The effects of relative water depth, L/d, on the attenuation character- 

 istics of a 25-percent porous freely floating parabolic beach and of 20- and 

 30-percent hinged parabolic beaches are shown in Figure 187. The moored 

 freely floating structure is evidently more effective in wave damping than the 

 hinged beach, particularly for the deeper water conditions. Ofuya (1968) 

 partially attributed the better performance of the floating beach to 

 interaction of the complete structure with waves in the region of large 

 kinetic wave energy concentration. The lower sections of the hinged beach, 

 located in a region of low kinetic wave energy, serve mainly as structural 

 support. Furthermore, oscillations of water between the slats and the partial 

 breaking of waves due to forced instability of waves progressing past the 

 structure cause large energy dissipation within the freely floating structure. 



2 3 4 



Ratio of Wavelength-to-Water Depth, L/d 



Figure 187. Effects of relative water depth, L/d, and 

 porosity on transmission coefficients, C t , 

 of hinged and freely floating parabolic 

 beaches (after Ofuya, 1968). 



If geometrical similarity is maintained between model and prototype, the 

 modulus of elasticity of the prototype parabolic beach material should be 

 several times greater than that of the model beach. Hence, a material other 

 than wood (which was used in the model) will be required for the construction 

 of prototype parabolic beaches. Ofuya (1968) found the floating breakwater 

 to be more effective, in general, than the hinged beach for wave damping. 

 Furthermore, the method of mooring by an anchored mooring line appeared more 

 practical than providing a pivotal hinge on the ocean floor. 



247 



