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Comparing different methods of bed shear stress estimates in simple and complex flow fields
Author(s) -
Biron Pascale M.,
Robson Colleen,
Lapointe Michel F.,
Gaskin Susan J.
Publication year - 2004
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.1111
Subject(s) - shear stress , turbulence kinetic energy , turbulence , boundary layer , mechanics , drag , geology , shear (geology) , simple shear , reynolds stress , critical resolved shear stress , reynolds number , drag coefficient , geotechnical engineering , shear rate , physics , thermodynamics , rheology , petrology
Bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport. It is, however, difcult to estimate this variable accurately, particularly in complex ow elds. This study compares shear stress estimated from the log prole, drag, Reynolds and turbulent kinetic energy (TKE) approaches in a laboratory ume in a simple boundary layer, over plexiglas and over sand, and in a complex ow eld around deectors. Results show that in a simple boundary layer, the log prole estimate is always the highest. Over plexiglas, the TKE estimate was the second largest with a value 30 per cent less than the log estimate. However, over sand, the TKE estimate did not show the expected increase in shear stress. In a simple boundary layer, the Reynolds shear stress seems the most appropriate method, particularly the extrapolated value at the bed obtained from a turbulent prole. In a complex ow eld around deectors, the TKE method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the deectors. It is suggested that when single‐point measurements are used to estimate shear stress, the instrument should be positioned close to 0·1 of the ow depth, which corresponds to the peak value height in proles of Reynolds and TKE shear stress. Copyright © 2004 John Wiley & Sons, Ltd.