Experimental study on the effects of infragravity waves on the merging of multiple bores and the resulting runup

Wave runup is an important process that contributes to coastal flooding and erosion. In addition, very large runup events can be dangerous for beach goers. Observations have shown that the merging of multiple bores can create exceptionally large runup. Recent studies have shown that infragravity waves are an important contributor to bore-bore capture. In particular, a numerical study by García-Medina et al. (2017) showed that changes in the phase relationship between the infragravity wave and the wave group can lead to up to 30% difference in maximum runun. This study aims to further explore this effect in a laboratory setting. Our experiments were carried out in the Large Wave Flume at the Hinsdale Wave Research Laboratory at Oregon State University. The flume has an 87 m effective length and 3.7 m width. Our setup is a flat bottom offshore at 1.8 m water depth followed by a planar 1:36 beach slope. Water level elevations are measured at 6 gages offshore and 20 gages nearshore. In addition, two video cameras are used to capture evolution of bores and runup. Three types of wave conditions are used, including 1) bichromatic waves where an integer number of individual incident waves fit in each wave group, i.e. all wave groups are identical, 2) bichromatic waves where a non-integer number of incident waves fit in each wave group, and 3) random waves with a JONSWAP spectrum. We are presenting preliminary results showing the effect of infragravity runup phase on maximum runup from our experimental study and qualitative comparisons with numerical modeling results.