Late research and developments show a trend towards integrated models to simulate the urban drainage cycle to offer a complete picture of the system’s performance. However, in regard to integrated models considering water quality, only few actual case studies exist. We developed such a model for the urban drainage system of Graz, Austria containing runoff generation, a sewer system, actuators and the wastewater treatment plant (WWTP) of the city. This integrated model uses an interface approach, which connects commonly known sub-models of the various subsystems by automated scripts. Following this methodology results in the advantage of an understandable and easier to maintain integrated model for the sewer operator. So far the model has been used to evaluate the impact of a newly constructed combined sewer storage tunnel (central storage tunnel – CST) on the existing WWTP and to derive best management practices (BMPs) for the integrated operation of the system in regard to minimizing the total emission load to the receiving water.