Interaction between the water particle kinematics of a partial clapotis (partly standing wave) and those of the washing motion (wave runup and downrush) is extremely important with respect to the wave forces exerted on sloping structures.
breaking wave, plunging breaker
The water motion occuring at slopes in the presence of waves can be interpreted as a constrained vibratory motion with a plurality of degrees of freedom.
Water level deflections corresponding to partial reflection on the one hand and washing motions on the other can therefore be associated with distinctive degrees of freedom.
In all such systems influencing one degree of freedom has an effect on the remaining degrees of freedom.
hollow block revetment
At the process of breaking waves on a slope the washing motion (degree of freedom) can be changed extraordinarily by hollow concrete elements allowing the inside passage of the backwash water of previously broken waves.
Hence, the lacking water at the leeward side of the actually breaking wave compells the formation of a different type of breaker disposing of less height also.