OVERTOPPING RATE IN CU FT/SEC/FT 

 1:3 SMOOTH SLOPE 

 FREEBOARD = 5 FT 

 DEPTH = 10 FT 



15 

 T, SEC 



Figure 5. Dimensional overtopping rate plot, Example 2 



Discussion 



19. The SPM method for estimating overtopping created by monochromatic 

 waves, Weggel's equation (Equation 1), agrees well with Saville's data. This 

 is not surprising since Saville's data comprise the data set from which the 

 equation was derived. Though Weggel's equation predicts monochromatic over- 

 topping well, the assumptions made in extrapolating the equation to irregular 

 seas should be examined. 



20. Ahrens makes several assumptions when he applies Weggel's equation 

 to irregular seas. His basic assumption is that runup is Rayleigh distributed 

 (Ahrens 1977b). More recent results by Ahrens (1983) show runup to fit a 

 Weibull distribution, of which a special case is a Rayleigh distribution. A 

 Rayleigh distribution is a reasonable assumption for the purposes of the SPM 

 overtopping-estimation method. A second assumption is that the significant 

 deepwater wave H« /o causes the "significant" runup R^ ,? . While Ahrens 

 does not state that he made this assumption, he has to assume that some spe- 

 cific wave causes some specific runup in the runup distribution. This gives 

 him a reference for his Rayleigh distribution of runups. That the H^o 



13 



