WAVE TRANSFORMATION ON A CORAL-REEF

Wave transformation of regular waves was measured in a laboratory model of a fringing reef with a steep face and an outer reef-top slope gradually decreasing in the landward direction. Data was obtained for various wave conditions and water levels. A nonlinearity parameter, F(co) = g1.25H(o)0.5T 2.5/h(e)1.75, based upon one proposed by Swart and Loubser (1979), is proposed as a suitable parameter for classifying wave transformation regimes on this reef. In particular, when F(co) > 150, waves plunge on the reef edge and the amount of wave energy reaching a shore or structure is small (< 16%). When F(co) less-than-or-equal-to 100, waves spill on the reef-top but the greater part of their energy is transmitted over the reef-top. The maximum values of the wave height to water depth ratio on the reef-top were found to be consistent with Nelson's analyses for laboratory and field data which indicate that the maximum stable wave height to depth ratio H/d on a horizontal bottom never exceeds 0.55 for shallow water waves (F(c) > 500). The experimental data confirms that the maximum value of H/d decreases when F(c) decreases but that it also increases when the bottom slope increases.