Observations of Nearshore Infragravity Waves: Seaward and Shoreward Propagating Components

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. C8, 10.1029/2001JC000970, 2002 Observations of nearshore infragravity waves: Seaward and shoreward propagating components [I] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased impo...

Estimation of infragravity waves at intermediate water depth

“…However the present data set does not allow for a complete validation of the infragravity breaking mechanism and the analysis outlined above is only an indication of the potential importance of dissipation due to infragravity wave breaking. The analysis does suggest that the reflection of infragravity waves near the water line is close to unity, consistent with the results obtained by Sheremet et al (2002), and supports the use of a fully reflective boundary condition in the model.…”

Propagation and Dissipation of Infragravity Waves on a Dissipative Beach With Energetic Wave Forcing

“…Incoming ( + ) and outgoing ( -) energy E and cross-shore energy fluxes F at each discrete frequency f are calculated using the method of Sheremet et al (2002) as…”

Wave modelling – The state of the art

“…A bottom scattering source term can be derived for random topographies of small amplitudes (Ardhuin and Herbers, 2002),…”

“…This phenomenon is formally similar to the scattering of long electromagnetic waves over the ocean surface, a phenomenon used for mapping sea surface currents with High-Frequency radars. For linear waves, it can be represented by a Bragg-like bottom scattering source term S bscat in the right-hand side of (7.1) (Ardhuin and Herbers, 2002;Magne and Ardhuin, 2006). This source term accounts for the interaction of triads involving two wave trains and one bottom Fourier component.…”