Estimation of Nonpoint Source Runoff from Urban Area and Its Control Measures

In an urban area the ratio of pollutant loads from nonpoint sources to total discharging loads is increasing. It is important to quantitatively estimate nonpoint source runoff and have accurate perspective of nonpoint source control for water quality management. Systematic researches on nonpoint source runoff and evaluation of control options, however, have not performed in Japan. Problems caused by nonpoint source pollutants are not only organic pollution or eutrophication but also environmental risk caused by hazardous chemical materials and pathogenic bacteria. Rainfall runoff is regarded as main processes of discharging materials that cause environmental risk. So, systematic investigations are needed for problem identification.The author has estimated annual pollutant runoff loads during wet weather by simulation method using model parameters obtained from the result of analysis of field survey data. And the author has discussed control alternatives to improve urban wet weather loads. In this paper, principles and measures to control nonpoint pollutant runoff are discussed. Some simulation results have shown that it is necessary to combine some control measures, which are put into practice at different control point, to decrease nonpoint pollutant runoff. As for street cleaning, although main purpose of which is to beautify urban area, cost-effectiveness to decrease nonpoint source runoff is comparable to other control options.