CGRG Bibliography of Canadian Geomorphology
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Author : Crawford, A.M.; and Hay, A.E.
Date : 1999.
Title : Linear transition ripple migration and wave orbital velocity skewness
Publication : 1999 Fall Meeting of the American Geophysical Union, December 13-17, 1999 , San Francisco, California (abstract).
Issue :
Page(s) :
Abstract
Field observations were made in 3.5 to 4 m water depth of linear transition ripple geometry and migration using a high-resolution laser--video bed profiling system and acoustic scanning sensors during both the growth and decay phases of a fall storm event. Linear transition ripples are long crested, low steepness bedforms in the anorbital ripple class. The transition ripples presented here occurred at relatively high wave energies just below the flatbed threshold, and had wavelengths of 8.5 pm 0.5 cm and heights of 0.3 pm 0.1 cm. The maximum observed migration rate was 0.7 cm/min. Migration was offshore during storm growth, and onshore during storm decay. The observed ripple migration rates are highly correlated (r2 approx 0.8) with nearbed wave orbital velocity skewness. During storm growth, the incident wave spectrum was strongly bimodal and the orbital velocity skewness was negative. During storm decay, the wave spectrum was essentially unimodal and the skewness was positive. Bispectral analysis shows that the main contribution to negative skewness during storm growth was from frequencies corresponding to a difference interaction between the two principal components of the bimodal spectrum. Positive skewness during storm decay was due to self--self interaction of the narrowband swell. These observations are shown to be consistent with second--order wave theory.
Bibliography of Canadian Geomorphology