National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 1983

Transformation of wave spectra at a tidal inlet

González, F.I., and C.L. Rosenfeld

In Proceedings of the 1983 International Geoscience and Remote Sensing Symposium, II, San Francisco, CA, 31 August–2 September 1983, 5.1–5.7 (1983)

In-situ and SLAR ocean wave observations offshore and at the entrance of the Columbia River have been acquired during slack tide and during a peak ebb period when the current speed was estimated to be in excess of 2 m/s. Two dominant swell systems characterized the offshore wave spectra, a long (300-400 m) system propagating due east and a shorter (150-200 m) system propagating north by northeast. On the ebb, the longer wave system was amplified at the entrance by a factor of 1.6, in contrast to the shorter system which underwent little or no increase in wave height. This selective modification is interpreted in terms of linear wave-current-bathymetry interaction. In the case of the longer system, shoaling and simple opposition by a current should have produced an amplification of only 1.3; it is concluded that the observed enhanced amplification of 1.6 is attributable to bathymetric and current refraction. In the case of the shorter system, the absence of any amplification is attributed to the fact that the observed incidence angle of the waves was approximately 50° off the main axis of the current.

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