Impact Of Bioretention On Urban Stormwater Runoff

With the development of the society and economy,the problems caused by urbanization are more serious.The urbanization has changed the characteristics of hydrology,and has increased the runoff volume which would lead to flood.The runoff contaminants have got into the rainwater pipe and the river system,leading to nonpoint source pollution.To solve these issues,the government has popularized the low impact development(LID)and has established effective LID practices according to certain conditions in China.This study choosed bioretention,one of the representative LID practices as the object of the study.After investigated the characteristics of the runoff pollutants in Wuhan,we built a bioretention model in laboratory.We selected the sandy loam as the media.Then,the quality control and quantity control of bioretention units were discussed.The experiment provided the guidance for application in this locality.The main contents and conclusions of this study are as follows:(1)We analyzed the quality of road runoff and roof runoff in Wuhan and calculated the concentration variation of pollutants.The pollutants included TN,DN,PN,nitrate nitrogen,ammonia nitrogen,COD,DCOD,PCOD.The rainwater formula in subsequent runoff simulation experiment based on it.(2)The runoff events simulations were applied in peat soil bioretention unit and sandy loam bioretention unit,the inflow used tap water and analog runoff in medium concentration respectively.By comparing the purification effects in peat soil bioretenion unit and sandy loam bioretention unit,we discovered sandy loam was more appropriate as the media in bioretention devices.(3)The bioretention which used sandy loam as the media was selected in the study.We applied runoff simulation to investigate the contamination removal effects in bioretention units.And four influencing factors were considered.The factors were inflow concentration,the return period of rainfall,the duration of rainfall and the area ratio.The bioretention was more effective in removing particulate pollutants than in removing resolvable pollutants.When inflow concentration was low,the bioretention had no effects on nitrogen removal and phosphorus removal.When inflow concentration was high,the removal rates in nitrogen and phosphorus were better than the inflow concentration was medium.In the condition of three stormwater runoff pollution concentrations,the COD removal efficiencies were obvious,and the removal rates were above 70%.(4)The comparison between the sandy loam bioretention and green space showed the following conclusion: compared with the former one,the percentage of conduit volume in quantum of rainfall decreased around 10%,and the peak flow in effluent of bioretention cut by 44%~87%.The analyzations of the characteristics in stormwater runoff as well as the results of quality control and quantity control in bioretention units can provide supports to promote the application of bioretention in Wuhan.