Current topics

Sediment Bypass Tunnels (SBTs) are an efficient measure for managing reservoir sedimentation by routing sediment-laden flows around reservoirs. The Solis SBT, located on the Albula river in the Eastern Swiss Alps, was constructed to reduce or even stop sedimentation and contribute to the restoration of sediment connectivity between the upstream and downstream river reaches. With high sediment loads and flow velocities, the invert of SBTs is prone to hydroabrasion, which can lead to high maintenance costs and potential risks to structural integrity. In this thesis the hydroabrasion resistance of six invert materials at the Solis SBT, including different types of concrete, cast basalt plates, steel plates, and high-strength materials, shall be investigated. The study makes use of data from 3D laser scanning of the tunnel invert and from continuous bedload transport monitoring by a Swiss plate geophone device, along with hydraulic data from the operator, ewz (Zurich Electric Company). The primary goal is to determine the spatially averaged, maximum, and minimum abrasion depths and patterns along the tunnel, and to analyze the impact of sediment and hydraulic conditions on abrasion rates. We offer the student the opportunity to participate in the 4th International Workshop on Sediment Bypass Tunnels in Munich, taking place from 8 to 10 September, to become acquainted with the topic of this study.

The goal of this thesis is to investigate the hydroabrasion resistance of six different invert materials in the Solis SBT by: (i) analyzing abrasion depths and patterns over time using 3D laser scanning data obtained between 2012 and 2025, (ii) assessing bedload transport rates and correlating them with abrasion patterns and hydraulic conditions, (iii) validating the mechanistic abrasion prediction model enhanced by Demiral-Yüzügüllü (2021), and (iv) comparing the abrasion resistance of the invert materials with other materials used in Swiss SBTs. The outcomes of this study will inform cost-effective SBT design and contribute to the sustainable management of hydraulic infrastructure susceptible to hydroabrasion.

For further information, please contact Ismail Albayrak (albayrak@vaw.baug.ethz.ch).

Dynamic river widening is used as a local restoration measure in affected watercourses. By removing the fixed bank protection along a particular reach, lateral erosion processes and dynamic channel migration are initiated within a limited perimeter. However, the temporal and spatial development of bank erosion in the widening depends on numerous parameters, the effects and interactions of which are still insufficiently understood. Start date: 22.09.2025 Project language: English or German 1 student for Master’s or Project thesis No specific programming skills are required. However, the lecture “River Morphodynamic Modellings” is mandatory.

The goal of this thesis is to investigate the morphodynamic processes within river widenings in relation to different floodplain offset heights and length of the widening. The 2D morphodynamic simulations will be performed with the software BASEMENT and the model will be calibrated and validated with experimental data that will be provided from large-scale laboratory experiments at VAW. Comparison to experimental data has the advantage of clearly defined boundary conditions and topographic measurements of high temporal resolution.

For further information please contact Paul Demuth (demuth@vaw.baug.ethz.ch)

Die Wasserkraftanlage Nuova Biaschina ist die letzte Stufe der Leventina-Kette im Kanton Tessin. Dem Tagespeicher Val d’Ambra mit einem Nutzvolumen von 370‘000 m3 fliesst das Wasser aus den Oberstufen mittels eines Druckstollens zu. Zudem wird das Wasser des direkten Einzugsgebiets gefasst. Von der Seewasserfassung startet ein Schrägschacht bis zur Zentrale, welche mit drei Maschinengruppen mit je 18 m3/s bzw. 49 MW ausgerüstet ist. Das Management von Sedimenten inkl. Schwebstoffen ist aufwändig und direkt an die Verfügbarkeit der Energieproduktion gekoppelt. Um die Verstopfungsgefahr zu reduzieren, wurde der Einlaufrechen mit einem einzigartigen Reinigungssystem ausgerüstet: durch Leitungsrohre wird Druckluft gegen den Rechen geblasen, um das abgesetzte Feinmaterial wieder aufzuwirbeln (resuspendieren). Das Vorgehen hat nur eine beschränkte Wirkung und muss bei unterbrochenem Betrieb der Zentrale ausgeführt werden, was die Flexibilität der Anlage einschränkt. Im See werden jährlich ca. 1‘500 m3 Sedimente mechanisch entfernt und auf eine Deponie gebracht. Die Reinigung benötigt eine Woche Zeit mit entsprechenden Produktionsverlusten. Dazu wird die Beschaffung von Deponievolumen immer schwieriger.

