Abstract
Reservoir siltation is a major challenge in dam operation, resulting from the interruption of natural sediment fluxes and the consequent accumulation of material upstream of hydraulic structures. Understanding sediment production, transport, and deposition processes at the basin scale is essential to develop effective management strategies. This chapter investigates the case of the Fortezza dam, located in South Tyrol (Italian Alps), with a focus on quantifying sediment dynamics within its contributing catchment. Sediment transport along the stream network is continuously simulated over the study period, incorporating both bed erosion and deposition processes. In contrast, sediment supply from hillslope erosion is modelled only during selected erosive rainfall events, which are the main drivers of sediment pulses entering the stream system. A detailed analysis focuses on the event with the highest observed suspended sediment concentration, under three hypothetical management scenarios representing different water storage volumes prior to the selected event. The comparison of these scenarios demonstrates the strong influence of pre-event storage conditions on the extent and spatial distribution of sediment deposition within the reservoir. Results suggest that timely drawdown of the reservoir before major sediment-laden floods can significantly mitigate siltation, preserve storage capacity, and reduce operational disruptions. These findings highlight the importance of integrating short-term hydrometeorological forecasting and sediment transport modelling to support anticipatory reservoir management. Accurately estimating sediment yields in response to rainfall events, combined with flexible reservoir operation strategies, emerges as a key approach to limit the long-term impacts of sedimentation in alpine dam systems.