do Prado, Ariel Henrique (2024). From UAV imagery to grain size analysis: Implications for understanding bedload transport in coarse-grained streams. (Thesis). Universität Bern, Bern
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24doprado_ah.pdf - Thesis Available under License Creative Commons: Attribution (CC-BY 4.0). Download (33MB) | Preview |
Abstract
Rivers play a crucial role in shaping landscapes and transporting sediment from erosional areas to depositional sites. Therefore, studying sediment transport dynamics in rivers is essential for understanding the formation of sedimentary deposits and managing flood risks. This thesis highlights the use of remote sensing technologies, including UAV imagery and photogrammetry, to enhance the understanding of bedload transport in coarse-grained streams. These technologies are employed to produce Digital Elevation Models (DEMs) and orthomosaics of multiple gravel bars in Swiss rivers. Such a dataset provided valuable information on key parameters for bedload equations, such as grain sizes, slope, and surface roughness. This thesis is organized into three main studies, each focusing on different aspects and applications of bedload concepts. Accordingly, the first study in the thesis, Chapter 2, investigates the influence of grain size sorting on riverbed roughness characterization. By comparing field-acquired digital elevation models (DEMs) with synthetic surfaces generated from a stochastic model, the study reveals that poorly sorted riverbeds exhibit higher roughness compared to well-sorted beds, even when the characterizing grain size is kept constant. In addition, it is demonstrated that poorly sorted material tends to exhibit meter-scale patches with distinct roughness patterns due to the stochastic arrangement of grains. This arrangement can influence mechanisms such as selective deposition and downstream fining. These findings underscore the importance of accounting for grain sorting in roughness characterization and understanding bedload transport mechanisms. In the second research study presented in Chapter 3, a new mechanism responsible for the stability of non-vegetated gravel-cobble bars, termed "bar shielding," is proposed. This study reveals that eroded edges of gravel-cobble bars show a coarsening of grain size by 50% at the 84th percentile compared to surrounding bedforms. This coarsening at the bar edges suggests increased stability of the bars by raising the critical shear stress required for bank erosion. Additionally, analysis of orthomosaics from the Sense River indicates that these coarser bar edges offer greater resistance to sediment entrainment, thereby enhancing bar stability during low flow conditions. Thus, the presence of this bedform is associated with a reduction in bedload flux during low flood flows. The third study, presented in Chapter 4, assesses the impact of engineering structures, specifically check dams, on sediment transport in the Gürbe River, Switzerland. By applying bedload equations and comparing conditions with and without check dams, the study finds that these structures reduce bedload capacity by at least 90% and buffer sediment supply during peak discharges. Additionally, the presence of check dams stabilizes the riverbed, preventing incision and thus contributing to the stabilization of the surrounding terrain by reducing the activation of landslides. Overall, this thesis demonstrates the effectiveness of high-resolution DEMs and orthomosaics in improving bedload transport models and offers new insights into the mechanisms governing sediment stability and engineering impacts in coarse-grained river systems.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 13 September 2024 |
| Subjects: | 500 Science > 550 Earth sciences & geology |
| Institute / Center: | 08 Faculty of Science > Institute of Geological Sciences |
| Depositing User: | Hammer Igor |
| Date Deposited: | 13 Nov 2025 11:17 |
| Last Modified: | 14 Nov 2025 20:15 |
| URI: | https://boristheses.unibe.ch/id/eprint/6876 |
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