scholarly journals ON PREDICTING INFRAGRAVITY ENERGY IN THE SURF ZONE

1984 ◽  
Vol 1 (19) ◽  
pp. 130
Author(s):  
Asbury H. Sallenger ◽  
Robert A. Holman
Keyword(s):  
Incident Wave ◽  
Surf Zone ◽  
Standing Waves ◽  
Wave Mode ◽  
Edge Wave ◽  
Flow Data ◽  
Edge Waves ◽  
Infragravity Waves ◽  
Synthetic Spectra ◽  
Wave Conditions

Flow data were obtained in the surf zone across a barred profile during a storm. RMS cross-shore velocities due to waves in the infragravity band (wave periods greater than 20 s) had maxima in excess of 0.5 m/s over the bar crest. For comparison to measured spectra, synthetic spectra of cross-shore flow were computed using measured nearshore profiles. The synthetic spectra were calculated assuming a white runup spectrum of mode-4 edge waves of unit amplitude, although the results would be essentially the same for standing waves or any edge-wave mode above 2. The structure, in the infragravity band, of these synthetic spectra corresponded reasonably well with the structure of the measured spectra. Total variances of measured cross-shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra. These nondimensional variances were independent of distance offshore and increased with the square of the breaker height. Thus, cross-shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions.

scholarly journals EDGE WAVES AND THE LITTORAL ENVIRONMENT

1972 ◽  
Vol 1 (13) ◽  
pp. 67 ◽  
Author(s):  
Anthony J. Bowen
Keyword(s):  
Surface Waves ◽  
Broad Spectrum ◽  
Surf Zone ◽  
Wave Mode ◽  
Dominant Mode ◽  
Edge Wave ◽  
Wave Spectra ◽  
Edge Waves ◽  
Wave Processes ◽  
Induced Changes

Several types of beach features seem to have a rather regular, longshore pattern. This pattern may indeed he sufficiently uniform to be described in terms of a recognisable longshore wavelength. A likely explanation for such features lies in the motion of edge waves, surface waves trapped by refraction to the shoreline. These waves, by themselves or by interaction with the normal, incoming surface waves breaking on the beach, can generate longshore features having a wavelength equal to or half the edge wave wavelength. If a broad spectrum of edge wave modes were present any longshore variation should appear rather irregular. The existence of regular features therefore suggests that a particular edge wave mode is often dominant, the characteristics of the dominant mode depending on the geometry of the nearshore area and the width of the surf zone. Any new, artificial structure stretching seawards provides new boundary conditions, almost certainly altering the characteristic of the edge wave spectra. This is particularly obvious in the case of a regularly spaced structure such as a s'et of groynes. A deeper understanding of the edge wave processes is needed so that the induced changes in the edge wave spectra are the least deleterious or, an intriguing possibility, advantageous.

scholarly journals EXCITATION OF LOW FREQUENCY TRAPPED WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 25
Author(s):  
Robert King ◽  
Ronald Smith
Keyword(s):  
Incident Wave ◽  
Standing Waves ◽  
Low Frequency ◽  
Nonlinear Interactions ◽  
Edge Waves ◽  
Constant Depth ◽  
Side Band ◽  
Rectangular Basin ◽  
Trapped Wave ◽  
Narrow Wave

Weak nonlinear interactions in water of non-constant depth between an incident wave, a side-band incident wave and a relatively low frequency trapped wave are shown to lead to the generation of the trapped wave. Three situations are considered in detail: edge waves in a wide rectangular basin, progressive edge waves on a straight beach, and standing waves in a narrow wave tank.

Regularly-spaced grooves on shore platforms in north Northumberland, UK

2020 ◽  
Vol 63 (2) ◽  
pp. 124-134
Author(s):  
Alison M. Tymon ◽  
Barry G. Tymon
Keyword(s):  
Incident Wave ◽  
Wave Energy ◽  
Surf Zone ◽  
High Water ◽  
Edge Waves ◽  
Shore Platform ◽  
Bedding Planes ◽  
High Water Mark ◽  
Incident Wave Energy ◽  
Shore Platforms

Unusual regularly-spaced grooves are found between low water mark (LWM) and high water mark (HWM) on several shore platforms in north Northumberland. References in the literature are sparse, so data were collected to establish the nature of the grooves and to elucidate the processes that might have formed them. Groove formation is confined to strata with widely spaced bedding planes on shore platforms dipping at no more than 5° towards the sea. The grooves are symmetrical, bifurcation is common and grooves on sandstones are deeper and more sinuous than those on limestones. Grooves at mid-tide levels are wider than grooves near LWM and HWM and the trend of the grooves is not related to joint trends. The process that has formed the characteristically smooth surfaces of the grooves is considered to be abrasion by sand and pebbles carried by waves in the surf zone of the shore platform. The width of the grooves is remarkably regular, and it is suggested that this may be due to the effects of the increase in incident wave energy given by edge waves.

