and the spectrimi of the momentum flux components, S^y. Details are beyond 

 the intended scope of this review. The calculation method stems from 

 Longuet-Higgins, Cartwright, and Smith (1963)-'^° and complete details can 

 be found in Higgins, Seymour, and Pawka, in preparation, 1981,. They also 

 made laboratory tests with irregular waves and field comparisons with a 

 large linear array of five pressure sensors. Comparisons were judged to 

 be excellent and quite good, respectively. 



Use of the slope array device during the NSTS experiments showed its 

 sensitivity to alinemen't errors along the coast relative to wave direc- 

 tionality. At Torrey Pines, California, alinement inaccuracy with the 

 straight coastline was judged to be about 3° and greater than the wave 

 directions observed (Seymour, 1981, NSTS Workshop, Scripps Institute of 

 Oceanography, La Jolla, California, personal communication, February 1981), 

 Consequently, a linear array of five pressure sensors more than 360 

 meters long was employed to measure the directional spectrum. The pro- 

 nounced variability in bottom topography and large incident wave angles 

 due to narrow wave windows present at Santa Barbara, California, made use 

 of the slope array device ideal for this location. 



4. Laboratory .Systems . 



There is another way to create a uniform longshore current profile 

 (i.e., infinite beach) in the laboratory other than the method developed 

 at the Delft Technical University (Visser, 1980). End effects are elimina- 

 ted, and a zero mean slope in the longshore direction results. The tech- 

 nique, described by Dalrymple and Dean (1972), involves a spiral waveraaker 

 generating waves in the center of a circular basin. A vertical right- 

 circular cylinder oscillates in a small circle about its vertical axis to 

 generate the waves. Wave crests move out in an Archimedian-type spiral 

 and crests impinge on the circular beach everywhere at the same angle of 

 incidence. A theory for the amplitude of generated waves based on shallow- 

 water theory was confirmed in the laboratory. Dalrymple and Dean (1972) 

 conducted littoral drift experiments with the device, and they recommend 

 it for further sand transport studies. However, scale effects preclude 

 obtaining quantitative results for this purpose. It could be an excellent 

 tool, however, for confirmation of longshore current theory. 



V. SUMMARY 



More than 60 years of observations and measurements of longshore 

 currents, nearshore circulations, and rip currents worldwide has been 

 briefly reviewed. Magnitudes and directions of these currents depend 

 upon the following factors: 



1{ 



LONGUET-HIGGINS, M.S., CARTWRIGHT, D.E. , and SMITH, N.D. , "Observa- 

 tions of the Directional Spectrum of Sea Waves Using the Motions of 

 a Floating Buoy," Ocean Waves Spectra^ Conference Proceedings, Prentice- 

 Hall, Englewood Cliffs, N.J. , 1963 (not in bibliography). 



62 



