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Despite the mechanisms of reservoir sedimentation being well known for a long time, sustainable and preventive measures are rarely taken into consideration in the design of new reservoirs. To avoid operational problems of powerhouses, sedimentation is often treated for existing reservoirs with measures which are efficient only for a limited time. Since most of the measures will lose their effect, the sustainable operation of the reservoir and thus the water supply, as well as production of valuable peak energy is endangered. Today’s worldwide yearly mean loss of reservoir storage capacity due to sedimentation is already higher than the increase of capacity by the addition of new reservoirs for irrigation, drinking water, and hydropower. Depending on the region, it is commonly accepted that about 1–2% of the worldwide capacity is lost annually. In Asia, for example, 80% of the useful storage capacity for hydropower production will be lost by 2035. The main sedimentation process in narrow and long reservoirs is the formation of turbidity currents, transporting fine sediments near to the dam every flood season, increasing sediment levels up to 1 m per year. The outlet devices including intakes and bottom outlets are often affected after only 40 to 50 years of operation, even in catchments with moderate surface erosion rates. The effects of climate change will considerably increase the sediment yield of reservoirs in the future, mainly in Alpine regions due to glacier retreat and melting of permafrost grounds. The today’s challenge of dam owners and engineers is to guarantee with adequate mitigation measures, the future sustainable use of the vital reservoirs supplying water for drinking, food and energy production. Research and development is still urgently needed to identify efficient mitigation measures adapted to the main sedimentation processes involved in reservoirs.