PART III: COMPARISON OF METHODS 



47. This section will compare the four methods of estimating irregular 

 wave overtopping by (a) summarizing the methods' regions of applicability, (b) 

 comparing the results of the methods, and (c) comparing the methods with the 

 limited available data. 



Summary of Regions of Applicability 



48. Each of the four methods for estimating overtopping is applicable 

 to specific design situations. The SPM method is limited by the range of 

 structures which Saville tested: sloped, vertical, and recurved seawalls. 

 The only quarrystone structure tested by Saville was a stone layer placed on 

 an impermeable 1:1.5 slope. Also, since Saville only tested a small number of 

 wave conditions for each structure, difficult interpolation is often necessary 

 when using the SPM method. Owen's method is derived for smooth structures 

 with slopes between 1:1 and 1:4. However, Owen's method should not be used 

 when the experimental ranges on F* , Q* , d/H g , and H /L are not met. 

 In particular, Owen's range of wave steepnesses is narrow. Owen's method is 

 the only method which specifically includes composite slope structures. Owen 

 suggests an unverified way to extrapolate his smooth slope theory to rough, 

 e.g. rubble-mound, structures. Battjes' method is applicable to gently 

 sloped, smooth structures. Battjes (1974) did not attempt to apply his method 

 to rough slopes. Goda's method is derived for vertical walls. These general 

 regions of applicability of the methods are summarized in 



Figure 14. 



49. The SPM method is the most cumbersome of the four methods. Using 

 any of the other three methods requires only the application of one dimension- 

 less figure or equation. The SPM method, because of its dependence on runup 

 and Q* - a figures, is a multiple-step procedure and is, therefore, more 

 time-consuming. 



50. The methods' estimates can be compared for design situations in 

 which more than one method is applicable. Figure 14 and the discussion in the 

 previous section show that for vertical seawalls the SPM method can be 

 compared with Goda's method. For mildly sloped structures, i.e., when waves 

 break on the structure (Figure 12), the SPM method and Battjes' method can be 



27 



