The project HORA 3 focuses on flood modelling for all rivers and streams of Austria. The results are detailed flood risk maps for different annual probabilities that will be published on the HORA Website. Using these maps, citizens can estimate the vulnerability of their buildings and premises to possible future flood hazards. The project combines methods from rainfall-runoff modelling, hydrodynamic simulation, and geospatial analytics using our software Visdom. A major challenge lies in the processing of multiple and heterogeneous large-scale data sets to automatically derive parameters for our flood simulation engine. In our system, flood simulations can be triggered instantly without having to deal with a complex setup process. Users only have to draw a region of interest anywhere in Austria and then select a flood probability value, e.g., HQ100 (a flood that statistically occurs every 100 years). Behind the scenes, the system processes the hydrological and geospatial input data to automatically compute inflow, outflow, and interior flow conditions required by our 2D flood simulator. The simulator itself operates at interactive rates, providing immediate visual feedback on the temporal development of the flood hazard. The project has been commissioned by the Austrian Ministry of Sustainability and Tourism together with the Austrian Insurance Association. It is a joint cooperation of the VRVis with the Institute for Hydraulic Engineering and Hydrology as well as with the Department of Geodesy and Geoinformation of the TU Vienna.