Simulation Study On Water Environment Of Dianchi Based On The EFDC

Dianchi Lake is the largest freshwater lake in the southwestern of China,and its status is closely related to the development of Kunming.The hydrodynamic process of lakes is the basis of water environment research.Based on the data of 2014,the present study uses EFDC model to establish the hydrodynamic model of Dianchi Lake to simulate the flow field,water temperature,water level,pollutant migration and diffusionof Dianchi Lake.The simulation results are as follows:1)By comparing the two-dimensional hydrodynamic model and the three-dimensional hydrodynamic model,it is found that the simulation results of the three-dimensional hydrodynamic model converge when it stratifies more than four layers,which is more reasonable.2)The flow field of Dianchi Lake is affected by wind driving in most areas,and influenced by river driving in estuary location.Affected by the southwest wind all the year round,the circulation of the Dianchi Lake is mainly counterclockwise.Dianchi Lake's water level is about 14.9m(The actual water level = The relative water level +1871.5m).The water level is the highest in spring,up to 15.1m.and it is the lowest in the summer and autumn,reaching 14.7m.The main factor influencing the water level of Dianchi Lake is the flow of in and out of the lake.The influence of wind on the flow field and water level of the lake is significant.The change of the wind direction will cause the change of lake water flow and lake water level.while the change of wind speed will cause the variation of the velocity and the maximum water level difference of the lake.3)The average annual water temperature of Dianchi Lake is around 16 ?,and the maximum reaches about 25?.The sensitive parameters of lake temperature changing are convective heat transfer coefficient(RCHC)and evaporative heat transfer coefficient(REVC).There is stratification between surface water temperature and bottom water temperature in Dianchi Lake,and the maximum temperature gradient can reach 1.1 ?/m.The stratification is especially obvious in the summer and autumn.4)In Dianchi Lake,the migration and diffusion paths of pollutants are mainly related to the flow field,also there is lateral diffusion.After setting the degradation rate of the three degradation rates,the range of migration and diffusion of pollutants is basically the same,while the decay of pollutant relates definitely with the degradation rate.Through the hydrodynamic simulation of Dianchi Lake,The present study found that:water level and flow field are the most important factors in the hydrodynamic process of lake and the wind has great influence on the changes of them.Through the comprehensive understanding of the hydrodynamic process,the temperature change,the material migration and transformation law of the Dianchi Lake etc,it can provide the theoretical support for the study of sediment and water quality in the future.