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Hydro-Abrasion at Hydraulic Structures and Steep Bedrock Rivers

Titel Englisch Hydro-Abrasion at Hydraulic Structures and Steep Bedrock Rivers
Gesuchsteller/in Boes Robert Michael
Nummer 166253
Förderungsinstrument Projektförderung (Abt. I-III)
Forschungseinrichtung Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie ETH Zürich
Hochschule ETH Zürich – ETHZ
Hauptdisziplin Bauingenieurwesen
Beginn/Ende 01.01.2017 - 31.12.2019
Bewilligter Betrag 218'008.00
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Alle Disziplinen (4)

Disziplin
Bauingenieurwesen
Geomorphologie
Fluiddynamik
Materialwissenschaften

Keywords (7)

bedrock river incision; flow-sediment interaction; hydro-abrasion; linvert lining ; particle motion; sediment flushing channel; sediment bypass tunnel

Lay Summary (Deutsch)

Lead
Die Nachhaltigkeit mancher Talsperre ist infolge von Sedimentation gefährdet. Die Suche nach aktiven Gegenmassnahmen führt zu einem starken Bedarfsanstieg an Sediment-Umleitstollen (SBT) sowie an Sediment-Spülungen bzw. -Durchleitungen (SFSF), um die Nachhaltigkeit der Talsperren sowie die Sediment-Kontinuität zu gewährleisten. Dabei ist jedoch zu beachten, dass hohe Fliessgeschwindigkeiten in Kombination mit grossen Sedimentfrachten bedeutende Abrasionsschäden an diesen Anlagen sowie eine Erosion von felsigen Flusssohlen hervorrufen können. Das bessere Verständnis dieser Prozesse sowie die Entwicklung von realistischen Abrasionsmodellen sind deshalb Schlüssel sowohl zur Bemessung und nachhaltigen Bewirtschaftung von wasserbaulichen Anlagen als auch zur Modellierung der durch Flüsse gebildeten Landformation.
Lay summary

Inhalt und Ziel des Forschungsprojekts

Dieses Projekt hat zum Ziel, die physikalischen Prozesse des hochturbulenten Abflusses, der sohlnahen Bewegung von Sedimenten und deren hydro-abrasive Wirkung in hochbeanspruchten Anlagen wie SBT und SFSF sowie deren gegenseitige Beeinflussung zu erforschen. Die Einflüsse von Fliessgeschwindigkeit, Abflusstiefe, Partikelgrösse, -härte, -form und -transportrate sollen in einem Labormodell untersucht werden, welches SBT und SFSF simuliert. Zusätzlich sollen Felddaten von existierenden SBT gesammelt werden, um die Modelldaten auf den Naturmassstab hoch zu skalieren. Schliesslich soll ein Modell entwickelt werden, um Hydroabrasion in Zukunft sowohl im Modell als auch im Prototypen vorherzusagen.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts

Das Projekt ist von hoher Dringlichkeit sowohl für Energieerzeuger, Wasserbauer und Bundesämter im Zusammenhang mit der Energieerzeugung (BFE), der Wasserversorgung und der Umwelt (BAFU) als auch für die Forschungsgemeinschaft. Das Projekt trägt zudem zur erfolgreichen Realisierung der ‚Energiestrategie 2050‘ bei.

Direktlink auf Lay Summary Letzte Aktualisierung: 27.04.2016

Lay Summary (Englisch)

Lead
The sustainability of many reservoirs is threatened by sedimentation. The need for active sediment handling using Sediment Bypass Tunnels (SBT), or Sediment Flushing and Sluicing Facilities (SFSF), amongst others, will consequently increase considerably in the future to maintain reservoir sustainability as well as sediment connectivity. However, high speed flows and high sediment transport rates can cause severe hydro-abrasion at such hydraulic structures as well as river bed incision. Better understanding of the abrasion mechanics and development of a realistic abrasion model are keys for both design and sustainable use of hydraulic structures, and for landscape evolution modelling.
Lay summary

Aims of the research project

The project aims at improving knowledge on the physical processes of turbulent flow characteristics, bedload particle motion, and hydro-abrasion and their interrelations in high speed flows. Effects of flow velocity, water depth, particle size, hardness, shape and transport rate on hydro-abrasion of various bed materials will be systematically investigated in a laboratory flume, simulating SBT, SFSF and high-gradient mountain streams. In addition, field data from existing SBT in Switzerland and literature data will be collected to use upscaling the laboratory results to prototype dimensions. Finally, an abrasion model to forecast hydro-abrasion at both laboratory and prototype scales will be developed.

