Lake Group Water Environment Mathematical Model And Its Applications

As an important water carrier on land, lakes are the natural basement on which people liveand keep sustainable development. However, lake eutrophication, the typical one of manyenvironmental issues, has become a bottleneck of Chinese economy. In the past few years,river-lake connection, a new way to prevent the lake eutrophication, has been tried in thelake group located in the middle and lower reaches of Changjiang River and also beendetermined as a significant hydraulic development stragety in China. In thenatural-artificial river systems formed by connection projects, the way of connecting andits effect are the two essential problems, which directively involve the improvement effectof the projects. Lake water environment mathematical models, an important approach tosolving the two problems, are always the focus and front field.A lake water environment mathematical model often consists of a hydrodynamicmodel which is the basement and a water quality and temperature model. In thedissertation, the project of East lakes ecological water network in Wuhan is the object, anda lake group water environment mathematical model based on hydrostatic models wasdeveloped. The water diversion scheme and environmental effects of the project werestudied using this model. Because hydrostatic models have a limited application range,they are unable to simulate the flows with significant vertical velocity, such as flows overabruptly changed bottom, short wave, and so on, a depth-integrated and a verticalnon-hydrostatic model were developed, respectively. Multiple innovative solution methodsand their computational efficiency are studied. The main work and innovations are asfollows.(1) A depth-integrated hydrodynamic and water quality model was developed, whichincluded Sha lake, East lake, Yanxi lake, and Bei lake. Using the model, the improvementeffects of three water diversion schemes were simulated and one of them wasrecommended. After that, three sizes of inflow of the recommended scheme were alsosimulated, and the relationship between its inflow and improvement effect wasinvestigated. The obtained results provided a scientific support to the project.(2) A three dimensional hydrodynamic model which was coupled with water temperature and quality model was established, including Sha lake and East lake. Usingthe data from a typical temperature year, two scenes, which are before and aftern theproject, respectively, were simulated using the model. By comparing the lake current,water exchange between sub-lakes, and water temperature field in the two scenes, thehydrodynamical and environmental effects induced by the change of river-lakerelationship were analyzed. In addition, by analyzing the water exchange rate and totalphosphorus in the second scene, an exploratory diversion tactics―three cycles‖wasproposed.(3) The governing equations of a depth-integrated, non-hydrostatic model werederivated. Three solution method, an explicit method, a θ method, and a new ADI method,were applied to solve the equations. The new ADI method not only avoids the conventionthat the dynamic pressure at the open boundary is set as zero, but also has a highefficiency.(4) A new vertical two dimensional non-hydrostatic model with a single layer wasproposed. Unlike the other established vertical models which have multiple vertical layersand need much time to solve the equations, the present model has only one layer. As aresult, it’s accurate and highly efficient.At last, the achievement in the dissertation was summarized and some worthyresearch orientations were proposed.