On the radiation damping of finite-amplitude progressive edge waves

1990 ◽  
Vol 431 (1883) ◽  
pp. 419-431 ◽  
Keyword(s):  
Wave Theory ◽  
Wave Dispersion ◽  
Wave Mode ◽  
Finite Amplitude ◽  
Edge Wave ◽  
Water Model ◽  
Edge Waves ◽  
Transfer Energy ◽  
Oblique Waves ◽  
Weakly Nonlinear

Using small-amplitude expansions, it is demonstrated that weakly nonlinear periodic edge waves, travelling along the shoreline of a beach, can be attenuated owing to radiation of oblique waves out to sea. A few beach profiles, for which edge-wave dispersion relations are known in closed form, are discussed, and necessary conditions are determined for such radiation to occur due to nonlinear self-interactions. In particular, it is shown that quadratic nonlinear interactions cause the second edge-wave mode on a uniformly sloping beach of slope α to radiate when 1/18π < α < ⅙π; a detailed derivation to find the amplitude of the radiated wave and the attendant decay rate of the edge wave is presented, using the full water-wave theory. Also, it is pointed out that a concomitant nonlinear mechanism can transfer energy from incoming oblique waves to subharmonic edge waves – a plausible mechanism for the generation of travelling edge waves in coastal waters – and the details of this process are discussed within the framework of a shallow-water model.

scholarly journals BEACH CUT IN RELATION TO SURF ZONE MORPHODYNAMICS

1980 ◽  
Vol 1 (17) ◽  
pp. 60 ◽  
Author(s):  
L.D. Wright
Keyword(s):  
Incident Wave ◽  
Field Experiments ◽  
Surf Zone ◽  
Subharmonic Resonance ◽  
Southeastern Australia ◽  
The World ◽  
Wave Conditions

Field experiments on the coast of Southeastern Australia, supplemented by systematic observations in a variety of environments in other parts of the world, indicate at least three quasi-discrete modes of subaerial beach cut, each of which is related to a distinct set of mechanisms. For any given set of incident wave conditions, the operation or non-operation of a particular mode of cutting depends on the morphodynamic state of the surf-zone and beach. Steep, reflective, beaches are susceptible to cut under moderate swell conditions by accentuated runup and berm overtopping associated with subharmonic resonance. Appreciably more energy is required to cut flat dissipative beaches. Cut of dissipative beaches involves high setup which oscillates at infragravity frequency and allows the bores of broken waves to penetrate to the backshore. Beach states intermediate between the reflective and dissipative extremes are subject to cut by both the modes just described as well as by scour in the embayments of topographically arrested rips which can cause significant localized erosion even when the coast regionally is accreting. Beaches which most commonly exhibit intermediate topographies are the least stable and most mobile.

scholarly journals SURF ZONE RESONANCE AND COUPLED MORPHOLOGY

1978 ◽  
Vol 1 (16) ◽  
pp. 80
Author(s):  
John Chappell ◽  
Lynn Donelson Wright
Keyword(s):  
Spectral Data ◽  
Incident Wave ◽  
Surf Zone ◽  
Harmonic Wave ◽  
High Energy ◽  
Edge Wave ◽  
Dissipative Medium ◽  
Spectral Peaks ◽  
Dissipative Case ◽  
Incident Frequency

The edge wave hypothesis for periodic inshore morphology and circulation is tested for five beaches and is supported by resulting wave-current spectral and cross-spectral data. Beach types range from a reflective, narrow surf zone, case through various dissipative medium to high energy beaches including some with inshore bar-trough morphology and one broad surf zone troughless one. In all cases beachface reflectivity is moderately high (E < 2.5) and inshore resonance occurs, indicated by strong spectral peaks at lower than incident frequency with wave-current co-peaks being 90°out of phase. Several different edgewave frequency and mode combinations are indicated. The reflective beach shows an n = o subharmonic edgewave (i.e. at half incident wave frequency) which Guza and Davis (1974) predict as the most likely case, viz. the (o,o) triad. The troughless dissipative case shows a (1,0) edgewave triad; the same occurs in some bar-trough dissipative cases but in other cases is supplanted by the (o,o) sub-harmonic wave and/or by a lower subharmonic wave at h, incident frequency. The likelihood of a given edge .waveset appears to be regulated by surf friction, and a change of edge wave set appears likely to explain observed changes of inshore circulation.

Subharmonic edge wave excitation by narrow-band, random incident waves

2019 ◽  
Vol 868 ◽  
Author(s):  
Giovanna Vittori ◽  
Paolo Blondeaux ◽  
Giovanni Coco ◽  
R. T. Guza
Keyword(s):  
Incident Wave ◽  
Narrow Band ◽  
Bottom Friction ◽  
Edge Wave ◽  
Random Waves ◽  
Wave Excitation ◽  
Edge Waves ◽  
Similar Time ◽  
Wave Phase ◽  
Incident Waves

