energy wind waves were responsible for berm building. This is not surprising 

 since, as previously mentioned, these waves are largest during storms and have 

 their greatest amplitudes at the shoreline. The infragravity component of runup 

 was found to accelerate berm erosion two ways. When runup occurs at a low 

 frequency it remains longer on the beach and increases groundwater saturation, 

 causing a rise in the water table. This results in a seepage out of the beach face 

 below the berm that enhances sediment suspension and berm erosion. Erosion 

 will be more severe if the runup goes beyond the berm crest where the lower 

 beach slope slows the rundown and increases saturation. A second effect is a 

 local deepening of water at the shoreline with the infragravity wave crest, 

 allowing incident waves to progress further shoreward, dissipating their energy 

 higher up the beach face. 



Present quantitative modeling capabilities are not able to predict beach 

 morphology evolution with confidence. Different models are capable of 

 explaining particular aspects of morphology changes and sediment transport 

 under different conditions. A major problem is that our limited understanding of 

 nearshore sediment transport dynamics often requires models to include 

 simplifying assumptions of littoral processes, whereas actual hydrodynamics are 

 often complex, three-dimensional, and unsteady. Storm processes appear as 

 highly dynamic transient processes which produce large-scale morphology 

 changes at times when it is most difficult to measure. Furthermore, the complex 

 nature of the incident and infragravity wave fields and their interactions with 

 each other, as well as with morphology and currents, are extremely difficult to 

 measure in the field. Additional field measurements are required for better 

 characterization of the hydrodynamics and for improvement of quantitative 

 predictions of nearshore morphology changes. 



Chapter 3 Infragravity Waves, Nearshore Morphology, and Sediment Transport 29 



