Laboratory Experiment on Long Wave Generation by Time-Varying Breakpoint

Nagase, Satoru; Mizuguchi, Masaru

doi:10.1061/9780784402429.102

Cited by 6 publications

(14 citation statements)

References 8 publications

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“…Furthermore, the power relationship between the amount of short wave dissipation A s10−26 (amplitude A at x = 10m subtracted from A at x = 26m) and the infragravity waves (generated by the short wave dissipation) is calculated. In contrast to the nearly quadratic relationship observed for the free waves that were generated together with the short waves, the breakpoint forced waves have a linear relationship with short wave amplitude m = 1 ( Figure 5.5), suggesting that those waves were generated by a dynamic setup Huntley, 2002, Nagase andMizuguchi, 2001). …”

Section: Identifying Breakpoint Forced Waves By Controlling Short Wavmentioning

confidence: 84%

“…In the transient scenario, this is not the case and by assuming the constant as zero the bound wave becomes then a pure depression, and changes in shape are constantly balanced by free waves. Even though the generation of free waves have been discussed in different studies (Mei and Benmoussa, 1984, Nagase and Mizuguchi, 2001, Nielsen and Baldock, 2010, it is not clearly addressed in others and the interpretation of the results relies on the steady solution (Baldock, 2006, Battjes et al, 2004, Janssen et al, 2003, Masselink, 1995. Whether the generation of free waves happens for real waves it is not clear and perhaps difficult to confirm.…”

Section: The Key Questionsmentioning

confidence: 85%

“…This initial result suggests bound wave dominance at P T of f and at P T in strong bound wave dissipation, and/or strong influence of long waves generated by breakpoint forcing, which are linearly dependent on H Huntley, 2002, Nagase andMizuguchi, 2001).…”

Section: Power Relationship Between Short and Infragravity Wave Heightmentioning

confidence: 98%

“…To the author's understanding both Janssen et al (2003) and Battjes et al (2004) did not considered free wave generation and its effects on ∆φ to estimate shoaling rate and energy transfer. Nagase and Mizuguchi (2001) suggested that the observed smaller growth rate of the bound wave is a consequence of the superposition of forced and free waves. In this case, the free waves are generated due to the transient behavior of the bound (forced) wave on the slope (Mei and Benmoussa, 1984).…”

Section: Bound Wave Shoalingmentioning

confidence: 99%

“…For instance, bound waves are proportional to H 2 sh , and the breakpoint forcing goes as H sh (Nagase and Mizuguchi, 2001). Battjes et al (2004) and later Baldock (2012) have discussed the implication of these dependences on the relative importance of each mechanism for specific conditions.…”

Section: Infragravity Wave Dependence On Short Wave Amplitudementioning

confidence: 99%

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Infragravity wave forcing in the surf and swash zone

Moura¹,

Rolim²

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Infragravity waves, also known as surf beat, are important morphodynamic drivers in shallow water, especially inside the surf and swash zone where the short wave energy is dissipated due to breaking. In the past decades, great progress has been acquired in the understanding of surf beat and its implication in the coastal environments. However, many key features are still not fully understood, especially for complex natural systems. This thesis investigates infragravity wave dynamics in the surf and swash zone through a re-analysis of laboratory data, new numerical modelling and novel field measurements.The generation of infragravity waves in the surf zone is commonly associated with two individual mechanisms: release of second-order group-forced long waves and long waves generated by group-induced surf zone breakpoint oscillations. Both mechanisms are forced by radiation stress gradients, but due to their individual nature, different relationships between short and infragravity waves are expected.Determining these relationships, their effectiveness, and the governing hydrodynamic and morphodynamic conditions for each mechanism is complex. In the field, observations are still, to some extent, limited and generally restrained to small wave conditions. The first part of the thesis presents a comprehensive study of different infragravity wave generation mechanisms that includes a critical literature review, a re-analysis of previous laboratory data and an extensive numerical modelling investigation.This work provided new information about the implication of the different processes associated to bound wave shoaling, release and dissipation. In addition, key aspects related to the propagation patterns of infragravity waves have been identified. From the numerical investigation and the large amount of laboratory data re-analysed, clear and distinct relationships between the breakpoint and shoreline excursion have been established for each generation mechanism. The second part of the thesis presents a novel method to determine the dominant infragravity mechanism in the inner surf and swash zone in the field. In the field, the breakpoint oscillations and the shoreline motion are measured remotely via video and ii their relationship identified via cross-correlation. The identification of the dominant forcing mode, either bound wave or breakpoint, is interpreted based on the specific relationships previously determined.The results of thirteen field data sets collected from three different beaches indicate that, inside the surf zone, the dominance of bound wave or breakpoint forcing is strongly dependent on the surf zone width and the type of short wave breaking.Infragravity generation by bound wave release was stronger for conditions with relatively narrow surf zones and plunging waves; breakpoint forcing was dominant for wider surf zones and spilling breaker conditions, suggesting also that the bound waves remained forced inside the surf zone, being dissipated during short wave breaking. The numerical and laborato...

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Section: Identifying Breakpoint Forced Waves By Controlling Short Wavmentioning

confidence: 84%

Section: The Key Questionsmentioning

confidence: 85%

Section: Power Relationship Between Short and Infragravity Wave Heightmentioning

confidence: 98%

Section: Bound Wave Shoalingmentioning

confidence: 99%

Section: Infragravity Wave Dependence On Short Wave Amplitudementioning

confidence: 99%

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Infragravity wave forcing in the surf and swash zone

Moura¹,

Rolim²

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Remote sensing of the correlation between breakpoint oscillations and infragravity waves in the surf and swash zone

Moura

Baldock

2017

JGR Oceans

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A novel remote sensing methodology to determine the dominant infragravity mechanism in the inner surf and swash zone in the field is presented. Video observations of the breakpoint motion are correlated with the shoreline motion and inner surf zone water levels to determine the relationship between the time‐varying breakpoint oscillations and the shoreline motion. The results of 13 field data sets collected from three different beaches indicate that, inside the surf zone, the dominance of bound wave or breakpoint forcing is strongly dependent on the surf zone width and the type of short wave breaking. Infragravity generation by bound wave release was stronger for conditions with relatively narrow surf zones and plunging waves; breakpoint forcing was dominant for wider surf zones and spilling breaker conditions.

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