Comparison with Data 



57. The four overtopping methods should be evaluated by comparing how 

 they agree with laboratory and field data. Unfortunately, no conclusive, 

 comprehensive set of overtopping volumes caused by irregular waves has been 

 published. Paape (1960), Sibul and Tickner (1956), and Tsuruta and Goda 

 (1968) conducted experiments before the present generation of laboratory 

 irregular-wave generators was developed. Therefore, they could not generate a 

 realistic, controlled irregular sea. Unfortunately, neither Jensen and 

 Sorensen (1979) nor Owen (1980, 1982) published the data from which they 

 derived their design curves. 



58. Aaen (1977) measured overtopping in both the laboratory and the 

 prototype to investigate scale effects in overtopping modeling. He measured 

 actual overtopping over a breakwater at Hundested, Denmark, during six storms. 

 He then reproduced the structure and storm conditions in the laboratory at two 

 scales, 1:8 and 1:10. Since only one structure is considered, Aaen's data 

 cannot be used to comprehensively evaluate the overtopping estimation methods. 

 However, Aaen's data can be used as a rough "spot-check" verification of the 

 methods for that specific structure and three specific wave conditions. The 

 Hundested breakwater has a 1:2 slope of rounded sea stones. 



59. Figure 14 shows that Owen's method is applicable and that the SPM 

 method is nearly applicable. For the sake of an order-of -magnitude compari- 

 son, the SPM method will be compared with Aaen's data by ignoring the differ- 

 ence in slope (1:2 instead of 1:1.5) and the difference in armor layer (round 

 sea stone instead of rough, angular quarrystone) . In calculating the 

 overtopping estimates, a roughness and porosity correction factor r of 0.65 

 is assumed, and the methodology presented in the SPM for accounting for the 

 effect of wind on overtopping is used (wind increases overtopping from 30 to 

 50 percent). The storm data are presented in Table 2 with the model data and 

 estimates from both the SPM and Owen's methods. The results of the three 

 largest storms are plotted in Figure 18. 



60. The SPM method underpredicts Aaen's data while Owen's method pre- 

 dicts Aaen's data. The relationship between the two estimates agrees with the 

 trend of Figure 17; that is, for low overtopping rates, Owen's method esti- 

 mates much more overtopping than the SPM method. 



61. Considering both the inherent assumptions of the SPM method and the 



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