The Study And Application Of Two-dimensional Hydrodynamics And Water Quality Coupled Model On Ecological Diversion Water In Dongchang Lake

Lake eutrophication is one of serious water environment problems all over theworld, majority of lakes in China have presented eutrophication tendency in recentyears, among others Dongchang Lake, as a representative of the "northern hydropenicurban lake", is located in the city and lack of the connectivity with natural water. Atthe same time, a large number of urban sewage discharged into the lake increases thenutrient concentration and causes water degradation. All of these have greatly affectedthe urban landscape and people life. How to improve the water quality conditions andhow to keep benign operation state of northern urban lake under double threat ofwater quality and quantity are important scientific problems of water environmentresearch in our country. At present periodic ecological diversion water throughartificial source is one of effective improvement measures. However, as the uniquesource, the Yellow River contains a large number of suspended silts which have animportant effect on the migration and transformation of pollutants. Hence, aiming atthe characteristics of Dongchang Lake, the two-dimensional hydrodynamics andwater quality coupled model is established to simulate the ecological diversion waterprocess, and the comprehensive technology research with lake eutrophicationmanagement, water resources allocation and water pollution prevention could make acontribution to the theory and practice of lake water pollution control and waterresources management and has important scientific value and practical significance.In order to study the ecological diversion water in Dongchang Lake, differentmonitoring section were set to research the change of hydrodynamics and waterquality. According to the measured data, the template based on programming principleof MIKE21Ecolab, the water quality simulation software developed by DHI, hasbeen secondary developed so as to accord with the characteristic of artificial ecological diversion water in Dongchang Lake. The hydrodynamics model coupledwith water quality template is established by MIKE21FM software to simulate thecurrent situation of Dongchang Lake. Then through the comparison with themonitoring data, the model parameters are calibrated and the simulation results areverified. Based on this,8kinds of feasible ecological diversion water programs arefurther designed and simulated by the two-dimensional hydrodynamics and waterquality coupled model. Finally, the optimal program is filtered to give some guidancefor the water resources management and effective utilization in the Dongchang Lake.The simulation result of current hydrodynamic condition shows that the dragcoefficient is an important parameter of wind-driven flow. The accuracy was muchbigger when the wind drag coefficient was varied with real wind field than when itwas constant. Among the six formulae of the wind drag coefficient, the one proposedby Wu has the best simulation result. Winter in the north is quite cold and waterfreezing has significant effected on numerical simulation of wind-driven flow,especially in the zone of ice cover. The influence of wind stress on water flow hasbeen weakened or counteracted under water freezing.On the basis of classical Dissolved Oxygen-Biochemical Oxygen Demand-Nutritive Matter model, the water quality template also takes suspended sand andbasic sediment into account so as to completely simulate the water quality changeduring the ecological diversion water in Dongchang Lake. Analysis shows that thelarge number of suspended sand contained in the Yellow River water has a greateffect on simulation results by adsorption and desorption of pollutant, besidessettlement and resuspension process.Through study the development planning of ecological diversion water inDongchang Lake,8kinds of different ecological diversion water programs aredesigned by applying the scenario analytical method, taking water source, inflowquantity, inlet setting and replenishing pattern as influencing factor. At last, the resultssimulated by the hydrodynamics and water quality coupled model are analyzedthrough Fuzzy Synthesize Evaluation and Trophic Status Index. Comparative analysisshows that the influence of different program in different lake region has large differences. The means of increasing inflow quantity, adding water inlet and focuswater filling could improve water quality to varying degrees, thus the6thprogramwith best effect is recommended.