loading page

Water Level Modulation of Wave Transformation, Setup and Runup over La Saline Fringing Reef
  • +1
  • William Sami Bruch,
  • Emmanuel Cordier,
  • France Floc'h,
  • Stuart Grant Pearson
William Sami Bruch
Mediterranean Institute of Oceanography

Corresponding Author:[email protected]

Author Profile
Emmanuel Cordier
Université de La Réunion
Author Profile
France Floc'h
Institut Universitaire Européen de la Mer (UBO)
Author Profile
Stuart Grant Pearson
Delft University of Technology
Author Profile


Coral reefs represent an efficient natural mechanical coastal defense against ocean waves. The focus of this study is the La Saline coral reef, located in the West of La Reunion Island in the Indian Ocean. The area is microtidal and frequently exposed to Southern Ocean swell as well as cyclonic events. The objective of this paper is to provide a better understanding of the coastal defense characteristics of the reef system for a range of Southern Ocean swell events and tides. Pressure sensors were placed across the reef to measure water level fluctuations and to determine gravity wave and infragravity wave components and their transformation across the coral reef. A numerical model (XBeach surf beat), validated using field observations, was used to deepen understanding of wave transformation, wave setup and runup. Field measurements and model outputs show that as gravity waves break over the reef, the reef acts as a low-pass filter. Study results also suggest frequency-dependent dissipation of infragravity waves by bottom-friction. The resulting wave-induced setup is found to be the dominant hydrodynamic component. The setup and runup are each 95% and 71% driven by the significant wave height (HS) with which they increase, and transfer functions relating incident wave characteristics to reef system hydrodynamics are proposed. At a semi-diurnal tidal timescale, the setup and runup are in anti-phase, as the runup is highest in conditions of reduced wave dissipation on the reef flat, corresponding with high tides. These conditions also result in a lower wave setup.