Infragravity‐wave dynamics in a barred coastal region, a numerical study

Abstract

This paper presents a comprehensive numerical study into the infragravity-wave dynamics at a field site, characterized by a gently sloping barred beach. The nonhydrostatic wave-flow model SWASH was used to simulate the local wavefield for a range of wave conditions (including mild and storm conditions). The extensive spatial coverage of the model allowed us to analyze the infragravity-wave dynamics at spatial scales not often covered before. Overall, the model predicted a wavefield that was representative of the natural conditions, supporting the model application to analyze the wave dynamics. The infragravity-wave field was typically dominated by leaky waves, except near the outer bar where bar-trapped edge waves were observed. Relative contributions of bar-trapped waves peaked during mild conditions, when they explained up to 50% of the infragravity variance. Near the outer bar, the infragravity-wave growth was partly explained by nonlinear energy transfers from short waves. This growth was strongest for mild conditions, and decreased for more energetic conditions when short waves were breaking at the outer bar. Further shoreward, infragravity waves lost most of their energy, due to a combination of nonlinear transfers, bottom friction, and infragravity-wave breaking. Nonlinear transfers were only effective near the inner bar, whereas near the shoreline (where losses were strongest) the dissipation was caused by the combined effect of bottom friction and breaking. This study demonstrated the model's potential to study wave dynamics at field scales not easily covered by in situ observations.

Relevance of infragravity waves in a wave‐dominated inlet

“…Different types of approaches and numerical models have been considered to numerically model the generation and propagation of infragravity waves. Two main approaches or types of models can be distinguished: (1) phase‐resolving [e.g., Herbers et al ., ; Madsen et al ., ; Kennedy et al ., ; Torres‐Freyermuth et al ., ; Bonneton et al ., ; Zijlema et al ., ; Ma et al ., ; Ruju et al ., ; Rijnsdorp et al ., ; Sheremet et al ., ] and (2) phase‐averaged models [e.g., Reniers et al ., ; Uchiyama and McWilliams , ; Long and Özkan‐Haller , ; Roelvink et al ., ; Eldeberky , ]. Phase‐resolving models account for the nonlinear gravity wave transformations and possible nonlinear energy transfer from the IG band to the gravity band.…”

Beach steepness effects on nonlinear infragravity‐wave interactions: A numerical study

“…We use the numerical model SWASH to simulate the transformation of nearshore wavefields over variable profiles. SWASH is a nonhydrostatic model based on the nonlinear shallow water equations [ Zijlema et al ., ] and has shown to accurately capture the nearshore processes of breaking [ Smit et al ., ], infragravity wave dynamics [ Rijnsdorp et al ., ], run‐up oscillations [ Ruju et al ., ] and nonlinear wave dynamics [ Smit et al ., ].…”

“…The total infragravity‐wave signal is however not affected considerably by the rather poor predictive skill of the outgoing waves, and shows high values 0.95, for all three conditions. This overestimation of infragravity‐wave dissipation was also observed in field‐scale simulations using SWASH for a natural site [ Rijnsdorp et al ., ]. Varying our friction coefficient affected the model predictions only slightly, and did therefore not result in more accurate predictions.…”

“…We use the numerical model SWASH to simulate the transformation of nearshore wavefields over variable profiles. SWASH is a nonhydrostatic model based on the nonlinear shallow water equations [Zijlema et al, 2011] and has shown to accurately capture the nearshore processes of breaking [Smit et al, 2013], infragravity wave dynamics [Rijnsdorp et al, 2012[Rijnsdorp et al, , 2015, run-up oscillations [Ruju et al, 2014] and nonlinear wave dynamics [Smit et al, 2014]. Because the SWASH model will be used here to study wave propagation in a cross-shore/one-dimensional setting, the governing equations can be written as @g @t 1 @ @x ð g 2d udz50;…”

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

“…However, the bathymetry at Secret Harbour, despite having a sandbar, was not conducive to the amplification of bar-trapped edge waves. In previous observations of bar-trapped edge waves at Duck, North Carolina [37] and Egmond aan Zee, Netherlands [38], the bars were in deeper water (2-4 m), so the phase speed of edge waves was higher on the bar than at Secret Harbour. In those locations, the edge waves satisfying the phase speed condition were of higher modes and presented antinodes which could be trapped and amplified by the bar.…”