Author(s): Ye Yao; Jijian Lian; Kui Xu; Chao Ma
Keywords: Hydrodynamic characteristics; Vertical two-dimensional model; Numerical simulation; Water exchange; Three Gorges Reservoir
Abstract: After the impoundment of the Three Gorges Reservoir, hydrodynamic characteristics of river change dramatically, with the reservoir level rising, the turbulence intension decreasing and the water velocity reducing. Deteriorative hydrodynamic conditions lead to large-scale water blooms in river bays of near-dam tributaries. Exploring the hydrodynamic characteristics of the mainstream and tributaries will provide a solid theoretical foundation for improving the hydrodynamic conditions of reservoirs by human dispatch solutions, which has been verified to control water blooms significantly. In this study, a vertical two-dimensional hydrodynamic model of Yangtze River and Xiangxi River based on CE-QUAL-W2 is developed with measured data. Data from Dec. 5, 2009 to Feb. 8, 2010 is used to calibrate the model. The sensitive and important control parameters include channel roughness, eddy viscosity, eddy diffusivity and wind sheltering coefficient. The analysis based on the calibration scenario indicates the following three aspects. Firstly, the water flow field of the mainstream is influenced by reservoir geometry, outlet position, wind shear effect, bottom shear effect, water temperature difference comprehensively. Secondly, Xiangxi River is sensitive to heat exchange owing to its relative small capacity that the thermal stratification is obvious. Thirdly, the mainstream water plunges into Xiangxi River in the form of thermal stratified shear flow, which could be divided into plunging from the surface layers, middle layers and bottom layers according to the different plunging positions. The vertical profiles of the longitudinal velocity could reflect the reach of the stratified flow, which is equivalent to the intension of the water exchange. And how to establish the relationship between water blooms and water exchange will be discussed in the further studies.