Nonlinear generation and loss of infragravity wave energy

Abstract

[1] Nonlinear energy transfers with sea and swell (frequencies 0.05-0.40 Hz) were responsible for much of the generation and loss of infragravity wave energy (frequencies 0.005-0.050 Hz) observed under moderate-and low-energy conditions on a natural beach. Cases with energetic shear waves were excluded, and mean currents, a likely shear wave energy source, were neglected. Within 150 m of the shore, estimated nonlinear energy transfers to (or from) the infragravity band roughly balanced the divergence (or convergence) of the infragravity energy flux, consistent with a conservative energy equation. Addition of significant dissipation (requiring a bottom drag coefficient exceeding about 10 À2 ) degraded the energy balance.

Reef Flat Wave Processes and Excavation Pits: Observations and Implications for Majuro Atoll, Marshall Islands

“…Based largely on scaling arguments obtained from laboratory experiments and models (Massel and Gourlay, 2000), PMP2013 contend that (1) wave breaking may be a more important dissipation mechanism than bottom friction on the reef flat; (2) acrossshore changes in sea and swell (SS) and infragravity (IG) wave energy levels may be due to nonlinear energy transfer (Henderson et al, 2006;Thomson et al, 2006), as opposed to the claim of FPM2012 that these changes are due to spatially variable dissipation and disruption of the cross-shore IG energy structure caused by the presence of the excavation pit; (3) that the IG energy on the reef flat is due to bound waves; and (4) that lateral variation of incident wave conditions and shoreline reflectivity might explain lower wave heights landward of the excavation pit relative to the unmodified reef.…”

Fully Nonlinear Boussinesq-Type Modelling of Infragravity Wave Transformation Over a Low-Sloping Beach

“…In particular, the relative importance of the different dissipation mechanisms could be assessed through the computation of the energy balance for the IG waves (e.g. Henderson et al, 2006, Ruju et al 2012). However, it should be noted that the methodology developed by Henderson et al (2006) assumes weakly nonlinear infragravity waves, and that their amplitude is much smaller than the short waves.…”

“…Henderson et al, 2006, Ruju et al 2012). However, it should be noted that the methodology developed by Henderson et al (2006) assumes weakly nonlinear infragravity waves, and that their amplitude is much smaller than the short waves. These conditions are not satisfied in our case, in particular just seaward of the swash zone, where the nonlinear parameter is of order 1 for the IG waves.…”

“…Early studies suggested that this dissipation could result from the effects of bed friction (e.g., Herbers et al, 1995). Field data analysis by Henderson et al (2006) and Thomson et al (2006) showed that the observed energy loss was resulting from nonlinear energy transfer back to the short waves. Recently, van Dongeren et al (2007) demonstrated that the breaking of the infragravity waves themselves could be an important dissipation mechanism for low values of the normalized bed slope β.…”

Review of Long Wave Dynamics over Reefs and into Ports with Implication for Port Operations

“…After IG waves are generated and are released from the wave groups, they propagate to the coast, where they may dissipate due to bottom friction [21,22], IG wave breaking [23], nonlinear transfer back to the short waves [24] or reflect off the coast and propagate back out to sea as free waves. Depending on their angle of incidence these waves may be refractively trapped on the coast as "edge waves" or may escape to deeper water as leaky waves.…”