

1.0 









0.8 





REFLECTED NORMALLY 



INCIDENT WAVE 





0.6 









0.4 







+ 





 -0.2 



VI lf\ \ \X 1 



n -2 



1 p^ 1 1 | N| | | | 



— i // / \ ^ 

 I If /^~ n ' ' ~ 



30 / 40 50 "V6Q— "70 



^N^_____^^--^^»n -3 





-0.4 









-0.6 







Figure 4. 



Cross-shore profile of low mode edge waves and leaky wave 

 (after Holman 1983) 



increasing similarity in the higher modes. Also note that these waves have their 

 largest amplitudes at the shoreline and decay exponentially offshore with an 

 ^-folding distance of k~ . Ursell's (1952) full solution has an e- folding of 

 (k cos P)" 1 , but on shallow beaches cosP ~ 1 and the two solutions are nearly 

 identical. 



Since on most simple beach profiles the largest elevation excursion is at the 

 shoreline, these waves are often measured in swash oscillations. Although 

 swash variance and spectra can be obtained from these measurements, 

 determination of the modes is not possible using only swash data. Alongshore- 

 aligned arrays of in situ instruments are required to resolve the infragravity wave 

 modes (Huntley, Guza, and Thornton 1981; Oltman-Shay and Guza 1987). 

 Recent work by Bryan and Bowen (1996) and Byran, Howd and Bowen (1998) 

 also cautions against the use of swash measurements for amplitude determination 

 on beaches with pronounced sandbars, particularly for higher frequency edge 

 waves, which may have maximum amplitudes in the vicinity of the bar(s). 



Suhayda (1974) presented a description for the structure of normally incident 

 leaky waves as 



Chapter 2 Infragravity Wave Dynamics 



