a. LONGSHORE VELOCITY 



b. CROSS-SHORE VELOCITY 



8 %Pwr • 



I s | S 1 " Log?" — 

 Cyclic Alongshore Waraunnlw (nr 1 ) 



<? 9 1 



Cyclic Alongshore Wavemnnber (m ') 



g a " LogPw - 



s s s s 



%ftjwtr 



S S ? 

 %Power 



Figure 6. Typical /r - /spectra, from NSTS experiment at Leadbetter Beach, CA . Edge 



wave dispersion lines are drawn for a plane-beach assumption. Note that mode 

 edge waves are better resolved in the longshore current based k y -f (v) spectra 

 (top) than in the cross-shore current k y -f (u) spectra (bottom). The shading 

 density indicates the percent power in the frequency bin that lies in the half- 

 power bandwidth of the peak (from Oltman-Shay, Howd, and Birkemeier 1989) 



Research is ongoing to investigate these different mechanisms for generating 

 shear waves, the growth and dissipation of these instabilities, and their role in 

 modifying the incident and infragravity wave fields (e.g., Slinn et al. 1998). 

 Modulation of the edge wave field and incident waves would be expected 

 considering the magnitude of these shear oscillations. Clearly, the similar spatial 

 scales of shear waves and sandbar morphology lends intrigue into their potential 

 role in nearshore sediment dynamics. 



12 



Chapter 2 Infragravity Wave Dynamics 



