Suspended sediment and hydrodynamics above mildly sloped long wave ripples

Journal of Geophysical Research C: Oceans
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Abstract

We investigate the spatial and temporal distribution of suspended sediment and the associated hydrodynamics over mildly sloped long wave ripples on the inner shelf. These bedforms had wavelengths of approximately 1 m and heights of approximately 5 cm, in a mean water depth of 4 m. The vertical and temporal structures of the suspended sediment concentration (SSC) are consistent with the entrainment of sediment on the offshore flank of the ripple, and rapid vertical mixing at the time of flow reversal, followed by advection onshore by the onshore fluid motion. This work confirms that the mechanism for sediment suspension above low-amplitude, long wave ripples is similar to the vortex formation process expected over steeper vortex ripples. Numerical simulations of the flow using the Dune2d model indicate that a separated rotational flow structure is generated at the flank of the ripple on the seaward side of the ripple crest, near the time of flow reversal. The simulations indicate that only one vortex is formed during each wave period, in agreement with the field observations. This asymmetry is due mainly to the presence of an offshore mean near-bed current of approximately 6 to 8 cm/s. The SSC is calculated by the model and compared to the field observations. A hydraulic bed roughness of 10 to 15 median grain diameters (d50) was used in order to match the model prediction to the observed SSC approximately 1 cm above the seabed (cab). However, the modeled SSC and turbulent kinetic energy were significantly lower than the field observations at elevations exceeding approximately 2 cab.

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Publication type Article
Publication Subtype Journal Article
Title Suspended sediment and hydrodynamics above mildly sloped long wave ripples
Series title Journal of Geophysical Research C: Oceans
DOI 10.1029/2003JC001900
Volume 109
Issue C7
Year Published 2004
Language English
Publisher American Geophysical Union
Description C07022, 16 p.
Country United States
State North Carolina
City Duck
Other Geospatial U.S. Army Corps of Engineering Field Research Facility
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