Persistence of Wave Heights 



Table B5 shows the number of times in 1992 when the specified wave height was equaled or 

 exceeded at least once during each day for the duration (consecutive days). Data for 1980 through 

 1992 are averaged and given in Table B6. An example is shown below: 



Height 



ID 















Consecut 



ve 



DaY(s) or Longer 













1 

 18 



2 

 15 



_i 



4 

 14 



5 

 13 



6 

 12 



_7 



8 

 11 



9 

 10 



10 11 12 13 

 9 



14 

 8 



15 



16 17 



7 



18 



19+ 



0.5 



1.0 



50 



34 



24 



21 



18 



14 



12 



8 



7 



3 2 













1.5 



41 



19 



8 



6 



2 



1 





















2.0 



22 



9 



5 



1 

























2.5 



10 



5 



2 



























3.0 



6 



1 





























3.5 





1 





























4.0 



1 































This example indicates that wave heights equaled or exceeded 1.0 m 50 times for at least 1 day; 34 

 times for at least 2 days; 24 times for at least 3 days, etc. Therefore, on 16 occasions the height 

 equaled or exceeded 1.0 m for 1 day exactly (50 - 34 = 16); on 10 occasions for 2 days; on 3 occa- 

 sions for 3 days, etc. Note that the height exceeded 1 m 50 times for 1 day or longer, while heights 

 exceeded 0.5 m only 18 times for this same duration. This change in durations occurred because the 

 longer durations of lower waves may be interspersed with shorter, but more frequent, intervals of 

 higher waves. For example, one of the times that the wave heights exceeded 0.5 m for 16 days may 

 have represented three times the height exceeded 1 m for shorter durations. 



Spectra 



Monthly spectra for the offshore Waverider buoy (Gage 630) are presented in Figure B8. The 

 plots show "relative" energy density as a function of wave frequency. These figures summarize the 

 large number of spectra for each month. The figures emphasize the higher energy density associated 

 with storms, as well as the general shifts in energy density to different frequencies. As used here, 

 "relative" indicates the spectra have been smoothed by the three-dimensional surface drawing routine. 

 Consequently, extremely high- and low-energy density values are modified to produce a smooth sur- 

 face. The figures are not intended for quantitative measurements; however, they do provide the 

 energy density as a fiinction of frequency relative to the other spectra for the month. 



Monthly and annual wave statistics for Gage 630 for 1992 and for 1980 through 1992 are 

 presented in Table B7. 



Figure B9 plots monthly time histories of wave height and period. 



B2 



Appendix B Wave Data for Gage 630 



