Tidal Modulation of Incident Wave Heights: Fact or Fiction?

• Published in: Journal of coastal research Vol. 24; no. sp2; pp. 151 - 159
• Main Authors: Davidson, M. A., O'Hare, T. J., George, K. J.
• Format: Journal Article
• Language: English
• Published: Fort Lauderdale Coastal Education and Research Foundation (CERF) 01.03.2008; Allen Press Inc
• Subjects: Beaches; Buoys; Coasts; Damping; Diurnal variations; Height; Intermediate water; Marine; Research Papers; Sediment transport; Shear stress; surfing; tidal modulation; tidal push; Tidal range; Tidal waves; tides; Time series; Water depth; wave damping; wave dissipation; Wave energy; Wave height; Wave power; Wave propagation; Waves; Wave–current interaction
• ISSN: 0749-0208; 1551-5036
• DOI: 10.2112/06-0754.1

This contribution investigates the hypothesis that incident wave power is modulated by the tide. Eulerian measurements of wave height recorded by three wave buoys in intermediate water depths (8–45 m relative to the lowest astronomical tide), over a 7-year period were analysed in a search for evidence of this semidiurnal variability in incident wave heights. The study site (Perranporth, U.K.) was a highly macrotidal environment with a maximum spring tidal range of approximately 7.5 m. Autospectra of wave height time series displayed a significant peak at semidiurnal frequencies that was coherently coupled to the tidal displacement. At this site maximum wave power was seen to occur on the rising tide, on average 1 hour 6 minutes before high water. The observed semidiurnal variability in wave height increases in magnitude toward the shoreline. This contribution presents field evidence for tidal modulation of incident wave power by the tide and suggests a possible explanation for the observations in terms of an analytical model for attenuation of wave power by contratidal flows.