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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 681

Last Page: 681

Title: Tidal-Current Sand Waves in Vineyard Sound, Massachusetts: ABSTRACT

Author(s): S. R. Briggs, J. B. Southard

Article Type: Meeting abstract

Abstract:

Response of bed forms to tides and storms was studied for 8 months on Middle Ground Shoal, Vineyard Sound, Massachusetts, which has a nearly bi-directional tidal ellipse parallel with the shoal axis. Bed forms are on three scales: sand waves (H, one to several m; ^lgr, 20 to 200 m), megaripples (H, up to 1 m; ^lgr, 1 to 20 m) and ripples (H < 10 cm; ^lgr < 1 m). Ripples are superimposed on both sand waves and megaripples; megaripples are commonly superimpsed on large sand waves. Four transponder-navigated surveys with ± 1 m accuracy were made with 200-kHz narrow-beam echo sounding and side-scan sonar. Successive charts of sand-wave crest positions were inter-compared to measure sand-wave migration. One wave at the edge of the sand-wave field was studied during everal deployments of a tetrapod instrumented with four acoustic-travel-time velocity sensors at 30, 50, 100, and 300 cm from the bed, a bottom camera, and a 4-mHz sonic profiler to record bed heights. Sand waves show a slight upslope component of migration. Flood and ebb waves are separated by a 100 to 200-m belt of symmetrical waves at the shoal axis; some crests are continuous across the entire shoal. Flood or ebb migration ranged from 2 to 28 m during the 8-month period, but certain segments of waves migrated much more than other segments. Superimposed megaripples, which migrate too rapidly for survey-to-survey correlation, were monitored by divers using a staked and measured line over a sand wave; these forms, with H up to 1 m and ^lgr up to 20 m, migrated a full wavelength in up to several weeks.

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