(, 0-1 











WAVE HEIGHTS 





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6 11 1973 



leos h 



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30 sec 



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20 30sec 



LONGSHORE CURRENT 



Figure 5. Time history of longshore velocity and wave height in surf zone 

 of North Sea, Isle of Sylt, Germany, November 1973 (from 

 Dette and Fuhrboter, 1974). 



Six biaxial EM current meters were used to study variability of long- 

 shore currents in the inner surf zone at Torrey Pines Beach, California, in 

 March 1977 (Guza and Thornton, 1978). The ultimate goal was to test 

 theories relating mean longshore current and offshore values of radiation 

 stress (see Ch. 4). Figure 6 shows the meter array locations and some 

 longshore current values based on a 1,024-second (17.07 minutes) means of 

 the continuous records. They concluded that even on a relatively straight 

 beach such as Torrey Pines, with no obvious rip structures or visible 

 variations of the incident wave field, considerable time variations of 

 mean longshore currents can occur; considerable longshore spatial varia- 

 bility of the longshore current is also present. Spectral analysis of 

 more than 100 records over a month period (60 hours of observations) showed 

 the presence of large, low-frequency (long-period) components in the long- 

 shore current similar to those described by Woods and Meadows (1975) and 

 Meadows (1976, 1977). The temporal fluctuations are not site- or wave 

 regime-related since they have been observed in southern California, on the 

 Great Lakes (Woods and Meadows 1975), and also in the Atlantic, Nova Scotia 



31 



