Optimized series of rainfall events for model based assessment of combinded sewer system

Often, two different models are provided for the same sewer system, namely a hydrodynamic model for the hydraulic verification and a conceptual model for the verification of compliance with standards for combined sewer overflows (CSO). However, a combined verification using only one model has many advantages. For the necessary calculation of water levels for the hydraulic verification, only hydrodynamic models are applicable. Consequently, a hydrodynamic model has to be used for a combined verification if the same model should be used for both applications.
Often, the verification and assessment of CSOs asks for long-term simulation. The use of hydrodynamic models in combination with continuous simulation of a couple of years up to several decades regularly leads to unacceptable high computation times. As an alternative, a series of rainfall events can be used for the simulations instead of the precipitation continuum leading to dramatically reduced computational times.
This paper introduces a method to generate such a series of rainfall events. This series is optimized to match the overflow volumes of the continuous simulation and to reduce the overall computation time of the series simulation.