Simulation And Control Of Rainfall Runoff Pollution In Sponge City Construction Demonstration Area Based On MIKE 21

Sponge City,as an innovative expression of promoting the construction of green buildings,the development of low-carbon cities and the formation of smart cities,is an organic combination of modern green new technology and social,environmental,cultural and other factors under the background of new era characteristics.As the skeleton of a complete city sponge,urban river and lake system has the functions of hoarding,regulating,purifying and recycling.Therefore,it is an important part of the construction of sponge city to carry out the comprehensive improvement of regional water environment,protect and repair the spatial and ecological functions of urban rivers and lakes.In this study,Shanghai Lin-Gang Special Area was taken as the study area,and the water pollution assessment was completed by analyzing the water quality monitoring data.MIKE 21 software was used to establish the hydrodynamic water quality model of the study area,Simulated the changes of water quality in the study area under different rainfall conditions and calculated the cutting rates of pollutants in rainfall runoff.The impact of different parametrical conditions on the water quality was analyzed to determine the optimal parametrical conditions.The main work content and conclusions of this study are as follows:(1)16 representative monitoring sections in the study area were selected to analyze and evaluate the water quality status,and to grasp the changes of various water quality indicators.The single factor index evaluation method was used to analyze the unattainment rate of water quality,and determine the main exceeded water quality indexes were TN and TP.(2)Collected the data for modeling such as topography,hydrology and climate characteristics of the study area,and used MIKE 21 hydrodynamic and transport modules to establish a hydrodynamic water quality model,and used trial and error method to repeatedly determine the relevant parameters.The average simulation error of hydrodynamic model is 1.90 %;the water quality model simulated the average error of TN and TP concentrations in the Dishui Lake were 11.90 % and 10.94 %,and the water quality model simulated the average error of TN and TP concentrations in regional rivers were 11.90 % and 10.94 %.The accuracy of hydrodynamic and water quality model was reasonable,which can provide technical support for subsequent study;(3)Simulated the changes of TN and TP in the study area under different rainfall conditions,and calculated the cutting rates of pollutant in rainfall runoff to ensure that the TN and TP concentrations meet the corresponding water standards at fourth day.The results show that under the rainfall reappearing periods of one,two,five,ten,twenty and fifty,the cutting rates of TN in rainfall runoff were 13.58%,20.15%,25.31%,28.66%,33.89% and 36.38%,and the cutting rates of TP in rainfall runoff were 13.33 %,23.75 %,29.58 %,33.33 %,36.24 % and 39.17 %.(4)Analyze the impact of different runoff coefficients,EMC and pollutant degrade coefficients to water quality.The results show that the parametrical conditions have a great influence on the concentration of TN and TP in the water body after rainfall,and the order of correlation between the parametrical conditions and the water quality was pollutant degrade coefficients> EMC> runoff coefficients.According to the improvement degree of TN and TP concentration by different parametrical conditions,it is determined that increasing pollutant degrade coefficients is the most effective parametrical condition to improve the pollution of TN and TP after rainfall in the study area.