current meters in perpendicular arrays as shown in Figure 18 for the Torrey 

 Pines Experiment. Twenty-two EM current meters were alined normal and along 

 the beach with some bunching up in the surf zone. A similar configuration 

 was established for the Santa Barbara experiments where a total of 25 EM 

 current meters were employed. These alined arrays proved to be very 

 successful in obtaining instantaneous and simultaneous longshore and cross- 

 shore velocity time histories through and beyond the entire surf zone and 

 down the beach near the midsurf position (Guza and Thornton, NSTS Workshop, 

 Scripps Institute of Oceanography, La Jolla, California, personal communica- 

 tion, February 1981). All the raw data from both the Torrey Pines (Gable, 

 1979) and Santa Barbara, California (Gable, 1981 ) experiments were made 

 available on magnetic tape. Data were recorded at 64 samples per second, 

 then later low pass-filtered and reduced to 2 samples per second. These 

 then became the raw data tapes. They can be obtained for nominal cost from 

 the National Oceanic Data Center (NODC) in Washington, D.C, Some of the 

 early results will be discussed in Chapter 4. These data sets form an 

 extensive and excellent data source for future analysis. 



Unfortunately, however, no EM current meters were alined in the ver- 

 tical for either of the NSTS field experiments. Plans to do so at Santa 

 Barbara were scrapped due to the storm conditions encountered. Thus it 

 was not possible to observe the vertical current structure nor know if 

 circulations about horizontal axes were present. 



3. Wave Direction . 



Wave direction is an important parameter in surf zone current genera- 

 tion. It is also difficult to determine for irregular wave trains striking 

 the coast. Linear arrays of pressure sensors have been quite successful in 

 measuring directional wave data at the coast (e.g., Pawka, 1974). Other 

 devices have been proposed (Hallermeier and James, 1974). The most prac- 

 tical and successful for measuring wave direction is the slope array, as 

 developed by the Scripps Institute of Oceanography (Seymour, 1977; 

 Seymour and Higgins, 1977; Higgins, Seymour, and Pawka, in preparation, 

 1981). Besides wave direction, pressure measurements from the device can 

 also be used to calculate the longshore component of shoreward-directed 

 momentum flux (S^^y) due to the waves. The device is also called an S^^y- 

 meter. As such it provides a valuable tool for comparison with theories 

 which use sea-surface variation and wave angle to calculate S^y. 



The slope array device is very simple. Four pressure transducers 

 are mounted at the corners of a square frame, 6 meters on a side. The 

 orientation of the sides on the bottom of the frame is determined rela- 

 tive to a reference longshore direction. Coordinate rotation yields the 

 desired surface slope components from any array alinement. The real part 

 of the cross-spectrum of the sea-surface slope components in the longshore 

 and cross-shore directions is then used to compute a significant direction 



GABLE, C.G., Report on Data from the NSTS Experiment at Ledbetter 

 Beach, Santa Barbara, California, Jan-Feb., 1980," IMR Ref. No. 

 80-5, Scripps Institute of Oceanography, Mail Code-A022, La Jolla, 

 Calif., 1981 (not in bibliography). 



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