The hydrodynamic effects of reconnecting a lake group with the Yangtze River were simulated using a three-dimensional hydrodynamic model. The model was calibrated and validated using the measured water temperature and total phosphorous. The circulation patterns, water temperature, and water exchange conditions between sub-lakes were simulated under two conditions： （1） the present condition, in which the lake group is isolated from the Yangtze River; and （2） the future condition, with a proposed improvement in which connecting the lake group with the Yangtze River will allow river water to be diverted into the lake group. The simulation period selected was characterized by extremely high temperature and very little rain. The results show that the cold inflow from the river has a significant effect on the water temperature only near the inlets, and the effect is more obvious in the lower water layers than that in the upper ones. The circulation pattern changes significantly and small-scale vortices only exist in part of the lake regions. The water exchange between sub-lakes is greatly enhanced with the proposed improvement. The water replacement rate increases with water diversion but varies in different sub-lakes. Finally, a new water diversion scheme was proposed to avoid contamination of some lakes in the early stage.
A new depth-integrated model deploying a non-hydrostatic pressure distribution is presented.With the pressure divided into hydrostatic and dynamic components,the horizontal momentum equations were obtained by integrating the Navier-Stokes equations from the bottom to the free surface.The vertical momentum equation,in which the convective and viscosity terms were omitted,was approximated by the Keller-box scheme.The model has two steps.First,the dynamic pressure gradient terms were discretized semi-implicitly and the other terms were in explicit scheme.Second,the velocities expressed as the unknown dynamic pressure were substituted into the continuity equation,resulting in a five-diagonal symmetric matrix linear system that was solved by the conjugate gradient method.The model was validated with the propagation of a solitary wave and sinusoidal wave,indicating that it can predict free surface flows well.
The vertical two-dimensional non-hydrostatic pressure models with multiple layers can make prediction more accurate than those obtained by the hydrostatic pres- sure assumption. However, they are time-consuming and unstable, which makes them unsuitable for wider application. In this study, an efficient model with a single layer is developed. Decomposing the pressure into the hydrostatic and dynamic components and integrating the x-momentum equation from the bottom to the free surface can yield a horizontal momentum equation, in which the terms relevant to the dynamic pressure are discretized semi-implicitly. The convective terms in the vertical momentum equation are ignored, and the rest of the equation is approximated with the Keller-box scheme. The velocities expressed as the unknown dynamic pressure are substituted into the continuity equation, resulting in a tri-diagonal linear system solved by the Thomas algorithm. The validation of solitary and sinusoidal waves indicates that the present model can provide comparable results to the models with multiple layers but at much lower computation cost.
