Wave Breaking Type as a Typical Sign of Nonlinear Wave Transformation Stage in Coastal Zone

Experimental data demonstrate dependence of wave breaking type on wave amplitude-frequency-phase structure that is determined by nonlinear wave transformation. The spilling and plunging breaking waves are differed in the symmetry of the wave profile and the ratio of the amplitudes of the 1st and 2nd harmonics in breaking wave. The wave profile symmetry, in turn, is determined by the phase shift between these harmonics. In spilling breaking waves, it is close to zero, which corresponds to symmetrical waves. In plunging breaking waves, the phase shift is negative, which corresponds to the forward shifted 2nd harmonic. The ratio of the amplitudes of the 1st and 2nd harmonics in spilling breaking waves is less than that in plunging breaking waves. The periodic energy exchange between harmonics during near resonant triad wave interactions is the reason for the change in the types of wave breaking for waves propagating above a gentle inclined bottom. Due to the different structure, plunging breaking waves contribute to the erosion of the cross-shore underwater profile, while spilling breaking waves contribute to the accumulation of sand on it.