| Urban green space,which can effectively regulate the rain,and then alleviate urban storm water,plays a key role in resourceful treatment of rainfall and improving the urban ecological environment.In order to study the runoff yield mechanism and the effect of regulating surface runoff of lawn and the sunken greenbelt by simulating rainfall experiments,this paper takes the typical urban green space(lawn,sunken greenbelt)as the object.As for ordinary lawn,based on the bare land we studied its runoff characteristics,the change process of runoff coefficient and the reduction effect of rainfall runoff by simulating rainfall experiments,under different rainfall intensities(30,60,90mm/h),different coverages(60%,90%),and different gradients(5°,10°,20°).The results showed that:(1)When the coverage of the lawn was 90%,the all ordinary lawns had better effect of the delayed initial runoff time and runoff peak time,under different experimental conditions which delayed 17.6-38.5mins and 20.5-46.5mins respectively.(2)The effect of the delayed initial runoff time of lawn with 60%coverage was not significant under rainfall intensity of 90mm/h,and the delayed time was only 0.5min on average.But under other experimental conditions,it had a remarkable effect on delaying the runoff peak time,and the delayed time was between 8.1 mins to 17.5 mins.(3)The lawn with different coverages could reduce the peak runoff in different degree.Compared with the bare land,the peak runoff rates of the lawn with 60%and 90%coverage had reduced by 10.90%-18.80%and 12.77%-30.37%,respectively.(4)The lawn with two different coverages can both effectively reduce runoff,but the degree of reduction gradually decreased with the increase of rainfall intensity.When the rainfall intensities were 30mm/h,60mm/h,and 90mm/h,the runoff reduction rate of the 60%coverage lawn were 31.05%,20.72%,and 13.40%,respectively.As for the 90%coverage lawn,the runoff reduction rate could be more than 40%.(5)The runoff coefficients of 60%and 90%coverage lawn were 0.29-0.58 and 0.20-0.39,respectively.And they were decreased by 21.96%and 50.76%on average compared with bare land.(6)The statistical model of the runoff coefficient of lawn with the rainfall intensity,coverage,gradient and rainfall time was established under experimental conditions.After verification,Nash-Sutcliffe efficiency coefficient of the model was greater than 0.80,that was to say,this model could be trusted.As for sunken greenbelt,we studied its runoff characteristics,the change process of runoff coefficient and the effect of rainfall runoff reduction under different rainfall return periods(1,3,5a),height of the rainfall overflow inlets(4,6,8cm),infiltration materials(gravel layer,gravel-free layer),rainfall temporal patterns(typeⅣ,type Ⅱ,type Ⅰ),based on the sunken greenbelt experimental device.The results showed that:(1)When the rainfall return period was 1a,there was no flow under different height of the rainfall overflow inlets.The initial runoff time exceeds 60mins under other conditions.(2)The rainfall time-runoff rate curve of sunken greenbelt was influenced by the infiltration material.As for the sunken greenbelt,which had the gravel layer,the runoff rate would increas with the extension of water intake time,and then it reduced rapidly after a period of peak stability.As for the sunken greenbelt,which had the gravel-free layer,the runoff rate would increas in a terraced way with the extension of water intake time,and then it reduced rapidly after vibrating around the peak value.(3)The sunken greenbelt had a very significant impact on reducing runoff.When the rainfall return periods were 1,3,and 5a,the runoff reduction rate were 100%,70.48%,69.41%on average,respectively.(4)When the rainfall return periods were 3a and 5a,the runoff coefficients were 0.07-0.25 and 0.10-0.35,under different height of the rainfall overflow inlets conditions.At the same time,the correlation between runoff coefficient of sunken greenbelt and the impact factors was infiltration material>height of the rainfall overflow inlet>rainfall return period>rainfall temporal patterns.(5)The statistical model of the runoff coefficient of sunken greenbelt with the rainfall return period,height of the rainfall overflow inlet,water intake time was established under experimental conditions.After verification,Nash-Sutcliffe efficiency coefficient of the model was 0.74,that was to say,the model could be trusted. |
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