TY - CHAP A1 - Auel, C. A1 - Boes, R.M. T1 - Sustainable reservoir management using sediment bypass tunnels T2 - Proc. 24th ICOLD Congress, Q92 R16, Kyoto, Japan N2 - Reservoir sedimentation is an increasing problem affecting the majority of reservoirs both in Switzerland and worldwide. As many dams are more than 50 years of age, this problem is becoming more and more serious nowadays. Res-ervoir sedimentation leads to various severe problems such as a decisive de-crease of the active reservoir volume leading to both loss of energy production and water available for water supply and irrigation. These problems will intensify in the near future, because sediment supply tends to increase due to climate change. Therefore, countermeasures have to be developed. They can be divided into the three main categories sediment yield reduction, sediment routing and sediment removal. This paper focuses on the sediment routing using sediment bypass tunnels. Sediment bypass tunnels are an effective means to decrease the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater, sediment accumulation is reduced significantly. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and maintenance costs. The main problem of all bypass tunnels is the invert abrasion due to high velocities in combination with high sediment transport. Three Swiss bypass tunnel examples suffering invert abrasion are presented in this paper. Furthermore, VAW started a research project to investigate the invert abrasion process by conducting hydraulic scale tests in the laboratory. The goal of this research project is to establish general design criteria for optimal flow con-ditions where both sediment depositions in the tunnel are avoided and the result-ing abrasion damages are kept at a minimum. Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151605 SP - 224 EP - 241 PB - ICOLD ER - TY - CHAP A1 - Auel, C. A1 - Boes, R.M. T1 - Sediment bypass tunnel design - hydraulic model tests T2 - Proc. Hydro 2011 - Practical solutions for a sustainable future N2 - Reservoir sedimentation, a serious problem affecting the majority of reservoirs worldwide, was not systematically accounted for in the past. After 50 years of operation, a constantly decreasing reservoir volume becomes currently a serious challenge for reservoir owners, against which countermeasures have to be developed. This research focuses on sediment routing using a bypass tunnel to convey sediments past a dam. By transporting sediments into the tailwater past a dam, their accumulation in the reservoir is reduced significantly. However, the global number of sediment bypass tunnels is limited primarily due to high investment and maintenance cost. The main problem of all bypass tunnels is the massive invert abrasion due to high flow velocities combined with high sediment transport rates. Therefore, VAW started two research projects to counter this problem. The main goal of the first project Layout and design of sediment bypass tunnels is to investigate the invert abrasion process by conducting hydraulic laboratory tests and to establish general design criteria for optimal flow conditions in which both sediment depositions in the tunnel are avoided and the resulting abrasion damages are kept at a minimum. The second project Optimizing hydroabrasive-resistant materials at sediment bypass tunnels and hydraulic structures investigates the hydraulic resistance of different tunnel invert materials, such as high performance concrete or cast basalt plates in prototype tests at the Solis bypass tunnel. The sediment transport measurement technique used in this project was optimized during preliminary model tests. Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151625 PB - Aqua-Media International Ltd CY - Prague, Czech Republic ER - TY - CHAP A1 - Auel, C. A1 - Boes, R.M. T1 - Sediment bypass tunnel design – review and outlook T2 - Proc. ICOLD Symposium - Dams under changing challenges (Schleiss & Boes, eds.), 79th Annual Meeting of ICOLD, Lucerne, Switzerland N2 - Reservoir sedimentation is increasingly affecting the majority of reservoirs all over the world. As many dams are more than 50 years of age, this problem is becoming more and more seriou403s nowadays. Reservoir sedimentation leads to various severe problems such as a decisive decrease of the active reservoir volume leading to both loss of energy production and water available for water supply and irrigation. These problems will intensify in the very next future, because sediment supply tends to increase due to climate change. Therefore coun-termeasures have to be developed. They can be divided into the three main categories sediment yield reduction, sediment routing and sediment removal. This paper focuses on sediment routing by means of sediment bypass tunnels. Sediment bypass tunnels are an effective measure to stop or at least decrease the reservoir sedimentation process. By routing the sediments around the reservoir into the tailwater in case of flood events sediment accumulation of both bed load and suspended load is reduced significantly. However, the number of sediment bypass tunnels in the world is limited primarily due to high investment and above all maintenance costs. The state-of-the-art design criteria of constructing bypass tunnels are summarized herein; major problems such as tunnel invert abrasion are discussed. The need for further research regarding sediment transport in bypass tunnels and invert abrasion is highlighted. Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151631 SN - 978-0-415-68267-1 SP - 403 EP - 412 PB - Taylor and Francis CY - London, UK ER - TY - CHAP A1 - Auel, C. A1 - Berchtold, T. A1 - Boes, R.M. T1 - Sediment management in the Solis reservoir using a bypass tunnel T2 - 8th ICOLD European Club Symposium N2 - The Solis reservoir is located in the Alps in Grisons, Switzerland and is operated by the electric power company of Zurich (ewz). Since its construction in 1986, high sediment input during flood events has led to major aggradations in the reservoir. Up to date, nearly half of the original reservoir volume has been filled with sediments from upstream mountain torrents. The deltaic deposition starts extending into the active water volume. Therefore, ewz plans a sediment bypass tunnel to flush the incoming bedload around the dam to the downstream reach. In a first step the reservoir level during flood events is lowered to the minimum operation level. The delta is subjected to free surface flow and the bedload is transported over the delta and deposited further downstream. This sediment relocation decreases the delta volume within the active storage. During further flood events, the incoming sediment is led to the bypass tunnel intake using a guiding structure and flushed through the tunnel. If the flood exceeds the capacity of the bypass tunnel, the surplus flow passes the tunnel intake towards the bottom outlets with the bedload still being flushed through the tunnel. A skimming wall located upstream from the tunnel intake prevents driftwood blocking by leading it to the reservoir front where it can be safely removed. Both the sediment relocation due to water level drawdown and the flushing through the bypass tunnel are investigated and optimized in a hydraulic model at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich. Additionally, the sediment relocation process in the model is compared with a relocation test in the prototype. Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151647 SP - 438 EP - 443 CY - Innsbruck, Austria ER - TY - CHAP A1 - Auel, C. A1 - Albayrak, I. A1 - Sumi, T. A1 - Boes, R.M. T1 - Saltation-abrasion model for hydraulic structures T2 - Proc. 1st Int. Workshop on Sediment Bypass Tunnels, VAW Mitteilungen 232 N2 - The derivation of an abrasion prediction model for concrete hydraulic structures valid in supercritical flows is presented herein. The state of the art saltation-abrasion model from Sklar and Dietrich (2004) is modified using the findings of a recent research pro-ject on the design and layout of sediment bypass tunnels. The model correlates the im-pacting parameters with the invert material properties by an abrasion coefficient kv. The value of this coefficient is verified by a similarity analysis to bedrock abrasion in river systems applying a correlation between the abrasion rate and the bed material strength. A sensitivity analysis reveals that the saltation-abrasion model is highly dependent on an adequate estimation of kv. However, as a first order estimate the proposed model en-ables the practical engineer to estimate abrasion at hydraulic structures prone to super-critical flows. N2 - In diesem Beitrag wird ein Abrasionsvorhersagemodell für wasserbauliche Anlagen vorgestellt, die hohen Fliessgeschwindigkeiten ausgesetzt sind. Das Modell beruht auf dem Ansatz von Sklar und Dietrich (2004) und beinhaltet neue Erkenntnisse über die Partikeltrajektorien und Aufprallgeschwindigkeiten in schiessendem Abfluss. Das Mo-dell verbindet die Einwirkungs- mit den Materialwiderstandsparametern der Sohle mit Hilfe des Abrasionskoeffizienten kv. Der Wert dieses Koeffizienten wurde anhand einer Ähnlichkeitsanalyse zur Flusssohlenabrasion durch eine Korrelation der Abrasionsrate mit der Sohlmaterialfestigkeit verifiziert. Eine Sensitivitätsanalyse zeigt den grossen Einfluss dieses Parameters auf die Abrasion auf. Dennoch ist das vorgeschlagene Mo-dell als praktische Hilfe für den Ingenieur in der Praxis geeignet, um die Abrasion an wasserbaulichen Anlagen abzuschätzen Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151528 SP - 101 EP - 121 PB - ETH Zurich ER - TY - JOUR A1 - Auel, C. A1 - Albayrak, I. A1 - Sumi, T. A1 - Boes, R.M. T1 - Sediment transport in high-speed flows over a fixed bed. 2: Particle impacts and abrasion prediction JF - Earth Surface Processes and Landforms N2 - Single bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high-gradient non-alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient kv was found to be vary around kv ~ 105 for hard materials (tensile strength ft > 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model. Y1 - 2017 U6 - http://dx.doi.org/10.1002/esp.4132 SP - 1365 EP - 1383 ER - TY - JOUR A1 - Auel, C. A1 - Albayrak, I. A1 - Sumi, T. A1 - Boes, R.M. T1 - Sediment transport in high-speed flows over a fixed bed. 1: Particle dynamics JF - Earth Surface Processes and Landforms N2 - Particle dynamics are investigated experimentally in supercritical high-speed open channel flow over a fixed planar bed of low relative roughness height simulating flows in high-gradient non-alluvial mountain streams and hydraulic structures. Non-dimensional equations were developed for transport mode, particle velocity, hop length and hop height accounting for a wide range of literature data encompassing sub- and supercritical flow conditions as well as planar and alluvial bed configurations. Particles were dominantly transported in saltation and particle trajectories on planar beds were rather flat and long compared with alluvial bed data due to (1) increased lift forces by spinning motion, (2) strongly downward directed secondary currents, and (3) a planar flume bed where variation in particle reflection and damping effects were minor. The analysis of particle saltation trajectories revealed that the rising and falling limbs were almost symmetrical contradicting alluvial bed data. Furthermore, no or negligible effect of particle size and shape on particle dynamics were found. Implications of experimental findings for mechanistic saltation-abrasion models are briefly discussed. Y1 - 2017 U6 - http://dx.doi.org/10.1002/esp.4128 SP - 1384 EP - 1396 ER - TY - CHAP A1 - Auel, C. A1 - Albayrak, I. A1 - Boes, R.M. T1 - Bed-load particle motion in supercritical open channel flows T2 - Proc. 36th IAHR World Congress, Delft - The Hague, the Netherlands N2 - Supercritical sediment-laden open channel flows occur in many hydraulic structures including dam outlets, weirs, and bypass tunnels. Due to high flow velocities and sediment flux severe problems such as erosion and abrasion damages are expected in these structures (Jacobs et al., 2001). Sediment bypass tunnels (SBT), as an effective measure to decrease reservoir sedimentation by bypassing sediments during floods, are exceptionally prone to high abrasion causing significant annual maintenance cost (Sumi et al., 2004; Auel and Boes, 2011). The Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich conducted a laboratory study to counteract these negative effects (Auel, 2014). The main goals of the project were to analyze the fundamental physical processes in supercritical flows as present in SBTs by investigating the mean and turbulence flow characteristics (Auel et al., 2014a), particle motion (Auel et al., 2014b; 2015b), and abrasion development caused by transported sediment. Besides new insights into the three listed topics, paramount interest is given to their inter-relations and the development of an easily applicable abrasion prediction model (Auel et al., 2015a). This paper presents selected results on the second topic, i.e. the analysis of saltation trajectories of single coarse particles in supercritical flow. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151559 PB - IAHR ER - TY - CHAP A1 - Auel, C. A1 - Albayrak, I. A1 - Boes, R.M. T1 - Bedload particle velocity in supercritical open channel flows T2 - Proc. 7th River Flow, Int. Conference on Fluvial Hydraulics (Schleiss et al. eds.) N2 - Single glass sphere motion recordings were conducted in a transitional-rough bed open channel at steady and highly supercritical flow similar to hydraulic conditions in sediment bypass tunnels. A high speed camera with a maximum resolution of 2,560 × 2,160 pixels was used to record the movement of bedload particles with diameters of D = 5.3, 10.3 and 17.5 mm. An in-house developed Particle Tracking Velocimetry (PTV) program was used to determine the transport mode and velocities of each particle for a wide range of Froude numbers up to Fo = 6. The relative roughness defined as the ratio of the bed roughness height ks to the water depth h varied from ks/h = 0.02–0.03. Particles were observed to move in rolling and saltation modes depending on the Shields number. The particle velocity shows a linearly increasing relationship with both friction velocity and Froude number nearly independent on the particle diameter. A linear relationship was also found between rolling and saltating particle velocities indicating that particle velocity does not depend on the transport mode in the range of the investigated hydraulic conditions. Scaling of particle velocity with the wave celerity plotted as a function of the Froude number adequately merged external data sets with the present data. As a consequence, a linear fit for a large Froude number range was obtained. Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-151579 SN - 978-1-138-02674-2 SP - 923 EP - 931 PB - Taylor and Francis ER - TY - CHAP A1 - Auel, C. A1 - Albayrak, I. A1 - Boes, R.M. T1 - Laborversuche über die Partikelbewegung in schiessendem Abfluss (Laboratory experiments on particle motion in supercritical flows) T2 - Proc. Int. Symposium “Wasser- und Flussbau im Alpenraum”, VAW Mitteilungen Y1 - 2014 SP - 147 EP - 156 PB - ETH Zurich ER -