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- Title
Phase‐Resolved Modeling of Wave Interference and Its Effects on Nearshore Circulation in a Large Ebb Shoal‐Beach System.
- Authors
Zhang, Yu; Shi, Fengyan; Kirby, James T.; Feng, Xi
- Abstract
A time‐domain Boussinesq model was applied to modeling wave interference and its effects on nearshore circulation in San Francisco Bar and the adjacent Ocean Beach, CA. The model predicted the wave interference phenomena caused by the ebb shoal, with interference scales consistent with the radar observation and are persistent with nodal lines unchanged with time. Nearshore circulation predicted by the model shows small‐scale flow structures tied with the wave modulation patterns. However, the small‐scale modulation in the wave field seems not to generate alongshore variation in wave setup at similar scales. Therefore, in a large‐scale view, the alongshore currents predicted by the Boussinesq model still keep the general features shown in a wave‐averaged model, such as the flow divergence caused by the pressure gradient force associated with the alongshore variation of wave setup. The further analysis based on idealized short crest waves on a plane beach suggests that the alongshore pressure gradient is mainly balanced by the gradient of radiation stresses in the antinodal region, while by the flow advection in the nodal region. The rip current behavior is forced locally near breakers, rather than by gradients in wave setup close to shore. The time‐domain Boussinesq model predicted the spatial variability of wave‐induced processes. The alongshore‐varying wave breakers caused by wave interference are the source of the vorticity generation, inducing energetic vortex eddies nearshore. Plain Language Summary: Ocean wave interference, caused by the oblique interaction or superposition of two or more trains of plane waves, is a common phenomenon caused by surface wave interaction with seabed topography, nearshore structures, or coastal currents. Conventional spectral wave models cannot predict interference patterns as they do not preserve phase information for the individual wave components. The objective of the present study is to use a time‐resolved model to examine previously observed wave interference occurring landward of the ebb‐tidal delta offshore of the Golden gate, San Francisco, CA. The model shows interesting small‐scale features caused by wave interference, with spatial scales consistent with the radar measurements. The model results reveal that the small‐scale fingering structures in the wave height distribution result in a significant alongshore variation in nearshore circulation and energetic vortex eddies in the surf zone, but do not induce a small‐scale modulation in wave setup at the shoreface. To explain the phenomena, we carried out a momentum balance analysis for an idealized case of two intersecting waves propagating onto a plane beach, and show that the alongshore variability in forcing needed to balance variations in set‐up is largely absent landward of where breaking becomes saturated in the alongshore direction. Key Points: A time‐domain Boussinesq model reproduced wave interference observed at Ocean Beach, CAThe model reveals small‐scale persistent fingering structures in the wave height distribution tied with nearshore flow structuresAlongshore‐varying wave breakers caused by wave interference are the source of vorticity generation, inducing energetic vortex eddies nearshore
- Subjects
SAN Francisco (Calif.); RIP currents; PLANE wavefronts; CIRCULATION models; VORTEX motion; SURFACE interactions; OCEAN waves; BEACH erosion
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 10, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC018623