BREAKING WAVES 



Breaking waves are usually classified into three categories: (l) 

 spilling breakers, (2) plunging breakers, and (3) surging breakers. 

 Spilling breakers are characterized by the appearance of white water at 

 the crest; they break gradually. Plunging breakers are characterized 

 by a curling over of the top of the crest and plunging down of this mass 

 of water; the front of the crest first becomes steep and then concave. 

 Surging breakers are observed when waves of small steepness travel on 

 very steep slopes; they are essentially bores in character. The whole 

 front face of such a breaker becomes unstable and "boils" all at once 

 rather than gradually, as in a spilling breaker. 



It is the wave steepness and the beach slope that determine how 

 the wave will break. 



The most reliable theory for calculating runup values of breaking 

 long waves is the method of characteristics, applied in each particular 

 case. This method, however, requires the profile of the wave to be 

 known somewhere off the coast before the wave breaks. This profile then 

 provides the input data for the calculation. 



Le Mehaute (Wilson, et al, I96U) suggests the following as a rough 

 approximation of runup calculation. 



If the bottom slope s > 0.01 at the point where the wave height - 

 water depth ratio is H/d =0.78 (McCowan's breaker limit for solitary 

 waves), the runup is approximately twice the breaking wave height (de- 

 pending on the slope). If s < 0.01, take the wave height H = 0.78 d 

 where the slope becomes 0.01; the runup then is twice this breaking 

 wave height. This will be the maximum possible runup. 



C-4 



