Effects of Urbanization on Frequencies of Overflows and Pollutant Loadings From Storm Sewer Overflows: A Derived Distribution Approach

On the basis of exponential density functions for volume of runoff, interevent time, and duration of runoff event and beta density for the rescaled pollutant (biochemical oxygen demand) concentration, and gamma density for river flow volumes during a critical period, new distributions are derived for overflow volumes and for quality of pollutant in the river after mixing with the untreated overflows of the overtaxed system. This is accomplished by means of hydrological relationships between different variables. The current data on runoff volume, duration of runoff events, etc., are transformed to account for future urbanization activities. The newly formed variables are used in the derivation of probability distributions for overflows and receiving body pollutant concentration after urbanization. The analytical model is compared with the simulation model “STORM.”