A simple stochastic rainfall disaggregation scheme for urban drainage modelling

An alternative method to both the design storm approach and the continuous simulation of historic or synthetic storms is presented. The method is based on, and uses as the only input, the intensity-duration-frequency (IDF) curves of the particular urban catchment of interest. The main concept is to keep the design storm approach for the determination of the total characteristics of the design storm event, i.e. duration and depth extracted from the IDF curves of the particular region, and use a disaggregation technique to generate a ensemble of alternative hyetographs (instead of adopting a unique arbitrary design time profile). The stochastically generated hyetographs are then entered into a rainfall - runoff model and then routed through the sewer network in order to simulate the hydraulic performance of the sewer network. This enables the determination of the conditional distribution of the outflow peak, which can then be utilised for studying the design characteristics and the behaviour of the sewer network.