In the present study, after considerable inspection of videotapes of breaking 

 waves, the break point was defined as the point where any portion of the 

 forward face of the wave became vertical. Regardless of which method is used, 

 defining the break-point location is rather subjective because a wave does not 

 always transform from a shoaling wave to a broken wave in an abrupt manner. 

 Judgment is always involved; therefore, it is important to state how the break 

 point was determined in reporting of results. Unfortunately, not all authors 

 specify this. 



23. It is also important to state the datum at which the depth at 

 breaking was measured. Note from Figure 4 that the water depth at breaking 

 h b is measured from the still-water level (SWL) under the crest of the wave. 

 This definition was used in all tests in the present study, although h b has 

 also been measured from the mean water level (MWL) in some studies. The 

 equipment available for data analysis in the present study made the SWL more 

 convenient to use as a datum. 



Review of monochromatic wave studies 



24. Many studies have been performed to develop relationships to denote 

 the wave height at breaking. The term "breaker index" is used to describe 

 nondimensional breaker height. The two common indices are of the form 



H b 

 7b = — (13) 



in which 7 b will be called the breaker depth index, and 



H b 

 fib = — (14) 



H„ 



in which fy, will be called the breaker height index. 



25. Although the present study involves only periodic waves, most 

 earlier studies on breaker indices were conducted with solitary waves. Two 

 widely quoted studies are noted here. McCowan (1891) theoretically determined 

 the value of 7 b for a solitary wave on a horizontal bottom as 0.78. Munk 

 (1949) derived the following expression for breaker height index from solitary 

 wave theory: 



20 



