Infragravity waves and bore merging

Abstract

The phenomenon of bore merging is investigated using two high-resolution laboratory experiments including bichromatic and irregular wave conditions. The locations at which waves start merging are identified and the hydrodynamic conditions in the vicinity of the merging points are examined. Bore merging takes place in the inner surf zone for all conditions considered. The infragravity- to short-wave height ratio is close to or larger than one at the merging point, indicating that bore merging occurs in a part of the surf zone that is already dominated by the infragravity waves. Our data analysis is supplemented by numerical simulations that confirms the importance of infragravity waves in the occurrence bore merging. Moreover, our simulations suggest that bore merging has a very limited effect on the infragravity wave field. This casts doubts on the importance of bore merging as an infragravity wave generation mechanism.