SOUTHERN HEMISPHERE SWELL AND WAVES FROM A 

 TROPICAL STORM AT LONG BEACH ,CALIFORN I A 



This paper is published as a companion piece to the 

 paper, "Wave Refraction at Long Beach and Santa 

 Barbara^ California", by Mo Po O'Brien, published in 

 the Beach Erosion Board Bulletin, Vol» 4-5 NOo 1, 

 January 1950= The paper was prepared by Paul Lo 

 Horrer and represents results of research carried out 

 for the Hydrographic Office and the Office of Naval 

 Research of the Department of the Navy under contract 

 with the University of California « Scripps Contribu- 

 tion NOo 47 5 o 



Introduction 



On two occasions nine years apart large waves entered San Pedro Bay 

 and caused extensive damage to the harbor breakwaters in the Long Beach- 

 San Pedro areao During the period April 20 to 24, 1930, intensive wave 

 action resulted in the displacement of 20,000 tons of superstructure stone 

 from the Long Beach breakwater o On September 24 and 25, 1939, large waves 

 caused some damage to the San Pedro Breakwater and great damage to the Los 

 Angeles-Long :teach Detached Breakwater (Figure l)o The present study was 

 undertaken in an attempt to analyze the meteorological conditions which 

 produced the damaging wave action in this region and to provide information 

 which may be used in planning future modification and improvement of the 

 breakwaters,, 



As indicated by O'Brien (1947) it seems impossible that waves from 

 westerly directions could bring sufficient concentration of wave energy to 

 effect material damage to these breakwaters » Except for a narrow exposed 

 western sector between Santa Rosa and Santa Barbara Islands all swell from 

 the west must undergo diffraction and such great refraction around islands 

 that little energy can reach this portion of San Pedro Baj^^ The only un- 

 sheltered directions of approach for swell lie within a wider sector to 

 the soutli between the coast and the islands of Santa Catalina and San 

 Clemente o Two distinct types of waves which could damage the breakwaters 

 may enter through this exposed southern sector,, These are swell propagated 

 from storms in the southern hemisphere and wind waves or swell produced by 

 northern hemisphere storms located south of Long Beach c It is necessary 

 to stress the importance of each type separately » 



The synoptic weather maps for the critical period in April, 1930 do 

 not reveal any northern hemisphere storm which could generate large waves 

 or swell which would pass through the exposed southern sectoro This leaves 

 only the possibility of a long, low swell from a storm in the southern 

 hemisphere o Refraction diagrams (Figures 2-5) have been constructed for 

 San Pedro Bay according to the procedure given by Munk and Traylor (1947 )o 

 These diagrams indicate that San Pedro Shelf, the submarine plateau due 



