Abstract

Glacier retreat in the Alps has dramatically progressed since the 1980s due to climate change, and glacier shrinkage will be even more pronounced in the future. As a result, the flow regime and the sediment yield from watersheds will be subject to significant changes. Reservoirs are exposed to continuous sedimentation, reducing their storage volume and posing exploitation and security risks. The methodology is mainly based on literature review, combining various sources and datasets in order to answer the title question. This chapter discusses the case study of the Gries watershed (including the outlet, the reservoir, the glacier, and the Gries dam), which is currently mostly glacier covered at an altitude above some 2400 m asl. The change in length of the Gries glacier has been recorded since 1847, and data related to the annual mass balance is available starting in 1961. Future glacier evolution models, coupled with a hydrological model, that consider global warming show that the length of the glacier will continue to decline, and it is expected that around 2060 the entire catchment area will be virtually glacier free. Glacier runoff and erosion will be shifted to a pluvio-nival regime, and the water resources associated with this system will become less reliable. Past sediment yield and reservoir sedimentation surveys allow for the reservoir sedimentation patterns to be characterized, which are dominated by plunging turbidity currents. Sustainable sedimentation management measures preserve the reservoir storage volume, safety and economic operability beyond the disappearance of the glacier.