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.

Abstract

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.

Citation

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. https://doi.org/10.1002/2014gl060906

• 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
• DOI: https://doi.org/10.1002/2014gl060906
• Keywords: Bed forms, Permeability, Turbulence, Hyporheic flow, Coarse sediments, Morphodynamics.