and Sallenger 1985; Huntley, Guza and Thornton 1981; Guza and Thornton 1982, 

 1985; Oltman-Shay and Guza 1987; Beach and Sternberg 1987). It was pointed 

 out in Part I that on a dissipative beach the infragravity contribution can 

 dominate the surf zone. On such beaches, infragravity band variance has been 

 shown to exceed that of wind waves by a factor of 4 (Wright, Guza, and Short 

 1982; Guza and Thornton 1982) with heights at the shoreline (vertical swash 

 excursions) of approximately 70 percent of the incident significant wind wave 

 heights (Guza and Thornton 1982). Goda (1975) showed infragravity heights, 

 1 m in depth, to be between 20 and 40 percent of the offshore wind wave 

 heights. An extremely dissipative beach on the Oregon coast was observed to 

 have vertical swash excursions of approximately 60 percent the incident sig- 

 nificant wave height, with infragravity frequency completely dominating the 

 run-up spectrum with 99.9 percent of the variance (Holman and Bowen 1984). 



23. Differences in the relative amount of infragravity energy observed 

 on any one beach have been demonstrated to be a function of the Irribaren num- 

 ber (Holman and Sallenger 1985; Holman 1986). The dimensionless surf- 

 similarity parameter that measures the dissipative/ref lective nature of a 

 beach under varying incident wind wave conditions is 



o / H \1/2 



_o 



L 

 o 



where 



H - incident significant deep-water wave height 



L = deep-water wavelength 

 Swash excursions are observed to be dominated by the incident wind wave fre- 

 quency band for Irribaren numbers greater than 1.5. However, for lower val- 

 ues, swash becomes increasingly dominated by infragravity band energy (Holman 

 1986). Since storms are frequently associated with low Irribaren numbers, it 

 is clear that infragravity long waves must be considered when shoreline ero- 

 sion is examined. 



24. Until recently, the link between infragravity motion and sediment 

 transport had only been implied by the observed importance of infragravity 

 energy in the surf and swash. A recent study attempting to directly address 

 this link occurred on an extremely dissipative beach on the coast of Oregon 



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