Seeing through the fluid dynamics of flexible vegetation and canopy turbulence
- 1Energy and Environment Institute, University of Hull, Hull, United Kingdom (email@example.com)
- 2Mechanical Science and Engineering Department, University of Illinois, Urbana, United States (firstname.lastname@example.org)
- 3Departments of Geology, Geography & GIS and Ven Te Chow Hydrosystems Laboratory, University of Illinois, Urbana, United States (email@example.com)
Submerged aquatic vegetation within river and coastal environments alters the local flow hydraulics, in turn influencing sediment dynamics and bed morphology. Vegetation canopies complicate bottom topography, with flexible elements often invoking complex spatial variability. Acquisition of quantitative, long time-scale data concerning the fluid dynamics associated with flexible aquatic canopies has remained limited due to the physical and visual obstruction presented by vegetation.
The experimental based research detailed here implements a novel Refractive Index Matching (RIM) technique, combined with Particle Image Velocimetry (PIV), to acquire flow field measurements within, and above, a dynamically scaled surrogate flexible seagrass canopy. RIM provides an undistorted optical view through the vegetation canopies, facilitating the investigation of coherent flow structures and canopy dynamics at five different Reynolds numbers. A flexible vegetation canopy of length 1.4m, width 0.45m, and height 0.12m, occupied the entire width of the 2.5m long RIM flume facility at the University of Illinois. The flume was operated in a free surface mode with a flow depth of 0.36m. Results from a counterpart rigid canopy also offer comparability and broader application of these findings to a range of flow-biota environments. Transparent rods formed the rigid canopy, while the flexible canopy elements comprised of four thin polymer blades extending from a short rigid stem. Vegetation elements were placed in a staggered arrangement to form canopies with a density of 566 stems m2.
The results provide insights into canopy-based turbulence processes, including mixing layer properties associated with the canopy and vortex penetration. Deflection of the canopy and its waving motion is quantified, and linked to distinct hydrodynamic differences between the rigid and flexible canopies. Spatiotemporal variability associated with deflection of the flexible canopy, combined with the plant morphology, is shown to promote the spatial heterogeneity in turbulence distribution. Elucidation of instantaneous turbulent flow structures at various time intervals also reveals the links between above-canopy and in-canopy flow processes. This research provides new insights into the hydraulic processes of complex vegetated beds, including quantification of coherent flow structure evoultion. Application of these findings will help advance our knowledge of associated sediment transport dynamics, which is essential for interpreting larger-scale morphodynamic response and its role in environmental management.
How to cite: Houseago, R. C., Hong, L., Best, J. L., Parsons, D. R., and Chamorro, L. P.: Seeing through the fluid dynamics of flexible vegetation and canopy turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19155, https://doi.org/10.5194/egusphere-egu2020-19155, 2020.