PART V: SUMMARY AND CONCLUSIONS 



68. Four methods of estimating overtopping rates caused by irregular 

 waves are briefly described in Part II. Three of the methods, SPM, Goda, and 

 Battjes, extrapolate monochromatic laboratory results to irregular seas. The 

 fourth method, Owen, is based on irregular-wave laboratory data. 



69. The four methods were derived for different situations. The 

 general ranges of applicability are summarized in Figure 14. 



70. Comparison of the methods' results indicates that (a) for vertical 

 seawalls, the SPM method estimates more overtopping than Goda's method except 

 in very shallow water; and (b) for sloped structures, the SPM method generally 

 estimates less overtopping than Battjes' method and Owen's method. 



71. Data to adequately evaluate the methods have not been published. 

 For one specific structure and very little overtopping, the SPM method agrees 

 with the data, and Owen's method overestimates the data. 



72. Available methods provide only a broad, general estimate of 

 overtopping rates. The question "How well do the available methods estimate 

 overtopping?" cannot be conclusively answered at this time. The methods 

 discussed in this report provide the best available estimate. Until better 

 data are available, these estimates should be considered to be within, at 

 best, a factor-of- three, and conservatively, an order-of-magnitude of the 

 actual overtopping rate. This conclusion is made considering: 



a. The lack of comprehensive, conclusive data and the 

 discrepancies between the methods' estimates and the very 

 limited published data. 



b. The assumptions made in the derivations of the methods. 



c. The factor-of-three confidence band that Owen claims for his 

 method, which is the only method of the four based on 

 irregular-wave overtopping data. 



d. The scale effects found by Aaen. 



e. The order-of-magnitude difference between estimates from 

 different methods. 



73. Model tests with irregular waves are recommended for a more 

 precise, site-specific estimate of volume rate of overtopping. 



74. More data are needed to improve the available methodology for 

 estimating wave overtopping. Laboratory tests with irregular waves are 

 needed. Prototype data are needed to determine scale effects in overtopping 



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