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Turbulent structure of high-density suspensions formed under waves

Lamb, Michael P. and D'Asaro, Eric and Parsons, Jeffrey D. (2004) Turbulent structure of high-density suspensions formed under waves. Journal of Geophysical Research C, 109 (C12). C12026. ISSN 0148-0227.

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We performed a series of laboratory experiments on the interactions between turbulent wave boundary layers and a predominantly silt-sized sediment bed. Under a wide range of wave conditions similar to those observed on storm-dominated midshelf environments we produced quasi-steady high-density benthic suspensions. These suspensions were turbulent, while containing large near-bed concentrations of suspended sediment (17–80 g/L), and were separated from the upper water column by a lutocline. Detailed measurements of the vertical structure of velocity, turbulence, and sediment concentration revealed that the wave boundary layer, while typically >1 cm thick in sediment-free conditions, was reduced substantially in size, often to <3 mm, with the addition of suspendible sediment. This likely resulted from sediment-induced stratification that limited vertical mixing of momentum. Despite boundary layer reduction the flows were able to support high-density suspensions as thick as 8 cm because turbulent energy was transported upward from this thin but highly energetic near-bed region. Standard formulations of the Richardson number for shear flows are not applicable to our experiments since the suspensions were supported from transported rather than locally produced turbulence.

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Additional Information:© 2004 American Geophysical Union. Received 27 February 2004; accepted 22 September 2004; published 22 December 2004. Financial support was kindly provided by the National Science Foundation (EAR-0309887), the Office of Naval Research (N000140310138), and the University of Washington. M.P.L. was funded by a National Defense Science and Engineering Graduate Fellowship. Rex Johnson and Randy Fabro built and helped design the U tube and provided invaluable assistance before and during the experiments.We thank Mike Gregg, Jim Riley, Mark Stacey, and two anonymous reviewers for helpful comments that clarified many of the topics presented in this paper.
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Office of Naval Research (ONR)N000140310138
University of WashingtonUNSPECIFIED
National Defense Science and Engineering Graduate FellowshipUNSPECIFIED
Subject Keywords:wave boundary layer; oscillatory; high-density suspension; fluid mud; turbulent kinetic energy budget
Record Number:CaltechAUTHORS:20110920-115405172
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Official Citation:Lamb, M. P., E. D'Asaro, and J. D. Parsons (2004), Turbulent structure of high-density suspensions formed under waves, J. Geophys. Res., 109, C12026, doi:10.1029/2004JC002355.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25369
Deposited By: Jason Perez
Deposited On:20 Sep 2011 20:47
Last Modified:26 Dec 2012 13:41

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