Effect Of Rainfall Pattern On Grassed Swale For The Stormwater Runoff Regulation

As an important symbol of the transformation of urban development concept and construction mode,sponge city construction in China is in full swing.As a single measure of sponge city,grassed swale integrates natural infiltration and purification,which can better complete the collection,transfer and discharge of rainwater runoff.At present,it is difficult to control the rainfall parameters artificially in the field experiment of grassed swale,and the simulation experiment of grassed swale is mainly based on the constant flow of water,which has a large deviation from the actual rainfall process in time and space.In this experiment,based on the simulation experiments of different rainfall pattern and rainfall return periods,the regulation effect of grassed swale on urban rainwater runoff process,total runoff and peak runoff was discussed,and the influencing factors were analyzed.Based on the analysis of the existing classification methods of rainfall patterns and 80 rainfall events,seven types of rainfall patterns are concluded according to the location and coefficient of rainfall peak.When the return period of rainfall is 0.5 year,2 years and 5 years,the control effect of grassed swale on runoff is analyzed.The experimental results show that with the increase of rainfall return period from 0.5 year to 5 year,the total runoff reduction of grassed swale gradually increases from 0.144m~3 to 0.370 m~3,and the total runoff reduction rate gradually decreases from 39.86%to14.59%;the peak runoff reduction of grassed swale gradually increases from 0.375m~3/h to 1.614 m~3/h,The reduction rate of runoff peak decreases with rainfall return period increasing.In the range of 11.60%~45.98%,the delay time of runoff peak decreases gradually,in the range of 1 min~7 min.Moreover,the runoff regulation efficiency of different types of swales is quite different.The higher the position of the rain peak in the single peak type,the better the runoff control efficiency.In the two peak rain pattern,the effect of the?in the front middle pattern is the best.The delay time of runoff peak presents the rule is constant flow>uniform rain pattern>double peak rain patterns>single peak rain pattern.In addition,with the increase of rainfall return period from 0.5 year to 5 year,the total runoff reduction and reduction rate,peak runoff reduction and reduction rate,and the change range of peak delay time are:0.251 m~3~0.394 m~3,32.24%~43.88%,0.128 m~3~0.175 m~3,7.96%~11.99%,11.08 min~24 min.the effect of total runoff reduction and the delay time of peak runoff are not as long as the constant flow under the seven rain patterns,and the effect of peak runoff reduction is better than the constant inflow under the seven rain patterns.It can be seen that the runoff regulation efficiency of lid facilities such as grassed swale simulated by constant flow inflow is not equal to the actual rainfall intensity distribution.Therefore,in the construction of grassed swale,the local rainfall characteristics should be fully considered to select appropriate engineering parameters.