Comprehensive Evaluation Of Runoff Control Effect Of LID Measures Based On Analytical Probability Equation And Model Simulation

Under the combined effects of urbanization and climate change,the pressure on the city integrated management system is increasing day by day.For this reason,China has extensively carried out the construction of sponge cities with low impact development（LID）system construction as the core content.By regulating stormwater runoff discharge and trapping pollutants to relieve the adverse effects of the increase in urban rainfall and impervious area.To comprehensively evaluate the effectiveness and adaptability of LID to runoff control effects,it is necessary to be rooted in the basic principle of water balance,and to study and reveal the relevant laws of LID on runoff and pollution control.And this provides scientific guidance for the development of sponge city construction strategies.Therefore,this thesis focuses on the two core issues of urban runoff reduction and non-point source pollution control.With LID performance simulation technology and LID scale efficiency optimization methods as the research focus,a comprehensive evaluation system of LID cost effectiveness is constructed basing on optimization algorithms and scheme optimization methods.And the application analysis was made with Guangzhou Tianhe Smart City as the main research area.The main results of the research are as follows:（1）By using the synchronized monitoring data of runoff water quantity and water quality in the study area,the parameters of the constructed SWMM model were calibrated and verified.Sensitivity analysis of the model parameters was carried out based on the Morris method.The results show that the SWMM model has high accuracy in the simulation of rainfall runoff and pollutant concentration in the study area.The most sensitive parameters affecting the runoff,peak flow and pollution load simulation results are the maximum infiltration rate（Max Rate）,the Manning coefficient of the impervious area（N-Imperv）and the washoff exponent（Exponent）,respectively.Meanwhile it is pointed out that the effect of antecedent dry days on water quality results is greater than that of water quantity results.A full understanding of the impact of model parameters on simulation results will lay a solid foundation for the application and analysis of the model.A full understanding of the impact of model parameters on simulation results will lay a solid foundation for the application and analysis of the model.（2）According to the 33-year historical rainfall data from 1980 to 2012 in Guangzhou,the rainfall characteristics of the study area were statistically analyzed.It was pointed out that the frequency of rainfall volume,rainfall duration and rainfall time interval obeyed the exponential probability density function distribution.Combine the analysis of the probability model to explore the water balance principle of LID measures under long-term rainfall conditions,and solve the average runoff reduction rate of LID measures.Then the NAGA-II algorithm is used to optimize the construction scale of different LID measures to provide a scientific and simple method for the rational planning of LID measures.The analysis results show that,in the LID measures per unit area,the runoff reduction capacity of the bioretention cell is the largest;and permeable pavement has the advantage of construction scale,so the overall benefit is greater than the bioretention cell.In addition,increasing investment costs and setting up LID measures with water storage layers will help reduce the scale of construction.（3）Based on the principal component analysis method,the characteristics and correlation of runoff pollutants on different underlying surfaces in the study area were analyzed,and the first flush effect of runoff pollutants was described qualitatively and quantitatively.The SWMM model was further used to simulate and analyze the impact of LID measures on runoff pollution load and first flush effect,which fully illustrates the effectiveness of LID measures on runoff pollution control.The results show that COD and BOD₅ in runoff pollutants are significantly related,and TN and NH3-H are significantly related.In the discharge process of runoff pollution on different underlying surfaces,the concentration of pollutants emitted from the roof is more stable than that of roads and parking lots.In addition,first flush effect of roads and parking lots occur more frequently and with greater intensity.The LID measures can effectively reduce the EMC value of road and parking lot runoff pollutants,while reducing the intensity of the first flush effect,and the larger the LID setting ratio,the more obvious the reduction effect.（4）Coordinate the analysis of the runoff,peak flow,and pollution load reduction rates of LID measures and their life-cycle cost analysis.Comprehensive evaluation and optimization of8 typical LID construction plans were conducted based on TOPSIS analysis.Combined with the climate change conditions,the adaptability and effectiveness of LID measures against future rainfall scenarios were further discussed.The analysis results show that when the cost weight is relatively larger,the solution based on bioretention cell and vegetated swale can save costs.When the weight of the runoff reduction rate is greater,choosing a scheme based on permeable pavement and green roof can improve the rate of runoff reduction.Increasing rainfall under climate change conditions will reduce the cost-effectiveness of LIDs.To deal with the impact of climate change,it is necessary to increase the construction scale of LIDs reasonably.Optimize the LID construction plan according to the actual situation,and effectively improve the adaptability,flexibility,and targeted guidance of the decision-making process of LID construction.