Analysis Of The Hydrological Characteristics And Water Temperature-Hydrodynamic Modeling Of The Xiangxi River

Since the first impoundment of the Three Gorges Reservoir in 2003, large-scale water bloom has broken out in several of its tributaries. Hydrodynamic condition is the foundation of outbreaks of water bloom, and water temperature structure is an important component of hydrodynamic conditions. So the changes of water temperature and hydrodynamic conditions are of great significance for water bloom research. This paper analyzed the variations features of hydrological properties in the Xiangxi River during 2003-2012 carefully, and preliminarily mastered the background of hydrological characteristics during water bloom. In addition, we also established a three-dimensional hydrodynamic model of the Xiangxi River watershed, analyzing the stream field and temperature field at the confluence of the Yangtze River intersection. The main conclusions are as follows:(1) It appears that the smaller the amount of rainfall and discharge are, the more frequently the bloom outbreaks happen. When the average monthly rainfall is more than 8 mm, and the average monthly flow is more than 85 m3/s, there is no outbreak of water bloom. The annual average temperature is relatively stable in the 10 years from 2003 to 2012, except the abnormal phenomenon of low temperature in early January 2008. Water level change in the Yangtze River is larger than the upstream of the Xiangxi River. The water level fluctuation is relatively smaller in the months of the outbreaks of water bloom than other months, and the average amplitude of the water level sliding within 5 days is mostly below 0.5 m, which benefits the outbreak of water bloom.(2) According to the measured data, we established a three-dimensional hydrodynamic model of the Xiangxi River watershed. The mainstream influences velocity evidently at the points near the estuary, while it has an ambiguous effect at the other points. The impact on the velocity of each layer is determined by the relative size of surface circulation and bottom circulation in the Xiangxi River estuary.(3) The Xiangxi River flow influences more on the velocity of surface and middle layer than the bottom layer. The flow velocity of each layer decreases from upstream to downstream. The Xiangxi River shows a very low temperature region on surface near the estuary of the study area during the heating period, which is caused by the vertical circulations in the bottom bringing the cold water into the surface.