Michelle Müller-Hagmann


Last Name

Müller-Hagmann

First Name

Michelle

ORCID

0000-0002-5514-9238

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2017 - 20204
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Publications 1 - 4 of 4
  • Field Investigation on Hydroabrasion in High-Speed Sediment-Laden Flows at Sediment Bypass Tunnels
    Item type: Journal Article
    Müller-Hagmann, Michelle; Albayrak, Ismail; Auel, Christian; et al. (2020)
    Water
    Wear due to sediment particles in fluid flows, also termed ‘hydroabrasion’ or simply ‘abrasion’, is an omnipresent issue at hydraulic structures as well as in bedrock rivers. However, interactions between flow field, particle motion, channel topography, material properties and abrasion have rarely been investigated on a prototype scale, leaving many open questions as to their quantitative interrelations. Therefore, we investigated hydroabrasion in a multi-year field study at two Swiss Sediment Bypass Tunnels (SBTs). Abrasion depths of various invert materials, hydraulics and sediment transport conditions were determined and used to compute the abrasion coefficients kv of different abrasion models for high-strength concrete and granite. The results reveal that these models are useful to estimate spatially averaged abrasion rates. The kv‑value is about one order of magnitude higher for granite than for high-strength concrete, hence, using material-specific abrasion coefficients enhances the prediction accuracy. Three-dimensional flow structures, i.e., secondary currents occurring both, in the straight and curved sections of the tunnels cause incision channels, while also longitudinally undulating abrasion patterns were observed. Furthermore, hydroabrasion concentrated along joints and protruding edges. The maximum abrasion depths were roughly twice the mean abrasion depths, irrespective of hydraulics, sediment transport conditions and invert material.
  • Hydroabrasion in high speed flow at sediment bypass tunnels
    Item type: Monograph
    Müller-Hagmann, Michelle (2017)
    VAW-Mitteilungen
  • Hydroabrasion by High-Speed Sediment-Laden Flows in Sediment Bypass Tunnels
    Item type: Doctoral Thesis
    Müller-Hagmann, Michelle (2018)
    Reservoir dams impound flowing water to balance a fluctuating water supply and demand. All reservoirs situated on natural watercourses are subjected to sediment inflow. Water-carried sediments continuously settle in the quiescent environment of a reservoir resulting in accumulation, negatively affecting their functions. Sediment bypass tunnels (SBTs) are an effective measure against reservoir sedimentation by diverting sediment-laden water past the dam and allowing for re-establishing the natural sediment continuity. However, high-speed sediment-laden flows in SBTs can cause severe invert abrasion, putting SBT operation at risk and provoking high maintenance costs. Mitigation of hydroabrasion problems requires a better understanding of governing parameters, namely flow characteristics, particle and invert material properties, sediment transport and their interactions. Despite a large number of small-scale laboratory studies on hydroabrasion, upscaling of their results to prototype scale is questionable due to a lack of prototype data. Therefore, this study aims at filling this research gap by in-situ investigation of hydroabrasion in combination with laboratory tests. Various invert materials, i.e. concretes, granite, steel and cast basalt, were installed in the Solis, Pfaffensprung and Runcahez SBTs in Switzerland. The abrasion patterns and rates, flow conditions, sediment transport rate and sediment properties in the rivers, reservoirs and SBTs were determined and their interrelations were analyzed with an emphasis on hydroabrasion, bypass efficiency and operating regime of the SBTs and respective reservoirs. The results of the abrasion measurements showed that hydroabrasion is a self-intensifying process, triggered by discontinuities and constructional weaknesses resulting in characteristic material-dependent abrasion patterns. In addition to this, the abrasion pattern was found to be affected by 3D flow structures induced by either tunnel bends or low tunnel width to flow depth ratios. The resulting ratio of maximum to spatially averaged abrasion depths ranged from 1.6 to 2.2, which is of prime importance regarding the dimensioning of the invert material thickness. Invert material selection and dimensioning requires cost-effectiveness analysis, which is a function of abrasion rate, material cost, abrasion conditions and target life time. For the first, three existing abrasion prediction models were evaluated and calibrated based on the present field data. The resulting abrasion coefficients generally agreed with literature data. However, application of material-specific abrasion coefficients was found to significantly enhance the model prediction accuracy and is therefore recommended. Based on that, present cost-effectiveness analysis revealed that hard rock and (ultra-)high-strength concretes are more suitable for long-term application under severe abrasion conditions, whereas less expensive materials are more economical for moderate to low abrasion conditions or short-term application, despite the lower abrasion resistance. The present study revealed that the bypass efficiency of a SBT strongly depends on the location of the SBT intake and the operational regime of both the reservoir and the SBT. To achieve an optimum bypass efficiency, the SBT and reservoir operations need to be coordinated and optimized, which requires a continuous and real-time monitoring of the hydraulic and sediment transport conditions in the river, reservoir and SBT. Overall, this study provides new insights into the flow and sediment transport characteristics in SBTs and reservoirs and advances the understanding of hydroabrasion processes in high-speed sediment-laden open channel flows. The main results are the applicable recommendations with a focus on hydroabrasion and bypass efficiency, contributing to a sustainable and efficient design and operation of SBTs.
  • Ausbaupotential der bestehenden Speicherseen in der Schweiz
    Item type: Journal Article
    Felix, David; Müller-Hagmann, Michelle; Boes, Robert (2020)
    Wasser Energie Luft
Publications 1 - 4 of 4