F' for the existing seawall configuration at Roughans Point without a riprap 

 revetment protecting the wall. Considering the complexity of the irregular 

 wave overtopping process, the ability of F 1 to consolidate the overtopping 

 data into a well-defined trend is surprising. 



18. A simple exponential model using F' was found to be very useful 

 for evaluating the overtopping performance of a seawall/revetment configura- 

 tion or for comparing the performance of two or more configurations. The 

 model can be written 



Q = Q o exp (C^F') (2) 



where Q is a coefficient with the same units as the overtopping rate, i.e., 

 o 



volume per unit time per unit length of seawall crest, and C 1 is a dimen- 



sionless coefficient. Both Q and C, are determined by the data for a 



o 1 



particular seawall/revetment configuration either by regression analysis or 

 occasionally by subjective curve fitting, if that seems more appropriate. A 

 regression curve fit to the data using Equation 2 is shown in Figure 10. 

 Since a regression equation of the form of Equation 2 tends to reduce the in- 

 fluence of the conditions with high overtopping rates, as compared to a linear 

 equation, it was sometimes convenient to subjectively fit an equation of the 

 form of Equation 2 to obtain a better fit to the data having high overtopping 

 rates. In Figure 11, a comparison is shown between a regression curve and a 

 subjectively fit curve for a seawall with a 1.0-ft cap fronted by a revetment 

 with a berm. In Figure 11 the nonregression curve fits the data with high 

 overtopping rates better than the regression curve. For many configurations, 

 the regression curves seem quite satisfactory, but for some cases, a nonre- 

 gression curve provides a more conservative trend which would be preferable 

 for design purposes. Possibly a more suitable approach would be to use an 

 equation with the form of Equation 2 with a weight function proportional to 

 either the overtopping rate or F' . In any event the form of Equation 2 fits 

 the data well and is similar to the form used by Owen (1982b) in a study on 

 irregular wave overtopping of sea dikes. Data trend curves of the form of 

 Equation 2 provide a simple way to evaluate the effectiveness of various 

 seawall/revetment configurations, i.e, the less area under the curve the more 

 effective the configuration is at reducing overtopping. 



19. The various seawall /revetment configurations discussed in this 



18 



