1 Introduction 



Waves in tidal inlets steepen and break on strong ebb currents. Although wave 

 breaking at inlet entrances impacts navigation, sediment transport, and wave 

 penetration into the inlet, the wave breaking process in the presence of a current is 

 poorly understood. 



Background 



Previous laboratory studies of wave breaking on a current include Hedges, 

 Anastasion, and Gabriel (1985); Lai, Long, and Huang (1989); and Suh, Kim, 

 and Lee (1994). Hedges, Anastasion, and Gabriel developed a limiting spectral 

 shape for waves breaking on a current in deep water and tested it with four 

 spectra in a wave-current flume. Suh, Kim, and Lee extended the Hedges, 

 Anastasion, and Gabriel formula to finite water depths and tested it with nine 

 spectra in a flume. In both studies, littie of the data is presented, and results are 

 given in the form of limiting spectra. Lai, Long, and Huang performed a detailed 

 flume experiment of wave-current interaction kinematics in deep water. They 

 observed that linear theory predicted kinematics well, if the Doppler shift is 

 included; they confirmed deep-water blocking of waves if the ratio of ebb current 

 velocity to wave celerity exceeded 0.25; and tiiey observed a downshifting of the 

 peak wave frequency for breaking on a strong current. Ris and Holtuijsen (19%) 

 used Lai, Long, and Huang's deepwater breaking data to evaluate breaking 

 criteria and found that the whitecapping formulation of Komen, Hasselmann, and 

 Hasselmann (1984) under-estimated dissipation. Supplementing this whitecapping 

 with the Battjes and Janssen (1978) breaking algorithm gave significantiy better 

 agreement with the data. In this study, we will evaluate dissipation formulations 

 with a new data set that includes shallow to intermediate relative water depths. 



Objectives 



In this report, wave breaking on a current is examined through physical-model 

 measurements in an idealized inlet with a steady ebb current. Wave and current 

 measurements are used to evaluate wave dissipation models. The goal of the study 

 is to determine a dissipation function for wave breaking on a current that is based 

 on integrated wave parameters, is applicable for arbitrary water depths, and is 

 robust. 



Chapter 1 Introduction 



