Hydrology and water quality of rainfall-runoff in combined sewerage system along Suzhou creek in central Shanghai

In order to obtain the processes of hydrology and water quality of urban combined sewerage system (CSS) in highly urbanized region, the precipitation, discharge and pollutant concentration of four different intensity rainfall (light rain, moderate rain, heavy rain and storm) were measured from Jul. to Sep. 2007 in the Chendulu CSS along Suzhou Creek in Shanghai. The results show that the shapes of runoff graph are similar to rainfall graph, with a weaker fluctuation range and a 15-25 min delay between rainfall and runoff graph. Runoff coefficients of the four different rainfall are 0.33, 0.62, 0.67 and 0.73, respectively. The 30/30 first flush phenomenon is found in Chendulu CSS. The peak of pollutant concentration graph lags rainfall peak about 30-40 min. The pH and event mean concentration (EMC) of Cu, Zn, Cr, Cd, Pb and Ni totally measure up to environmental quality standards V for surface water of China besides COD, BOD₅, NH₄⁺-N and TP, and the EMC of COD, BOD₅, NH₄⁺-N and TP are 225.0-544.1, 31.5-98.9, 8.9-44.2 and 1.98-3.52 mg·L^-1, respectively. The rainfall-runoff pollutant concentration in Chendulu CSS is close to those of other foreign cites. At the confidence level of p < 0.01, good relationships exist between SS and COD, BOD₅, NH₄⁺-N and TP, respectively, and the average proportion of particulate organic pollutant and nutrient is 70.21%.