Sand Ripple and Wave Directions in the Nearshore
Abstract
In this study we investigate the assumption that the crests of wave-formed sand ripples are aligned perpendicularly to the incoming wave direction. The ripples studied are long-crested, 2-D linear transition ripples of the anorbital type with typical wavelengths of ~10 cm and heights of a few mm. Rotary fanbeam sonar images and electromagnetic (EM) flowmeter data from 2 stations in ~3-m water depth separated by 40-m cross shore distance from SandyDuck97 were used. The data extend over more than 70 days including 12 major storm events. Linear transition ripples were found to be the most frequent bed state during the experiment as determined by manually scanning through the images. For this study a method was developed to detect linear transition ripples in the sonar record automatically. The direction of the normal to the ripple crests was calculated for each instance of linear transition ripple occurrence and compared to the direction of the incoming waves as determined from the EM flowmeter measurements and the offshore pressure gauge array. The data indicate that the ripple and wave directions are similar, within 10° of each other on average. However there is an offset between the two directions, ~5° on average during storm decay, and >10° on average during storm buildup and between storms. Possible reasons for the offset, and particularly the difference in offset between storm buildup and decay, are discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMOS41C0612M
- Keywords:
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- 3020 Littoral processes;
- 3022 Marine sediments: processes and transport;
- 4211 Benthic boundary layers;
- 4546 Nearshore processes;
- 4558 Sediment transport (1862)