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-80 -ISO -240 -320 

 LONGSHORE (M) 



17.1 34.1 51.2 



TIME(min.) 



(b.cdj Longshore current at different surf lone loMtlons 



Figure 6. Temporal variation of averaged (1,024 seconds) longshore currents 

 at five locations in surf zone, Torrey Pines Beach, California, 

 March 1977 (from Guza and Thornton, 1978). 



(Holman, Huntley, and Bowen 1978) . To study further the question of averag- 

 ing time, Guza and Thornton (1978) made additional 256-second (4.3 minutes) 

 averages from five closely spaced current meters (14-meter maxim.um separation) 

 at Scripps Institute Beach, La Jolla, California. Figure 7 shows how the 

 variations occur together indicating all meters were operating. Since a varia- 

 tion as much as 20 centimeters per second occurs at essentially the same loca- 

 tion, the 4.3-minute averaging time is not representative of the mean for longe' 

 time scales. It is concluded that: 



"An appropriate temporal averaging time for mean long- 

 shore currents is not known." (p. 768) 



'+HOLMAN, R.A., HUNTLEY, D.A., and BOWEN, A.J.. "Infragravity Waves in Storm 

 Conditions," Proceedings , I6th Coastal Engineering Conference^ Vol. I, 

 Hamburg, 1978, pp. 268-284 (not in bibliography). 



32 



