Author(s): Schnauder; Yagci Oral; Kabdasli Sedat
Linked Author(s):
Keywords: Emergent vegetation; Turbulence; Plant permeability; Floodplain flow; Canopy flow
Abstract: The present study introduces a physical model of a single emergent and leafy plant in a straight and 1 m wide flume. Two acoustic Doppler velocimeters (ADV) were used to measure vertical profiles of the streamwise and vertical velocity components in the centreline of the wake of the plant. A cypress plant (cupressus macrocarpa) was used in the experiments of which the topmost 30 cm of the crown were installed in the flume. This species has finestructured branches and needles and makes an ideal model plant with a high geometric similarity to real-sized bushy floodplain vegetation. The aim of the study was to determine the effect of the permeability of the plant canopy on the flow. Hereby, the plant was wrapped in cling-film and made hydraulically impermeable. Results are compared with the fully permeable plant and show significantly different velocity and turbulence distributions. The recirculation zone in the near wake is much more pronounced for the impermeable plant causing a single large vortex street. In case of the permeable plant, the turbulence characteristics in the near wake are more isotropic due to the occurrence of multiple vortex streets on much smaller scales around branches and needles. The findings of this study show that the classical flow theory past immersed impermeable bodies is not directly transferable to vegetation with natural canopies. In the latter case, the permeability has to be taken into account as an additional parameter. This implies limitations to the approach of modelling natural vegetation as rigid cylinders which is common practice in numerical and physical models.
Year: 2007