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equation? To develop an answer to this question, the irregular wave condi- 

 tions are assumed to cause the runup to have a Rayleigh distribution of the 

 type commonly associated with wave heights. This technique, which was used 

 by Ahrens (1977) to predict irregular wave runup, appears reasonable but 

 possibly somewhat conservative. The runup with a Rayleigh distribution is 

 used in the SPM's wave overtopping equation to predict average overtopping 

 rates for irregular waves having a particular significant height. This 

 approach generally yields overtopping rates that are considerably lower 

 than the corresponding monochromatic rates except for structures with high 

 relative freeboards where the irregular wave overtopping rates can then 

 exceed the monochromatic rates. This behavior is consistent with the 

 trends observed by Tsuruta and Goda (1968) in their laboratory study of 

 overtopping caused by both monochromatic and irregular waves. 



Example problems are given to illustrate how this technique can be used 

 to predict overtopping rates for irregular wave conditions. A table, which 

 can be used to calculate the irregular overtopping rate using the monochromatic 

 rate for equivalent wave conditions is also given. 



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