The predominant characteristics common to all the preceding re- 

 fraction diagrams can be attributed to specific features of the bottom 

 topography o In each case a zone of divergence is produced by the sea 

 valleys located on either side of the San Pedro Shelf,, And, these 

 valleys aid in producing greater convergence over the extended shelf 

 lying between thera^ Slight changes in wave direction result in size- 

 able displacenent of the zones of convergence and divergence j while the 

 effect of wave direction upon the magnitude of the refraction factor 

 is sonewhat less markedo Because of interference between wave trains, 

 the largest waves at certain parts of the breakwater may contain 

 greater intensity of energy than the amount indicated by the refraction 

 factors o 



The computed wave height and direction of approach of the tropical 

 storm waves agree with observed conditions « Without additional ob- 

 servations of both wave height and period, it is impossible to test 

 the accuracy of the existing technique for estimating waves from a 

 tropical stormo The computations indicate that waves at Long Beach 

 from such a tropical storm contain far greater energy than wind waves 

 or swell from other northern hemisphere storms which pass to the south 

 of Long Beach o However, because of the rarity of occurrence of tropical 

 storms which can produce damaging waves in the Long Beach region it 

 may be more economical and practical to plan to repair the existing 

 breakwaters after each of these storms than to build the breakwaters 

 heavy enough to withstand such wave attack. 



Acknowledgements 



The Uo So Weather Bureau, Department of ComiTErce, and the Calif- 

 ornia Institute of Technology have furnished the meteorological data 

 needed for this study, Mr, Ro Oo Eaton, Corps of Engineers, has pro- 

 vided information pertaining to wave observations and damage to harbor 

 structures in the Long Beach-San Pedro area, 



■)!-)HHH;i^-5HHi-JHHc-4i-X-S(-!H}- 



Footnotes 



1 Measurements of wave height were made by Mr, R, 0, Eaton, Corps 

 of Engineers and communicated by letter to Dr, Walter H, Ifunk of 

 Scripps Institution of Oceanography, Wave heights of 15 and 18 

 feet were recorded in depths of 37 and 27 feet, respectively, 



2 Lieut, H, F, Nowak, U,SoNo, has recently given a verbal descrip- 

 tion of the height of the wave crests as he observed it from 

 aboard the aircraft carrier Lexington on September 2^, 1939 o The 

 Lexington was at anchor in water betvi^een 50 and 60 feet deep east- 

 northeast of the eastern end of the detached breakwater. Lieut, 

 Nowak estimated the tops of the wave crests to be about 2^ feet 

 above mean water level. If it is assumed that the trough of the 

 waves is one-fourth of the wave height below the mean water level 

 the total wave height is 32 feet. The computed wave height in this 

 area, allowing for refraction and depth, is between 32 and 39 feet, 

 depending upon the exact position for which the refraction factor 

 is computed, 



17 



