en'i of the decay area, Hq and Tq ^ which are shown in Table 2, have been 

 computed using the effective decay distance, Dg, where applicable. In 

 the computations no diffraction correction (Francis, 194-'!+) has been 

 applied because (1) no decay distance existed until after 0/i30 P.ScTo, 

 September 25 and (2) after this time the fetch no longer resembled the 

 circular fetch characteristic of a tropical storm. 



The waves from the tropical storm may be divided into four parts 

 as shown in the lower part of Figure So The short period wind waves 

 from the earlier local fetch increased rapidly in height at about 1200 

 PoSoTo, September 2U and remained predominant until about 14.30 P.S.T.., 

 September 24,. At that time waves from the long effective fetch arrived. 

 These had not traveled through decay areas and were still growing under 

 the influence of strong winds when arriving at San Pedro Bay. They were 

 of great height and relatively long period o The rapid build-up in wave 

 height shown in Figure 8 would have been even more accentuated if the 

 earlier local fetch had not developed. Such a quick build-up of wave 

 height is a characteristic common to waves from tropical storms, and it 

 has been reported for certain other tropical storms that strong winds and 

 very high waves arrived simultaneously. Seen after the arrival of waves 

 from the long effective fetch the computed wave height was greater than 

 28 feet and the corresponding period 14. seconds. For almost 12 hours 

 these waves maintained great height^ but their period steadily decreased 

 with time . 



The waves shown between 0500 and 0700 September 25 represent swell 

 from the small fetch to the south decayed under calm or variable winds. 

 After 0700 when the winds at San Pedro backed to northeast the waves 

 represented swell decayed under opposing winds, and the height and period 

 decrease fairly rapidly. Not until about 0500 September 26 did the swell 

 from the west become larger than the swell from the weak rasidual fetch 

 located to the south. 



Refraction pattern and distributing of damage . - As indicated by the 

 geographical locations of the tropical storm's wind field shown in Figure 

 7 the wind waves and swell from this storm approached Long Beach from 

 directions varjring between 150° and 190° in deep water. Figure 9 is a 

 portion of tte refraction diagram for 175° and 14 seconds period. This 

 corresponds to the period of the highest waves from the long effective 

 fetch reaching San Pedro Bay. The complete diagram from which Figure 9 

 is taken is shown in the inset and was drawn with a crest interval of 2 

 waves on a detailed chart of the bottom topography. The refraction 

 factors are presented in the same manner as on the diagrams for southern 

 hemisphere swell. 



The damaged portions of the Los Angeles-Long Beach Detached Break- 

 water and the intensity of the damage within these areas are also shown 

 in Figure 9o It is evident that the amount of damage was increasingly 

 great from west to east along this breakwater while the Long Beach break- 

 water escaped without damage. From this it appears that the wave forces 

 were considerably greater near the easterly end of the detached break- 

 water. Because of its seaward location, the detached breakwater apparently 

 provided shelter for the undamaged Long Beach Breakwater. 



1/i 



