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Turbulence Structure in Depth-Limited, Vegetated Flow: Transition Between Emergent and Submerged Regimes

Author(s): H. M. Nepf; E. R. Vivoni

Linked Author(s): Heidi M. Nepf

Keywords: Turbulence; Vegetated Flow; Depth-Limited Flow; ExperimentalHydrodynamics

Abstract: Laboratory experiments were used to explore the flow characteristics and turbulence structure within and above submerged vegetation. The study focused on the role of water depth in limiting shear-layer development above the vegetation, and in particular on the as yet unexplored transition between submerged and emergent regimes. The experiments were carried out in an open channel flume with a model vegetative meadow. Velocity was measured using both acoustic (threecomponents) and laser (two-components) Doppler velocimetry. The momentum and turbulence fields within the canopy were characterized by the penetration of turbulent stress from the overlying flow; the balance of sweep and ejection events; and the relative contribution of terms to the turbulent kinetic energy budget. Turbulence production within the canopy was associated with two components: generation within the strong shear-layer at the top of the canopy, and generation within the stem wakes. The relative importance of these sources varied with characteristic depth, H/h, where H was the total flow depth and h the canopy height. Across the range of H/h considered[1 (emergent) to 2. 75], the transition from emergent to submerged conditions was captured by a shift in penetration depth, h p, a measure of the region within the canopy for which vertical turbulent exchange with the overlying water was dynamically significant to the momentum and turbulence structure within the canopy.


Year: 1999

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