where 



K t = total wave transmission coefficient 

 K to = overtopping transmission coefficient 

 K n = through transmission coefficient 



This method was programmed as one of the modules in the Automated 

 Coastal Engineering System (ACES) (Leenknecht, Szuwalski, and Sherlock 

 1993) titled "Wave Transmission Through Permeable Structures." Seelig's 

 approach provides a method to estimate wave transmission for a wide range of 

 structure types and geometry and for a wide range of wave conditions. 



Ahrens (1987) developed a method to estimate wave transmission based on 

 about 200 laboratory tests of reef breakwaters. Irregular wave tests were 

 performed on both submerged and nonsubmerged reefs. Ahrens' approach is 

 based on the use of two formulas which are selected depending on the relative 

 freeboard (JRJH^ value. 



For relatively high reefs, R c /H mo > 1.0, the dominant mode is 

 transmission through the reef. The transmission coefficient is largely a 

 function of one variable which is the product of wave steepness and the bulk 

 number. 



1.0 



1.0 + 



mo t 



\0.592 



K L , D > 



(38) 



When the dominant modes of transmission result from wave overtopping or 

 waves propagating over the crest of a submerged reef (R c /H mo < 1.04), a 

 rather complex relation involving several variables is required to predict 

 transmission coefficients. 



1.0 



1.0 



\0.26l 



h L 



exp|0.529|— -| + 0.00551 



a; 



3/2 



D'L 



(39) 



It should be noted that Ahrens does not use the traditional definition of the 

 transmission coefficient involving the incident wave height at the toe of the 

 structure. A transmission coefficient, which is the ratio of the transmitted 

 height to the height which would be measured at the same location in absence 

 of the reef, is preferred since it eliminates loss of energy due to wave 

 breaking which would have occurred if the structure were not present (Ahrens 

 and Cox 1990). It is this type of coefficient predicted using Ahrens' equations 

 which may cause them to be slightly higher than traditional coefficients. 



Van der Meer (1991) developed a new formula for wave transmission at 

 low-crested structures. After re-analyzing several data sets involving 



Chapter 4 Structural Design Guidance 



91 



