Bay (XXB), a typical tributary water body of the Three Georges Reservoir. As it is difficult to obtain sufficient hydrodynamic information through expensive field monitoring, in this paper, a three-dimensional hydrodynamic model is developed to simulate the flow field of XXB in spring. In order to study the influence of thermal density flow on the hydrodynamics of this tributary, two typical scenarios for the spring of 2005 are considered here: with and without the temperature sources. Our modeling results show that the flow around the mouth of XXB is mainly controlled by the mainstream of the Yangtze River, and: if the temperature effect is considered, the computed maximum influence range of the Yangtze River can reach up to about 12 km upstream from the mouth of XXB. However, if the temperature effect is ignored, the influence range is only about 1 km. In reality, due to the vertical temperature difference, the stratified flow is formed and the mainstream flow can reach up to 12 km upstream from the mouth. The modeled results show that, the flow of Yangtze River enters into XXB in the upper layer, while the water of XXB flows out through the bottom layer. A huge vertical circulation was formed in the XXB, which enhances the exchange capacity between the Yangtze River and the XXB. The field survey also found that. It is included that the water temperature must be included in hydrodynamic numerical simulation for XXB in spring. The study is a useful supplement to field survey, and can provide technical support for eutrophication control in other tributary of Three Gorges Reservoir.