Infragravity Wave Energy Partitioning in the Surf Zone in Response to Wind-Sea and Swell Forcing

Abstract

An alongshore array of pressure sensors and a cross-shore array of current velocity and pressure sensors were deployed on a barred beach in southwestern Australia to estimate the relative response of edge waves and leaky waves to variable incident wind wave conditions. The strong sea breeze cycle at the study site (wind speeds frequently > 10 m s−1) produced diurnal variations in the peak frequency of the incident waves, with wind sea conditions (periods 2 to 8 s) dominating during the peak of the sea breeze and swell (periods 8 to 20 s) dominating during times of low wind. We observed that edge wave modes and their frequency distribution varied with the frequency of the short-wave forcing (swell or wind-sea) and edge waves were more energetic than leaky waves for the duration of the 10-day experiment. While the total infragravity energy in the surf zone was higher during swell forcing, edge waves were more energetic during wind-sea periods. However, low-frequency (0.005–0.023 Hz) edge waves were found to be dominant in absence of wind-sea conditions, while higher-frequency (0.023–0.050 Hz) edge waves dominated when wind-sea conditions were present.

An Analytical Spectral Model for Infragravity Waves over Topography in Intermediate and Shallow Water under Nonbreaking Conditions

“…Infragravity (IG) waves are ocean surface waves of low frequencies, typically between 0.004 Hz and 0.04 Hz, that distinct from the wind waves or swells of frequencies between 0.04 Hz and 1 Hz (Bertin et al 2018). IG wave plays an important role in many coastal processes, such as resonance in harbors (Bowers 1977;Okihiro et al 1993;Maa et al 2010;Thotagamuwage and Pattiaratchi 2014a;Gao et al 2019;Gao et al 2020), morphological evolution (Roelvink et al 2009;Mendes et al 2020;Ruffini et al 2020), and hydrodynamics in surf zones (Guedes et al 2013;Padilla and Alsina 2018;Contardo et al 2019) and on coral-reef flats (Nwogu and Demirbilek 2010;Pomeroy et al 2012;Liu and Li 2018). The generation, evolution, and dissipation of IG waves in intermediate and shallow water have therefore been the focus of numerous studies in the past decades (Longuet-Higgins and Stewart 1962;Symonds et al 1982;Herbers et al 1994;Sheremet et al 2002;Janssen et al 2003;Battjes et al 2004;Henderson et al 2006; Thomson et al 2006;Baldock 2012;De Bakker et al 2015;Li et al 2020).…”