14. Table 7-8 in the SPM (1984) presents the values for K^^ recom- 

 mended by the Corps for use in the Hudson formula. Values are presented for a 

 variety of quarried materials and artificial concrete shapes. Each value is 

 associated with a number of factors, including: 



a. Shape characteristics of the armor units (i.e., smooth, rough, 

 round, or elongated rock). 



b. Position of units on the trunk or head of the breakwater. 



c. Wave form (i.e., whether or not the wave is breaking directly 

 on the structure). 



d. Slope or range of slopes (in some cases). 



e. Method of placement (random versus special individual 

 placement) . 



f. Number of layers of armor units to be placed on the slope. 



g. Relative gradation and smoothness (for quarried rock). 



15. An important point to note about the K^ values in the SPM (1984) 

 is that 58 percent of them were derived from monochromatic wave model test re- 

 sults, while the rest are interpolated values. Another factor of importance 

 is that some of the armor unit types for which K^ values are presented have 

 actually been used in only a small number of prototype breakwaters. All of 

 the units lack systematically documented prototype verification of their rela- 

 tive stability, though efforts are currently under way to consolidate histori- 

 cal performance of Corps constructed breakwaters. Uniform rough angular quar- 

 rystone, riprap (graded rough angular quarrystone) , and dolosse have been most 

 extensively tested in scale models and currently have the best documentation 

 of prototype experience (Jackson 1968a and Carver 1983). 



16. The coefficient K. , as applied in the Hudson formula with its 



basis in the assumptions of Iribarren, does not directly account for as many 



as 20 or more design conditions (Ligteringen and Heijdra 1984) that are now 



known (in at least a qualitative sense) to affect breakwater stability. Some 



investigators (Brorsen, Burcharth, and Larsen 1974 and Burcharth 1979) have 



questioned whether the Hudson formula is reliable for predicting stability of 



dolosse and other slender concrete armor units. In the future, these units 



may require variable K^ factors related to slope and other conditions not 



now inherent in the values presented in Table 7-8 of the SPM (1984). Some of 



the other conditions of concern include: 



a. Influence of wave period or the steepness of individual waves 

 (Ahrens and McCartney 1975 and Losada and Gimenez-Curto 1979). 



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