dissipative beach, the incident wind wave energy is observed to linearly 

 decrease from a maximum at the breaker location to zero at the shoreline (Fig- 

 ure 2). Any increase in wind wave height serves only to broaden the surf zone 

 and not to increase local surf or swash at wind wave frequencies. However, 

 increased wind wave heights offshore will increase surf and swash at infra- 

 gravity frequencies (Holman 1981; Guza and Thornton 1982; Holman and Sallenger 

 1985; Holman 1986) . 



2. Reflective beaches often become dissipative during storms and, as 

 such, experience infragravity dominance. Infragravity band energy may there- 

 fore be of tremendous significance to some coasts and man-made structures, 

 dominating many shorelines during storm conditions when erosion and sediment 

 transport are most acute. Researchers are only now beginning to appreciate 

 the ubiquitous nature of infragravity energy and are far from fully under- 

 standing its generation and behavior. However, it is known that in the quest 

 for good working models that predict the dynamics of the nearshore, infragrav- 

 ity energy cannot be discounted. 



3. The purpose of this report is to introduce the reader to the infra- 

 gravity energy band of nearshore motions and to explore past and present 

 infragravity research that has helped in understanding the nature of this 

 energy. In particular, attention will be given to research that addresses the 

 importance of the infragravity band, implicating it in surf and swash zone 



— EDGE WAVE AMPLITUDE 

 ---INCIDENT WAVE AMPLITUDE 



still-water level 



Figure 2. Offshore transect showing response of incident wave 



(dashed lines) and long wave (solid lines) energy to storm and 



calm conditions (after Holman 1983) 



