Wave reflection occurs on the offshore side of the breakwater. While waves passing the structure
are diffracted, the portions striking the breakwater are reflected like a billiard ball from a cushion. If the
structure is a smooth vertical wall, the reflection is nearly perfect, and if the wave crests are parallel with
the breakwater, the reflected and incoming waves will reinforce each other to form standing waves,
which are twice as high as the incoming waves and may cause considerable scouring of the bottom. If
the waves approach at an angle, no standing waves will form, but the resulting water surface will be
confused and choppy because the reflected waves will cross the path of the incoming waves. This could
also contribute to erosion and scouring of the bottom.
The final important wave characteristic is evident when waves break either on a beach or structure.
The uprush of water after breaking is called runup and it expends the wave's remaining energy. The
runup height depends on the roughness and steepness of the structure or beach and the characteristics of
the wave. Increased roughness reduces runup.
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