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Roughness Calibration to Improve Flow Predictions in Coarse‐Bed Streams
Author(s) -
Ferguson Robert I.
Publication year - 2021
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2021wr029979
Subject(s) - calibration , bed load , hydraulic roughness , surface finish , streams , flow (mathematics) , geology , flow measurement , logarithm , metric (unit) , hydrology (agriculture) , geotechnical engineering , mean squared error , mechanics , environmental science , soil science , mathematics , sediment transport , statistics , geometry , sediment , geomorphology , materials science , mathematical analysis , engineering , computer science , computer network , physics , composite material , operations management
Logarithmic and variable‐power equations that use the bed D 84 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 D 84 . 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.