ESTIMATION OF WAVE TRANSMISSION COEFFICIENTS 

 FOR PERMEABLE BREAKWATERS 



by 



William N. Seelig 



I . INTRODUCTION 



The primary purpose of a breakwater is to reduce wave energy in an 

 area to be sheltered. One of the important characteristics of a break- 

 v\fater is the magnitude of the wave transmission coefficient, defined as 

 the ratio of the transmitted wave height to the incident wave height. 



Two basic types of wave transmission are: (a) by overtopping that 

 occurs when wave runup exceeds the crest elevation of the breakwater, 

 overtops the breakwater, and generates waves in the lee; and (b) through 

 a permeable structure that occurs because some of the wave energy is not 

 dissipated by the breakwater and is transmitted through the breakwater. 

 The total wave transmission coefficient, Ky, is given by: 



% =y(Kro)2 + (Krt)2 = Hy/Hj (1) 



where 



Km = transmission by overtopping coefficient 



Ky^ = coefficient of transmission through the structure 



Hj = incident wave height 



Hm = transmitted wave height 



These and other symbols are defined in Figure 1. 



Since the prediction method is complex, particularly for transmission 

 through the structure, a computer program is presented in an Appendix to 

 this report. The program incorporates the analytical model to determine 

 Ky^ by Madsen and White [1976)1 and an empirical equation to determine 

 Krp^ developed by Seelig (in preparation, 1979)2. 



iMADSEN, O.S., and IVHITE, S.M., "Reflection and Transmission Character- 

 istics of Porous Rubble-Mound Breakwaters," MR 76-5, U.S. Army, Corps of 

 Engineers, Coastal Engineering Research Center, Fort Belvoir, Va. , Mar. 

 1976. 



^SEELIG, W.N., "Two-Dimensional Tests of Wave Transmission and Reflec- 

 tion of Laboratory Breakwaters," U.S. Army, Corps of Engineers, Coastal 

 Engineering Research Center, Fort Belvoir, Va. (in preparation, 1979). 