Scientific and social context of the research project

The project is of prime importance for hydropower companies, hydraulic engineers, and federal agencies dealing with energy (Swiss Federal Office for Energy), water supply and environment (Swiss Federal Office for the Environment) as well as for the research community. Furthermore, the project contributes to a successful realization of the ‘Energy Strategy.

Direktlink auf Lay Summary Letzte Aktualisierung: 27.04.2016

Verantw. Gesuchsteller/in und weitere Gesuchstellende

Mitarbeitende

Name Institut

Abstract

Sediment transport in melting water draining from glacier basins, rivers and waterways, and reservoir sedimentation both in the Alpine regions and worldwide have strongly increased under the strong impact of climate change. As a consequence, high transport rates of bed load particles in combination with high flow velocities cause severe abrasion such as (I) bedrock incision in high-gradient mountain streams, and (II) hydro-abrasive erosion of concrete and cavitation damages at hydraulic structures including dam outlets, weirs, and particularly Sediment Bypass (SBT) and Sediment Flushing Tunnels (SFT). Therefore, a realistic and mechanistic abrasion model is of fundamental importance for both river and landscape evolution and sustainable design and operation of hydraulic structures. Despite the large number of studies mainly in alluvial channels, only few exist for steep bedrock rivers and non-movable bed open channels. However, their applicability is still in question for highly supercritical flow due to the lack of information on the physical processes of turbulent flow characteristics, bed load particle motion, and abrasion and their inter-relations. Moreover, effects of fundamental variables such as dynamically changing roughness during the abrasion process, the channel width to water depth aspect ratio on particle motion; and particle hardness, shape and density and supply rate on abrasion rate and pattern have not been systematically investigated. The proposed project aims at filling these research gaps by a systematic laboratory investigation. The out-puts of the project will contribute to the sustainable design and operation of hydraulic structures exposed to heavy sediment load and modeling of river bed and landscape evolution as well as improved knowledge on bed load transport needed in scientific disciplines such as geomorphology, sedimentology and river engineering.By means of high-speed video technique, 3D precise laser scanning and 2D Laser Doppler Anemometry (LDA), we intend to systematically investigate: (I) small- and large-scale turbulence structures of 2D and 3D high-speed flows, (II) bed load particle motion; and (III) hydro-abrasion processes, i.e. grinding stress-es, impacts of rolling and saltating particles in a laboratory flume, and (IV) to develop an hydro-abrasion predictive model. The experimental campaign will cover a range of flow depth-to-channel width ratios, Froude numbers, F, up to 4, sediment properties and rates, and bed lining materials.In Task A, systematic velocity measurements will be conducted using a LDA of high temporal resolution in a laboratory flume. By measuring instantaneous 2D velocities, mean velocities, turbulence intensities, bed and Reynolds shear stresses will be studied. A particular focus will lie on effects of Froude number, low aspect ratios and varying bed roughness due to abrasion.In Task B, transport modes of particles differing in size and hardness, i.e. rolling, sliding and saltating, and cover effects, will be investigated for the hydraulic conditions as in Task A over fixed and abraded beds in parallel to Task C, using high-speed camera and LDA techniques. Particle velocity, saltation trajectories and impact energy will be directly determined from the captured images using an edge detection software and Particle Tracking Velocimetry (PTV) developed at VAW. Subsequently, a link between 2D/3D flow patterns in a supercritical open-channel flow and the determined parameters will be established, and bed roughness effect and particle-flow interactions will be analyzed.In Task C, the abrasion damage on the channel bottom in the same flume will be investigated under the same hydraulic conditions as in Task A, varying the sediment characteristics (hardness, size), the sediment supply rate, and the invert material properties (Young’s Modulus, compressive and tensile strengths, fracture toughness and elastic strain energy density). With a combined consideration of the proposed small-scale model tests, standard abrasion drum tests, and prototype and literature data, upscaling of the laboratory results to prototype dimensions will be aimed at. Finally, in Task D, an abrasion model will be proposed to forecast hydro-abrasion in steep rivers and at hydraulic structures. It will enable to optimize both the channel hydraulics and the tunnel invert material to minimize hydro-abrasion. This task is therefore particularly an essential result for the application of the present research at hydraulic structures.The particular and innovative features of the proposed project for research and engineering practices are summarized as: (I) high speed turbulent flow characteristics and particle motions over smooth and rough beds at low aspect ratios, i.e. 3D flow, (II) test of foam and various mortars as invert material, (III) test of various sediment particle properties, (IV) hybrid approach of laboratory and field studies, (V) investigation of scale effects, and (VI) development of a hydro-abrasion predictive model.
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