FLOCCULATION OF SEDIMENT FROM THE TANSHUI RIVER ESTUARY

Experiments on the flocculation of fine-grained sediments from the Tan shui River estuary, Taiwan, were carried out. The effects of fluid she ar, sediment concentration and salinity on flee growth were investigat ed. The ranges of these parameters were 12.5 to 400 s(-1) for the shea r, 50 to 600 mg L(-1) for the sediments concentration and 0% to 100% s ea water for the salinity. The results showed the following. (1) The t ime required to reach a steady state ranges from 2 to 44 h and median flee sizes range from 100 to 520 mu m. (2) The steady-state median fle e size decreases with the increase in sediment concentration. (3) The flee size increases as the shear increases. (4) Increasing the proport ion of sea water from 0% to 50% decreases the floc size to one-fourth of that of freshwater flocs, and a further increase in salinity does n ot decrease Roc size significantly. (5) The time required to reach a s teady state decreases with the decrease in shear, the increase in sedi ment concentration and the increase in salinity. (6) The larger the st eady-state flocs, the longer they take to form. Comparison of these re sults with those obtained in similar studies of Lake Erie sediments sh ows that the flocculation properties of Tanshui sediments are substant ially different from those of Lake Erie sediments. Tanshui sediments a re much more difficult to aggregate, but once flocs are formed they ar e larger. The reasons why different types of sediment behave different ly should be studied further.