Megaripple migration in the nearshore
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Authors
Walker, Angela Holcombe
Subjects
Advisors
Gallagher, Edith L.
Thornton, Edward B.
Date of Issue
1999-12
Date
December, 1999
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
Seafloor morphology in the surf zone of a sandy ocean beach was measured nearly continuously for 2 months with a 1.4 X 1.4 m coherent array of 7 sonar altimeters. Migrating megaripples, seafloor bedforms with amplitudes of O(10-50 cm) and lengths of O(1-5 m), were observed in about 2 m water depth in the trough between a sand bar and the shoreline for a wide range of wave and current conditions. Megaripple migration speed and direction are estimated from the array data using cross-correlations between seafloor elevation time series observed along the cross- and alongshore array legs. Megaripples were shown to be aligned in a direction that maximized the gross sediment transport normal to the bedform crest (Rubin and Hunter, 1987; Gallagher, et al. 1998). It is hypothesized that megaripple migration rate is related to the net transport in the direction of bedform alignment. The speed of megaripple migration is compared with the magnitude of the velocity field normal to the bedform crest in the direction of the mean, wave orbital, and resultant velocities.
Type
Thesis
Description
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NPS Report Number
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Format
vii, 33 p.;28 cm.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.