Modelling nearshore circulation in a fringing reef system: Ningaloo Reef, Australia

The reef-lagoon circulation of Ningaloo Reef, Australia’s largest fringing coral reef system was investigated using data collected during a six-week field experiment and numerical modelling. The observed circulation followed a consistent pattern, with cross-reef flows driven over the reef flat and offshore directed return flows out the reef gaps (channels).
A three-dimensional coupled wave-circulation model was developed for an ~10 km section of Ningaloo Reef at Sandy Bay, using the Regional Ocean Modelling System (ROMS) coupled to the wave model SWAN. The coupled model was forced with offshore wave conditions, tides and wind, and then compared to observations of currents and waves measured throughout the reef-lagoon system. Results demonstrated the capability of the coupled model to successfully reproduce the dominant wave and circulation patterns within this morphologically-complex system. It is concluded that surface wave breaking is the major mechanism driving the mean reef-lagoon circulation, with tides playing a secondary role. The response of the circulation to winds was found to be insignificant during the study period.