55 



Table 3-5 



Summary of Maximum Wave Heights, Maximum of the Burst- Averaged Standard 



Deviation in Near-Bottom Current Speeds, Background (Pre-Storm) Concentration of Total 



Suspended Solids (TSS), Maximum TSS during Storms, and Duration of Elevated TSS 



during Nine Storm Events during the Period from February 27 to May 14, 1996 



Storm 



Date 



Significant 



Max 



Background 



Max TSS 



Duration 



Event 





Wave 



SDCS 



TSS Cone. 



Cone. 



Elevated 







Height (m) 



(cms 1 ) 



(mgl 1 ) 



(mg-1 1 ) 



TSS (hrs.) 



1 



March 8 



3.0 



10 



<1 



8 



21 



2 



March 14 



3.2 



6 



<3 



3 



- 



3 



March 20 



3.6 



10 



<1 



10 



12 



4 



March 26 



2.2 



2 



<3 



7 



20 



5 



April 8 



3.5 



15 



<1 



65 



32 



6 



April 10 



4.0 



12 



<2 



8 



33 



7 



April 16 



5.8 



16 



<3 



40 



22 



8 



April 26 



2.7 



4 



<4 



9 



10 



9 



May 1 



2.0 



2 



<2 



1 



- 



Summary of Storm Results 



The time series data from each of the nine storms (Figures 3-1 la through 3-1 li) suggest that 

 sediment resuspension is initiated during storms attaining maximum significant wave heights 

 in excess of about 3 m (e.g., storms 1, 3, 5, 6, and 7), whereas significantly elevated 

 turbidity levels were not evident during storms 2, 4, 8, and 9 which had smaller waves. To 

 further assess the potential relationship between wave characteristics and sediment 

 resuspension, the maximum SDCS for each of the nine storms (Table 3-4) has been plotted 

 versus the maximum significant wave height for each storm (Figure 3-12). This presentation 

 illustrates that high-frequency, near-bottom currents (as represented by the SDCS) are 

 correlated with significant wave height at the PDS: for wave heights less than approximately 

 3 m, maximum SDCS values were less than 8 cms" 1 whereas for greater wave heights, 

 SDCS values ranged from roughly 10 to 16 cms" 1 . 



Maximum suspended particulate concentrations during each storm event (Table 3-5) 

 are also shown in Figure 3-12. Although it appears that substantial sediment resuspension 

 occurred during storms 5 and 7 (having suspended particulate concentrations of 65 and 

 40 mg-1" 1 , respectively) when maximum SDCS values exceeded 14 cms" 1 , one should not 

 assume that SDCS and significant wave height are the only key physical parameters 

 governing sediment resuspension at the PDS. For example, when SDCS values were less 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



