SEMINAR: Hydrodynamic Processes within a Fringing Reef System: Ningaloo Reef, Western Australia

The circulation driven by wave breaking, tides and winds within a fringing coral reef system (Ningaloo Reef) in Western Australia was investigated using field observations and numerical modeling of a section of reef at Sandy Bay. 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 numerical model of the study area was developed using the three-dimensional ocean circulation model (ROMS) coupled to the wave model SWAN, which was able to accurately predict the waves and currents throughout this morphologically complex reef-lagoon system when forced with realistic offshore wave conditions, tides and wind. The relative importance of waves, tide and wind on the circulation and flushing of Sandy Bay was investigated using both the observations and modeling, and revealed the dominant role wave breakingplays in driving the overall reef-lagoon circulation. However, these wave-driven currents were found to be modulated at tidal frequencies, suggesting that the wave-drivencurrents responded to tidal variations in the mean water level over the reef. Finally, the validated numerical model was used to investigate the response of Ningaloo’s circulation and flushing over a full seasonal cycle when wave and wind conditions significantly differ (i.e., extrapolated outside of the field study period), as well as under different forcing scenarios (e.g., due to a projected rise in mean sea level).