132 Shallow Water Wave Transformation through External Factors 

 Combining equations (V.23), (V.27), and (V.28) leads to equation 



K b = 



(V.29) 



Figure 61 presents a comparison between the positions of the wave crests 

 according to Fig. 60 and the positions computed from these formulas. 



ft 20 



-1000 



1000 



2000 



Scale, 



Legend 



Computed wave crest 



Wave crests from photograph 



Depth contours 



Control markers 



Fig. 61. Comparison between observed position of wave crests shown in Fig. 60 and posi- 

 tions computed according to Snellius's law (Sverdrup and Munk). 



Waves coming from an angle into a beach with straight and parallel depth 

 contours are reduced in height according to equation (V.26), but the re- 

 duction is uniform along the entire beach, and no variation in wave height 

 along the beach will result. As an example of variation in wave height, 

 consider a coastline which forms a sharp bend at point B (Fig. 62). On both 

 sides of point B the coastline and the depth contours are straight and 

 parallel. Assume that waves of 14-second periods come from the north- 

 north-west. The angle a is drawn between the orthogonals and the bottom 

 gradient, which is consistent with our earlier definition. Table 17 gives the 

 computed direction and relative height at the 10-foot contour, which is 

 assumed to lie outside the breaker zone. Along the beach section A-B, 

 which is relatively exposed to the incoming swell, waves are about 50% 

 higher than along section B-C. This can also be seen from the fact that the 

 divergence of orthogonals along A-B is less than the divergence along B-C 

 (Fig. 62). 



