43_ 



Table 3-4 



Summary of Maximum Wave Heights, Peak Wave Periods, Duration of Wave Heights 



Greater than 3 m, and Maximum of the Burst- Averaged Standard Deviation in Near-Bottom 



Current Speeds during Nine Storm Events during the 



Period from February 27 to May 14, 1996 



Storm 



Date 



Significant 



Peak 



Duration 



Max 



Event 





Wave 



Wave 



Wave Ht. 



SDCS 







Height 



Period 



> 3 m (hrs) 



(cms" ) 







(m) 



(s) 







1 



March 8 



3.0 



10.8 



- 



10 



2 



March 14 



3.2 



10.8 



- 



7 



3 



March 20 



3.6 



10.0 



10 



10 



4 



March 26 



2.2 



7.0 



- 



2 



5 



April 8 



3.5 



11.1 



17 



15 



6 



April 10 



4.0 



10.0 



8 



12 



7 



April 16 



5.8 



10.0 



17 



16 



8 



April 26 



2.7 



8.1 



- 



4 



9 



May 1 



2.0 



8.3 



- 



2 



As indicated in Table 3-4, four storms (3, 5, 6, and 7) had maximum significant wave 

 heights of 3.5 m or greater, and durations of 8 to 17 hrs when significant wave heights were 

 3 m or greater and peak wave periods were at least 10 s; the other five storms were less 

 intense. Assessment of the time series results from Storm 3 (Figure 3-1 lc) reveals that near- 

 bottom turbidities at both sensor levels rose significantly beginning at mid-day on March 20, 

 at approximately the same time as significant wave heights achieved 3 m. As the wave 

 heights fell below 2.5 m about 16 hrs later, near-bottom turbidity values dropped sharply. 

 During this storm event, maximum turbidities (on the order of 10 mgT ) at both sensor levels 

 were encountered at approximately the same time, but as expected for near-bottom suspended 

 sediments, the highest turbidity and the longest duration of elevated turbidity levels were 

 encountered closest to the seafloor. 



The monotonic progression from short- to long-period (e.g., 5- to 10-sec) waves 

 during storm 3 (Figure 3-1 lc) suggests that surface wave energy would penetrate to greatest 

 depth near the end of the storm when significant wave heights were still about 3 m while 

 wave periods reached 10 sec. This dependency of sediment resuspension on wave period and 

 height is evident during storm 3 as maximum turbidities occurred after the maximum wave 

 heights were encountered and elevated turbidities persisted for some time thereafter. As 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



