24 



To facilitate comparison of marine meteorological conditions during 1996 with those 

 of prior years, Figure 3-3d presents buoy observations from January through May 1996. 

 Unfortunately, the anemometer on the buoy was inoperable for three time periods during this 

 five-month record, but the wave, water temperature, and atmospheric pressure data are 

 complete, and sufficient for this analysis. During the period from January through May 

 1996, three events were encountered having significant wave heights in excess of 4 m during 

 winter and late spring (note that this is similar to the amount of storm activity observed 

 during the period from 1993 through 1995). 



Also evident in the 5-month buoy time series from 1996 (Figure 3-3d) is a gradual 

 decrease of wave periods from numerous values in excess 10 sec during January through 

 March, to fewer wave periods less than 10 sec thereafter. This seasonal trend toward shorter 

 wave periods in spring and summer can be expected due to less severe storms. 



Inspection of the surface water temperature record from 1996 (next to lowest tier in 

 Figure 3-3d) reveals that 10°C water was encountered on May 22, which was one to two 

 weeks earlier than during the prior three years. This may reflect a somewhat milder 

 winter/ spring in 1996, but this would not affect the processes governing near-bottom currents 

 and sediment resuspension at PDS. 



3.2.2 Annual Wave Statistics 



The time series results from the NOAA buoy illustrated that 1993 contained more 

 storm activity than either 1994, 1995, or the first five months of 1996. To facilitate analysis 

 of the interannual variability in wave characteristics in the vicinity of PDS, frequency 

 distribution tables of the percent frequency of occurrence of significant wave height versus 

 peak (most dominant) wave period are presented in Appendix A for each of the four years 

 from 1993 through May of 1996. To summarize the annual wave statistics, Table 3-1 

 presents the percentage of time (per year) that hourly observations of significant wave heights 

 were within various 1-m wave height ranges. For example, wave heights ranging from 3 to 

 4 m were observed 1.8% of the time in 1993 versus 1.0% of the time in 1995, with results 

 from the 3 complete record years being very similar. Three- to 4-meter waves were 

 observed more often (2.4%) during 1996, but this was partially a result of summer and fall 

 data not having been included in the 1996 data. 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



