Method for identification of the initial loss of combined sewer catchments

Intense, short periods of rainfall cause the greatest number of operational overflows, leading to the discharge of untreated sewage in combined sewerage systems of large cities. The annual amount of pollution can be estimated based on meteorological, orographic, surface coverage and hydraulic information, by using a detailed hydraulic model of the sewerage system. The most widely used hydrological models require input for the initial loss in order to define the amount of water remaining in the catchment, which decreases the load of the sewer and potentially, the amount of overflow. Earlier measurements of the initial loss were made only in rainwater channels. The results range from 0–6mm in urban territory, which makes the case-by-case identification of this model parameter very important. A methodology is presented in this paper for calculating the amount of initial loss in a combined system catchment without any on-site measurements. The initial loss was identified for a 4500 ha catchment of Budapest. In addition, the dependence of the initial loss on the environmental temperature was analysed