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.
Highlights
Infragravity (IG) waves, with frequencies ranging from 0.005 to 0.050 Hz, often account for an important part of the wave energy spectrum in the surf zone, and their energy increases with greater incoming short-wave height [1]
The vertical lines represent the theoretical frequency of nodes in elevation for the first three edge-wave modes (Equation (5)) and cross-shore standing leaky waves
In the presence of an alongshore current, the nodes are shifted toward higher frequencies for edge waves propagating with the alongshore current [19]
Summary
Infragravity (IG) waves, with frequencies ranging from 0.005 to 0.050 Hz (periods 20 s to 3 min), often account for an important part of the wave energy spectrum in the surf zone, and their energy increases with greater incoming short-wave height [1]. When wave groups approach the beach, the bound waves are said to be released, either when the wave groups break [3] or when the bound waves satisfy the free wave dispersion relationship [4,5]. Another mechanism for the generation of free IG waves in the nearshore is due to time-varying breakpoint forcing [6,7]. Eng. 2019, 7, x FOR PEER REVIEW potpeonTttehinaTetlhiaaΦenla(aΦxnl,(yayxtl,,ytiyc)t,aitoc)lvaoeledveregdaregap-ewl-pawalnavaenveebesebosaeolcualuhcthito[io3[n3n0s0]s]tatoaorretteh:h:ee lliinneeaarr sshhaalllloowwwwaatteerreeqquuaatitoionnofomf motoiotinofnofroarvaevloecliotycity
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