INFRAGRAVITY ENERGY AND ITS IMPLICATIONS IN NEARSHORE 

 SEDIMENT TRANSPORT AND SANDBAR DYNAMICS 



PART I 



INTRODUCTION 



1. The study of extreme runup during storm conditions is a topic of vital 

 interest, motivated in part by the costs incurred from coastal erosion and 

 structure damage. Technically, runup refers to the maximum elevation of wave 

 excursion up the shoreline above the still-water level. Contributing compo- 

 nents to runup are set up due to breaking incident wind waves and swash motion 

 about the setup. Setup is a well-understood phenomenon (Longuet-Higgins and 

 Stewart 196M) and can be predicted and modeled. Swash, however, is more com- 

 plex, composed of a full spectrum of motions. Energetic swash motion contains 

 both wind wave (1 to 20 sec) and infragravity (30 sec to several minutes) 

 period oscillations (Figure 1). Swash motion at wind wave frequencies is 

 found to dominate on steep, reflective beaches where incident waves have not 

 fully dissipated. On the other hand, infragravity frequency swash motions 

 dominate on shallow-sloped, dissipative beaches (Holman 1981; Guza and 

 Thornton 1982; Holman and Sallenger 1985; Holman 1986). On a fully 



I0" 3 I0" 

 Frequency (c/») 



Figure 1. Approximate distribution of ocean surface wave energy 

 illustrating the classification of surface waves by wave band, 

 primary disturbing force, and primary restoring force 



