期刊
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
卷 118, 期 7, 页码 3651-3669出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/jgrc.20267
关键词
swash; infragravity; wave dissipation; wave energy fluxes; video imagery; saturation
类别
资金
- (New Zealand) Foundation for Research, Science and Technology
- MetOcean Solutions Ltd (New Zealand)
- Cantabria Campus Internacional Augusto Gonzalez Linares Program
Field observations of swash and ocean waves show that runup saturation at infragravity frequencies (<0.05 Hz) can occur under mild offshore energy conditions if the beach slope is sufficiently gentle. Infragravity saturation was observed for higher-frequency (>0.025-0.035 Hz) infragravity waves, where typically less than 5% of the (linear) energy flux was reflected from the beach and where, similar to the sea swell band, the swash energy was independent of offshore wave energy. The infragravity frequency range of saturation was determined by the tide, with saturation extending to lower frequencies at low tide when the local beach face slope over the concave-shaped profile was gentler. Runup was strongly dominated by infragravity frequencies, which accounted on average for 96% of the runup variance, and its energy levels were entirely consistent with strong infragravity wave dissipation observed in the surfzone, particularly when including the nonlinear contributions to the wave energy fluxes. The infragravity wave dissipation was strongly associated with breaking of sea swell waves, which abruptly decreased nonlinear transfers to infragravity frequencies and made infragravity dissipation prevail over forcing within the breaking region. Our observations show evidence of nonlinear interactions involving infragravity and high-frequency, harmonic waves and suggest that these harmonics could play a role in the wave energy balance near the shoreline on low-sloping, dissipative beaches.
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