Case Study: Effect of Submerged Aquatic Plants on Turbulence Structure in a Lowland River
Publication: Journal of Hydraulic Engineering
Volume 136, Issue 7
Abstract
Interactions of aquatic plants with turbulent flows in fluvial systems have attracted considerable interest. While there have been recent advances in theories that describe vegetation-flow interactions in idealized laboratory flows, their practical application is still problematic due to limited knowledge of effects caused by heterogeneously (patchy) distributed plants in naturally formed vegetative mosaics in rivers. This paper reports on a study in a lowland river, aimed at quantification and parameterization of vegetation effects on redistribution of mean and turbulent characteristics of the flow and their consequences for hydraulic resistance. The measurements were carried out in summer on a river reach with a patchy mosaic dominated by submerged flexible aquatic plants and repeated at the same water level in early spring before the plants start growing. This design of the study allowed for quantitative evaluation of the effects caused by flow-plants interactions on bulk flow parameters at comparable submergences of riverbed roughness elements (sediment grains and sand bars). The study indicates that symmetrical quasi-two-dimensional open-channel flow structure in unvegetated riverbed was transformed into highly fragmented complex flow pattern spatially arranged by patches and free paths in the mosaic. Despite complexities and three dimensionality of the flow, normalized mean velocity profiles in the patches were satisfactory described by hyperbolic tangent function while flow in the free paths, similarly to unvegetated channel, was in a reasonable agreement with the conventional logarithmic law.
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Acknowledgments
The writers acknowledge the help of Nicolas Arnaut and Ingo Schnauder in carrying out field studies. Comments and suggestions of two anonymous reviewers and the associate editor helped improving the paper and are greatly appreciated. Financial support was provided by the Deutsche Forschungsgemeinschaft (Grants Nos. DFGSU 405/2 and DFGSU 629/1).
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 136 • Issue 7 • July 2010
Pages: 434 - 446
Copyright
© 2010 ASCE.
History
Received: Dec 22, 2008
Accepted: Dec 22, 2009
Published online: Dec 28, 2009
Published in print: Jul 2010
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