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Flow and sediment suspension events on the inner shelf of central California

Marine Geology

By:
and
DOI: 10.1016/S0025-3227(01)00267-5

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Abstract

The US Geological Survey conducted a field experiment in the late spring and early summer of 1998 off northern Santa Cruz County, California, to study sediment fluxes along the central California shelf. As part of this study, a bottom-mounted instrument package was deployed in a sediment-filled paleo-stream channel (h=12 m) off a pocket beach to measure waves, currents, suspended-sediment concentration, temperature, salinity, and seabed-level changes. The observations of suspended-sediment concentration revealed intermittent, intense periods of sediment suspension near the bed that were associated with the passage of individual large waves or wave groups. We used an ensemble averaging technique to characterize the temporal structure of near-bed sediment suspension events (SSEs) defined as when the near-bed instantaneous concentration exceeded the mean by three standard deviations. During the 800 h of deployment, over 9500 SSEs occurred. The 3917 SSEs that began under onshore flow were found to have a different temporal structure than the 5650 events that began during offshore flow. The longer mean duration of the onshore flow events caused an average of 83% of the sediment suspended during the course of the events to be carried offshore after the reversal of flow. All of the sediment suspended during the offshore events was carried offshore due to the shorter mean duration of these events. SSEs are shown to contribute 12% on average and up to 95% of the total sediment suspended by mass, demonstrating the importance of these events to sediment transport in this type of environment. Suspended-sediment transport models developed for the shelf, which use the product of the mean current and the mean suspended-sediment concentration, cannot accurately model the magnitude and direction of suspended-sediment transport on this energetic inner shelf due to the lack of information regarding the instantaneous coupling between fluid flow and sediment suspension. We conclude that time-variant models must be used to accurately model suspended-sediment transport in this type of environment.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Flow and sediment suspension events on the inner shelf of central California
Series title:
Marine Geology
DOI:
10.1016/S0025-3227(01)00267-5
Volume
181
Issue:
1-3
Year Published:
2002
Language:
English
Publisher:
Elsevier
Contributing office(s):
Pacific Coastal and Marine Science Center
Description:
19 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Marine Geology
First page:
195
Last page:
213
Country:
United States
State:
California
County:
Santa Cruz County
Projection:
Mercator Projection
Scale:
450000