Figure 14. Positioning of rip currents at alternate antinodes of 

 standing edge waves on a plain beach with regular 

 incident swell waves (from Komar, 1976). 



dissipative beaches, Sasaki (1977) proposed that infragravity waves 

 30-second to 5-minute periods) present in the surf zone trigger the 

 rip currents with corresponding large spacings. In between, and in- 

 stability domain was said to exist. This middle type of mechanism 

 was classed as wave-current interaction by Dalr3raiple (1978) . 



Huntley (1976a) and Sasaki and Horikawa (1978) reported field obser- 

 vations of edge waves with periods in the infragravity domain that are 

 a major component of low-frequency energy. It remained to show where the 

 edge waves with large periods come from. Gallagher (1971)^^ developed a 



50 



