Assessment of environmental impact of urban drainage overflows

This paper describes an innovative procedure for estimating pollutant masses discharged by sewer system overflows after a rain storm, also classifying the “environmental impact” of each overflow structure of an urban drainage network with regard to a given receiving water body. Specifically, the term “environmental impact” is defined as the value of the pollutant mass discharged from the point of interest, during any storm event. Since, the “environmental weight” is defined as the ratio between such a discharged mass and the whole mass discharged during the same event from the entire set of considered discharge points. The procedure proposed here for estimating the environmental impact is of practical application; it requires just to know some relatively simple data on catchments and networks, which are the input of an appropriate multiregressive algorithm calibrated on numerous real and theoretical cases. Then the procedure allows to optimize the decisions about where the feasible interventions should be located, and which priorities should be chosen to achieve the pre-established level of pollution reduction in the receiving water bodies.