Intertidal Sedimentary Structures on Macrotidal Beaches

Abstract

ABSTRACT A one-month survey of three macrotidal beaches located in south Wales has shown that the distribution of bed forms in the intertidal zone is controlled primarily by wave climate and tidal range. The areas near the high- and low-water marks reflect the predominance of swash-zone action, whereas the middle part of the beach is more likely to contain bed forms formed in either the breaking or shoaling wave zones. Since none of the structures were formed by current action, changes in tidal range affected only the width of the areas, not the type of bed forms produced. The bed forms observed varied directly with changes in wave height; on high wave-energy beaches, the model of Clifton et al. (1971) is valid, whereas on lower energy beaches it must be modified. The rapid response of the bea hes to changes in wave climate makes it unlikely that bed forms will be preserved except possibly during extremely severe storms, when the lowermost part of the bed forms might be preserved as part of a vertical sequence produced by migrating facies.