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High-Density Suspensions Formed Under Waves

Lamb, Michael P. and Parsons, Jeffrey D. (2005) High-Density Suspensions Formed Under Waves. Journal of Sedimentary Research, 75 (3). pp. 386-397. ISSN 1527-1404. doi:10.2110/jsr.2005.030.

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We performed a series of laboratory experiments to investigate the interactions of a turbulent wave boundary layer with a predominantly silt-size sediment bed. Quasi-steady, turbulent, high-density suspensions (HDS) formed over a wide range of wave conditions and had near-bed (~1 mm above bed) concentrations ranging from 17 to 81 g/l scaling roughly with the wave orbital velocity. HDS were defined by the presence of a lutocline, an abrupt change in vertical concentration gradient. Despite the initial bed being 70% silt and 20% sand, HDS had significant near-bed sand fractions ranging from 27 to 78%. Winnowing of the bed caused more concentrated HDS to be coarser grained, which in turn caused the suspensions to be thinner because of the greater settling velocity of the sediment. Our experiments are consistent with a dynamic feedback model where suspended sediment is limited through sediment-induced stratification expressed with a bulk Richardson number. However, our computed values of the bulk Richardson number converge to a value that is an order of magnitude less than the critical value of 0.25 that is typically assumed. The experimental wave orbital velocities (15–60 cm/s) and periods (3–8 s), as well as the characteristics of the HDS and the bed in our experiments, were comparable to observations made on the Eel shelf, California, during storm conditions when fluid mud has been observed.

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Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2005 SEPM Society for Sedimentary Geology. Received 4 February 2004; accepted 13 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 Utube, and provided invaluable assistance before and during the experiments. Gavin Fieger performed much of the grain-size analysis. This manuscript improved from early reviews by Joanne Bourgeois, Paul Myrow, and Chuck Nittrouer. We thank Pat Wiberg, Peter Traykovski, and Gail Kineke for comprehensive and insightful reviews that strengthened the final manuscript.
Funding AgencyGrant Number
Office of Naval Research (ONR)N000140310138
University of WashingtonUNSPECIFIED
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20090917-124646906
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Official Citation:Lamb, Michael P., Parsons, Jeffrey D. High-Density Suspensions Formed Under Waves JOURNAL OF SEDIMENTARY RESEARCH 2005 75: 386-397
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15914
Deposited By: George Porter
Deposited On:05 Oct 2009 17:50
Last Modified:08 Nov 2021 23:23

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