For Europe, a reduction of 80% of the potential storage volume due to reservoir sedimentation is predicted by 2080. Sedimentation processes trigger the decrease of the storage volume and a related restriction in hydropower production. Further, the artificial downstream flushing of deposited fines has manifold effects on the aquatic ecology, including changes in morphology and sediment quality, as well as increased turbidity and subsequent stress for aquatic species. However, it is common to lower the water surface of reservoirs for technical inspections, which is not comparable to reservoir flushing operations. The presented case study deals with such a controlled drawdown beyond the operational level of the Gepatsch reservoir (Tyrol, Austria). Based on the awareness of possible ecological consequences, an advanced set of measures and an integrative monitoring design, consisting of a detailed event-based quantification of suspended sediments, changes in the morphology, especially with respect to fine sediments, and analyses of the biological quality element fish on the reach scale along the Inn River have been developed.

An unexpected and massive redistribution of fine sediment in a large Alpine reservoir was triggered by a further lowering of the water level to conduct maintenance work. This caused the need of a total redesign of the existing head race intake for a high head power plant in the Austrian Alps. Two main geometry options for the trash rack support structure are compared with numerical simulations (ANSYS-CFX) as well as with a scale model test (scale 1:20). The laboratory experiment substantially benefited from the preliminary numerical investigation in respect of the location and implementation of the model boundaries. In return was the confidence in the numerics strengthened by the successful validation of the local head loss and the velocity distribution for the main operation cases. This allowed that the main inputs for the structural design and the further optimisation is conducted only with the 3D-numerical tool. The paper presents the interlaced concept as well as the main finding of the investigation, which lead to a successful adaptation of the intake structure.

The Tiroler Wasserkraft AG (Tiwag) currently operates eleven large hydropower stations (> 8 MW) and more than 30 smaller plants (< 5 MW) generating electricity for commercial consumption. Most of the larger stations are storage schemes in the high mountains, intended to be able to balance the opposing seasonal supply and demand situation in the Alps and current fluctuations in the network. The headrace tunnels and penstocks of the high‐pressure power stations of Tiwag are some of the most highly loaded of their type in the world. Great emphasis is placed on sustainable use and low maintenance costs, starting with the construction. Some stations have already been in operation for more than 60 years. This article describes the experience with the headrace tunnels of some of the larger hydropower stations.Bei der Tiroler Wasserkraft AG (Tiwag) sind elf große Wasserkraftwerke (> 8 MW) und über 30 Kleinanlagen (< 5 MW) in Betrieb, die elektrische Energie für den kommerziellen Gebrauch erzeugen. Die meisten Großanlagen sind als Hochgebirgsspeicherkraftwerke ausgelegt, um die jahreszeitlich entgegengesetzte Angebot‐ und Nachfragesituation in den Alpen sowie Stromschwankungen im Netz ausgleichen zu können. Die für die Hochdruckanlagen der Tiwag gebauten Triebwasserwege und Kraftabstiege gehören zu den am höchsten beanspruchten derartigen Anlagenteilen der Welt. Es wurde bereits beim Bau großer Wert auf eine nachhaltige Nutzung mit geringem Instandhaltungsaufwand gelegt. Manche Anlagen sind bereits seit über 60 Jahren in Betrieb. In diesem Beitrag werden die Erfahrungen mit den Triebwasserwegen einiger größerer Wasserkraftanlagen dargestellt.

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