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20. ABSTRACT (Continued): 



and an analysis of collateral wind data to support the results of the analysis 

 of hindcast wave data. 



The Wave Information Study (WIS) hindcast data applicable to the Kodiak 

 area was surveyed for extreme wave conditions. This survey resulted in a 

 sample of 62 significant wave heights for the years 1956 through 1975 (Appen- 

 dix A). The 62 significant wave heights were scaled and plotted according to 

 several extreme probability models. The Extremal Type I or Fisher-Tippett 

 Type I model demonstrated a better fit with the data than did the other models 

 (Figure 1). Extrapolated significant wave heights based on the Extremal 

 Type I model are listed versus return period in Table 7. The extreme wave 

 predictions computed using monthly maximum significant wave height values from 

 measured wave data (Table 9) tended to be smaller than the hindcast predic- 

 tions. This difference was best explained by the fact that the measured data 

 covered a time span of about 2 years; whereas, the hindcast data represented 

 20 years of wave climate. The longer record had a better chance of capturing 

 a representative sample of extreme events than the short record. 



Extreme wave heights computed with long-term wind data provided by the 

 National Weather Service agreed well with results from the analysis of WIS 

 hindcast data and supported the overall validity of the study. 



Measured wave data provided by the Alaska Coastal Data Collection Pro- 

 gram were analyzed to obtain a wave energy attenuation factor for the long- 

 period swell crossing the reefs into St. Paul Harbor at Kodiak. The atten- 

 uation factor represented the fraction of deepwater wave energy that is not 

 dissipated in the transition across the reefs into St. Paul Harbor. The at- 

 tenuation factor had a value of 0.374; therefore, a significant wave height 

 of 1 m in deep water corresponded to 0.374 m inside the harbor. 



The long-term extreme wave height prediction from the analysis of hind- 

 cast data was adjusted to represent the long-term wave climate inside St. Paul 

 Harbor by means of the attenuation factor. Values for attenuated long-term 

 significant wave heights are listed in Table 24. These estimates represented 

 the best estimates for the extreme wave climate at St. Paul Harbor, based on 

 analyses of all the presently available data. 



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