The Application Of MIKE21 Hydrodynamic And Water Quality Coupling Model In Upper-reach Lakes Of Lake Nansi

With the rapid development of the economy,the population is:increasing,the pollution problem is exacerbating,and water resources problems are becoming more serious worldwide.China's water resources average per capita is small,with spatial and temporal distribution.Water resources are more in the summer than in the winter,and more in the south than in the north,and more in the east than in the west.The water resources issue has become an important factor restricting China's economic and social development.The South-to-North Water Diversion Project is a major engineering measure to solve the uneven distribution of water resources in China and promote the optimal allocation of water resources.The water quality problem is the key to tihe success or failure of the South-to-North Water Diversion Project.As the most important storage site for the East Route of.the South-to-North Water Diversion Project,Nansi Lake has a vital impact on the water quality of the East Route project.The hydrodynamic-water quality coupling simulation of the upper lake of Nansi Lake,and the variation law of water quality in the upper lake,and the pollution control measures of the Nansi Lake Basin,which has very important scientific value and practical significance.The authors consulted the relevant literature to understand the research progress of hydrodynamic and water quality models at home and abroad,and selected MIKE21 software to simulate the hydrodynamic-water quality coupling of the upper lake in Nansi Lake.The main research results of this paper are as follows:(1)The hydrodynamic model,convective diffusion model and ECO Lab water quality model of the upper lake of Nansi Lake were established respectively.The simulation results were verified and analyzed.Finally,the ECO Lab water quality model and the hydrodynamic model were selected to simulate the scenario.(2)The simulant scenario plan is divided into non-water transfer period and water transfer period.In the non-water transfer period,the water quality change process of the upper lake in the wet,flat and dry years are simulated with the entering water quality of Class IV and V In the water transfer period,on the basis entering water quality of Class IV and V,it is assumed that the flow of 50m3/s,100m3/s and 200m3/s into the lake in the 30 days before the upper lake respectively simulates the process of water quality change in the lake.The simulation of scenarios select the derived variables total nitrogen TN and total phosphorus TP as pollutant indicators.(3)According to the simulation results of the scenarios,the water quality changes of the upper lake in Nansi Lake are summarized as follows:1)In the non-water transfer period,the concentration of pollutants in the lake rises at first and then falls,and the water quality in the lake is the worst between July and August.In wet years,the flow and pollutants into the lake is the most,the water quality is the worst,followed by flat years,water quality in the dry year is the best;2)In the water transfer period,the overall water quality in the lake gradually getting better,the more the flow into the lake in the early stage,the more pollutants entering the lake,the worse the water quality in the lake.The water quality of the exit section of the Liangji Canal in the first 3 months basically did not meet the water transfer requirements.With the pollution entered the lake later.is completely diffused,the concentration of pollutants in the lake and in the outlet section of the Liangji Canal is close in different entering flow;3)When the flow into the lake is constant,the worse entering water quality,the longer time required for self-purification,the worse water quality in the lake;4)When the entering water quality is constant,the more the flow into the lake,the more pollutants entering the lake,the worse the water quality in the lake,the longer time required for self-purification;5)Compared to TN,the TP concentration at the exit section of the Liangji Canal is more likely to aggregate and rise in water transfer period,and the longer time water quality does not meet the water transfer requirements for Class ?.6)The velocity of flow is relatively slow at the lakeshore and the upper part of the lake,and the pollutants are easily collected in these places,which is difficult to degrade and spread,and it needs to be treated with emphasis.(4)According to the law of water quality change of the upper lake in Nansi Lake,the corresponding management suggestions are put forward to provide theoretical basis for pollution control of the upper lake in Nansi Lake.