Structure orientation 



73. In most situations, detached breakwaters should be oriented paral- 

 lel to the preproject shoreline. However, if the predominant wave direction 

 at the structure is very oblique to the shoreline (>30°) the breakwater may be 

 oriented parallel to the waves to block the incident energy. Waves from other 

 directions will be blocked less efficiently. A diffraction analysis should be 

 performed to identify any important changes in the wave pattern or distribu- 

 tion in wave height due to the structure orientation. 



Modeling 



Physical modeling 



74. The initial design(s) for a major detached breakwater project 

 should be tested and refined using physical model experiments. Physical hy- 

 draulic models have proven to be a practical tool for the functional design of 

 detached breakwaters. This section will discuss how these model studies are 

 conducted and how they can be used to assist in developing a design. Four 

 previous model studies performed at the US Army Engineer Waterways Experiment 

 Station (WES) are briefly examined in Appendix C. 



75. As seen in Part IV, many variables must be considered in designing 

 detached breakwaters. A physical model can be used to great advantage for 

 such situations, since parameters such as wave height, wave period, wave spec- 

 trum, wave angle, water level, structure height, segment length, distance off- 

 shore, etc., can be varied within model limits and the effects on wave height 

 and wave-generated currents determined. Sediment movement trends can be qual- 

 itatively reproduced. 



76. Since short-period wind waves are usually the primary force respon- 

 sible for nearshore sediment transport, a physical model for detached break- 

 water design is based on Froude's Law and is constructed geometrically similar 

 to the prototype. Previous detached breakwater studies have varied in scale 

 ratios from 1:50 to 1:100. Larger scale ratios minimize wave attenuation by 

 surface tension, internal friction, and friction in the bottom boundary layer. 

 Proper scaling of the equivalent hydraulic size for the sediment used in 

 movable-bed models and bottom friction effects create significant problems 

 with modeling sediment transport. However, in large-scale models (i.e., 1:50 



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