These losses were observed to be considerable for the most severe wave condi- 

 tions during calibration of the channel. In effect, K measures attenuation 

 of wave energy because of the presence of the breakwater and eliminates addi- 

 tional energy losses caused by natural wave breaking processes occurring be- 

 tween the incident and transmitted wave gages. Using the above definition of 

 K will allow evaluation of wave energy dissipating characteristics of reef 

 breakwaters in the next section. Because of the definition used, K should 

 be somewhat conservative, i.e., higher than the more traditional definition of 

 the transmission coefficient. 



31. Wave transmission has proved to be a very difficult characteristic 

 of reef breakwaters to predict partly because this study includes both sub- 

 merged and nonsubmerged rubble-mound structures. Seelig (1980) found that the 

 relative freeboard parameter F/H was the most important variable in ex- 

 plaining wave transmission of submerged and overtopped breakwaters, where 

 freeboard F is equal to crest height minus water depth, i.e., F = H - d . 

 However, a confusing trend will be obtained using this variable when there is 

 a transition in the dominant mode of transmission from that due to wave runup 

 and overtopping to that due to transmission through the structure. Figure 17 

 identifies the dominant mode of transmission as a function of the relative 

 freeboard and shows a schematized data trend. The difficulty in parameteriz- 

 ing the wave transmission process can be appreciated partly by considering the 

 influence of the wave height. When a reef breakwater is submerged, the pri- 

 mary mode of transmission results from wave propagation over the crest and, 

 generally, the smaller the wave the greater the K . When the crest is just 

 above the water level, the dominant mode of transmission results from wave 

 runup and overtopping, and the larger the wave the larger the K . If the 

 relative freeboard is greater than about one, the dominant mode of transmis- 

 sion is through the structure; and the smaller the wave the greater the K . 

 A number of other factors tend to further confuse the above generalities. 



32. The easiest way to discuss development of a general wave transmis- 

 sion model for reef breakwaters is to first consider relatively high struc- 

 tures where relative freeboard F/H is greater than one. When the dominant 



mo 



mode is wave transmission through the reef, K is a function largely of one 



variable which is the product of wave steepness and bulk number. Figure 18 



shows a plot of K versus the reef transmission variable (L d 5o)A H mo A t^ 



for the 37 tests where F/H > 1.0 . This one variable caused the wave 



mo 



29 



