Impacts And Simulation Of The Yangtze River Water Transfer Project On The Hydrodynamic Water Quality Of Lake Chaohu

As the starting stage of the Yangtze River Water Transfer project,it undertakes the important task of improving the water quality of Lake Chaohu,and the selection of water transfer routes has a key impact on the water quality improvement effect.Based on the MIKE21 model,a hydrodynamic water quality model of Lake Chaohu was constructed,which simulated the spatiotemporal distribution characteristics of Lake Chaohu flow field,total nitrogen and total phosphorus concentration in the scenarios of wet year,normal year and dry year,the distribution of water exchange cycle,and the influence of different water transfer routes,different water transfer flows and different water transfer water quality on the water quality of Lake Chaohu in each typical year.The results show:(1)Compared with the AD convection diffusion module,the ECO-Lab water quality module has relatively high accuracy and is more suitable for complex water quality simulation processes,especially when the study area is large,there is a lot of runoff into the lake,the meteorological conditions are complex,and a variety of biochemical reaction processes are involved.(2)In the wet and normal years with strong hydrodynamic conditions,the circulation structure mainly appeared in the nearshore area of the center of the middle lake and the West Lake area.In dry years with poor hydrodynamic conditions,the circulation structure mainly occurs in the center area of West Lake and Middle Lake.In terms of inter-annual variation,due to the influence of the flow into the lake,the difference in spring flow field in different typical years is small,and in the rest of the seasons,the flow rate of wet year is the largest,and the flow rate of dry year is the smallest.From the perspective of intra-year changes,the flow field changes greatly between different seasons of the wet year and the normal year.The flow field in summer and autumn is stronger than in spring and winter.The flow field changes relatively little between different seasons of dry years,especially in summer,autumn and winter.(3)The circulation structure of Lake Chaohu flow field is due to the combined effect of throughput flow and aeolian flow.In different typical years,the flow field corresponding to the wet year showed the strongest hydrodynamic conditions,and the hydrodynamic conditions in the dry year were the weakest.Compared with the flow field of wind flow,the former has a greater impact on the hydrodynamic conditions of Lake Chaohu.(4)The distribution of total nitrogen and total phosphorus in each typical year Lake Chaohu showed obvious spatial heterogeneity,and the concentration of total nitrogen and total phosphorus in the West Lake area was significantly higher than that in the East Lake area.In terms of inter-annual variation,due to the large load of lake inflow in the wet year and the normal year,the nitrogen and phosphorus concentration of the lake was higher than that in the dry year.In terms of intra-year changes,affected by the difference in lake load,the total nitrogen concentration was higher than that in summer and autumn in spring and winter,and the total phosphorus concentration was lower than that in summer and autumn in spring and winter.(5)The common trend of water renewal time in different typical years is that the relatively high part is mainly located near the Yuxi River(Chaohu gate),which shows the overall trend of high in the east and low in the west,and the water renewal time in the West Lake area is less than 120 days in each typical year.The renewal time of the water body in the center of the lake is about 120 to 180 days;The renewal time of water bodies in East Lake District is greater than 180 days.The renewal time of Lake Chaohu is the shortest in the wet year and the longest in the dry year.(6)The outflow route of Baishitian River mainly improved the hydrodynamic conditions of West Lake District and Middle District,and reduced the pollutant concentration in West Lake Area.The inflow of the Zhao River mainly improves the hydrodynamic conditions of Middle District and the East Lake area,and the improvement of the water quality of Middle District and the east lake area mainly depends on the water quality drawn from the Yangtze River.Compared with the inflow of Zhao River,the inflow of Baishitian River has a more obvious effect on the improvement of water quality of Lake Chaohu.The greater the flow of water diverted from the Yangtze River Transfer,the better the water quality into the lake,and the more obvious the improvement of the water quality conditions of Lake Chaohu.Affected by the runoff,topography and wind field of Lake Chaohu,there are circulation structures in different typical annual flow fields of Lake Chaohu,and the influence of aeolian flow on the flow field is greater.The spatial distribution of total nitrogen and total phosphorus in Lake Chaohu showed a trend of decreasing concentration from west to east,and the temporal distribution showed that the total nitrogen and total phosphorus concentration in wet and normal years was higher than that in dry year,and the total nitrogen concentration was higher in spring and winter and higher in summer and autumn.The renewal time of Lake Chaohu is the shortest in the wet year and the longest in the dry year,and the spatial distribution shows a trend of high in the east and low in the west.Compared with the two water diversion routes,the inflow of Baishitian River has the best effect on the improvement of water quality of Lake Chaohu compared with the inflow of Zhao River,and the larger the water diversion flow,the better the water quality into the lake,and the more obvious the improvement of the hydrodynamic water quality conditions of Lake Chaohu.