time series analysis parameters need a great deal of further development. 



52. Tests in wave basins to determine the overall susceptibility of a 

 rubble-mound breakwater to direct and oblique wave attack (with attention to 

 the head and elbows), to transitions between cross sections, and to the hydro- 

 graphic features offshore of the structure, are necessary for most projects. 

 Wave basin facilities are larger and more complex than wave flumes (Figure 9) 

 and therefore are more expensive to use. Tests of this nature not only reveal 

 unique information about breakwater stability and other characteristics but 

 also provide important confirmation of conclusions from flume tests. Basin 

 models are typically at smaller scales than most flume models; thus, Reynolds 

 scale effects are exaggerated. Basin model testing confirms the location of 

 the most critical cross section of which more precise stability tests should 

 be performed in a flume at larger scale. Wave transmission by diffraction 

 through the entrance channel or other breakwater gaps is one of the most im- 

 portant measurements in a basin test. Long-period oscillations resulting 

 from the enclosure of a harbor area by a breakwater are also important to 

 detect. Model tests including tidal fluctuations can reveal circulation pat- 

 terns inside a proposed breakwater (Headquarters, Department of the Army 

 1984). 



53. The last category of breakwater model test is most important for 

 large breakwaters requiring complex construction procedures and many months of 

 construction time. Provisions for interim protection of partially completed 

 breakwaters must be tested to justify what can be a significant additional 

 cost to the project. Wave basin testing is more often appropriate for this 

 work, but flume testing can be quite helpful also. 



54. The modeling procedures discussed above are the true basis of 

 virtually all the analytical tools available to rubble-mound breakwater de-j 

 signers. Quantitative measurements of prototype breakwater performance are 

 Just now becoming available and have yet to be applied toward reliable ana- 

 lytical design procedures. Each application of analytical procedures is an 

 interpolation or extrapolation of limited prior experience. More often than 

 not, refinements which reduce cost and improve performance result from model 

 tests of a proposed design. Vital confirmation of analytical assumptions, 

 both explicit and implicit, is provided by even the simplest model test. The 

 expense and time are worth it in every case. 



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