researchers leery of laboratory basins for verifying the new theory. 

 Gourlay (1976, 1978) avoided this problem by concentrating on the non- 

 uniform system generated on a beach behind an offshore breakwater. The 

 study employed an idealized geometry, in that the beach planform permitted 

 simultaneous wave breaking crests parallel to the beach at all times. The 

 alongshore gradient of breaking wave height resulted from diffraction in 

 the lee of the offshore breakwater. The wave-generated longshore current 

 and nearshore circulation system studied by Gourlay (1978) is shown in 

 Figure 8. Spherical floats made of sealing wax (19 and 13 millimeters) 

 were photographed with a movie camera to determine surface velocity dis- 

 tributions and circulation patterns (see Fig. 8). Current velocity pro- 

 files normal to the beach varied in shape at various positions along the 

 beach, as anticipated. Figure 8 shows maximum surface current at about 

 O.A meter per second along section I and well inside the surf zone. The 

 scale of this model and variables were similar to those previously dis- 

 cussed (wave heights up to 12 centimeters, periods from 0.7 to 1.5 seconds, 

 and a beach slope of 0.1). 



SHELTERED AREA 



LOW 



EXPOSED AREA 

 G RUN-UP LIMIT 



/RIP CURRENT 

 _/_ REGIO N ._ , 



H^/^ "XV "»' 



/PLUNGE ^*» POINT t 



/ laREAKJ POI^T 



\ 



V 



b(lM«) 



BREAKWATER 



■ 69mi Tal.Otf 

 W»w« Cr«ftt 



Figure 8 , 



Wave-generated current system behind offshore breakwater (from) 

 Gourlay, 1978). 



Gourlay (1978) also measured the longshore and onshore-offshore vert- 

 ical velocity distributions at section I in Figure 8. A specially con- 

 structed Pitot tube (pitometer) with forward and rear facing total head 

 tubes was developed and calibrated to give results said to be qualitatively 



35 



