The increased salinity of the overlying water and the pore fluid have 

 apparently resulted in a more coagulated sediment structure, and a lower 

 Sodium Adsorption Ratio (SAR), thus decreasing the erodability of the 

 sediments. A higher settling speed and lower water content also contributed 

 to the lower equilibrium concentration in high salinity water. 



This trend is exactly opposite to that of the kaolinite. Yeh (1979) 

 reported that the erodability of kaolinite decreased with the salinity of 

 water. He also reported that kaolinite in higher salinity water formed a less 

 densely packed bed with smaller floes, thus resulting in higher erodability 

 than the low salinity case. Kaolinite also has a much lower water capacity 

 than smectite. Consequently, the variation of erodability with salinity for 

 kaolinite is much less dramatic than for the smectite rich sediments used in 

 our study. 



Sediments from all four sites were tested for erodability in 30 ppt 

 salinity water in our flume. Site 3 sediments were also run at an 

 intermediate salinity value of 15 ppt. The effect of salinity on equilibrium 

 concentration is summarized in Figure 6.14. It appears that much of the 

 variation in erodability occurs between ppt and 15 ppt salinity. A more 

 precise functional relationship may be obtained if more flume runs are 

 performed in this salinity range. 



Effect of sediment type . 



Site 2 sediments, having a higher clay content, are generally more 

 erodable than sediments from other sites. Site 4 sediments, possessing the 

 lowest clay content and the highest fraction of sand, appear to have a 

 somewhat higher erodability than what it should have. This behavior is a 

 result of the bed preparation procedure. During the settling stage, heavier 

 sand particles settle to the bottom before the lighter clay particles or 

 floes. The result is that a graded bedding is produced. Much of the 

 relatively high concentration of suspended sediments is due to the 

 resuspension of the lighter clay particles or floes at the surface of the bed. 

 However, this will change somewhat if much higher shear stress is applied such 

 that more sediments are resuspended from the bottom. This problem could be 

 resolved by using a somewhat different procedure of bed preparation in future 



159 



