Impact of LID on urban rainfall and runoff process
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Abstract:
Urbanization can greatly change the underlying surface and thus have a large influence on the urban runoff process.Recently,most big cities in China have undergone serious waterlogging problems which are caused by many factors,such as the "July 21" urban flood in Beijing,the heavy rain in Wuhan on July 6,2016 and the "May 22" torrential rain in Guangzhou in 2020 all caused huge economic losses.Since 2013,China has promoted the construction of sponge cities to play the role of nature in regulating water bodies,reducing urban waterlogging and water pollution through a series of measures.Low impact development (LID) is considered as a useful practice for sponge city construction and can reduce urban surface runoff to a certain extent. To evaluate the influence of LID on urban runoff generation in sponge city construction,this work takes Guangming District of Shenzhen as the study area and analyzes the impact of different LID measures and their combinations on the urban rainwater process by establishing a regional SWMM model.After the verification by the observed rainfallrunoff,a reasonable and effective model is obtained to simulate the runoff process.The different return period of design rainfall (1 a,5 a,10 a,20 a,50 a,100 a) was input into the model,four LID layout schemes (green roof,permeable pavement,sunken green space,and combined layout) were designed,and three LID areas (10%,20%,30%) were laid into the model at the same time.Their simulated runoff results were compared with those of traditional NO-LID,respectively. The results show that the SWMM model constructed can well simulate the rainfall-runoff process in the study area,with Nash-Sutcliffe efficiency coefficient of 0.868 and relative error of 0.186.The greater the rainfall intensity is,the greater the peak value and flood amount of urban rainfall-runoff are under the design rainfall of different return periods,which indicates that the short-duration and high-intensity rainfall tends to form higher flood peak and flood amount of runoff,which is one of the causes of urban waterlogging.With the same rainfall intensity and LID type,it becomes more obvious for the reduction effect of LID measures on runoff with the increase of LID layout area.The impervious rate of urban underlying surface was changed by LID layout area,which could greatly affect the urban rainfallrunoff process.LID can reduce both the peak value and total amountof runoff,and delay the peak time to some extent.Besides,the larger the area of LID is,the more obvious the effect of LID on runoff reduction is.The combined layout scheme has a better regulation effect on runoff than the single layout scheme.While in the single layout scheme,the best runoff reduction effect is permeable pavement,the best peak runoff regulation effect is green roof,and the sunken green space has the worst runoff regulation effect among the three.Sponge measures on runoff coefficientand peak flow reduction effect is abate in designed rainfall with a return period of more than 10 years,meaning that the sponge measures reach saturation later,the urban waterlogging relief mainly reflected in the case of the small intensity of rainfall. Both the structure and area of the LID layout have an impact on urban rainfall and runoff,and the reasonable layout of LID can effectively alleviate urban waterlogging to a certain extent.The regulation effect of LID measures under low rainfall intensity is obvious,but its regulation effect quickly reaches saturation in view of heavy rain,and the regulation of urban rain and flood in sponge city is "elastic",so it is necessary to further optimize the layout scheme in view of heavy rain,such as considering the dynamic coordination of greygreen measures,increasing the saturation threshold of sponge measures,and grasping the whole from the perspective of urban ecosystem to realize the effective control and utilization of rainwater runoff.
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