For monochromatic wave tests, wave period, T, is defined as the period 

 of wave generator blade motion. For most of the monochromatic wave conditions 

 tested, 90 percent or more of the incident wave energy was found to be in the 

 spectral band containing the blade frequency (Fig. 6). At a given value of 

 wave steepness the amount of wave energy at higher harmonics of the blade 

 frequency increases as the relative depth, d/gT^ , decreases. This energy 

 shift occurs because the waveform becomes more cnoidal and less sinusoidal 

 in shape as d/gT^ decreases and H/d increases. 



100 



95 

 ;90 



85 



80 

 0.0001 



Figure 6. 



OT^l* I 



^ 



X X — -^ 0.055 



0.016 



BWI ds/h^l.O 



J 1__L 



0.001 



H/qT' 



0.01 



Percent of incident wave energy at the period 

 of wave generator blade motion for sinusoidal 

 wave generator blade motion. 



5. Breakwaters Tested . 



Cross sections for 17 breakwaters were tested for wave transmission and 

 reflection; the cross-section geometries are illustrated in Appendix A. Each 

 of the structures was assigned the letters BW and a number to identify the 

 structure. Breakwaters BWI to BW12 were built and tested on the flat bottom 

 of the flume. However, BW13 to BW17 were constructed with a 1 on 15 fronting 

 slope 25 centimeters high and 3.75 meters long. The fronting slope was used 

 fo simulate a sloping bottom and allow higher waves to break on the structure 

 being tested. 



Most of the breakwaters tested were of rubble-mound construction, because 

 this is the most common type built. However, BWI and BW14 were smooth and 

 impermeable. BW2 had an impermeable core, and BW8 and BW9 had dolos armor 

 units and an impermeable cap. BW3, BW4 , and BW15 were tested with and without 

 a vertical, thin impermeable plate placed in the center of the structure to 

 prevent transmission through the lower section of the breakwater. The symbol 

 W is used to indicate tests where the impermeable plate was used; e.g., BW3 

 tested with a plate is designated as BW3W. Materials used to construct the 

 breakwaters are described in Appendix B. 



6. Test Conditions . 



Each breakwater was built with a fixed geometry, then tested at various 

 water depths and wave periods. A number of wave heights were generally examined 

 for each wave period. Most of the experiments were run with monochromatic waves 



20 