A monochromatic, small amplitude, normally incident standing wave on a sloping beach is unstable to perturbation by subharmonic (half the frequency) edge waves. At equilibrium, edge wave shoreline amplitudes can exceed incident wave amplitudes. Here, the effect of incident wave randomness on subharmonic edge wave excitation is explored following a weakly nonlinear stability analysis under the assumption of narrow-band incident random waves. Edge waves respond to variations in both incident wave phase and amplitude, and the edge wave amplitudes and incident wave groups vary on similar time scales. When bottom friction is included, intermittent subharmonic edge wave excitation is predicted due to the combination of bottom friction and wave phase. Edge wave amplitude can be near zero for long times, but for short periods reaches relatively large values, similar to amplitudes with monochromatic incident waves and no friction.

scholarly journals BEACH CUSPS AND EDGE WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 81 ◽  
Author(s):  
D.A. Huntley ◽  
A.J. Bowen
Keyword(s):  
Incident Wave ◽  
Wave Motion ◽  
Field Measurements ◽  
Convincing Evidence ◽  
Edge Wave ◽  
Wave Frequency ◽  
Edge Waves ◽  
Wide Range ◽  
Beach Cusps ◽  
Resonant Waves

Beach cusps are very common, concave-seaward cuspate patterns at the shoreline of a beach, which tend to occur with a regular longshore spacing, but which can have a wide range of longshore wavelengths from a few centimeters to several kilometers or more. Edge waves, resonant waves trapped at the shoreline by refraction, have been suggested as the cause of beach cusps but it has proved difficult to establish a definitive link on natural beaches . This paper describes field measurements of nearshore velocities, in all three orthogonal directions, that show the presence of edge wave motion just before the formation of beach cusps of the corresponding wavelength, and thus provides convincing evidence that edge waves are responsible for beach cusps. The magnitude of the observed edge wave oscillatory and drift velocities are found to be large and apparently well able to form cusps of the observed size. The observed edge waves are at the subharmonic of the incident wave frequency and thus are the field equivalent of the laboratory observations of Guza and Inman (1975) and Guza and Bowen (1977). It is not clear, however, whether the developing cusp topography enhanced or suppressed the edge wave motion.

Field observations of long-period, surf-zone standing waves in relation to contrasting beach morphologies

1982 ◽  
Vol 33 (2) ◽  
pp. 181 ◽  
Author(s):  
LD Wright
Keyword(s):  
Surf Zone ◽  
Full Range ◽  
Wave Length ◽  
Standing Waves ◽  
Wide Band ◽  
Field Observations ◽  
Edge Waves ◽  
Long Period ◽  
Energy Height ◽  
Velocity Spectra

Field observations of water-surface oscillation and horizontal flow velocity spectra were carried out in the surf zones of contrasting beach-inshore morphodynamic states. The observations were made under conditions of long-period (7.5-11 s), moderate-energy (height 1 .2-2.3 m) swell on different beaches encompassing the full range of states from the steep. reflective extreme to the flat, dissipative extreme and including intermediate states involving different scales of rhythmic surf-zone topography and rip circulations. Experiments on all types of topography reveal standing surf-zone oscillations at periods longer than incident wave period. At least some of these appear to be edge waves. The actual frequencies are dependent on the morphodynamic state of the surf zone and beach. The standing waves with shortest period are zero-mode subharmonic edge waves which consistently occur on highly reflective beaches where they cause cusps spaced at one-half the edge-wave length. The standing waves with lowest frequency were observed on the flattest and most dissipative beach and comprised a wide band of infragravity frequencies. These oscillations could cause the multiple parallel bars. Intermediate frequencies occur in the presence of the pronounced bar-trough and rhythmic topographies of intermediate morphodynamic states.

scholarly journals RESONANT INTERACTIONS FOR WAVES BREAKING.ON A BEACH

1976 ◽  
Vol 1 (15) ◽  
pp. 31 ◽  
Author(s):  
Robert T. Guza ◽  
Anthony J. Bowen
Keyword(s):  
Incident Wave ◽  
Wave Breaking ◽  
Surf Zone ◽  
Breaking Wave ◽  
Edge Waves ◽  
Viscous Effects ◽  
Resonant Interactions ◽  
Maximum Value ◽  
Run Up ◽  
Subharmonic Resonances

A laboratory and theoretical study of the transition from strongly reflected surging to dissipative plunging breakers on a relatively steep plane beach (1:8) has revealed the following: (1) The run-up and offshore variation of sea surface elevation of surging waves are well predicted by linear theory. (2) The fluctuating part of the run-up (related to the amplitude of the reflected incident wave) reaches a maximum value; a further increase in incident progressive wave energy results in increased dissipation. (3) Subharmonic edge waves (the growing instabilities of surging waves) are driven primarily by the swash motion, which does not increase with increasing incident breaking wave height. However, the turbulence accompanying incident wave breaking, and the effective eddy viscosity, rapidly increases with increasing breaker height. As a result, subharmonic resonances do not occur with spilling or steep plunging waves; very strong viscous effects suppress the nonlinear instabilities. (4) edge waves generated by a surging incident wave can be suppressed by superimposing an additional breaking wave of different frequency on the incident wave field. Thus, any excited edge waves are likely to have length scales at least the order of a surf zone width.

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