Research On The Green Space Flow Of Influencing Factors And Runoff Coefficient

With the development of urbanization,the types and conditions of urban underlying surface are complicated,the design of green soil,vegetation and topographic structure is diversified,and the corresponding targets of modern urban drainage system are diversified.Therefore,by using the methods of literature review,model simulation(Hydrus-1D model),experimental measurement,theoretical calculation(Kinematic Wave equation,Soil Conservation Service Curve Number algorithm),mathematical analysis(Statistical Product and Service Solutions、Origin)and so on,taking Beijing area as an example,to study the effects of rainfall,vegetation,soil,topography and other factors affecting the yield and runoff coefficient of urban greenbelt,The variation of runoff time,total runoff,peak time,peak flow rate and runoff coefficient with the influencing factors is analyzed,and the key parameters and applicability of various methods for calculating the runoff coefficient of urban green space are compared.It provides theoretical basis and calculation method for the actual runoff production process and runoff coefficient of green space in complex urban environment.The main findings of the study are as follows:(1)The main factors affecting the process of green space production and flow are rainfall,vegetation,soil and topography.Rainfall affects the runoff production process through rainfall size and rainfall interval days(affecting soil moisture content in the early stage).The larger the rainfall,the less the rainfall interval days(the greater the water content in the early stage of soil),the greater the green runoff yield;the larger the vegetation cover area,the more obvious the effect on runoff reduction and the smaller the impact on the water quality of the initial runoff;the initial water content,saturated water content and water conductivity of the soil have an effect on the green runoff,and change with the change of soil thickness and species;the slope and leveling degree of topography affect the seepage storage and discharge of runoff,and then affect the runoff production and discharge.(2)The correlation analysis shows that the recurrence period,rainfall peak position and terrain slope have the significant positive correlation on the rainfall runoff coefficient,the rainfall interval,plant coating degree,soil thickness and terrain flatness show the significant negative correlation on the rainfall runoff coefficient,and the soil type on the value of the rainfall runoff coefficient.A study of green runoff coefficient under the combined action of various factors shows that the range of green runoff coefficient is between 0.02~0.52 under different rainfall,vegetation,soil and terrain conditions,and the range of green runoff coefficient is expanded compared with the experience value in engineering design.Therefore,all factors should be taken into account in the design of green space and the use of green runoff coefficient.(3)Under the same conditions,the runoff coefficient values obtained from KW equation,SCS-CN algorithm,Hydrus-1D model simulation and test measurement are different,which are different from the engineering experience,mainly for the different key parameters considered in calculating the runoff coefficient.Among them,KW equation is easy to calculate and more applicable to drainage planning;SCS-CN algorithm considers various factors and is closer to the results of test measurement;Hydrus-1D model simulation can change rainfall,vegetation,soil and slope,and other conditions,suitable for fine simulation of small range of plots;the test measurement can be accurate lack of soil property parameters and green runoff coefficient value under complex terrain.