Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams

Ferguson, Robert I.

Abstract

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.

Citation

Ferguson, R. I. (2021). Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams. Water Resources Research, 57(6), Article e2021WR029979. https://doi.org/10.1029/2021wr029979

• 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
• DOI: https://doi.org/10.1029/2021wr029979
• Public URL: https://durham-repository.worktribe.com/output/1268445