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Wave Breaking and Air Entrainment
Published in David M Kelly, Aggelos Dimakopoulos, Pablo Higuera, Advanced Numerical Modelling of Wave Structure Interactions, 2021
By observation, the Iribarren number or Iribarren parameter (also known as the surf similarity parameter or breaker parameter) is a dimensionless number used to describe the occurrence and the type of wave breaking on sloping beaches (Battjes, 1974). It has been established that there is a continuous spectrum ranging from spilling to surging breaking, varying according to three parameters: the slope of the beach (slope inclination from mild to strong), the steepness of the wave (the ratio between the height of the wave and its wavelength, which is an indicator of the degree of non-linearity of the wave) and the dispersion parameter (the ratio of the depth and wavelength). This last parameter, which reflects the influence of the bathymetry variations on the propagation of the wave, classifies if the water depth is shallow or deep. For an equivalent incoming wave condition, the breaking will be “softer” or “milder” for low beach slope, while the breaking will be more violent on steep slope (breaking plunging to frontal). Surging breaking is the limit of the spectrum, since we do not observe a large amount of foam nor a violent impact. The triggering of the breaking event occurs later when the beach goes from a gentle to a steep slope, when waves break closer and closer to the top of the beach. So, this confirms the intuition of the members the United States Army Corps of Engineers, who wanted to get information about the sea bed by observing breaking waves: when a wave breaks, we are often in the presence of a high point of bathymetry.
A study of wave reflection based on the maximum wave momentum flux approach
Published in Coastal Engineering Journal, 2018
M. Buccino, M. D’Anna, Mario Calabrese
The existence of a correlation between Kr and ξ was later documented by several laboratory studies, conducted with regular and random waves on both permeable and impermeable sloping structures (e.g. Ahrens 1981; Seelig and Ahrens 1981; Postma 1989; Zanuttigh and van der Meer 2008). For irregular waves the Iribarren number was calculated using the significant wave height and a spectral period, either peak or mean. The researchers ascertained that the relationship between Kr and ξ was, as a whole, of convex or sublinear type, which substantiates the idea that the Battjes’ hypothesis is valid only within a restricted range of (low) Iribarren numbers. Additionally, in a number of cases a remarkable scatter of the experimental data was observed, especially for highly permeable structures (e.g. Seelig and Ahrens 1981; Muttray, Oumeraci, and ten Oever 2006; Buccino et al. 2011). This lack of fit led Muttray et al. (1992) to comment that “the surf similarity parameter does not represent an optimal mean for the description of the reflection process.”