CREST ELEMENT 



^ZK^ty^-'"'" 



^^^^5^5^ 



Figure 5. Typical breakwater cross section with a monolithic crest element 



determine the total volume of primary armor per unit length of structure. 

 The conditions determining these dimensions will change along the length of a 

 breakwater. Transitions should be gradual with conservative allowances for 

 the limited confidence in the predicted variations in design conditions. All 

 of these considerations must account for both extreme high water conditions 

 and the possibility of a low tide condition which could greatly complicate the 

 stability of features near the toe. 



34. The dimensions of the armor layer generally are formulated as func- 

 tions of the primary armor weight. The armor thickness and crest width are 

 related to the weight of the armor unit by the following relation: 



r = nK. 



W 



1/3 



(9) 



where 



r = total average layer thickness or crest width 



n = number of armor units comprising the thickness or width 

 (usually 2 for the thickness and 3 for the crest width) 



K = "layer coefficient" (see Table 7-13, SPM 1984), an empirical 



measure of the thickness compared to that of the same number of 

 equivalent cubes 



35. The weight of the individual armor units, as determined by the 

 Hudson formula (Equation 1), is a function of the slope, the armor material's 

 density, the K^ factor, and the wave height cubed. A small increase in de- 

 sign wave height makes a substantial difference in the armor weight, i.e., a 

 10 percent increase in H corresponds to a 33 percent increase in W . The 

 armor thickness will increase only 10 percent. The in-place unit price of 

 armor material (both quarrystone and concrete) will vary directly with the 

 total weight of the units relating also to the practicalities of quarry 



23 



