Wave attenuation over the Great Barrier Reef matrix

This is the first large-scale study of the influence of an offshore reef matrix on wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16 yr-record of wave height, from seven satellite altimeters. Within the GBR matrix, wave height is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, waves that penetrate the matrix have little depth-modulation. There is no evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because an individual reef casts a wave shadow much larger than the reef itself; thus a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the matrix. Here, wave conditions depend largely on local wind speed, rather than wave conditions either seaward, or within the matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.