Errors in the Bed Shear Stress as Estimated from Vertical Velocity Profile
Publication: Journal of Irrigation and Drainage Engineering
Volume 132, Issue 5
Abstract
In this study, errors in determining bed shear stress caused by errors in theoretical bed surface data or roughness size selection using one-point velocity, two-point velocity, or a group of velocity measurements within the log-velocity region are systematically and quantitatively analyzed. The smaller the roughness element, the smaller the error in the bed shear stress estimate. For a fixed roughness size and absolute error in selecting the theoretical bed data, the closer to the bed the velocity measurement is taken, the larger the error in the friction velocity estimate. The velocity profile near the bed is very sensitive to the selection of the theoretical bed surface data. The velocity profile near the bed will deviate significantly from the true log profile if the theoretical bed surface data is over- or underestimated by or more. This study shows conclusively that using the upper measurement data points, instead of the near-bed measurement, in the regression analysis yields better roughness size and bed shear stress estimates.
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Acknowledgment
The authors thank Mr. L. K. Fong from the Maritime Research Centre, Nanyang Technological University, for his assistance in the experiments.
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Information & Authors
Information
Published In
Journal of Irrigation and Drainage Engineering
Volume 132 • Issue 5 • October 2006
Pages: 490 - 497
Copyright
© 2006 ASCE.
History
Received: Jul 2, 2004
Accepted: Jan 3, 2006
Published online: Oct 1, 2006
Published in print: Oct 2006
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