Hydraulic Radius for Evaluating Resistance Induced by Simulated Emergent Vegetation in Open-Channel Flows
Publication: Journal of Hydraulic Engineering
Volume 137, Issue 9
Abstract
The resistance induced by simulated emergent vegetation in open-channel flows has been interpreted differently in the literature, largely attributable to inconsistent uses of velocity and length scales in the definition of friction factor or drag coefficient and Reynolds number. By drawing analogies between pipe flows and vegetated channel flows, this study proposes a new friction function with the Reynolds number that is redefined by using a vegetation-related hydraulic radius. The new relationship is useful for consolidating various experimental data across a wide range of vegetation density. The results clearly show a monotonic decrease of the drag coefficient with the new Reynolds number, which is qualitatively comparable to other drag coefficient relationships for nonvegetated flows. This study also proposes a procedure for correcting sidewall and bed effects in the evaluation of vegetation drag.
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Acknowledgments
The writers gratefully acknowledge the help rendered by Professor Heidi M. Nepf, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, and Kenjirou Hayashi, Ph.D., Department of Civil and Environmental Engineering, National Defense Academy of Japan for sharing their experimental data.
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Information
Published In
Journal of Hydraulic Engineering
Volume 137 • Issue 9 • September 2011
Pages: 995 - 1004
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Jun 4, 2010
Accepted: Dec 2, 2010
Published online: Dec 20, 2010
Published in print: Sep 1, 2011
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