The simulation of run-off in Alpine catchment areas is essential for the optimal operation of high head storage hydropower plants (HPPs) under normal flow conditions, but also in case of flood events. A conceptual semidistributed numerical approach is presented, combining hydrologic modelling and operation of hydraulic works. Spatial rainfall and temperature distributions were taken into account for simulating the dominant hydrologic processes, such as glacier melt, snowpack constitution and melt, soil infiltration and run-off. The object-oriented modelling tool allowed run-off generation, simulation of the operating mode of complex HPP and its impact on the downstream river network for different scenarios. The paper briefly presents the hydrologic model and then the application for the upper Aare catchment in Switzerland, where about half of the area is operated by the Oberhasli hydropower scheme. The development, calibration and validation of the hydrologic model are discussed. Finally, the retention effect of the existing reservoirs and their management, including preventive turbine operations, on flood routing in the Aare River upstream of Lake Brienz is presented for the 2005 historical flood event.