Experimental study on bichromatic wave runup on a gently sloping beach

Abstract:

Wave runup plays an important role in coastal flooding and erosion. In addition, very large runup events can be dangerous for beach goers. A recent numerical study (García-Medina et al. 2017) shows that bichromatic waves on a gently sloping beach can produce runup events of considerably-variable magnitudes among different wave groups. The work discussed here is a laboratory study that aims to better understand this phenomenon and to relate observations of variable runup to wave conditions. The 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. The setup involves 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 the evolution of bores and the runup. Wave conditions vary by wave height, wave period, and group period. Preliminary results suggest that the highest runup is produced when the largest wave in the group is positioned slightly behind the infragravity wave crest prior to bore-bore capture events. In addition, a new dimensionless parameter is proposed for runup variability among wave groups.