Study On Rainfall Runoff Characteristics And Initial Pollution Control In Xi’an City

Rainfall runoff pollution has become the main cause of urban non-point source pollution,but also an important factor of urban water environment deterioration.Therefore,it is of great significance to master the pollution characteristics of rainfall runoff and study the pollution control of initial rainwater for urban rainfall runoff pollution control and management as well as improvement of urban water environment.This paper,taking xi’an city as the research object,based on the rainfall and runoff water quality from 2008 to 2018 in literature data and field monitoring data in 2019,with chemical oxygen demand（COD）,suspended solids（SS）,ammonia（NH₃-N）,total phosphorus（TP）and escherichia coli as the main indexes such as pH and dung,for direct rainfall and different functional areas（cultural and educational area,traffic area,industrial and commercial）of each underlying surface（roofing,road surface and the green space）pollution characteristics,the comprehensive evaluation of water quality and human health risk research,combined with early scouring effect analysis to define the early rain,The annual runoff volume,pollution control and rainwater reuse were studied respectively.First of all,the results of the study on the characteristics of rainfall and runoff pollution in xi’an city show that:（1）nitrogen pollutants are prominent in the direct rainfall;organic matter and suspended particulate matter are dominant in the roof and road runoff;phosphorus pollutants are relatively more in the green land runoff.（2）the direct rainfall water quality was assessed as relatively clean,and the pollution degree of road runoff in different functional areas was in turn the traffic area>commercial area>industrial area>cultural and educational ar-ea;The degree of roof runoff pollution is the industrial district>commercial district>cultural and educational area in turn,in which the pavement and roof runoff water quality level of cultural and educational area is moderate pollution and pollution,and the pavement and roof of other functional areas are heavy pollution and moderate pollution respectively.（3）the comprehensive evaluation of on-site monitoring rainfall and runoff water quality showed that the comprehensive evaluation grade of heavy rainfall and runoff water quality in the engineering industry was successively>roof>road surface>direct rainfall,green space and roof pollution,and others were relatively clean;The water quality grade of the northwest courtyard is>parking lot>roof>direct rainfall,the green space and parking lot are relatively clean,others are clean.The nemerow index of the roofing,green space and road runoff in the large area of engineering and engineering is 5.10,5.36 and 3.18 times of the direct rainfall,respectively,and the roofing,green space and parking lot in the northwest courtyard are more than 1.19,1.60 and 1.37 times respectively,so the sponge city reconstruction can effectively reduce the pollutants in runoff.（4）the rainfall runoff fecal escherichia coli in the whole concentration range at 2.0×10²¹.23×10⁶CFU/L,the average concentration of 1.04×10⁵CFU/L,beyond the surfaceⅤclass standard,the risk of possible threats to human health.Secondly,based on the characteristics of rainfall runoff pollution,this paper defines the initial rainfall in Xi’an,and the results show that:（1）the M（V）curve is used to analyze the initial scouring effect,and the average pollution load in the runoff generated by 30%rainfall is 60%under the condition of light rain,63%under the condition of moderate rain and 70%under the condition of heavy rain.（2）COD,SS and Zn in different pollutants tend to have strong initial scouring effect,while other indicators such as Pb,Cu,Cr,Ni,Cd and other metal ions have relatively weak initial scouring effect.（3）According to the definition of initial rainfall,the municipal pavement of Xi’an city is 4⁸mm,and the runoff depth is 3⁷mm.The pavement of the plot is 4⁶mm,and the runoff depth is 3⁵mm.The roof is 3⁵mm.Finally,according to the study of initial rainwater,the initial rainwater abandonment rate of Xi’an city under different control objectives is determined.The results show that when the target is 50%of the total annual runoff control rate,the initial rainwater abandonment rate is no less than 6.67mm.With pollution control as the target,the initial abandoned rainfall of xi’an municipal road surface is 7¹0mm,which can control more than 62%SS and 70%COD.The abandoned rainfall of the residential road surface is 5⁸mm,and the roof abandonment is3⁶mm.When taking rainwater recycling as the control goal,the abandonment treatment of initial rainwater on municipal pavement and residential pavement cannot meet the water quality requirements for recycling,but the abandonment of initial rainwater in the roof can meet the requirements when the initial rainwater is 5⁸mm.