Modelling Wave Breaking across Coral Reefs Using a Non-Hydrostatic Model

Wave breaking is the main mechanism to drive flow across shallow reef flats. The breaking process is more complex than on continental shelves due to the extreme geometries. This paper describes a non-hydrostatic model with shock-capturing capability to simulate the wave breaking process over two reef profiles. The two cases with and without ridge at the edge of reef crest are simulated, and the results are compared with data measured from laboratory experiment. The results show that the model can predict the surface elevation and mean sea level with good accuracy. The existence of a ridge can narrow the width of surfzone and increase wave-induced setup of sea level. The turbulent intensity and energy dissipation rate during wave breaking in the two reef profiles are analyzed. The comparison shows that the near-surface turbulence, energy dissipation rate and spanwise vortex are greatly enhanced by the existence of ridge, and the maximum value of turbulent kinetic energy at the breaking point can be two times larger than the case without the reef ridge. Moreover, the reef ridge decreases water depth in the surfzone, which makes the role of bottom friction in energy dissipation more significant. The interaction between breaking induced turbulence and the bed becomes more intense.