Date of Award

Winter 1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

John C. Ludwick

Committee Member

Chester E. Grosch

Committee Member

Dennis A. Darby

Committee Member

George F. Oertel

Abstract

A single, more or less isolated, sand wave in a sand wave field recently discovered in the lower Chesapeake Bay, Virginia, was studied intensively for morphology, sedimentology and in terms of dynamic processes. The morphologic investigation consisted of bathymetric surveys of the sand wave field and the specific sand wave. Twenty-five grab samples and four box cores were obtained from different segments of the feature studied. Textural parameters of the samples were determined, and a multivariate technique was utilized to identify subenvironments on the feature. The box cores provided information on the internal structure of the sand wave.

Observations of near-surface currents, and turbulent shear stresses at a level 5 cm above the bottom were made at five stations distributed along the profile of the sand wave. Simultaneously, vertical profiles of density were measured. Time series analysis of the shear stress data at 5 cm above the bed revealed three types of constituents: (a) long period trends, (b) wave-associated events, and (c) turbulence. The turbulent part of the record was found to be highly reduced in comparison with the other two components. Spectral analysis revealed that the energy of the horizontal component of the flow was smaller than the energy for the vertical component of the flow. Suspended sediments and stable density stratification are known to reduce turbulence, and doubtless have great effect in the present instance; however, the most affected was found to be u and not w as would have been expected.

A decrease in main flow velocity due to the three-dimensional shape of the feature is believed to result in a strong reduction in the horizontal component of the flow, as well as in the shear stress.

In the case of a more-or-less isolated feature, the flow can follow, or partly follow, a path of avoidance around the feature. The integrated results of the study suggested that the sand wave is a "solitary" bedform, originally formed by ebb currents, and presently is in static equilibrium with the circulation pattern.

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DOI

10.25777/98ep-ea94

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