27_ 



Overall, the year-to-year wave results are very similar, showing that significant wave 

 heights are less than 2 m from 90 to 95 % of the time during each year. Larger waves were 

 more prevalent during 1993 as discussed above. As shown in the middle portion of Table 

 3-1, the duration (expressed as total hours per year) of large waves in 1993 was roughly 

 twice that of the following few years for wave heights between 3 and 5 m; for larger waves, 

 interannual differences were less pronounced. The maximum significant wave height 

 observed in each of the four measurement years ranged from 5.6 to 7.3 m (lower portion of 

 Table 3-1). 



From this analysis it appears that wave characteristics during the first half of 1996 

 were typical of other recent years at this location. 



3.2.3 Seasonal Wave Statistics 



To further investigate the seasonal variability of wave conditions in the vicinity of 

 PDS, the frequency distribution of hourly significant wave height versus wave period has 

 been computed for four seasons using the 3.4 years of buoy data. Seasons have been defined 

 as winter (December-February); spring (March-May); summer (June- August); and fall 

 (September-November). Whereas the frequency distribution statistics for each season are 

 provided in Appendix B, a summary of the key results is presented in Table 3-2 and listed 

 below: 



• Mean significant wave heights in winter (1.22 m) are nearly twice those in summer 

 (0.68 m), while mean wave heights in spring and fall are approximately 1 m. 



• Maximum significant wave heights in summer were 2.7 m, compared to 6.0 m in winter 

 and approximately 7 m in spring and fall. 



• Mean wave periods were approximately 8 sec during all seasons, but the standard 

 deviation was approximately 3 sec. 



• Significant wave heights exceeded: 



• 1 m only 16.6% of the hourly observations in summer, compared to 38 to 52% in 

 winter, spring, and fall. 



• 3 m 4.4% of the hourly observations in winter, compared to roughly 2% in spring 

 and fall, and 0% in summer. 



• 5 m 0.2-0.3% of the hourly observations in winter, spring, and fall, compared to 

 0% in summer. 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



