Sustainable Water Management Solutions for Large Cities (Proceedings of symposium S2 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 293, 2005, 185-195

1 Department of Civil Engineering, Nagasaki University, 1–14, Bunkyo-machi,
Nagasaki 852-8521, Japan

2 Division of Construction Management, Nagasaki City, 2–22, Sakura-machi,
Nagasaki 850-0031, Japan

Abstract Many people live in a large city, so lots of pollutants wash off into receiving waters. If this occurs in a closed area, the water quality deteriorates, e.g. inducing eutrophication. A sewer system has already been constructed in almost all large cities, but there are problems like Combined Sewer Overflow (CSO) or Separate Sewer Overflow (SSO). Pollutant runoff from nonpoint sources has been investigated under wet weather conditions by field observation in the Dejima River basin in Japan. Based on the observed data, the detachment rate of pollutants has been estimated in detail, and correlated with not only the condition of the watershed, but also a rainfall time series consisting of antecedent rainfall and the current event. This paper shows that the wash-off rate of pollutants under wet weather conditions can be predicted exactly by considering the relevant factors.

Key words detachment coefficient; field observation; L–Q curve; nonpoint source; pollutant runoff; total nitrogen; urban area; wet weather