1 Introduction 



The study of physical processes that govern sediment transport on beaches is 

 a topic of vital interest to geologists, coastal engineers, and oceanographers. 

 This research is motivated in part by the expenses incurred from coastal erosion 

 and structure damage and by the desire to improve coastal engineering solutions 

 to problems associated with nearshore processes. Estimation of extreme runup 

 during storms is important for determining shoreline changes and designing 

 coastal structures. Measurements show that runup is composed of incident wave 

 (0.05 to 1 Hz) and infragravity wave (0.003 to 0.05 Hz) oscillations. 

 Observations of surf and runup during storms have shown the significance of 

 infragravity waves, with the spectra often dominated by energy in this band 

 (Holman and Bowen 1982, Guza and Thornton 1982, Holman and Sallenger 

 1985). 



This report provides the reader with a description of infragravity motions and 

 their significance in coastal engineering. A summary of previous investigations, 

 both theoretical and observational, is provided as background information in 

 Chapter 1 . A description of infragravity motions and the postulated generation 

 mechanisms is presented in Chapter 2. Particular emphasis is placed on the work 

 of Howd, Bowen, and Holman (1992) and Oltman-Shay and Howd (1993), 

 which noted the effects of longshore currents on infragravity edge waves. The 

 potential significance of these waves to nearshore morphology and sediment 

 transport is discussed in Chapter 3. Results from the SAMSON and DELILAH 

 field experiments held at the Waterways Experiment Station, Coastal Hydraulics 

 Laboratory's (CHL) Field Research Facility (FRF) are presented in Chapter 4 

 and Appendix A. The photogrammetric technique for measuring runup and 

 subaerial beach profiles is included in Appendix B. Finally, in Chapter 5, the 

 present knowledge of infragravity waves and the techniques used for measuring 

 these motions are reviewed, and future research needs are discussed. 



Technically, runup refers to the maximum elevation of wave excursion on 

 the shoreline relative to mean (still) water level. This defines runup as a discrete 

 measurement, but it is often referred to as the continuous process of water 

 movement at the shoreface. To avoid confusion in terminology, "runup" is 

 composed of setup due to breaking of incident wind waves and swash motion 

 about the setup. Setup is the mean water surface elevation above still-water 

 level, which is a well-understood phenomenon and can be predicted and modeled 



Chapter 1 Introduction 



