Flooding Simulation And Non-point Source Pollution Of ZongYang City Based On GIS And SWMM Model

Due to the relative lag between the construction of urban flood control and drainage facilities and the development of urbanization,China is still facing serious water environment problems.When extreme rainstorms hit,runoff washes over the ground and carries a large amount of pollutants into the stormwater network for discharge,contributing to a significant increase in the risk of urban flooding and increasingly serious surface source pollution.The paper takes the urban area of Zongyang as the research object,collects relevant data to build a SWMM model,simulates the drainage capacity and pollution load of the study area and explores feasible measures to prevent flooding and reduce surface pollution.In this paper,we use ENVI and ArcGIS software to analyze the subsurface of the study area to obtain the parameter data required for model construction,build a better SWMM model and verify the reliability of the model by parameter rate determination.The surface runoff characteristics and surface source pollution load characteristics of the study area under different recurrence rainfall conditions are analyzed,and the drainage capacity of the stormwater pipe network is evaluated in terms of nodal overflow and pipe overload;the total pollution load,scouring load distribution and pollution concentration changes are comprehensively considered to evaluate the current situation of surface source pollution.Based on the analysis of the current situation in the study area,the low impact development measures that can be taken for urban flooding risk prevention and runoff pollution control are explored to provide reference and suggestions for reducing flooding risk and pollution load in Fir Yang urban area.The main findings of this paper are as follows:（1）Using ENVI software to analyze the subsurface of Zong Yang urban area,the percentages of each category are 46.6%for green land,1.2%for water bodies,19.5%for roofs,11.3%for bare land and 21.4%for roads.Use ArcGIS software to delineate catchment areas,integrate various parameters needed for model building and build a complete stormwater system database.After the initial construction of the SWMM model,sensitivity analysis was performed on eight uncertain parameters,and the parameters were continuously adjusted to complete the model rate determination.（2）The current drainage capacity of the pipe network in the study area was analyzed and the overflow nodes and overloaded pipes and drains were classified according to the overflow or overload duration.The simulation found that the total percentage of overflow nodes in the stormwater pipe network was 27.75%,31.55%and38.91%during the short calendar rainfall of 2a,3a and 5a,respectively;and the total overload length of pipes and drains was 34.13%,36.95%and 42.52%,respectively.Zong Yang city current rainwater pipe network drainage capacity is not enough,in the 2a rainfall recurrence period,there are also part of the flooding points and flooding overload pipe section,the need for pipe network for the transformation or expansion.During the simulation of different rainfall recurrence periods,the total pollution loads of COD,TSS,TN and TP in the study area increased up to 14.99%,12.05%,26.20%and 33.73%compared to the previous recurrence period.（3）The simulation results show that the LID facilities can reduce the total surface runoff by 23.35%and the peak flow by 17.32%,which can effectively reduce the risk of urban flooding.LID facilities can reduce the total pollution load of COD,TSS,TN and TP by 34.11%,36.57%,30.81%and 22.42%respectively.In addition,the LID has a certain degree of energy saving and carbon reduction benefits,using the carbon emission factor method to account for carbon emissions during the construction and operation phases of the LID,the results show that the LID construction process will increase CO₂emissions,but in the operation phase of the LID on carbon emissions reduction rate of up to 32.38%.（4）The study found that the average reduction rate of COD,TSS,TN and TP could reach 21.46%,20.88%,24.78%and 24.68%in the reservoir.Figure[55]table[30]reference[87]...