Date of Award

Summer 1973

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

John C. Ludwick

Committee Member

Peter Fleischer

Committee Member

Gerald Shideler

Call Number for Print

Special Collections LD4331.O35W45

Abstract

The relationship between sediment texture and topography has been studied along five series of sand waves in Chesapeake Bay entrance, Virginia. Results indicate that two types of sand waves with reference to mean grain size are present: sand waves with coarse sediment on crests and fine in troughs, and sand waves with fine sediment on crests and coarse in troughs. Asymmetrical, migrating sand waves exhibit the first type; near-symmetrical, non-migrating sand waves exhibit the second type. In general, bimodal sediment is present on crests of migrating sand waves and in troughs of stationary sand waves. There is a progressive decrease in percentage of bimodal samples in the Bay entrance sand wave field. This decrease is to the southeast, the direction of net sediment transport.

An extensive application of analysis of variance has verified textural trends. A priori testing has shown asymmetrical, migrating sand waves to contain statistically significant crest and trough populations in the parameters mean grain size, standard deviation, and weight percent gravel. Near-symmetrical, non-migrating sand waves show trough sediment to differ from crest and slope sediment in mean grain size, sorting, weight percent CaC03, and weight percent gravel. A method of grouping zones along sand waves has been carried out for each sampling line using a posteriori testing. Three methods of multiple comparisons have been applied to each series of sand waves and the results compared. Crest and trough groups can be discerned.

An explanation is offered for textural differentiates in terms of a time distribution of competent velocity for bed-load transport. At times when currents are of sufficient strength to move all sediment sizes, it is likely that brown coarse sand may be carried from a source northwest of the sand wave field and mixed with the predominant gray fine sand. As velocities decrease, coarser sediment will be deposited. A winnowing process will continue to move finer sizes such that texturally distinct crests and troughs result.

Observations by SCUBA divers have revealed the widespread occurrence of small-scale bed-forms surmounting sand waves. A pilot study of small-scale bed-form textural trends, also employing analysis of variance, shows these trends insufficient to obscure observed sand wave textural trends.

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DOI

10.25777/2yjy-0b14

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