The influence of current speed and vegetation density on flow structure in two macrotidal eelgrass canopies

Limnology and Oceanography: Fluids and Environments
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Abstract

The influence of eelgrass (Zostera marina) on near-bed currents, turbulence, and drag was investigated at three sites in two eelgrass canopies of differing density and at one unvegetated site in the San Juan archipelago of Puget Sound, Washington, USA. Eelgrass blade length exceeded 1 m. Velocity profiles up to 1.5 m above the sea floor were collected over a spring-neap tidal cycle with a downward-looking pulse-coherent acoustic Doppler profiler above the canopies and two acoustic Doppler velocimeters within the canopies. The eelgrass attenuated currents by a minimum of 40%, and by more than 70% at the most densely vegetated site. Attenuation decreased with increasing current speed. The data were compared to the shear-layer model of vegetated flows and the displaced logarithmic model. Velocity profiles outside the meadows were logarithmic. Within the canopies, most profiles were consistent with the shear-layer model, with a logarithmic layer above the canopy. However, at the less-dense sites, when currents were strong, shear at the sea floor and above the canopy was significant relative to shear at the top of the canopy, and the velocity profiles more closely resembled those in a rough-wall boundary layer. Turbulence was strong at the canopy top and decreased with height. Friction velocity at the canopy top was 1.5–2 times greater than at the unvegetated, sandy site. The coefficient of drag CD on the overlying flow derived from the logarithmic velocity profile above the canopy, was 3–8 times greater than at the unvegetated site (0.01–0.023 vs. 2.9 × 10−3).

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The influence of current speed and vegetation density on flow structure in two macrotidal eelgrass canopies
Series title Limnology and Oceanography: Fluids and Environments
DOI 10.1215/21573698-1152489
Volume 1
Issue 2011
Year Published 2011
Language English
Publisher American Society of Limnology and Oceanography
Publisher location Waco, TX
Contributing office(s) Pacific Coastal and Marine Science Center
Description 18 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Limnology and Oceanography: Fluids and Environments
First page 38
Last page 55
Country United States
State Washington
Other Geospatial Puget Sound