Settling speeds of floes in fresh water and seawater

Abstract

The settling speeds of floes of fine‐grained, natural sediments approximately 10–200 μm in diameter have been measured in both fresh water and seawater. These floes were formed at fluid shears of 100, 200, and 400 s −1 and at sediment concentrations of 10, 100, and 400 mg/L, values typical of conditions in the near‐shore areas of lakes and oceans, especially during storm conditions. It is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe, but it is a weak function of salinity. For the same diameter and salinity, floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations. If the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored, it is shown that the settling speed of a floe is a weak function of diameter and salinity.