Figure 53. Terminology involved in performance characteristics of low-crested breakwaters 



Transmission 



Transmission of wave energy beyond rubble structures has been studied by 

 many researchers covering a wide variety of structures and resulting in 

 numerous methodologies and equations useful in predicting the characteristics 

 of transmitted waves. The majority of breakwaters used for shoreline 

 stabilization consist of low-crested permeable structures which have wave 

 energy transmitted both through and over the structure. Three methods or 

 procedures applicable to such structures are presented below to aid the 

 designer in determining a transmission coefficient K t to be used in functional 

 design. Each method was developed for a different range of structural and 

 incident wave conditions. The designer must determine which method is most 

 applicable. 



The transmission coefficient K t is generally defined as the ratio of the 

 transmitted wave height to the incident wave height. 



K. = 





(36) 



where 



H t = transmitted wave height 

 H t = incident wave height 



As stated previously, two types of wave transmission occur with low- 

 crested permeable structures: wave regeneration caused by overtopping of the 

 structure's crest, and wave energy transmitted through the permeable 

 structure. Seelig (1980) approached the transmission problem by making 

 independent estimates of energy transmitted by each condition and combining 

 the two components to obtain the total transmitted energy: 



*, = \/(*,o) 2 + (*/ 



(37) 



90 



Chapter 4 Structural Design Guidance 



