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Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams

Ferguson, Robert I.

Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams Thumbnail


Robert I. Ferguson


Logarithmic and variable-power equations that use the bed D84 grain size as a roughness metric reproduce the general trend of flow resistance in streams with coarse beds, but they are unreliable for predictions in individual reaches. For site-specific application of these equations, I propose that an effective roughness height can be calibrated by making a single flow measurement. I test this idea using published velocity-depth data for eight coarse-bed reaches of varied character. In 52 trials (8 reaches × 2 equations × 3 or 4 alternative calibration measurements), single-measurement calibration reduced the root-mean-square error in predicting velocity at all depths by up to 79% (median 66%) compared to using D84. This approach may be useful when prescribing environmental flows, estimating bankfull discharge, or predicting bedload transport in coarse-bed channels in which Manning's n is likely to vary considerably with discharge.


Ferguson, R. I. (2021). Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams. Water Resources Research, 57(6), Article e2021WR029979.

Journal Article Type Article
Acceptance Date May 29, 2021
Online Publication Date Jun 14, 2021
Publication Date Jun 14, 2021
Deposit Date Aug 13, 2021
Publicly Available Date Aug 13, 2021
Journal Water Resources Research
Print ISSN 0043-1397
Electronic ISSN 1944-7973
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 57
Issue 6
Article Number e2021WR029979


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Copyright Statement
© 2021. The Authors.<br /> <br /> This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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