Swell propagation across a wide continental shelf

Abstract

The effects of wave refraction and damping on swell propagation across a wide continental shelf were examined with data from a transect of bottom pressure recorders extending from the beach to the shelf break near Duck, North Carolina. The observations generally show weak variations in swell energy across the shelf during benign conditions, in qualitative agreement with predictions of a spectral refraction model. Although the predicted ray trajectories are quite sensitive to the irregular shelf bathymetry, the predicted energy variations are surprisingly weak, consistent with the observations. These results indicate that small amplitude swell is not significantly damped on the shelf. However, a large decrease in swell energy levels across the shelf (up to 7O%) observed with high energy incident swell, is not predicted by the energy conserving refraction model. These energy losses are likely caused by bottom friction.