Laboratory Measurements of Flow and Turbulence in Discontinuous Distributions of Ligulate Seagrass
Publication: Journal of Hydraulic Engineering
Volume 133, Issue 7
Abstract
Turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies. The reliability of velocity measurements obtained using an acoustic Doppler velocimeter within the canopy was shown using specifically designed experiments. In relatively fast flow (mean velocity ), the mean flow profile was logarithmic above the canopy, had an inflection point near its top, and uniformly low values within it. Within the gap, a recirculation cell formed. Reynolds stress maxima were approximately coincident with the mean flow inflection point. Quadrant analysis revealed an ejection-dominated upper layer, a sweep-dominated region around the top of the canopy and within the gap, and no dominant quadrant within the canopy. In slower flow (mean velocity ) the plants were quasiemergent and the flow fields more uniform. Sweeps similarly dominated the region near the top of the canopy and within the gap. In both flows, autocorrelation of longitudinal velocity fluctuations showed a Lagrangian time scale maximum at the downstream end of the gap.
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Acknowledgments
The writers would like to thank G. B. Ferreri for scientific advice and very useful suggestions for the manuscript. The writers also thank F. Ferrante for helping E. Cox to make the artificial plants, and D. Tuttolomondo and M. Di Falco for their technical assistance. This collaborative work was partly funded by the British Council, MURST (Ministero dell’Università e della Ricerca Scientifica e Tecnologia) and CRUI (Conferenza dei Rettori delle Università Italiane) for the British-Italian joint research program: “Laboratory Flume and Mathematical Modeling Studies of Seagrass Influence on Lagoon Hydrodynamics.” The insightful and constructive comments of three anonymous reviewers were greatly appreciated and significantly improved the quality of this paper.
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Information
Published In
Journal of Hydraulic Engineering
Volume 133 • Issue 7 • July 2007
Pages: 750 - 760
Copyright
© 2007 ASCE.
History
Received: Apr 15, 2005
Accepted: Dec 8, 2006
Published online: Jul 1, 2007
Published in print: Jul 2007
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