Study On The Characteristics Of Rainwater Runoff Pollution And The Control Effect Of Sponge City Facilities In A City

Stormwater runoff belongs to diffused pollution,and is contingent,random and universal to some extent.The diffused pollution caused by stormwater runoff has become one of the key factors of urban water pollution.To better address the problem of diffused pollution,the study of basic features of pollutant concentration variation in runoff during rainfalls is indispensable.The construction of sponge cities is an important path to urban sustainable development,as the facilities in sponge cities can remove diffused pollution and improve urban runoff control rate,emphasizing the extreme importance of the facilities'pollution control effect.In this paper,the downtown area of a city in northwest China is taken as the research area,the monitoring and analysis of runoff water quality are carried out on the local rainwater,its different underlying surfaces,typical sponge city facilities and pipe network outlets,and an estimation method of pollutant concentration in receiving water is established to conduct a simulation verification on the water quality fluctuations of local receiving water during rainfalls.In the process of a single rainfall,The peak concentration of COD_Cr of the city's rainfall water quality is between 35.67mg/L and 63.61mg/L,that of SS is between 14mg/L and 30mg/L,that of NH₃-N is between 1.61mg/L and 3.30mg/L,and that of TN is between2.16mg/L and 4.41mg/L.Combining water quality data from two of the rainfall events,and to evaluate the water quality of stormwater runoff in different underlying surfaces of the city with Water Quality Index Method?WQI?.The index of most of the underlaying sufaces were over 5.The lowest index also reached 4.6.The index of roadways is the highest,reached 14.5.The pollution of all kinds of underlying runoff in the city were very serious,most of their water quality were worse than Grade V.Various sponge city facilities have good removal rates of COD_Cr,SS and other pollutants,with an average removal rate above 70%;and the average removal rate of petroleum is also above 59%.Plant covered facilities such as high level flower beds and rainwater gardens have high removal rates of ammonia nitrogen,TN,BOD₅ and other pollutants,with an average removal rate above 66%,while that of facilities not covered with plants like porous pavements is relatively low,with an average removal rate of those pollutants only between 27%and 57%.The total runoff control rate of the five watersheds of the city is analyzed,and the average total runoff control rate of one watershed with a sponge transformation completion rate of 67.12%has reached 94.75%.Under the condition of no pipeline mixing,the higher the completion rate of sponge transformation is,the higher the average total runoff control rate will be.Last but not least,through the establishment of a simplified estimation model of pollutant concentration in receiving water,all factors influencing receiving water are analyzed,and parameter calibration and verification of the model are carried out according to the basic data from the research area.The average error between the simulated result after calibration and the actual result is as high as 24.01%;while that between the verified result and the actual result reaches 20.79%.The calibrated and verified result shows a similar variation trend with the actual result.Therefore,this model can competently demonstrate the actual situation of the research area and has certain predictability.