waves, the critical condition for stability occurs for relatively long waves that plunge on 

 the structure. 



A minor difficulty with Equation 3.7 and 3.8 is a potential source of 

 confusion because the stability number is given in terms of H2%, but the Iribarren 

 parameter is in terms oiH^. Finally, all of the previous damage empirical equations 

 listed above are limited to constant incident wave conditions and water level as well as 

 the initial condition of an undamaged structure. These equations are intended to predict 

 damage for a single design storm. Therefore, they caimot be used to predict damage 

 development over the life of a structure as is required in a life-cycle cost analysis. 



3 J Variability in Stability Results 



Carver and Wright (1991) conducted irregular wave stability experiments 

 primarily intended to determine random variations of damage initiation due to varying 

 armor placement and due to variations in wave time series realizations with constant 

 spectral parameters. Their tests progressed to low damage levels, varying up to 7.7 

 percent displacement, by count, of armor. The wave conditions were assumed to be 

 constant for a given test. But they did vary the wave height and period between 

 structure rebuilds if the damage had not progressed far enough. This testing strategy is 

 not typical and their interpretation of the data assumed damage caused by one wave 

 condition would be independent of the damage caused by the following wave condition. 

 They made note of the uncertainty in stability of traditional stone-armored breakwaters. 

 In Figure 3.3, for each value of relative depth, the stability coefficient is shown to 



50 



