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The Effect of biofilms on turbulent flow over permeable beds

Kazemifar, F. and Blois, G. and Aybar, M. and Calleja, P.P. and Nerenberg, R. and Sinha, S. and Hardy, R.J. and Best, J. and Sambrook Smith, G.H. and Christensen, K.T. (2021) 'The Effect of biofilms on turbulent flow over permeable beds.', Water resources research., 57 (2). e2019WR026032.


Despite an increasingly large body of work advancing our understanding of flow interactions occurring at the interface of a turbulent flow overlying a permeable bed, little is known concerning how such flow may be affected by the presence of biofilms, which exist in nearly all aquatic environments. This paper quantifies the effects on flow exerted by biofilms grown over experimental laboratory permeable beds until biofilm detachment, and then compares this to the residual effects after its detachment. The investigation is conducted in a flow channel by immersing two‐dimensional permeable beds with idealized geometry and different porosities in order to explore different bed permeabilities. Sequences of increasingly higher flow velocity conditions followed by lower flow, were considered to explore the effect of detachment. Measurements were performed using particle image velocimetry. The total wall shear stress and friction velocity were found to increase in the presence of pre‐grown biofilm, and decrease after biofilm detachment, when compared at the same pump frequency. The dimensionless Reynolds stresses, at constant pump frequency, collapsed for different bed configurations in the outer layer, while for the inner layer, the presence of biofilm led to a decrease in dimensionless Reynolds stress. Quadrant analysis shows that this decrease was primarily due to a reduction in strong Q2 contributions. These results suggest that models for flow and transport over permeable media in aquatic environments cannot neglect the role of biofilms in modifying turbulence.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:This is the peer reviewed version of the following article: Kazemifar, F., Blois, G., Aybar, M., Calleja, P. P., Nerenberg, R., Sinha, S., et al. (2020). The Effect of Biofilms on Turbulent Flow over Permeable Beds. Water Resources Research, 56, e2019WR026032., which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.
Date accepted:08 December 2020
Date deposited:20 January 2021
Date of first online publication:14 December 2020
Date first made open access:14 December 2021

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