causes the Rwo may be a reasonable assumption. Ahren's third assumption is 

 that the a , Q* , and H' in Weggel's equation (Equation 1) remain constant 

 as the overtopping contributions of the individual runups are summed. While 

 this assumption may be necessary, it is far from true. However, since no 

 satisfactory general expression for Q* and a has been found, in order to 

 apply Weggel's equation to irregular seas, Q* and a are usually considered 

 constant (Ahrens 1977a, Kobayashi and Reece 1983). Ahrens assumes that H' 

 can be held constant as H 1 = H . Since, in the derivation of Equation 1, 



OS 



Weggel (1976) used H' to nondimensionalize overtopping, perhaps irregular 

 wave overtopping can be nondimensionalized with H g . However, in the absence 

 of experimental verification, any wave height parameter could be selected. 



21. The trends shown by Ahrens' correction factors (Figure 3) appear to 

 be reasonable. Ahrens (1977a) points out that the trends in the correction 

 factors agree with trends in overtopping data from Tsuruta and Goda (1968). 

 The correction factor is less than one for low relative freeboard F/H and 

 greater than one for high relative freeboard. 



22. A very important limitation of the SPM method is that it is based 

 on the tests of Saville. In particular, most of the tests were done on smooth 

 slopes. The only rubble slope tested was a 1 on 1.5 riprap slope. 



Goda's Method 



Description 



23. Tsuruta and Goda (1968) and Goda (1971) present a graphical method 

 of estimating the rate of irregular wave overtopping over seawalls. This 

 method is called Goda's method in this report. Goda reanalyzes Saville 's 

 monochromatic results for vertical walls along with the results of several 

 Japanese monochromatic-wave overtopping studies. Goda presents curves which 

 estimate the monochromatic-wave overtopping rate in terms of deepwater wave 

 height, freeboard, and depth. 



24. Goda extrapolates his monochromatic-wave overtopping curves to 

 irregular wave overtopping by assuming that wave heights are Rayleigh 

 distributed and adding together the overtopping contributions from each wave 

 in an irregular sea. The result is presented in Figure 6. Goda duplicates 

 his vertical seawall work for seawalls covered with concrete blocks; however, 

 he does not define this situation well. 



14 



