Local and Nonlocal Impacts of Gaps on Submerged Canopy Flow

Although shear layers generated by submerged vegetation reach a steady state once production and dissipation are balanced within a canopy, shear layers found in gaps and after trailing edges of canopy patches are inherently different and thereby perturb the canopy's mean and turbulent fields. Experiments were conducted in a laboratory flume to study canopy systems in which two model patches of submerged, rigid cylinder arrays are interrupted by a gap of varying stream-wise lengths. Results show that, consistent with past studies, gaps locally enhance turbulence. However, this perturbation does not remain local within the gap, instead introducing enhanced turbulent energies throughout the water column that are transported downstream and thereby perturb the canopy flow. The study suggests a scaling, E=H-hcqU2L2, which compares the eddy turnover time of the turbulence produced by the gap to the advection time downstream the second patch, that can be used to predict if turbulence perturbations induced by an upstream gap will influence the turbulence at a given distance downstream.

Automated summary

The study shows that gaps in submerged vegetation enhance turbulence locally, but also introduce enhanced turbulent energies throughout the water column that are transported downstream, perturbing the canopy flow. A scaling equation was proposed to predict if turbulence perturbations induced by an upstream gap will influence the turbulence at a given distance downstream.