Ziel dieser Arbeit ist die Bearbeitung eines konkreten Vorschlags für die Optimierung des ganzen Einlaufbauwerks, inklusiv Stahlbetonstruktur, Grob- und Feinrechen, Reinigungsmaschine, Spülvorgang, usw. Das Projekt beginnt mit der Beschaffung von bestehenden Dokumenten (Pläne, Bilder, Berichte, Berechnungen, ..). Eine Begehung ist während der nächsten Seeentleerung Ende November 2025 vorgesehen. Der nächste Schritt ist die Bearbeitung von konzeptionellen Varianten mit der entsprechenden Auswertung und Kostenschätzung. In einem letzten Schritt wird ein Vorprojekt mit grober hydraulisch-konstruktiver Bemessung und Darstellung der Lösungsvorschläge entwickelt.

AET – Azienda Elettrica Ticinese, ing. Nicola Tatti (nicola.tatti@aet.ch); VAW, ETH Zurich, Dr. Simone Pagliara (pagliara@vaw.baug.ethz.ch)

Reservoir dams are critical infrastructure in modern society, supporting key functions such as hydropower production, flood control, climate change adaptation, irrigation, and drinking water supply. Low-level outlets (LLOs) serve as crucial safety structures of reservoir dams, enabling water level regulation and facilitating rapid drawdown during maintenance or emergency scenarios. The flow within LLOs is characterized by a transition from pressurized flow upstream to supercritical free-surface flow downstream of a regulating gate. In the free-surface tunnel section, the flow exhibits high turbulence and velocities, often reaching 30–60 m/s depending on the available head. These conditions result in significant air entrainment and transport, which can lead to sub-atmospheric pressures, causing potential challenges such as gate vibrations and cavitation. To mitigate these issues, flow aeration is indispensable, ensuring the safe and reliable operation of LLOs.

Recent experimental investigations at the Laboratory of Hydraulics, Hydrology, and Glaciology (VAW) have elucidated the influence of hydraulic parameters, tunnel geometry, wall roughness, and air vent design on LLO flow behaviour. These studies have yielded empirical equations that offer valuable guidance for the safe design of LLOs. However, the inherent scale effects in experimental models and the scarcity of high-quality prototype data pose challenges in validating these findings. In the summer of 2025, an experimental campaign will be conducted at the LLO of Spitallamm Dam (Switzerland), where air demand and high-velocity flow properties will be measured with sophisticated instrumentation. Complementing this effort, the present study involves experimental testing using the LLO physical model currently available at VAW. The tunnel geometry in the model will be modified to replicate the characteristics of the LLO tunnel of Spitallamm Dam. The primary objective of the thesis is to quantitatively assess scale effects, contributing to the development of safer design guidelines. This research provides the student with an opportunity to deepen his/her understanding of the hydraulics of high-velocity air-water flows while gaining hands-on experience with advanced laboratory instrumentation and data analysis techniques. The outcomes are expected to enhance the reliability of LLO designs and contribute to the advancement of hydraulic engineering practices.

For further information please contact Dr. Simone Pagliara (pagliara@vaw.baug.ethz.ch).

In many streams, it is necessary to secure the river bed during flood events by means of transverse structures. At the same time, longitudinal connectivity should be maintained or restored, meaning that fish and other aquatic species should be enabled to migrate upstream. A large variety of transverse structures are being built: Block ramps, artificial step-pool sequences, check-dam sequences and others. In many cases, bank protection between the transverse structures is needed, to avoid bank erosion and the subsequent stability issues of the transverse structures. However, these bank protection measures are usually very technical, expensive, and offer little ecological value. Thus, the question arises whether bank protection can be minimized or even omitted completely, if the transverse structures are sufficiently interlocked in lateral direction. To do this, bank erosion processes between the transverse structures must be investigated. - Start date: 22.09.2025 - Language of thesis: English or German

The goal of this thesis is to investigate bank erosion processes within check-dam sequences. The student will perform experiments in a laboratory flume at VAW’s laboratory facilities to quantify the development of the bank erosion. Thus the thesis includes: - Laboratory work (i.e. hands-on work while preparing and executing experiments and measuring hydraulic and morphological parameters) - Data analysis (i.e. analysing measurements using software like Python, QGIS, Excel, and others) - Reporting and presenting the findings

For further information please contact Andris Wyss (wyss@vaw.baug.ethz.ch).