Development And Application Of Three-Dimensional Hydrodynamic And Water Quality Model In A Shallow Eutrophic Reservoir

Eutrophication has been recognized as the most common and severe environment hazard in Lake Ecosystem, now China already become one of the worst countries in the world which reservoir pollution and algae blooms. Algae blooms are a common secondary ecological problem in the eutrophication water body, which seriously threaten the reliability of drinking water supply and has caused serious damage to the water source protection. It’s an urgent and important issue of reservoir studies to provide scientific guidance for the water environment management, ecological regulation and reservoir optimal scheduling. Development and application of mathematical model of water environment and numerical simulation of reservoir hydrodynamic and aquatic ecosystems is an important means to carry out for this research. To promote the construction of Tianjin and significantly improve the city’s ecological environment and the production and living conditions the masses, Tianjin government planning and implementation of the project named number one project for beautiful Tianjin in 2013. Clean the river water is one of five programs executed by Tianjin government, which requirement simultaneously conduct many measures about control, intercept and treatment the pollution sources, river restoration and diverse water from elsewhere and so on, build the water environment system to meet the claim of beautiful Tianjin. As the only drinking water source of Tianjin, Yuqiao reservoir had experienced several algae blooms in recent years, which had adversely impacted on the safety of drinking water supply and reservoir management. Therefore, it is of great significance to conduct research on eutrophication for yuqiao reservoir. For this challenge, a coupled three-dimensional EFDC hydrodynamic and WASP water quality numerical model and an artificial neural network model was conduct to research the eutrophication of Yuqiao Reservoir and made some results with theoretical significance and use value. The research contents and innovation achievements about this paper are outlined below:(1) The three-dimensional hydrodynamic model established based on sigma coordinate system in this thesis can effectively simulate three-dimensional flow structure of reservoir, the complex flow rate such as in and out flow, compensation current and wind-driven circulation, and the velocity differences of each layer in vertical direction, which in line with the current development trends of environmental fluid dynamics. In addition, this paper took the impact of the wind, in and out flow, topography to the flow structure of reservoir into account, which compensated the weak of former study only considering one of them in reservoir hydrodynamic research.(2) EFDC model successfully coupled with the WASP model and sent the hydrodynamic information of EFDC model into the WASP model, then the three-dimensional water environment numerical model has been triumphantly established, which overcomes the limitations of EFDC in water quality and WASP model in hydrodynamic simulation, and the weak of simulate water quality in reservoir only using single model. In addition, the established model was used to analysis water quality changes of the Yuqiao reservoir in time and space after the model validation. And then analyzes the causes of algal blooms in Yuqiao reservoir from the hydrodynamic conditions, the relationship between nitrogen and phosphorus ratio, dissolved inorganic nitrogen and algae growth. Finally, three assumptive scenarios about reducing the boundary load improve running water level and ahead of diversion time are modeled to discuss the method of reduce chlorophyll-a concentration in reservoir, and provide the basis for development of measures to control the eutrophication.(3) The meteorological conditions such as precipitation and solar radiation are took into consideration when predict water quality using artificial neural network model, which make up for the sidedness of previous neural network model only using water quality variable as input parameters. Using data mining technical such as the factor analysis when select the model input variables, which compensated the weak of former model only using empirical knowledge to select the input parameters and also improve the model prediction accuracy. The artificial neural network model established in this paper proved can successfully predict and forecast water quality variables in reservoir, and can also be used for short-term prediction of water quality. In addition, orthogonal experimental design has been introduced into artificial neural network model, and chooses reasonable controllable factor from the model sensitivity analysis results for orthogonal table design, then find the most reasonable environment variable control scheme to inhibition algal blooms by check the response chlorophyll-a concentration.(4) The eutrophication control measures were discussed for the Yuqiao reservoir and provide three different proposals from external and internal source pollution control engineering and integrated management measures within the watershed. the external source pollution control engineering including building constructed wetland system through use the pre-storage reservoir in conjunction with the construction of estuarine wetlands, the bulldozed fish pond around the reservoir and river wetlands corridor, the ecological restoration projects like construction lakeside belt and sewage interception ditch around the reservoir, the reservoir protection works such as install reservoirs protective nets, video surveillance systems and digital inspection systems to effective governance reservoir exogenous contamination. The internal source pollution control engineering contains the sediment dredging and the aquatic ecosystems repair system. The aquatic ecosystems repair system including artificial complex plant communities’ ecological restoration systems combine with enclosures extension technology, artificial floating beds and aquatic ecosystem manipulation. Integrated management measures include the establishment of reservoir watershed management regulations, the migration of residents around the reservoir, the treatment of production wastewater and sewage of Zunhua, ban cage fish culture of Panjiakou and Daheiting reservoir in upstream of Yuqiao reservoir and develop emergency management measures for crispus and cyanobacteria blooms in the reservoir.