interesting to see that, in between the ship surveys, bottom concentration 

 over 1000 mg/1 had been reached at station 17. Detailed verification of the 

 model simulation would require continuous measurements of concentration or 

 turbidity at properly selected stations. This could be accomplished with a 

 field study which incorporates in-situ measurements, ship surveys and remote 

 sensing. During the period with strong easterlies, due to the stronger wave 

 action, concentration is generally higher in the western Sound. The 

 easterlies also caused significant transport of suspended sediments towards 

 the west. 



7.6 Deposition, Entrainment, and Transport of Sediment during 

 9/20/80 to 9/25/80 



Ship Survey Data 



Sediment concentration distributions interpolated from the ship survey 

 data on 9/20/80 and 9/21/80 are shown in Figure 7.28. Low concentration 

 between 10 mg/1 and 20 mg/1 exists near the surface, while higher 

 concentration up to 200 mg/1 exists near the bottom. This is consistent with 

 our computations on the bottom shear stresses as presented in Section 7.4. 

 The relatively strong bottom stresses on 9/20 and 9/21 apparently resulted in 

 the entrainment of sediments and the higher near-bottom concentration. 



A subsequent ship survey conducted on 9/24/80 and 9/25/80 showed rather 

 low suspended sediment concentration (-- 20 mg/1) throughout the water column 

 (Figure 7.29). 



Model Simulation 



Our bottom stress computations indicated that relatively high bottom 

 shear stresses existed during 9/20/80 and the first several hours on 9/21/80. 

 This resulted in the relatively high bottom sediment concentrations at all 

 stations. During 9/23/80 and 9/24/80, significant wave-induced bottom 

 stresses only existed for approximately 10 hours. Thus the higher bottom 

 concentrations observed on 9/20/80 had decreased appreciably on 9/24/80 due to 

 deposition. 



205 



