Study On The Influence Of Rainstorm Characteristics On The Pollution Control Effect Of Typical LID Measures

Under the background of rapid urbanization,coupled with global climate change leads to frequent occurrence of extreme rainstorm events,frequent urban waterlogging,urban water problems such as the deterioration of water environment,low impact development as a new rain flood management measures are widely applied to solve the new urbanization under the background of urban water ecosystem,water environment,water safety and water resources and other problems In this paper,a low-impact development community in Xi Xian New Area,the first batch of pilot cities for sponge city construction in China,is taken as an example.This community includes two LID measures,rainwater garden and permeable pavement,and a SWMM Model for the study area is constructed.Because different hydrological and meteorological conditions play a key role in the regulation and control of LID facilities,this paper studied the influence of rainstorm characteristics,including return period,rain peak coefficient and discontinuous rainfall,on runoff and pollution control effect of LID measures,and and the following main conclusions were drawn:(1)With the increase of the return period,the runoff control rate of the study area decreases,the peak discharge of the outlet increases significantly and the peak occurrence time is advanced to a certain extent,the total pollutant load of the outlet increases significantly,and the pollutant load reduction rate decreases;Rain peak coefficient can affect the process of water quality and quantity within a certain range,but has little effect on the control of water quantity and total pollutant amount.With the increase of rain peak coefficient,the peak discharge of the outltet increases obviously and the peak time is delayed obviously,but the total pollutant load decreases slightly,the runoff control rate and pollutant load reduction rate remain basically unchanged.(2)With the increase of return period,runoff control rate and pollutant load reduction rate of single and combined LID schemes decrease.The runoff control effect of single measure is permeable pavement>rain garden>green roof and sunken green space;The peak flow control effect is permeable pavement>sunken green space>rain garden>green roof;Among the four LID single measure schemes,the green roof runoff pollutant control effect is the worst.The LID combination program has better effect on runoff control and runoff pollutant control than the LID single program.The runoff control rate,pollutant load reduction rate and peak discharge reduction rate of the four LID measures combination are higher than the three LID measures combination,and the three LID measures combination is higher than the two LID measures combination.However,the area of LID measures of LID combined scheme is higher than that of single LID scheme,and the control effect of LID measures per unit area is not necessarily better than that of single LID scheme.And the control of runoff and runoff pollutants by LID combination scheme is not a simple sum of all LID schemes.(3)Under the condition of non-continuous rainfall,with the increase of rainfall interval,the runoff control rate of LID measures in the study area increases.Although the increase range of runoff control rate is small,the backfield rainfall has a stagnant peak and obvious peak reduction effect.The total pollutant load and pollutant load reduction at the outlet first decrease and then increase.In this case,the pollutant load reduction rate is different from the runoff control rate,and the water quality process of discontinuous rainfall is more complicated compared with the water quantity.With the increase of rainfall intensity,the runoff control rate decreases and the pollutant load reduction rate decreases.Even for events with the same rainfall,the rainfall time allocation also affects the water quantity and the water quality process through the influence of the forefield rain on the backfield rain.(4)For single rainfall,there is a strong correlation between pollutant load reduction rate and runoff control rate.The influence of rainfall intensity and duration on runoff control rate and pollutant load reduction rate of non-continuous rainfall is the same as that of single rainfall.