Table 1. Recommended values of S*. 

 S* Wave condition 



4 Wind waves 

 12 Swell (short-to-moderate decay distances) 

 37 Swell (moderate-to- long decay distances) 



the wave energy and refraction coefficient, respectively, for a wave direction, 

 ■i, then the composite refraction coefficient for waves from several simultaneous 

 directions is taken as 



(2) 



where N is the number of wave directions. The computations in Appendix A were 

 performed by dividing the 360 circle into 4,000 equal angle segments (N = 4,000) 

 and using the spreading function in equation (1) . Individual refraction coeffi- 

 cients for each segment, K^, are computed from the standard methods described 

 in Section 2.32 of the SPM or McClenan (1975). The use of equation (2) in the 

 calculation is to obtain a better estimate of refraction coefficients for irreg- 

 ular waves than would be obtained if a single value of the refraction coefficient 

 obtained from linear theory were used. It is recognized that the design curves 

 in Appendix A do not account for changes in spectral shape. Note that as S* 

 approaches infinity the monochromatic wave refraction solution is obtained 

 (agrees with Fig. 2-19 in the SPM). 



3. Wave Refraction Analysis . 



Calculation of refraction coefficients and nearshore wave direction angles 

 using the design curves in Appendix A requires the dominant deepwater wave 

 direction angle, a , an estimate of S*, and the representative wave period, 

 T s . For irregular waves the period of peak energy density, which is approxi- 

 mately equal to the mean period of the highest one-third waves, should be used 

 as the representative wave period. Each figure in Appendix A is for a different 

 value of S*. The refraction coefficient, K^, is determined by finding the 

 intersection of the deepwater wave angle, a , on the abscissa with the value 

 of id/ (gT|) on the ordinate where d is the nearshore water depth of interest 

 and g is the acceleration due to gravity. K# is estimated by interpolation 

 between curves of constant K#. The nearshore angle of the wave energy vector, 

 a (also shown in terms of contours of constant values) is the angle that should 

 be used, for example, in determining the component of wave energy flux in the 

 longshore direction. 



Table 2 illustrates sample values of K^ and a for various values of S* 

 and a where d/ (gT§) = 0.01. ' Note that for small, deepwater wave angles the 

 wave refraction coefficient is smaller for lower values of S*; for large deep- 

 water wave angles the refraction coefficient is larger for smaller values of S* . 



12 



