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Effect of bed permeability and hyporheic flow on turbulent flow over bed forms

Blois, G.; Best, J.L.; Sambrook Smith, G.H.; Hardy, R.J.

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G. Blois

J.L. Best

G.H. Sambrook Smith


This paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms. The results demonstrate that flow downstream of coarse-grained bed forms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse-grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse-grained bed forms, the production of openwork textures in gravels, and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.


Blois, G., Best, J., Sambrook Smith, G., & Hardy, R. (2014). Effect of bed permeability and hyporheic flow on turbulent flow over bed forms. Geophysical Research Letters, 41(18), 6435-6442.

Journal Article Type Article
Acceptance Date Aug 25, 2014
Online Publication Date Sep 26, 2014
Publication Date Sep 28, 2014
Deposit Date Mar 6, 2015
Publicly Available Date Mar 24, 2015
Journal Geophysical Research Letters
Print ISSN 0094-8276
Electronic ISSN 1944-8007
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 41
Issue 18
Pages 6435-6442
Keywords Bed forms, Permeability, Turbulence, Hyporheic flow, Coarse sediments, Morphodynamics.


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Copyright Statement
© 2014. The Authors. 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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