WAVE ATTENUATION ON AN OFFSHORE CORAL REEF

T.A. Hardy, I.R. Young, R.C. Nelson, M.R. Gourlay

Abstract


The wave climate along the northeastern tropical coastline of Australia is controlled by The Great Barrier Reef (GBR). However, the processes by which the GBR attenuates and transforms waves are little understood. As the first part of an on-going study of the interaction between waves and coral reefs, a field experiment was conducted to study the processes that occur as waves break on an offshore reef and proceed across the reef flat into the lagoon. Eighteen wave, water level, and current measuring instruments were deployed and data for a wide range of tide and wave conditions were collected. Preliminary results for wave attenuation are presented. Results for wave attenuation across the reef show that wave heights on the reef flat and in its lagoon are controlled by the depth of water over the windward reef flat. As the waves travel across the reef flat, the ratio of significant wave height to water depth reduces to a value of 0.40, and the ratio of maximum wave height to water depth reduces to a value of 0.6 to 0.8. In the deeper water in the middle of the reef lagoon both the ratios of significant wave height to the depth over the reef flat and maximum wave height to the depth over the reef flat remain in the above ranges. However, at the mid-lagoon position these results are less general as wave heights inside a lagoon are also dependant on wind speed, direction, and fetch length inside the lagoon.

Keywords


coral reef; offshore reef; wave attenuation

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