The simulation of run-off in an alpine catchment area equipped with complex hydropower schemes is presented by the help of an especially developed tool, called Routing System, which can combine hydrological modelling and operation of hydraulic elements. The model allows simulating the operating mode of complex storage hydropower plants and its impacts on the downstream river system for different scenarios, taking into account natural and anthropogenic influences. The paper presents the modelling of the Oberhasli hydropower scheme, probably one of the most complex one in Switzerland.