Hydrology And Pollution Characteristic Of Urban Stormwater Runoff In Ancient Town Of Suzhou

With the rapid development of urbanization, the ratio of impervious surface in urban areas in increased gradually, leading to the urban stormwater runoff becomes the main cause of urban water environment deterioration. At the same time, compared with the traditional city, the ancient town urban land types and sources of pollution are more complex, the water environment was also particularly vulnerable. In addition,combined with the tension of land use, the urban non-point source pollution control and management is quite particularity and urgency, can't completely copy the type city experience, lack of theoretical basis in the design.Based on the water-quality monitoring data, the parameters of the rainfall-runoff models and the particles size analyses of 5 representative functional areas in the ancient town of Suzhou, such as the commercial districts, the modern residential area, the old residential area, the traffic area and the landscape tourist area, the EMC differentiation, the existing form of the main pollutants, and the dynamic changes of pollutants were studied, and the particulate matter particle size distribution, migration process and the influencing factors were analyzed as well. Besides, discussed the first flush effect of pollutants, and estimate the annual stormwater runoff pollution load of the ancient town. In the analysis, the characteristics of non point source pollution in the ancient town of Suzhou are summarized, and the basic data and theoretical basis for the control and reduction of the surface runoff pollution load in the ancient town of Suzhou are also summarized. The main conclusions can be summed up as follows.?1? Rainfall runoff process line was influenced by the different function areas of the city and the process of rainfall, and the process of road runoff is generally lagged behind the rainfall process, and the response of roof runoff to rainfall is more sensitive.?2? Particulate pollutants were an important output form in the ancient town of Suzhou. At the beginning of the rainfall, particulate nitrogen accounted for the highest level in the whole process of rainfall, and with the rainfall duration decreased continuously. But for phosphorus, the whole process of rainfall was dominated by particles, and the proportion of the decrease during the rainfall was small. Due to the influence of surface alkaline substances, the change of pH in stormwater runoff was generally inverted "U" type. The pollution in the ancient town of Suzhou is very serious, and TCOD, TN, NH₄⁺-N, TP and SS of different underlying surface types in most of the rainfall events were different degrees of beyond the surface water environment quality standards and the integrated wastewater discharge standard. And in different rainfall scenarios, the change process of the pollutants in the road and roof runoff of different urban functional areas showed great differences.?3? The results showed that the particle size distribution, the migration processes and the output characteristics in the stormwater runoffs were greatly different in these five functional areas, which indicates different control measures for the pollution of the runoffs should be taken in the design process. The antecedent dry period, the rainfall intensity and the amount of runoffs showed significant correlations with the particle size distribution, which means these are the important factors. The output of the particles was greatly influenced by the first flush in the early period of the rainfall, and the correlations of the amount of runoffs and the particle migration ability presented significant difference in 30%?early period? and 70%?later period? of the runoff volume. The major existence form of the output pollutants was particle, and the correlation analyses of different diameter particles showed that the particles smaller than 150?m were the dominant carrier of the pollutants via adsorption and accumulation processes.?4? In the ancient town of Suzhou, the first flush effect was relatively common. In most of the rainfall event, TP, TN, COD, NH₄⁺-N and SS in the runoff had different degrees of first flush phenomenon. But according to the first flush coefficient b value, the first flush effect is mainly weak erosion and moderate erosion, did not appear strong erosion of rainfall, which indicates that the rainfall runoff intensity of first flush is not relatively high in the ancient town of Suzhou. In the early period of roof runoff, the effect of roof type is higher than that of flat roof, and the slope of the roof is larger, and the erosion intensity is more obvious. The influence of rainfall characteristic parameters on first flush effect is small, and the correlation between most of the rainfall parameters and first flush coefficient b value is not significant, only the correlation between the first flush coefficient and the partial rainfall characteristics of TP and SS reached a significant level?p<0.05?.?5? The annual pollution load of SS, COD, TN, NH₄⁺-N, and TP in stormwater runoff from the ancient town of Suzhou was 1775.85 tons, 1782.32 tons, 32.08 tons, 17.15 tons, and 8.02 tons. Roof runoff pollution load contribution rate was less than the road, but the COD, TN and NH₄⁺-N in pollution load contribution rate was still high level, are the important factors that affect urban water environment.