30' 

 20 



I 



SETTLING 



VELOCITY OF SITE 



-1 SEDIMENT 





















Fresh Water 



10 

 n 









1 ^ 



30'- 



20 

 10 



I 



135 



Figure 10. 



Salt Water 



10- 



I 



10- 



10"' 



I 



-L-.^ 



w- (cm /sec) 



42.8 



13.5 



4.28 



-1— *. 



1.35 difim) 



Settling speed of Mississippi Sound Sediments in Fresh 

 and Salt Water. 



cohesion and collision of sediment particles. Clay mineralogy and 

 other chemical parameters determine the cohesion of sediment particles. 

 However, in coastal waters where flow is generally turbulent, collision 

 between particles play a more dominant role than cohesion in 

 determining the state of flocculation. The frequency of collision 

 between various groups of particles depends on the turbulent shearing 

 rate on the dissipation scale and differential settling. Although our 

 hydrodynamic model is capable of computing the small-scale turbulent 

 shearing rate, there is insufficient data at this time to allow for 

 precise determination of model coefficients for the flocculation model. 



Resuspension and Deposition Modes 



Resuspension and deposition of sediment at the sediment-water 

 interface play important roles in the distribution of suspended 

 sediment concentration. In general, resuspension and deposition depend 

 on (I) the hydrodynamic forces generated at the bed within the 

 turbulent bottom boundary layer; (2) bed properties such as sediment 

 composition, water content, bed preparation (settling) time, and 

 organic matter, bacteria, and benthos; and (3) fluid properties 

 including salinity, temperature, and pH of pore water and overlying 

 water. 



Effects of dominant parameters (shear stress, water content, bed 

 preparation time, and salinity) on resuspension and deposition were 



282 



Sheng 



