This paper aims to understand the characteristics of a tsunami propagating over a wide reef platform, which was observed during a field survey of the 2009 Samoan Islands Tsunami, by using a turbulence model. A Large Eddy Simulation (LES) model was used to simulate wave breaking and energy dissipation. The results of the numerical simulations were shown to reproduce well the results of the field survey of the 2009 Samoan Islands Tsunami. In particular after the 2004 Indian Ocean Tsunami, tsunamis propagating over coral reefs were observed in many countries, such as the Maldives, the southwest coast of Sri Lanka and Solomon Islands. The present method may also apply to these countries and contribute to considering regional tsunami mitigation strategies.