Numerical Simulation Research On The Characteristics Of Hydrodynamic And Mass Transport In Chaohu Lake

Chaohu Lake is the largest lake in Anhui Province.It is not only an important water source for agriculture,industry and residents living along the lake,but also the primary base for fishery production.In this paper,a watershed pollution database was established based on the calculated load of different pollution sources in Chaohu Lake Basin in 2013.Then,a SWAT(Soil and Water Assessment Tool)model was used to simulate runoff and pollutant generation(NH3-N,TP)in the basin,and used SWAT-CUP software for sensitivity analysis on the parameters of hydrological and water quality model.On this basis,the calibration and verification of hydrological and water quality models were carried out.The results show that the SWAT model can well simulate the runoff and pollution load process in Chaohu Lake Basin,and has strong applicability.Used Mike 3 to build a three-dimensional numerical model of Chaohu Lake.The results of runoff and pollutant generation in SWAT model were taken as the boundary conditions of the three-dimensional hydrodynamic model and water quality model,and the hydrodynamic and water quality of Chaohu Lake were simulated.The analysis shows that the simulation results can truly reflect the flow field and water quality changes of Chaohu Lake.On this basis,the hydrodynamic model and water quality model were used to simulate the change process of the hydrodynamic and water quality of Chaohu Lake under different wind and runoff effects.The results show that the circulating current can not be formed by the rivers around the lake,and the wind is the main factor of the circulating current,and the shape of the circulating current is mainly affected by the wind direction and topography.Under different winds,pollutants in Chaohu Lake are still concentrated in the western half of the lake,there is little pollution in the eastern half of the lake,and the water in the eastern and western half is not easily exchanged.In order to further understand the mass transport characteristics of Chaohu Lake,based on MIKE 3 hydrodynamic field,the Lagrangian Coherent Structure(LCS)based on the Finite-Time Lyapunov Exponent(FTLE)and the Lagrangian particle tracking were introduced to studied mass transport characteristics of Chaohu lake under different driving factors,and analyzed the relation and distinction between the two methods.The results show that the Lagrangian coherent structure method reveals the transport structure hidden in the water body of Chaohu Lake to distinguish different dynamic characteristics,which is located near the boundary between the eastern and western half of the lake,and explains the obvious difference of water quality distribution in Chaohu Lake and the difficulty of water exchange between the eastern and western half of the lake.The results of the Lagrange particle tracing show that the particles on both sides of the LCS almost do not mixed with each other,which proves that the LCS plays a role of mass transport barrier in the water,and also proves that the LCS is of great significance for understanding the dynamic mechanism of pollutant aggregation and diffusion in the lake.