Abstract: In order to characterize the settling properties of natural cohesive sediment adjacent to the Dez Dam wall (as a symbol of a large dam reservoir in arid and semi-arid zones), falling velocity of particles have been measured using a 2.50 m height and 0.30 m diameter column. In contrast to the traditional particle size based methods, an approach relying on time and depth variation of sediment concentration was employed to estimate the mean value of fall velocity at any depth and time. Particles in deeper depth, particularly for the samples with higher rate of sediment concentration accelerated faster and stayed at higher velocities for longer duration as a result of higher rate of flocculation. This confirms the greater effect of particle flocculation than their settling competition. The particles in all depths reached their maximum falling velocity same time around 15 min after the beginning of the tests. The low concentration samples reached higher maximum velocity as a result of lower rate of particle compaction but for a much lower duration in comparison to the higher concentrated samples.