University of Twente Student Theses
Flow-vegetation feedback of emergent and submerged rigid vegetation in staggered formations
Keijzer, Thomas Matthew (2024) Flow-vegetation feedback of emergent and submerged rigid vegetation in staggered formations.
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| Abstract: | Macrophytes are part of ecosystems within rivers and estuaries. The presence of macrophytes provides a habitat for aquatic life. To be able to provide sufficient management and conservation of these macrophytes, it is crucial to understand the flow-vegetationsediment feedback. This feedback can influence the evolution of macrophytes within ecosystems and is therefore important in conservation and management. Previous research has explored the flow behaviour of isolated emergent and submerged patches. These experiments have been conducted on rigid and flexible patches. After that, studies have explored neighbouring patch configurations for emergent patches. No research has been done on submerged neighbouring patches. Further research is therefore needed on the interaction between submerged patches to assess how this affects flow behaviour. Ultimately, this will add to the knowledge of flow behaviour around neighbouring patches. Changes in flow behaviour can influence evolution; patches can expand or develop in a new location in space, therefore enhancing ecosystem services within, for example, rivers. This study explores the flow-vegetation feedback of submerged staggered rigid patch configurations in uni-directional flow and aims to show the difference in flow behaviour compared to rigid emergent patches. Additionally, it aims to show the difference between submerged rigid isolated patches and submerged rigid patches in a staggered configuration. To be able to get an understanding of how submerged rigid patches can influence each other, experiments were conducted at the facilities of the Royal Netherlands Institute for Sea Research (NIOZ) in Yerseke. At the facility, a racetrack flume was used to be able to do measurements on different configurations. Within the flume, two experiments, emergent and fully submerged in staggered configurations, with rigid stemmed patches, were conducted. The interpatch spacing, relative to patch diameter(D), was 2D and 0.25D, respectively, longitudinal and transversal. Reference data for isolated patch experiments from Liu et al. (2018) and staggered emergent patch configuration from Kitsikoudis et al. (2020) were used to compare to experiments conducted at the NIOZ facility. The staggered patches experiments of the reference data had a spacing of 2.5D and 0.5D, respectively, longitudinal and transversal. For the experiments, an acoustic doppler velocimeter (ADV) was used. To be able to use the collected data, it was crucial to filter the data. Otherwise, contamination of data would influence the results. Within this study, the impact of filters using correlation and signal-to-noise ratio (SNR) on low-quality registered data was explored. Like in other literature, after applying quality thresholds, a 12-point interpolation filled in the missing data points. Good-quality data for the used ADV is considered to have a 70% correlation in combination with 15 dB SNR. These thresholds were applied to the raw data before applying a 12-point interpolation. When the suggested filter for good data was applied, too many data points had to be removed to be able to assess the underlying patterns and behaviours. Too low of a filter would result in too much white noise, and too much of a filter would not leave enough data points to assess flow behaviour. As a result, the -5/3 law of dissipation was used in combination with a power spectral analysis to select the correct filter for the raw data. When using the -5/3 law, the natural dissipation of energy in fluids can be approached. The dissipation of energy in the power-spectral analysis showed an optimal decay when applying a filter of 15% correlation combined with 4dB SNR that was closest to the -5/3 law line of decay. The water flow behaviour analysis was done using longitudinal and transversal profiles for both emergent and submerged patch configurations. The main difference between emergent and submerged staggered configurations shown in the longitudinal profiles was the greater turbulence and recirculation behind the submerged patches compared to the emergent patches. Additionally, the transverse profiles showed the same trends. Overall, the study suggests that submerged patches cause greater mixing due to the vertical vortex behind submerged patches. The vertical vortex of the upstream submerged patch induces turbulence, and when this turbulence is combined with the downstream vertical vortex, turbulence increases even more. This, in part, makes the evolution of submerged patches more difficult than emergent patches, as sediment suspension will likely be greater due to the extra mixing component of the vertical vortex. Also, the velocity is greater behind the submerged patches as flow is not obstructed as greatly compared to the emergent patches. To be able to have the evolution of patches, deposition behind the patches is needed to be able to have the chance for drifting vegetation fragments and seedlings to settle. A greater understanding of the water flow behaviour behind rigid stemmed submerged staggered patch configurations contributes toward the implementation of nature-based solutions in ecosystem development and management. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 56 civil engineering |
| Programme: | Civil Engineering and Management MSc (60026) |
| Link to this item: | https://purl.utwente.nl/essays/98481 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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