Simulation Of Hydrodynamic Force And Water Quality Processes Of Chaohu Lake Based On FVCOM Model

Chaohu Lake is located in the middle of Anhui Province in the middle and lower reaches of the Yangtze River,and is surrounded by Chaohu City and Hefei City.As one of the five largest freshwater lakes in China,Chaohu Lake has abundant water resources and a large drainage area.In addition,it is related to the socio-economic development of the surrounding two cities and five counties,and is an important hub for connecting the Yangtze water system and Huaihe river water system because is navigable throughout the year except in serious drought seasons.In recent years,Chaohu Lake basin has developed fastest among the great five lakes basins.But while getting the huge economic benefits with the rapid economic development,many problems are becoming more and more prominent,such as the entering of a large number of pollutants into the Chaohu Lake,more and more serious soil erosion,decrease of biodiversity,frequent occurrence of water blooms and serious water eutrophication,etc.As a result,the government has adopted relevant governance measures to alleviate the pollution status of Chaohu Lake to some extent,but its water quality is still not good.Moreover,a lot of manpower and material resources are required for water quality treatment every year,while water pollution of Chaohu Lake has become an important factor that restricts the socio-economic development of Chaohu Lake basin.Therefore,it is of great practical significance to evaluate and predict the water quality of Chaohu Lake through the simulation of its hydrodynamic force and water quality processes.Based on FVCOM model,a hydrodynamic force and water quality model of Chaohu Lake was established in this paper by dynamically coupling PCLAKE ecological model through the FABM framework.The simulation results fit well with the measured data of Chaohu Lake.On this basis,it carried out the research on hydrodynamic force and water quality processes of Chaohu Lake,and the influence of water diversion project on its water quality.The research results show that,Firstly,the water quality of Chaohu Lake has a strong seasonal variation law and spatial distribution law.In terms of time variation,there is a strong correlation between water blooms and water temperature,tending to peak at the end of June each year.Besides,the changes throughout the year maintains a dynamic balance and the nutrient salts and dissolved oxygen in water are negatively correlated with changes in water blooms.In terms of spatial distribution,the nutrient salts in the water are mainly concentrated in the west of Chaohu Lake where the runoff is more polluted.Under the action of horizontal drifts,the water blooms accumulate in both the west,and the southeast and north shore sides of Chaohu Lake.Simultaneously,the distribution trend of dissolved oxygen is basically opposite to that of water blooms;Secondly,the water body of Chaohu Lake updates slowly.The average water residence time of the whole lake is about 181 days and the water body exchange has a certain response time between the east and west;Thirdly,it can calculate the pollution sharing rate of each runoff into the lake to trace the pollution source that shall be mainly responsible for the pollution when pollution occurs in a specific space of Chaohu Lake.This method can provide thought and basis of the pollutant tracing for pollution control at source;Fourth,all the three water diversion schemes can improve the water quality of Chaohu Lake,in which Water Diversion Scheme A has the best improvement effect;Fifth,the efficiency of water diversion is the best at 3 billion cubic meters of annual water diversion volume.However,there are still significant water blooms in most of the year.When the annual water diversion volume increases from 3 billion cubic meters to 7 billion cubic meters,the duration of obvious water bloom phenomenon in the whole year reduces from 144.5 days to 61.5 days.Therefore,the increase in water diversion volume can ensure that the water quality of Chaohu Lake is good in most of the year in case not considering the efficiency and cost of water diversion.To sum up,the above research results can provide suggestions for water environment management of Chaohu Lake,ecological restoration in lake areas,control of pollutant discharge,pollutant tracing,and evaluation and optimization of water diversion scheme.