Frictional wave dissipation on a remarkably rough reef

We present a week of observations of wave dissipation on the south forereef of Palmyra Atoll. Using wave measurements made in 6.2 m and 11.2 m of water offshore of the surf zone, we computed energy fluxes and near‐bottom velocity. Equating the divergence of the shoreward energy flux to its dissipation by bottom friction and parameterizating dissipation in terms of the root‐mean‐square velocity cubed, we find that the wave friction factor, fw, for this reef is 1.80 ± 0.07, nearly an order of magnitude larger than values previously found for reefs. We attribute this remarkably high value of fw to the complex canopy structure of the reef, which we believe may be characteristic of healthy reefs. This suggests that healthy reefs with high coral cover may provide greater coastal protection than do degraded reefs with low coral cover. Key Points Shoaling waves observed on a healthy coral reef Damping of waves is an order of magnitude greater than observed previously High friction factor observed attributed to canopy flow dynamics