type current meter, and the surface current using paraffin flakes. The 

 drift current profile near the surface was checked with a hot-film 



anemometer . 



The directly obtained wave data are the apparent spectra, where 

 frequencies correspond to absolute phase speeds. To calculate these the 

 wave speed solution for a logarithmic drift current obtained by Kato 

 (1974) was used. By further assuming the conventional dispersion rela- 

 tion for the relative phase speed (corresponding to a uniform current 

 velocity distribution), the true spectra, corrected for the Doppler 

 effect, can be calculated. 



Wind friction velocities found from the wind profiles were larger 

 for adverse than for favorable currents. In the former case the lateral 

 current velocity distribution was almost uniform, while in the latter 

 velocities were largest in the central part. 



9 



The significant wave height, determined as 4 < n > with n being 

 the surface displacement, was chosen to represent wave heights. 

 Further, a "dominant" wavelength was introduced, corresponding to the 

 peak frequency in the true energy spectrum. Everything else being 

 equal, significant wave heights and dominant wavelengths were largest 

 for adverse currents. (The variation in wavelength is contrary to what 

 happens when waves move from still water into a current region.) 



For a given wlndspeed the high-frequency part of the true spectra 

 almost coincide, regardless of the current magnitude. This leads 

 authors to conclude that the most prominent effect of a water current on 

 the development of wind waves is a change in the effective fetch length. 



Coastal Engineering Significance. This is probably the first attempt to 

 evaluate quantitatively the effect of a current in the prediction of 

 wind waves. 



31. KENYON, K.E., "Wave Refraction in Ocean Currents," Deep Sea 

 Research^ Oxford, England, Vol. 18, No. 10, Oct. 1971, pp. 1023- 

 1034. 



Keywords . Current Refraction; Currents, Large-Scale; Currents, Ocean; 

 Currents, Shearing; Theory, Ray; Wave Reflection; Waves, Ocean; Waves, 

 Wind. 



Discuss ion . The paths or "rays" of packets of water-wave energy 

 propagating on a current with uniform transverse shear are computed. 

 Diagrams are given showing that they differ markedly from lines which 

 are everywhere perpendicular to the wave crests. Results are also 

 obtained for the curvature of rays. 



38 



