Research On Urban Flood Process Based On Overall Model In Changing Environment

Global climate change,urbanization is accelerating,and urban extreme weather is frequent.The resulting urban floods and water environment pose a huge threat to human society.As a large-scale city in northwestern China,Xi’an has been affected by urban floods in recent years.Therefore,this study is of great significance to the urban flood control in Xi’an.Based on the causes of urban flooding,this paper studies the evolution law of urban flood disasters in Xi’an,and constructs a city flood model based on the overall model based on the source emission reduction,process control and terminal treatment ideas in a certain area of Xi’an.Hydrodynamic process in urban floodplain.The research on surface runoff law,pollutant accumulation,intrinsic characteristics and corresponding control effects in the study area can be used to grasp the evolution law of flood disasters in the study area and provide guidance for the construction of sponge city.The main work and important conclusions of this paper are as follows:(1)Analyze the impact of climate change and urbanization factors on urban flooding.Remote sensing and other means were used to interpret the 1984-2016 chronological images of.’the study area,and combined with Arcgis,ENVI and other tools to obtain land use/cover data,used to reveal the temporal and spatial variation characteristics of the underlying surface of the study area.Based on the daily precipitation and temperature data of Xi’an and surrounding sites for nearly 60 years,combined with M-K test and non-parametric sen’s inclination test,the temporal evolution of rainfall and temperature was studied,and the spatial distribution characteristics of extreme rainfall were analyzed by urban-rural time-space contrast method.Using the temperature reanalysis data for the same period,the observation subtraction reanalysis(OMR)method is used to reflect the impact of urbanization on local temperature.The results show that the overall precipitation in Xi’an has shown a downward trend,but the situation of extreme rainfall is increasing.The annual average temperature in Xi’an has a significant growth trend.In 1994,there was a sudden change.Before that,it was lower than the average annual statistical value.After that,it was 0.99 ℃ higher than the average temperature.The urbanization factor accounted for 0.43 ℃.Using the principal component comprehensive model to obtain urbanization factors is the main reason for the formation of urban flood disasters.(2)The urban flood water quality model is constructed based on the overall model.According to the characteristics of the study area,the short duration design rainstorm process under the drainage standard and the long duration design rainstorm process under the flood control drainage standard are given.Based on the current land use type,DEM elevation,river water system and rainwater network data,a model of urban flood water quality based on the overall model was constructed to simulate rainfall,runoff,pipe flow,river entry,lake entry and urban pollution.The whole process of material production,migration,degradation and output was carried out by using the heavy rain on June 24,2016,and the heavy rain on June 26,2018 and July 2,to determine and verify the internal hemisphere and water quality of the model.It is required to accurately and comprehensively present the storm flooding process in the study area,and to estimate the pollution load in the study area.(3)Exploring the effects of gray-green combination measures on source reduction and process control under different rainfall conditions.According to the characteristics of the study area,the following low-impact development measures based on the characteristics of the study area and the grey facilities based on the storage tank and pumping station were added to study the source-level emission reduction and process control under different rainfall conditions.The effect,while assessing the removal effect of the gray-green measures on the pollutants.It is found that with the increase of rainfall return period,the source emission reduction rate is decreasing,the process control rate is increasing,the pollution load is gradually increasing,but the pollution load removal rate is gradually decreasing.(4)Exploring the effects of the combination of gray-green measures on urb an flooding under different rainfall conditions.Considering the three aspects of key intrinsic point,large piece of water accumulation and long-term flooding improvement,the main intrinsic characteristics and improvement effects of two standard depths(water depth≥15m and≥25m)are mainly in the process of heavy rain.According to statistics,this combination can effectively control the key intrinsic points under the 20-year rainfall;the improvement effect under the rainfall during each return period decreases slowly with the increase of the inundation time.Therefore,the combined measures for short-term water accumulation The effect of internal hemorrhoids is better;under the premise of the same amount of precipitation,rainfall with more uniform time-course distribution often causes more serious guilt in the study area.