Abstract

Side-scan sonar was used to survey 24 km of nearshore zone adjacent to the southwestern Rhode Island beaches in April, June, September, and December, 1977. The seafloor generally consisted of zones of clustered boulders and broad sand areas with occasional gravel patches. Sand bedforms included ripples, megaripples, and sand waves. Fields of low amplitude sand waves, 10-15 m in wave length, were discovered lying parallel to the shoreline at depths to at least 8 m in all surveys but September. The shapes of these features were unresolved except for December when some of the forms were judged to be asymmetrical toward land. The mechanism responsible for their genesis was undetermined. Narrow bands of megaripples also were found trending perpendicular to the coast line. These bands transect or partially blanket the sand waves. At 300-400 m offshore the bands tended to merge and terminate. Within the bands, long-crested megaripples of unknown symmetry were oriented parallel to shore. Working hypotheses proposed for the development of these megaripple bands are: a) rip currents, b) rip currents and subsequent wave action, and c) storm-generated, along-shelf flows followed by wave activity.

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