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Wave Energy Chapter | 5 121

5.2 WAVE TRANSFORMATION DUE TO SHOALING WATER
In general, waves that are generated as a result of a distant storm or localized
wind event propagate and ‘disperse’, relatively unhindered, until they encounter
shoaling water. At this stage, two processes influence waves: shoaling and
refraction.
5.2.1 Wave Shoaling

As water shoals, remembering that waves transport energy in the direction of
wave advance, it is important to make use of the principal that wave energy flux
per unit surface area, EC g , is constant. This assumes that no energy is dissipated
by the wave train, for example, by wave breaking or bottom friction, as it
propagates from deep to shallow water. If we apply a subscript ‘0’ to represent
deep water values, this implies that
EC g = E 0 C g0 = constant (5.46)

Therefore, if we have knowledge of ‘deep water’ wave properties, we can
determine the corresponding wave properties in shoaling water.
Consider a horizontally 1D case, in which the wave crests are everywhere
parallel to the depth contours (Fig. 5.6). As the waves propagate through

FIG. 5.6 Shoaling wave with an offshore wave height of 1 m (and period 8 s), assuming that waves
do not break. (A) Water depth; (B) group velocity; (C) wave height.