» Research Note « Experimental Study on Settling Velocity Changes of Cohesive Sediments using Settling Column

Document Type : Technical Note


1 Associate Professor, Water Resources Research Center, Shahrekord University, Shahrekord, Iran

2 M.Sc. Graduate Student, Water Engineering Department, Faculty of Agricultural, Shahrekord University, Shahrekord, Iran

3 Professor, Faculty of Water Engineering, Shahid Chamran University, Ahvaz, Iran

4 Graduated M.Sc. Student, Civil Engineering Department, Faculty of Islamic Azad University, Tehran, Iran


In this study, the settling velocity of cohesive sediments in a state of rest was investigated by performing experiments in a cylindrical plexiglass column with an internal diameter of 19 cm and a height of 300 cm. The experiments were carried out with 5 initial concentrations of 3, 5, 10, 15 and 20 g/l, and measurements of sediment concentration were measured at different times from 5 to 480 minutes after starting of sedimentation process. Also sediment concentration was measured by sampling from valves at 20 cm depth intervals in the model. To calculate the settling velocity of the sediment, a differential equation was used which had been proposed by Mclauglin (1959). The results show that the Mclauglin's equation is capable of describing the behavior of cohesive sediment deposition at rest state. In all experiments, the maximum settling velocity of sediment occurred at time of 15 minutes after the starting of the sedimentation process because of maximum flocculation forming. This was in agreement with the results of other researchers. By increasing the initial concentration in the experiments, the settling velocity of sediments decreased. The maximum settling velocity was measured for initial concentration of 3 g/l, and was equal to 5.84 mm/s. The minimum settling velocity was related to the initial concentration of 20 g/l, and was equal to 2.13 mm/s.


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