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Abstract The cross‐shore transformation of breaking‐wave roller momentum and energy on observed barred surfzone bathymetry is investigated with a two‐phase Reynolds Averaged Navier Stokes model driven with measured incident waves. Modeled wave spectra, wave heights, and wave‐driven increases in the mean water level (setup) agree well with field observations along transects extending from 5‐m water depth to the shoreline. Consistent with prior results the roller forcing contributes 50%–60% to the setup, whereas the advective terms contribute ∼20%, with the contribution of bottom stress largest (up to 20%) for shallow sandbar crest depths. The model simulations suggest that an energy‐flux balance between wave dissipation, roller energy, and roller dissipation is accurate. However, as little as 70% of the modeled wave energy ultimately dissipated by breaking was first transferred from the wave to the roller. Furthermore, of the energy transferred to the roller, 15%–25% is dissipated by turbulence in the water column below the roller, with the majority of energy dissipated in the aerated region or near the roller‐surface interface. The contributions of turbulence to the momentum balance are sensitive to the parameterized turbulent anisotropy, which observations suggest increases with increasing turbulence intensity. Here, modeled turbulent kinetic energy dissipation decreases with increasing depth of the sandbar crest, possibly reflecting a change from plunging (on the steeper offshore slope of the bar) to spilling breakers (over the flatter bar crest and trough). Thus, using a variable roller front slope in the roller‐wave energy flux balance may account for these variations in breaker type.
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Field Observations of the Evolution of Plunging‐Wave Shapes
Abstract There are few high‐resolution field observations of the water surface during breaking owing to the difficulty of collecting spatially dense measurements in the surf zone, and thus the factors influencing breaking‐wave shape in field conditions remain poorly understood. Here, the shape and evolution of plunging breakers is analyzed quantitatively using three‐dimensional scans of the water surface collected at high spatial and temporal resolution with a multi‐beam terrestrial lidar scanner. The observed internal void shapes in plunging breakers agree well with previously developed theoretical shapes at the onset of breaking, and become more elongated and less steep as breaking progresses. The normalized void area increases as the local bottom slope steepens and as the breaking depth decreases. The void shape becomes more circular as the local bottom slope and the ratio of breaking water depth to wavelength increase, as well as in conditions with opposing winds.
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- Award ID(s):
- 1948137
- PAR ID:
- 10362192
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 16
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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