To calculate the concentration of the particulate organic matter in eutrophic coastal area, it is necessary to estimate the settling velocity of the particulates correctly.
　Measurements of the settling velocity of the fine suspended matter in inner Osaka Bay are made both in the field and in the laboratory. Sediment traps are used in the field observation. The settling velocity of the fine particulate organics in the surface layer is estimated 0.6 m/d, and that of the resuspended sediment in the bottom layer is estimated 3 m/d. Electric particulate counter and settling tubes are used in the laboratory experiments. The settling velocity of the sediment is calculated 1 m/d from the particulate diameter. Because of the difference in coagulation state, which
depends on the settling depth of the tube and the initial concentration of the suspended matter, the settling velocity of the sediment by the tube tests varies widely from 0.9 m/d to 5 m/d.
　Among, many factors effecting to the settling velocity, Coagulation process is prooved to be very important in the estimation from the laboratory experiments.