Design Storms for First Flush Modelling at Sewer Inlets

First flush is one of the key phenomena in the dynamics of pollutants in urban drainage. It is affected by a number of factors, like the characteristics of urban surfaces and drainage systems, the rainfall patterns, the street sweeping frequency and efficiency, and the gully pot features. This paper discusses how a storm event can maximize pollution mass and concentration in first flush runoff. It turns out that the critical events derive from particular combinations of factors and not necessarily from the maximum values of rainfall depths or intensities.