Geoscience Reference
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Figure 3.17 (top) Comparing breaking events detected from the wavelet approach in dots with a
Lake George measurement (see Table 3.1 ) in vertical bars. (middle) Local steepness ak . The straight
line shows γ = 0 . 6, which is the chosen threshold value. (bottom) Instantaneous wave spectra in
relative units (shading scale below). The horizontal axis is the time axis, as in the top two panels.
Figure is reproduced from Liu & Babanin ( 2004 ) (copyright of Copernicus Publications on behalf of
the European Geosciences Union)
of experimental and analytical studies (e.g. Holthuijsen & Herbers , 1986 ; Babanin , 1995 ;
Babanin et al. , 2007a , 2009a , 2010a , among others), reported that the majority of break-
ing events take place within the group structure close to the peak of the group envelope,
although field observations indicated that an essential proportion of the breakings also
occurred outside the distinct wave groups ( Holthuijsen & Herbers , 1986 ; Babanin , 1995 ).
Figures 3.16 - 3.17 show that breaking does happen beyond the obvious groups of domi-
nant waves and the instantaneous spectra plotted in these figures indicate why this may be
the case.
Once the limiting acceleration criterion (2.60) is applied to the instantaneous wave
(3.35) - (3.38) which is characteristic of the instantaneous wave spectrum shown in the
bottom panels of Figures 3.16 - 3.17 , occurrence of the breaking event will depend on
the product of the characteristic amplitude a and the characteristic average frequency
σ
squared. The peak of the envelope of dominant waves will give rise to the amplitude a ,
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