Résumé
Abstract Wave frictional dissipation is a key process in rough seabed’s environments such as coral reefs, expected to significantly reduce incoming wave energy. In phase‐averaged models, wave dissipation is typically estimated through a wave friction factor which is dependent of the near‐bed orbital excursion and the hydraulic length, a proxy for the seabed substrate roughness. A field experiment was conducted in the South‐Western coral reef barrier of Mayotte (Indian Ocean) to compute through a frequency‐integrated wave energy balance. Significant time and space variations of have been observed, driven by the evolution of the wavefield and the diversity of coral geometry and scales found along the barrier. The fine reef architecture has been examined thanks to a high‐resolution multi‐beam echo sounder survey. This study has reassessed the established link between hydraulic roughness length and roughness standard deviation; it also indicates that second‐order roughness metrics may also significantly explain variations in . Future challenges remain in the proper definition of the length scales of seabed variability attributed to roughness and to bathymetry.