breaking and nonbreaking waves can occur in the same sea state. Others who 

 have investigated breakwater stability as a function of the surf parameter 

 (Equation 4) include Gunbak (1976) and Losada and Gimenez-Curto (1980). 



24. A relatively complete list of rubble-mound breakwater stability 

 formulae, proposed by various investigators over the years, was published by 

 the Permanent International Association of Navigation Congresses (PIANC) 

 (1976). The variety of model tests and prototype experience inherent in these 

 formulae and those developed since 1976 is but a small fraction of the many 

 thousands of monochromatic wave tests conducted to determine Hudson formula 

 parameters used to design hundreds of breakwaters all over the world. Use of 

 these other stability relations should, therefore, be applied only in conjunc- 

 tion with traditional procedures using the Hudson formula for comparison. A 

 conservative choice can then be made between the stable armor weights and 

 damage rates predicted by the Hudson formula and these alternate methods. 



Practical Considerations for Stability 



25. The analytical methods available for predicting rubble-mound break- 

 water stability have been shown not to include many important considerations 

 that could cause a structure to fail. Breakwater design has always involved a 

 great deal of subjective judgment and probably always will. Some of the most 

 pertinent practical considerations that must be made in determining rubble- 

 mound breakwater material characteristics and dimensions are reviewed below. 

 Comprehensive review of both practical and analytical considerations is avail- 

 able in the SPM (1984), Angerschou et al. (1983), Institute of Civil Engineers 

 (1984), Jensen (1984), and Bruun (1985). 



Incident wave conditions 



26. The incident wave conditions are traditionally defined as the wave 

 height at the seaward face of the structure with a further distinction as to 

 whether or not the waves are breaking. This breaking versus nonbreaking cri- 

 terion has been argued extensively over the years. The convention remains in 

 practice, however, due to obvious differences in design conditions for rubble- 

 mound structures built in shallow water, where wave heights are depth limited, 

 and in deeper water (depth > -15 m), where waves have not transformed to the 

 point of breaking in front of the structure. The natural irregularity of sea 

 states can be fairly well represented by a single height and period related to 



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