Characterization of runoff from various urban catchments at different spatial scales in Beijing, China.

In order to investigate the characterization of runoff in storm sewer from various urban catchments, three monitoring systems at different spatial scales have been installed separately. They have been held since July 2010 in urban area of Beijing (China). The monitoring data revealed that chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and NH(3)-N values significantly exceed the Class V surface water quality standard developed by Ministry of Environmental Protection of the People's Republic of China (MEP). A surface solids buildup and wash off model for small watershed was adopted to analyze and discuss the process of a runoff pollutant discharge. More than a half of pollutant parameters presented a good fit to the model. However, a slightly worse-fit to the wash off model appeared in less than half of the data. Due to the influence of sewer sediments, sewer system characteristics, catchment characteristics, and other reasons, first flush was seldom observed in storm sewer runoff from these three survey areas. Meanwhile, the correlation between TSS and any other pollutant was analyzed according to cumulative load of pollutants in runoff events. An event mean concentrations (EMCs) approach was adopted to quantify the pollution of runoff. EMCs of various pollutants in storm sewer runoff between different rainfall events were slightly higher than the typical values observed in similar areas at home and abroad, according to other studies reported in literature. Based on quantitative analysis, it can be concluded that urban non-point source pollution is recognized as the major causes of quality deterioration in the receiving water bodies. This is after the point source pollution has been controlled substantially in Beijing. An integrated strategy, which combines centralized and decentralized control, along with the conditions of meteorology, hydrology, urban planning, existing drainage system, etc., will be an effective and economic approach to urban runoff pollution control.