south of Long Beach, very effectively converged swell from the south upon 

 certain portions of the Long Beach Breakwater, which with the San Pedro 

 Breakwater formed the two principal structures protecting the harbor in 

 1930 o 



The intensive wave action which resulted in damage to the breakwaters 

 in 1939 was derived from a tropical storm in the northern hemisphere « The 

 characteristics of these waves differed materially from those of the swell 

 which caused the damage in 1930 o Therefore, the remainder of this discussion 

 is divided into two parts; (1) southern hemisphere swell, and (2) waves from 

 a tropical storm. 



Part I - Southern Hemisphere Swell 



The refraction of southern hemisphere swell has been examined for 

 directions of approach of 170°, 180°, and 190° using a wave period of 20 

 seconds o For all three directions refraction diagrams were first con- 

 structed on small-scale charts showing San Clemente and Santa Gatalina 

 Islands and the approaches to San Pedro Bay (Figure 2)„ This type of pre- 

 sentation gives an overall picture of the bay's protection from, or exposure 

 to, swell from given directions^ Figure 2 is drawn for 190°, which is 

 approximately the westernmost limit of the exposed southern sector from 

 which southern hemisphere swell can converge upon the breakwaters » From 

 directions west of 190° the zone of convergence shifts to the east of the 

 outer breakwater „ 



The influence of the islands upon swell from direction 190° is 

 illustrated by the extreme divergence of orthogonals a and b in Figure 2, 

 In contrast to this, the portions of the wave crest unaffected by the 

 islands between orthogonals c and e_ converge in crossing San Pedro Shslf o- 

 The waves passing both sides of the islands are refracted around the islands 

 and meet to form a confused, crisscross pattern in the leeo Only the crests 

 of the waves traveling around the east side of the islands have been drawn 

 up to the breakwater o The waves traveling around the west side experience 

 much greater divergence and contain negligible intensity of energy after 

 refraction o 



The boundary around San Pedro Bay in Figiu^e 2 denotes the area covered 

 by the detailed refraction diagrams presented in Figures 3-5° These large- 

 scale diagrams were constructed using a crest interval of one wave periods 

 ■fhe wave crests have been completed only up to the outer breakwater o In 

 order to show quantitatively the intensity of wave energy for the wave 

 crests at the breakwater and adjacent beaches bar graphs have been drawn. 

 The lengths of the bars are proportional to the refraction factors accord- 

 ing to the scale in the legend. The refraction factors have been computed 

 assuming breaking waves only where the bars are located on the beaches west 

 and east of the breakwater. 



The detailed refraction diagram for 190° (Figure 3) shows divergence 

 at the western part of the outer breakwater resulting primarily from the 

 effect of refraction around San Clemente and Santa Gatalina Islands. This 

 island effect is accentuated by refraction over San Pedro Sea Valley, the 



