Anomalous Dispersion of Fourier Components of Surface Gravity Waves in the Near Shore Area

Observed statistics of non-breaking ocean-surface gravity waves shoaling between 4 and 1 m depths are compared with the predictions of linear finite-depth theory and a nonlinear model. The linear theory included effects of the directional distribution of energy within each frequency component. The nonlinear model, which does not consider directional effects, is based on Boussinesq-type equations for a sloping bottom (Freilich & Guza 1984). Given initial conditions in 4 m depth, the nonlinear model more accurately predicts the evolution of energy spectra, coherence and phase speed between sensors, and lengths of runs of high waves than does the linear theory. In four out of five cases, observed trends in the evolution of sea-surface-elevation skewness are predicted by the nonlinear model, while linear theory predicts zero skewness. Neither model can explain changes in the directional spectra observed between 9 and 4 m depths.

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Energy saturation and phase speeds measured on a natural beach

Thornton¹,

Guza²

1982

J. Geophys. Res.

216

126

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Field measurements of wave height and speed from 7-m depth shoreward are described. The experiment plan consisted of a shore-normal transect of closely spaced (compared to a dominant wave length) velocity, pressure, and elevation sensors on an almost plane profile having an inshore slope of 1:50. As the waves shoal and begin to break, the dominant dissipative mechanism is due to turbulence generated at the crest, and wave heights become increasingly depth controlled as they progress across the surf zone. Wave heights in the inner surf zone are strongly depth dependent; the envelope of the wave heights is described by Hrm s = 0.42 h. The depth dependence of the breaking wave height is shown to be related to the kinematic instability criterion. Celerity spectra were measured by using phase spectra calculated between pairs of adjacent sensors. Inshore of 4-m depth, the celerity was found distant over the energetic region of the spectrum. A 'mean' celerity was compared with linear theory and was within + 20% and -10%, showing good agreement for such a nonlinear, dissipative region.

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Anomalous Dispersion of Fourier Components of Surface Gravity Waves in the Near Shore Area

Cited by 3 publications

References 0 publications

Wind Wave Transformation

Wind Wave Transformation

Shoaling gravity waves: comparisons between field observations, linear theory, and a nonlinear model

Energy saturation and phase speeds measured on a natural beach

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