Study Of Water Environment Simulation Of Chongqing Three Gorges Reservoir Area Under The City Driving Force Based On EFDC

With the advancement of urbanization in China,the development of industry and the concentration of large population pose a great threat to water environment security.The continuous expansion of the city and the change of original land-use type directly lead to the increase of the non-point source pollution,so a lot of rivers and lakes are polluted.As soon as the Three Gorge reservoir in Chongqing section was established,the water quality in the tributary estuary of backwater area was obviously decreased and there is water bloom in partial estuary with comparatively low water quality.Therefore,how to take effective measures to protect and treat the Three Gorge reservoir in Chongqing section has become a crucial issue at present.This paper takes the main stream of the Three Gorge reservoir in Chongqing section as the research project.Based on the hydrodynamic model and the water quality model built by water environment mathematical model EFDC,this paper has conducted calibration and verification of these models in accordance with the real-time measured hydrology and water quality data.The main research includes:(1)The rendering of the river grid: the paper uses the Delft3 D to draw the curve orthogonal grids of the water environment model of the Three Gorge reservoir via satellite map with 10611 grids in total.In addition,the shape of channel,tributary estuary and river basin are simplified and a simplified dry flow topographic map of Chongqing Three Gorges reservoir is constructed.(2)The hydrodynamic model of Chongqing Three Gorges reservoir is established in accordance with EFDC,which simulates the velocity and flow field in the main stream.What's more,Compared with the real-time measured data of the three sections Cuntan,Fuling and Wanzhou,the relative errors are 10.5%,18.6% and 8.1% respectively.Based on flow field of the Yangtze river,the paper analyzes the influence of season,geographical location and tributaries on the flow velocity in the Three Gorges reservoir.(3)Based on the established hydrodynamic model of reservoir area,the water quality model of Chongqing Three Gorges reservoir is established and the ammonia nitrogen,nitrous nitrogen,total phosphorus and chemical oxygen demand of the main stream of the reservoir are simulated.Among them,the data of the first half year(the winter and the summer period)are used to determine the rate,and the results showed that the average relative errors of the four indexes are 22.88%,20.63%,21,43%and 22.42% respectively.Besides,the paper uses the data of second half year(winter and summer months)to validate and the average relative errors are 21.06%,23.66%,27.39% and 14.96% respectively.(4)Based on the hydrodynamic model of chongqing Three Gorges reservoir,the water quality simulation is carried out in the following conditions: 1)the water quality simulation of existing pollution situation under the natural landform of the Three Gorges;2)the water quality simulation of current pollution condition under the condition of flood control limit;3)Water quality simulation of existing pollution situation under the condition of maximum operating water level;4)The water quality simulation after the renovation of the waste-water treatment plant under the condition of flood restricted water level;5)The water quality simulation after the construction of sponge cities on the line of tributary area under the condition of flood restricted water level.Besides,this paper analyses the area of pollution zone in various conditions.Obviously,the water quality decreased after the river into reservoir.Compared with the situation before thee river into reservoir,the area of pollution zone in flood restricted water level increased 30%~80% and the area of pollution zone under maximum operating water level raised 20%~60%;according to the simulation condition of upgrading and reconstruction,the pollution zone reduced 30.5% on average compared with the pre-upgrading and reconstruction period.What's more,according to the simulation condition of sponge cities' construction,the area of pollution zone decreased 48.1% on average compared with the pre-construction period.