Wave transformations across a Caribbean fringing-barrier Coral Reef

Wave measurements during three experiments at Tague Reef, St. Croix (U.S.V.I.) in April 1987 showed a net energy decrease across the reef profile of 65–71% between the forereef and crest, wave propagation to the backreef increased energy reduction to 78–88%. Tidally induced water depth changes (range of 0.3 m) increased wave energy dissipation by 15% between forereef and crest and 20% between forereef and backreef. Significant wave heights throughout the experiment were low (<0.5 m) and exhibited a tidal modulation in the backreef or lagoon. Wave transmission over the reef averaged 0.46 and modulated by the tide (0.32 at low tide vs 0.62 at high tide). The spectral time-delay model applied to analyzed wave transformations across the reef produced attenuation coefficients that averaged 0.62 between 0.05 and 0.1 cps (20–10 s) and afterwards oscillate between 0.22 and 0.35. For waves between the forereef and backreef, the attenuation coefficients from the time-delay model decay exponentially between 0.05 and 0.1 cps, afterwards they oscillate between 0.13 and 0.2. The steady wave-energy model with bottom friction, essentially form drag, and wave breaking dissipation yield wave heights modulated by the tides and errors of <19% in the crest and >20% at the backreef. The model revealed that while frictional and wave-breaking dissipation are equally important, frictional dissipation is greater.