WAVE TRANSFORMATION OVER PALM BEACH REEF

Abstract

Ocean wave parameters are influenced by shallowing water depth and varying bottom topography. Modelling and in-situ studies have found that as waves propagate over a reef, interaction in the form of friction with the shallower reef can alter wave height, wave spectra, wavelength, and wave direction. Quantifying wave transformation over submerged structures will inform and aid in the design of future coastal protection. The natural reef at Palm Beach on the Gold Coast, Queensland, Australia is a rock-based reef that extends seaward, surrounded by sand bottom. The seaward reef edge is 10 to 16 metres deep while the shore edge is 5 to 9 metres deep, hence the reef shallows towards the shore. The reef is generally exposed to a dominant south easterly swell but Point Danger to the south offers some protection. Waverider buoys were deployed at four strategic locations at the Palm Beach reef and used to determine how the reef influences wave characteristics as waves travel over the reef. Wave transformation occurs, with the presence of Palm Beach reef having an observable influence on wave height and wave direction. Windward to leeward of the reef significant wave height was reduced by up to 12.7 per cent, wave direction changed by up to 13.9 degrees depending on how the measurement station was aligned with propagation over the reef, peak wave period was not changed significantly.