HR: 0800h
AN: OS11A-0489    [Abstracts]
TI: Shoreline Setup Observations and Predictions
AU: * Apotsos, A A
EM: aapotsos@whoi.edu
AF: Woods Hole Oceanographic Institute, MS 9, Woods Hole, MA 02543 United States
AU: Raubenheimer, B
EM: britt@whoi.edu
AF: Woods Hole Oceanographic Institute, MS 9, Woods Hole, MA 02543 United States
AB: The importance of wave rollers to the breaking-wave-driven increase of the mean water level (setup) in shallow water is investigated by comparing observations with predictions of one-dimensional, depth- and time-averaged models that include (neglect) wave rollers. Wave setup was measured near Duck, NC (August to December 1997) with 9 Paroscientific pressure gages (+/- 0.5 cm accuracy for mean water levels) located on a 200-m-long cross-shore transect extending from the shoreline to approximately 4-m water depth. The setup models are driven with the cross-shore distribution of radiation stresses. To obtain radiation stress estimates every meter, observed centroidal frequencies and local bathymetry are linearly interpolated, observed wave directions are interpolated using Snell's Law, and wave heights are calculated by fitting parametric wave models to observations (least squared error less than 8%). The beach profile was surveyed approximately every other day. Offshore wave heights ranged from 20 to 200 cm. Consistent with previous observations, the models accurately predict setup in water depths greater than 1 m. However, the setup is increasingly underpredicted with decreasing water depth, partly owing to the assumption that energy dissipated by wave breaking is transferred immediately into the water column. The addition of a roller, defined as a passive region of circulating water carried shoreward by the breaking waves, in the radiation stress formulation delays the transfer of energy and momentum causing an increase or decrease in the predicted setup depending on whether the transfer is into shallower or deeper water. Preliminary analysis indicates that inclusion of a wave roller usually improves setup predictions in water depths less than 40 cm when offshore wave heights are greater than 100 cm (on average, errors are reduced by about 30%). This project was funded by ONR and NSF.
DE: 4203 Analytical modeling
DE: 4546 Nearshore processes
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting