| In recent years,extreme weather appears frequently,a short period of local storms continue to occur,resulting in frequent urban flooding.The runoff coefficient is an important parameter in the design of urban rainwater drainage system.The value of the runoff coefficient is mainly defined in the "Outdoor Drainage Design Code",and selected according to the surface type.Studies have shown that runoff coefficient is a dynamic variable that continues to change during rainfall.It is a key primary work to design the urban rainwater drainage system and low impact development rainwater system.Therefore,it is of great practical significance to carry out the research on the dynamic runoff coefficient for typical impervious surface based on rainfall process.It will provide scientific support for urban drainage system planning design and sponge city construction.Based on the background of Ma'anshan City,Anhui Province,China,this paper explores dynamic runoff coefficients of the asphalt pavement and cement concrete pavement as typical impervious surfaces under different rainfall scenarios(rainfall pattern,rainfall amount,rainfall duration,return period,etc.).A simulated rainfall device that includes water supply system,flow measurement and switching system,adjustable lift bracket system,the nozzle system and the flow control system was invented and developed,based on the analysis and comparison of the functions and characteristics of the existing artificial simulated rainfall devices.It can be used to achieve the Chicago rainfall pattern,uniform rainfall pattern,etc.For the asphalt pavement,Chicago rainfall pattern was used,and rainfall durations 30 min,45min,60 min,90min and 120 min were selected.The rainfall return periods were 1-yr,2-yr,3-yr,5-yr,10-yr,20-yr,30-yr,50-yr and 100-yr,respectively.Under Chicago rainfall pattern,the effects of dynamic runoff coefficient for asphalt pavement during different rainfall duration,different return periods and different rainfall intensities were discussed.The process profiles of rainfall and runoff under different rainfall scenarios were obtained.The relationship between return period,rainfall duration and rainfall intensity and runoff coefficient was obtained by analyzing the results.It shows that the peak and mean values of instantaneous rainfall intensity are logarithmically related to the peak and mean values of instantaneous runoff coefficients.The relationship between the rainfall duration and the peak value of the instantaneous runoff coefficient is linearly related to the mean value of theinstantaneous runoff coefficient.The logarithmic relationship between the peak value and the mean value of the return period and the instantaneous runoff coefficient.For the cement concrete pavement,the rainfall patterns of Chicago and Uniform were selected,and the rainfall durations were 30 min,60min and 120 min,respectively.The return periods of 2-yr,3-yr,5-yr,10-yr and 20-yr were selected.The results show that the initial times of runoff,the trends of instantaneous runoff coefficient and the peaks and runoff cutoff times are different due to the difference of rainfall patterns.The rainfall intensity is linear with the instantaneous runoff coefficient,and the instantaneous runoff coefficient increases with the rainfall intensity.Under certain conditions,the instantaneous runoff coefficient increases with the rainfall.The duration of rainfall and the instantaneous runoff coefficient increase logarithmically with rainfall in the early stage of rainfall,and the instantaneous runoff coefficient tends to 1 when the rainfall continuous for some time.Quantitative analysis was carried out using SPSS software.The quantitative relationship between the factors and the instantaneous runoff coefficient was obtained.For the asphalt pavement,the rainfall intensity has the greatest influence on the runoff coefficient,and the rainfall amount is the second.For the cement concrete pavement,the instantaneous runoff coefficient is determined by factors such as rainfall intensity,rainfall amount and rainfall duration in this study.The instantaneous runoff coefficient is a dynamic variable determined by multiple factors.Through the analysis of the results,the dynamic changes of the runoff coefficient of asphalt pavement and cement concrete pavement are similar in the trend with the influences of rainfall duration,rainfall intensity and rainfall amount. |
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