Morphodynamics of reflective and dissipative beach and inshore systems: Southeastern Australia

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 independent: the envelope of the wave heights is described by H/sub rms/ = 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.

Energy saturation and phase speeds measured on a natural beach

https://tspace.library.utoronto.ca/bitstream/1807/3087/1/13_frequency_dependent_2.PDF

Frequency dependent cross-shore suspended sediment transport. 1. A non-barred shoreface

This paper examines the problem of the survival of Salter’s duck wave-energy device in extreme waves, both experimentally in a narrow tank at Edinburgh University and theoretically, using programs originally designed to study nonlinear ship motions (Vinje & Brevig 1981). Both approaches are essentially two-dimensional, corresponding to waves normally incident upon the duck string, and comparison of the two sets of results for SL duck on a fixed axis shows good agreement.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112082001050

A theoretical and experimental study of the capsize of Salter's duck in extreme waves

Waves, Currents, Sediment Flux and Morphological Response in a Barred Nearshore System

The sight and sound of breaking waves and surf is so familiar and enjoyable that we tend to forget how little we really understand about them. Why is it, that compared to other branches of wave studies our knowledge of breaking waves is so empirical and inexact? The reason must lie partly in the difficulty of finding a precise mathematical description of a fluid flow that is in general nonlinear and time-dependent. The fluid accelerations can no longer be assumed t o be small compared t o gravity, as in Stokes's theory for periodic waves and the theory of cnoidal waves in shallow water, nor is the particle velocity any longer small compared to the phase velocity. The aim of this paper is to bring together s ome recent contributions to the calculation both of steep symmetric waves and of time-dependent surface waves. These have a bearing on the behaviour of whitecaps in deep water and of surf in the breaker zone . Since spilling breakers in gently shoaling water closely resemble solitary waves, we begin with the description of solitary waves of limiting amplitude, then discuss steep waves of arbitrary height. The observed intermittency of whitecaps is discussed in terms of the energy maximum, as a function of wave steepness, In Sections 6 and 7 a simpler description of steady symmetric waves is proposed, using an asymptotic expression for the flow near the wave crest. Finally we describe a new numerical technique (MEL, or mixed Eulerian-Lagrangian) with which it has been found possible to follow the development of periodic waves past the point when overturning takes place. Measurement of waves, and vertical and horizontal water particle velocities were made of spilling, plunging and surging breakers at sandy beaches in the vicinity of Monterey, California. The measured breaking waves, derived characteristically from swell-type waves, can be described as highly nonlinear. Spectra and cross spectra were calculated between waves and velocities. Secondary waves were noted visually and by the strong harmonics in the spectra. The strength of the harmonics is related to the beach steepness, wave height and period. The phase difference between waves and horizontal velocities indicates the unstable crest of the wave leads the velocities on the average by 5-20 degrees. Phase measurements between wave gauges in a line perpendicular to the shore show breaking waves to be frequency nondispersive indicating phase-coupling of the various wave components. The coherence squared values between the sea surface elevation and the horizontal water particle velocity were high in all runs, ranging above 0.8 at the peak of the spectra. The high coherence suggests that most of the motion in the body of breaking waves is wave-induced and not turbulent.

/pdf/kinematics-of-breaking-waves-5g4w6nay3y.pdf

Kinematics of breaking waves

Simultaneous measurements of waves, and vertical and horizontal water particle velocities were made at the breaker-line within the surf zone using a capacitance type penetrating wave staff, a pressure wave gauge, and an electromagnetic current meter. Wave measurements were also made at seaward and shoreward locations. The wave energy-density spectral components were converted to velocity spectral components using linear wave theory. These computed values compared well qualitatively with the measured velocity spectra. Quantitatively, the results showed that linear theory underpredicted wave-induced horizontal velocity spectral components by about 50 percent at the frequency of peak energy. Probability density functions were computed and compared to Gaussian and Gram-Charlier distributions using the chi-square goodness-of-fit test. The Gram-Charlier distribution qualitatively gave the better fit to the data. (Modified author abstract)

/pdf/the-kinematics-of-water-particle-velocities-of-breaking-180qyqzdfn.pdf

David Paul Richardson

Papers

Kinematics of breaking waves

The Kinematics of Water Particle Velocities of Breaking Waves within the Surf Zone.