Historical leather * f aps were examined and it was found that there existed 

 tvo storm centers capable of producing long-period raves , one to the north- 

 west and the other approximately west. Trie characteristics of the waves 

 to be expected from these storms Were "hindcast ,: by Lt. Robert Stump (AAii ) 

 following standard forecasting principles and procedures (2) (see Peach 

 Lrosion Board Rille/tin, Special Issue No. 1, July 1, 1%B). The only 

 exception to standard procedure being that the time of arrival was adjusted 

 so that the average velocity in the decay area equaled half the wave velo- 

 city in deep water just offshore. Trie computed' character i sties of these 

 waves are presented in table 1. Waves from storm Mo. 1 must have under- 

 gone refraction and diffraction around fianta llosa Island before approach- 

 ing the Long leach breakwater through the westerly sector. ' aves from 

 storm 'ic. 2 would approach the breakwater directly through this sector. 



In order to analyze the possible effect of these storms, a refraction 

 diagram v;as drawn for waves of 20-second period approaching from due vest 

 (figure .3). It appears that refraction of these waves Joes not produce 

 the observed effect, namely, concentration of wave energy at the Long 

 Beach breakwater and inappreciable wave action at adjacent points. It 

 seemed safe to conclude on this basis that neither of these storms gener- 

 ated the waves which damaged the breakwater and that their source must have 

 been outsiae of the area covered by the weather, maps. 



Almost due south of Long Beach there is a submerged ridge which might 

 force waves from this direction on the breakwater. Being deeply submerged, 

 it would affect only waves of unusually long period and thus would, in this 

 respect at least, satisfy the requirement that the phenomenon b?. of rare 

 occurrence. Figure L is a refraction diagram for waves of 20-second period 

 approaching along the axis of the ridge (line A-A). The convergence of 

 the orthogonals a-a and e-e shows that the energy of these waves would be 

 focused on the breakwater. The multiplying factor for the increase in wave 

 height exclusive of the effect of the shoaling bottom, is approximately 

 three. At all adjacent points along the shoreline and at the Can Pedro 

 breakwater, refraction would reduce rather than increase wave height, 



lhe shoaling bottom would increase the wave height over that in deep 

 water. Using figure 1 (Beach Lrosion Board Bulletin Vol. 3, No. 4, p. 31) 

 and assuming that the breakers were of 20-second period and broke in 20 feet 

 of water, 



d b _ 20 _ no( , 

 T* 400" ° 05 



j% = 0.017 ; H = 0.017 x 400 =6.8 ft. 



H h 



-rP= 1.85 H h = 12.2 ft. 



M D 



Mere, H is the height after refraction. Dividing by a factor of 3 9 to 

 account°for the convergence over the submerged ridge as indicated by the 



