The work presented within this paper deals with the crucial hydraulic and morphologic processes at confluences of steep torrent channels and receiving streams in case of exceptional extreme events. 2d numerical modelling is accomplished with the BASEMENT software for the confluence of Schnannerbach torrent channel and Rosanna River. There, the damage causing flood event from August 2005 is reconstructed. Processes of bedload deposition, flooding and overbank sedimentation, as they could be observed in August 2005 and analysed within a physical model at the University of Innsbruck, are simulated. The modelling results provide a valuable insight into the processes being crucial for the damages on the adjacent flood plain. Compared to the laboratory analysis, which delivers a very reliable and vivid process representation but is restricted to a rather small spatial extent, numerical modelling allows for an analysis of bedload transport and deposition further downstream in the Rosanna River and backwater effects upstream.