Infragravity Waves in the Nearshore Zone

This report summarizes the present state of knowledge on infragravity wave motions (nominally 0.003 to 0.05 Hz). Theoretical and observational studies are presented. Most of the studies discussed herein have been published elsewhere, however a few studies discussed in chapter 4 are presented for the first time in this report Measurements of nearshore waves and currents have shown that a significant amount of the total energy can be contained in the infragravity band, and on highly dissipative beaches the infragravity wave variance often dominates over energy in the incident wave band(0.05 to 0.3 Hz). An 8-month data set of infragravity variance measured at 8-m-depth at the shoreline (runup) was compared with incident wave variance. Analysis of the 8-m-depth data showed that high mode edge waves account for about 50 percent of the total infragravity variance, and as high as 80 percent at times. Significant edge wave heights greater than 20 cm were observed at the 8-m depth. Infragravity wave variance was shown to have a higher correlation with swell variance (C = 0.95) than with sea variance (C = 0.61). This report was motivated, in part, by the need to determine the significance of infragravity waves on coastal erosion and structure damage and by the desire to improve coastal engineering solutions to problems associated with nearshore processes.