Field measurements show rough fore reefs with spurs and grooves can dissipate more wave energy than the reef crest

Abstract

Coral reefs are widely recognized as effective dissipaters of wave energy. Spurs and grooves (SAG) are common features of fore reefs worldwide and are thought to be particularly efficient at dissipating wave energy. However, very few studies have collected in-situ hydrodynamic data to verify this and understand SAG interactions with hydrodynamic forces. We present in-situ wave data from contrasting SAG sites at Moorea, French Polynesia, and One Tree Reef in the southern Great Barrier Reef, Australia. We measured high rates of wave energy dissipation (up to 0.1 kW/m2) across the SAG zone. Interestingly, under the modal conditions measured, the SAG zones often dissipated wave energy at higher rates than the adjacent reef crest/flat zone. Rates of dissipation were the greatest at sites with high live coral cover in mesotidal environments (i.e., One Tree Reef sites), suggesting the structural complexity of live corals may increase bed friction and that tidal currents may also contribute to dissipation. Correlations between measured dissipation, wave height and depth allowed us to suggest that the SAG zone dissipates more energy under high wave conditions at low tides, while the reef crest/flat dissipates more energy at high tides under small wave conditions. Further study is required to better understand and model the hydrodynamics of SAG zones and the important role they play in reef dynamics and coastal protection.