Wave transformation of multidirectional waves were measured in a three-dimensional laboratory model of a coral reef with a steep slope and a horizontal reef flat. The experimental results showed that when the waves broke on the reef flat, the relative breaking wave height (H/d)b was influenced by the deep-water wave steepness and the relative water depth db/Lo, thus the criterion for the breaking waves on the reef flat was proposed. The nonlinear wave parameters and representative wave heights were analyzed and it was confirmed that the wave transformation on this terrain was influenced by the incident wave directions and directional spreading parameters slightly.
Coral reefs are present in many tropical and subtropical regions, they are usually described as a steep slope and a reef flat with shallow water. As wave propagates from deep water to shallow region, the wave profile becomes steep, and the wave breaks when the wave height reaches certain limit. It is essential to study the wave propagation characteristics on reef terrain for the evaluation of coastal processes and the design of coastal structures on the reef flats.
Wave breaking is one of the most important phenomena in wave propagation, most of the previous studies of wave breaking were conducted on the common coastal slopes. Munk (1949) described the relationship between the breaking wave height and deep-water wave steepness based on an evaluation of the breaking wave energy using the theoretical solitary wave equation. According to Airy wave theory, Komar and Gaughan (1972) modified the factor in Munk's formula using the available laboratory and field data. Goda (1970) proposed the formula about the relationship between the breaking wave height with the relative water depth and the gradient of slope. And according to the empirical formula of Goda (1970), some researchers proposed the modified breaking criteria by analyzing amount of experimental and field data (Kamphuis, 1991; Rattanapitikon and Shibayama, 2007; Seyama and Kimura, 1988). However, the criteria of wave breaking on coral reef terrain are rare.
