energy is subject to a mean horizontal force, F. The existence of a 

 horizontal momentum flux, or radiation stress, has been demonstrated 

 experimentally by Longuet-Higgins (1977), For non-breaking waves of low 

 amplitude (obeying linear wave theory), the mean horizontal force per 

 unit length has been shown by Longuet-Higgins (1977) by conservation of 

 momentum to be 



[9] F = P9 (a ,2 + a 2 . a 2)(i + ^^h 



A ^ r t sinh2kh 



where p = density of water 



g = gravitational acceleration 



a. = the amplitude of the incident wave 



a^ = the amplitude of the reflected wave 



a. = the amplitude of the transmitted wave 



k = 2tt/L 



L = wavelength 



h = water depth 



Floating tire breakwaters characteristically dissipate wave energy 

 through internal friction rather than reflection. Therefore, as a first 

 approximation, F has been calculated by assuming a^, = 0. The wave 

 amplitude is assumed to be half the wave height. For the water depths 

 and wavelengths present at La Salle Park, the factor (1 + 2kh/sinh kh) 

 equals unity. In Figure 15, the predicted loads (for a 5-module 



97 



