Simulation Study On Water Quality Response Of Dianchi Lake Under The Common Interference Of Model Parameters And Boundary Conditions

With the survival and development of human beings and the advancement of science and technology,we can realize water environment management by constructing models.There were multiple process interactions during the operation of the water quality model,which can efficiently simulate the real system process.With the increase in the complexity of the water quality model,the increase in the number of model parameters and the difficulty in obtaining numerical values lead to large model output error,which affect the analysis of water quality changes and pollution prevention.Sensitivity analysis can determine the parameters and boundary conditions that have a large impact on water quality model.Scenario analysis can simulate the characteristics of water quality changes in the water environment.Taking Dianchi Lake as an example,this paper used Python combined with the IWIND-LR model to analyze the sensitivity of the water quality parameters in the internal equations and the external boundary conditions of the model.Scenario analysis based on the global sensitivity of rivers,which set up different river plans to study the low feasibility reduction water quality impact of river load and explore the water quality response under high reduction of river load.The main conclusions of this study were as follows:The IWIND-LR model were simulated under the common interference of internal equation parameters and external boundary conditions,and the logarithmic Nash coefficient results of five indicators of Chl-a,TN,TP,NH₃-N and DO were calculated,and the Sobol global sensitivity analysis was performed to determine the globally sensitive water quality parameters and boundary conditions.The maximum global sensitivity of meteorological boundary conditions included wind speed,air pressure,air temperature,relative humidity and radiation.Secondly,water quality sensitive parameters included algae metabolism and growth,carbon cycle carbon mineralization process,oxygen cycle reoxygenation process related temperature parameters（TR_C,KTG2d;KTR;KTMNL）,inert particulate organic matter sedimentation rate（WSrp）.Sedimentary diagenesis sensitive parameters included r M2（the concentration of sediment in the second layer of sediment）,Th KC1（20°C,the degradation rate of G1 particulate organic nitrogen）,FCRP2（the ratio of inert particulate organic carbon in the water column converted to G2）.The river input boundary conditions were the least globally sensitive.Compared with other rivers,Panlong River,Haihe River,and Xinbaoxiang River had the most globally sensitive,and they had a positively correlation between flow and load.Different rivers had different impacts on water quality in different regions of Dianchi Lake.The IWIND-LR model internal equation parameters and external boundary conditions were sequentially interfered for simulation,and the results of calculating the logarithmic Nash coefficient of five indicators of Chl-a,TN,TP,NH₃-N and DO can further determine the locally sensitive water quality parameters and meteorol-ogical boundary conditions.Among them,the local sensitivity of meteorological boundary condition was the greatest,included wind speed,air pressure,air temperat-ure and radiation.Secondly,the parameters of the sedimentary diagenesis module had relatively high local sensitivity,included r M2 and Th KC1,and the water quality module parameters of the water body had relatively high local sensitivity,included TRc,KTR,and KTMNL.By comparing the results of global and local sensitivity logarithmic Nash coefficients,the number of local sensitivity water quality parameters and meteorological boundary conditions were small and only expressed as local sensitivity,which was not comprehensive enough.Through scenario analysis,which was evaluated the feasibility of low-cutting solutions to improve the water quality of the lake and explore the water quality response under high-cutting conditions.The Panlong River,Haihe River and Xinbaoxiang River had been reduced according to different rivers and different proportions.Based on the comparison of TN and TP reductions,the water quality response of Dianchi Lake was the best when the river’s high load reduction was 60%.When reducing Xinbaoxiang River alone was the first option,the maximum reduction in TN was 0.0875mg/L,and when reducing Haihe alone was the first option,the maximum reduction in TP was 0.0025mg/L.When the combined reduction process was the first choice to reduce three rivers at the same time,the maximum reduction of TN and TP was 0.1474 mg/L and 0.0063 mg/L.