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Flow resistance in gravel‐bed channels with large‐scale roughness
Author(s) -
Ferro Vito
Publication year - 2003
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.589
Subject(s) - froude number , sediment , mechanics , exponent , surface finish , geology , geotechnical engineering , flow (mathematics) , scale factor (cosmology) , scale (ratio) , drag , mathematics , soil science , materials science , geomorphology , physics , linguistics , philosophy , cosmology , quantum mechanics , metric expansion of space , dark energy , composite material
A previously published mixing length (ML) model for evaluating the Darcy–Weisbach friction factor for a large‐scale roughness condition (depth to sediment height ratio ranging from 1 to 4) is briey reviewed and modied (MML). Then the MML model and a modied drag (MD) model are experimentally tested using laboratory measurements carried out for gravel‐bed channels and large‐scale roughness condition. This analysis showed that the MML gives accurate estimates of the Darcy–Weisbach coefcient and for Froude number values greater than 0·5 the MML model coincides with the ML one. Testing of the MD model shows limited accuracy in estimating ow resistance. Finally, the MML and MD models are compared with the performance of a quasi‐theoretical (QT) model deduced applying the P‐theorem of the dimensional analysis and the incomplete self‐similarity condition for the depth/sediment ratio and the Froude number. Using the experimental gravel‐bed data to calibrate the QT model, a constant value of the exponent of the Froude number is determined while two relationships are proposed for estimating the scale factor and the exponent of the depth/sediment ratio. This indirect estimate procedure of the coefcients ( b 0 , b 1 and b 2 ) of the QT model can produce a negligible overestimation or underestimation of the friction factor. Copyright © 2003 John Wiley & Sons, Ltd.