• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.1
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• pp.40-49
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• 1999

A laboratory flume experiment, using turbulence-generating acryl tank and natural sediments, was conducted to investigate the effects of salinity, concentration of suspended sediment, turbulence and clay minerals on the flocculation and settling of fine-grained suspended sediments. While experiments were run, a sequence of water samples were taken near the bottom of the tank to analyze the variations of size distribution and relative contents of clay minerals. The results of the salinity experiment indicate that median settling velocity ($W_{50}$) increases linearly with salinity. Different settling processes of suspended sediments under variable concentrations appear to be predictable, depending upon the range of the suspension concentration. At concentrations less than 200 mg/l, $W_{50}$ is rarely varied with concentration probably because of the individual--grain settling mode. In the range of 200 to 13,000 mg/l show $W_{50}$ and concentration a good relationship following an empirical formula: $W_{50}=0.45C^{0.44}$. This relationship, however, no longer holds in concentrations exceeding 13,000 mg/l; instead, a more or less reverse one is shown. This result suggests an effect of hindered settling. The turbulence effect is somewhat different from that of concentration. Turbulence accelerates the flocculation and settling susepended sediments at low concentration (200 mg/l), whereas at high concentration turbulence breaks floes down and impedes the settling. Size distribution of suspended sediments sampled near the bottom of the tank tend to be more negatively skewed and leptokurtic in turbulent conditions compared to those in static conditions. The clay mineral analysis from the sequential water samples shows that over time the content of smectite decreases most rapidly with illite remaining concentrated in suspension. This means that smectite, among other clay minerals, plays the most effective role in the flocculation of fine-grained sediment in saline water.