The Evolution Of Water Quality In Gucheng Lake And Its Hydrodynamics And Water Quality Model

The worsening deterioration of water environment quality of rivers, lakes, and ports and estuaries has become a prominent water environmental problem in China. To facilitate the prediction, management and control of water pollution, the mixing, transport and exchange of contaminants in waters should be well understood, and their distribution should be clearly displayed. With water system of Gucheng Lake as research object, water quality evolutional law and water pollution causes are given and discussed in details. In addition, the one-dimensional hydraulic and water quality model is initially established, and based on that, two- and three-dimensional hydraulic and water quality models, and control equations of k?? turbulence model are further constructed in a curvilinear coordinate. The water quality model considers more than 10 kinds of water quality variables, including temperature, ammonia nitrogen, nitrate nitrogen, inorganic phosphorus, phytoplankton, C-DOB, dissolved oxygen, organic nitrogen, organic phosphorus, conductivity, and p H value etc. The model aims to explore the dynamics of interaction relations and the rules of transport and transformation between water quality variables.In this decade, quality deterioration of the water environment in Gucheng Lake is getting obvious. To find out the reason of water contamination, two kinds of valuation methodologies are used to analyze water quality in Gucheng Lake during 2001-2010. One is the combination of individual water quality index evaluation and worst factor distinguishing analytical method, and the other is a comprehensive pollution index method. Using the mass balance principle, a mathematical model of total nitrogen and phosphorus is established. By using Spearman rank correlation coefficient method, relevance judgment is calculated between the generated amounts of nitrogen(N) and phosphorus(P) in crab breeding and the amounts of total nitrogen(TN) and total phosphorus(TP) in the lake. Furthermore, the study explores whether the worsening of water quality and the fast growth of total T and P of crab breeding are relevant. The Result will provide reliable scientific bases for water quality improvement and ecological protection and restoration in Gucheng Lake and the sustainable development of economy in Gaochun.The one-dimensional hydraulic and water quality model provides mathematical formulas describing the changes of both flow and water quality in the domain of river network. Based on this, a revised fourth-order Runge-Kutta explicit format and a compact finite difference scheme of a high precision are used for equations discretization of the above model in time and space coordinates, respectively. The validity of the numerical method presented is verified by comparison with analytic solutions. Therefore, the algorithm is applied to Guanxi River, which is a natural course of river, and the estimates of water quality variables are obtained following a detailed computation and analysis.The distortion when simulating of complicated boundaries of natural river courses, lakes, and ports and estuaries can be minimised by using the boundary curve fitting method. Grids under curvilinear coordinates are established to overcome computational difficulties caused by complicated boundaries. On this basis, we can derive two-dimensional shallow water equations, k?? equations and water quality model equations in curvilinear coordinate system. With alternating direction implicit format, it implements the numerical solution of hydraulic-water quality model equations under an arbitrary curvilinear coordinate system in the domain. And the numerical simulation results are compared with plane curve flume tests results to testify the validity of the numerical simulation method. At this point, it provides an effective calculation means for any hydraulic-water quality models with complicated boundary of natural river courses and lakes. And finally, we successfully employ this approach to the application in Guanxi River, and thus receive some significant conclusions.This paper is going to design a new method, which is a kind of high precision numerical method for solving three dimensional hydrodynamic equations, k?? equations and equations of the water quality model under a curvilinear coordinate system. As for space derivatives in three directions of ξ、η and ζ, this method uses high precision compact finite difference scheme and facing wind compact finite difference scheme for the nonlinear terms. And as for time derivatives, the revised fourth order Runge-Kutta explicit format is used. In order to verify the correctness of this algorithm for solving the three-dimensional hydrodynamic model under a curvilinear coordinate system, same physical parameters as those in curve flume experiment are selected for numerical experiments. Results include water level, flow velocity etc. Moreover, the numerical simulation results are contrasted with the experimental ones and with numerical results via SIMPLEC method. The validity of the numerical simulation method is testified. The result shows that the high precision compact finite difference algorithm established here is reasonable for numerical simulation of problems depicted by three kinds of equations mentioned above, and is useful for predictability of hydrodynamic study on Guanxi River and the control of water contaminants.