BOAT, y',''-^ 



' SURF ZONE 



I • •» 



X 



Figure 17. Schematic of BAGS nearshore current system (from Sasaki, 1977) 



Prins (1975, 1976), Coakley, et al. (1978), Bradshaw, et al. (1978), and 

 Allender, et al. (1978). The newest U.S. sled has been developed for 

 simultaneous bottom profiling, wave height, and two-axis current measure- 

 ments with one EM meter (Sallenger, et al., 1980). Field tests of the 

 latter device at Monterey, California, in 6-meter breakers over a 100- 

 meter wide surf zone measured bottom current greater than 3.5 meters per 

 second (Sallenger, et al., 1980). 



The major problem with use of sleds is data interpretation. Some type 

 of temporal stationarity of the currents must be assumed (Guza and Thornton, 

 1978, p. 768). If not continually moving, how long should the sled remain 

 at each station to record information? Figure 6 showed considerable tem- 

 poral variation between successive 17.1-minute ((1,024 seconds) averages 

 at a plain beach for each gage location. If 17.1-minute records are taken 

 at each station, it could be several hours between data taken at the outer 

 and inner reaches of the surf zone. Can this data be combined to yield an 

 instantaneous profile of the 17.1-minute mean longshore current? 



To eliminate the need to make arbitrary assumptions regarding temporal 

 stationarity, NSTS researchers choose to employ a large number of fixed 



59 



