Study On Rainfall Runoff Pollution Characteristics And Pollution Load In Typical Campus In Wuhan

With the rapid process of urbanization,urban runoff has become a prominent problem.After urbanization,the total amount of runoff increases,the peak runoff occurred earlier,and the infiltration decrease.These lead to frequently-occurring waterlogging in the urban areas and serious pollution in receiving water bodies caused by discharged urban runoff with a large number of pollutants.Hubei University of Technology with combined drainage system locates at the east of Xunsi River,which has a great influence on the deterioration of the water quality of the river.With the implementation of water-related policy in Wuhan,the contribution of non-point source pollution to the water environment will be more prominent.Study on urban runoff from campus areas can plays a positive role for water environment improvement.This paper chose Hubei University of Technology as the research area,obtained the rainfall-runoff pollution characteristics of the campus by field monitoring,built a campus rainfall-runoff pollution load model based on Storm Water Management Model（SWMM）,and analyzed the trend of rainfall-runoff pollution load under different conditions.Based on the rainfall runoff pollution load model,the Low Impact Development（LID）was retrofit to provide suggestions for the reduction of campus rainfall runoff pollution.The main conclusions are as follows:（1）The main pollutants in the runoff in courtyard/square in the campus are TN and COD_Mn.Most of the pollutant concentrations exceed the Environmental Quality Standard of Surface Water V level.Within the first 20 mins of runoff,concentrations of pollutants are obviously fluctuating,after that,concentrations show decreasing trends.The change of a pollutant concentration is related to pollutant type,rainfall characteristic and accumulation of pollutants.The higher the rain intensity is（>2.2mm/5 min）,the more serious the first flush effect will be.There are different kinds of correlation ships between TSS and the pollutants.TSS is highly correlated with TP,while moderately or highly correlated with NH₃-N and COD_Mn.In order to protect the local water environment,the initial 6 mm rainwater should be discarded for the courtyard/square.（2）Compus rainfall-runoff pollution load model is built based on SWMM by dividing 101 subcatchments and generalizing 96 junctions and 30 outfalls.The land use types in research area are divided into 5 kinds of units such as roofing,pavement,green space,courtyard/square,playground and set different initial parameters of hydrological water quality.The weighted average values of the parameters are obtained according to the area ratio of each unit in each subcatchment.Taking the roof and courtyard/square as examples,the hydrologic parameter were calibrated and validated.The average errors of roof runoff discharge and runoff volume are 4.37%and 16.20%,respectively,and the corresponding errors for square/courtyard runoff were 2.29%and 8%.These values indicate the model can operate with errors within an acceptable range.（3）By assuming different scenarios such as"different rainfall intensity conditions"and"different rainfall types conditions"for runoff pollution load forecasting during single rainfall events,the results show that a pollutant concentration increases with the increase of the recurrent period of a rainstorm.With the increase of a rainfall peak coefficient,the rainfall peak timing occurs later.As a result,the runoff peak value and runoff load from the campus are increasing.The change of annual rainfall-runoff pollution load is predicted by setting different"designed hydrological years".The results show that pollution loads from different designed hydrological years are different.The annual pollution loads of TSS,CODMn,TN and TP from the campus during the wet year are 51016.47 kg、14640.60 kg、1437.60 kg、63.60 kg,about 1/4,1/3,3/5 and 1/3of pollution load per area in Wuhan city.The pollution load of rainfall-runoff from the campus is lower than that from Wuhan city.（4）Surface areas of different types of road,roof,green space,courtyard/square,and playground area of Hubei University of Technology accounted for 9.84%,32.43%,20.23%,29.22%,7.52%of the campus area.The impervious ratio reached 79.02%,which led to a quick rain-fall runoff response（5¹0 min）and a quick runoff pollution into the river.Three kinds of land use types（roofs,green space,courtyard/square）were retrofitted with LID technology in SWMM,including green roofs,permeable pavements,and bio-retention cells.After the retrofit,when the storm return period was10,the reduction in the runoff peak reached 47.82%and the reduction in total runoff reached 35.73%.The runoff coefficient reduced from 0.93 to 0.60 and the pollution load reduction ratio exceeded 30%.When the storm return period was 1,the reduction in the runoff peak reached 56.25%and the reduction in total runoff reached 43.23%,the runoff coefficient reduced from 0.78 to 0.45,the reduction rate of the pollution load exceeded30%.